Need a few hints here...

1986 Eldorado, HT4100, bought it new, 178,000 miles. Ran relatively fine a few months ago, then it began to struggle while climbing hills until I shift down so that the engine runs a little faster. Car runs fine on freeway going 75 mph. But it seems whenever the engine is stressed, say going 40 mph in high gear up a somewhat gentle slope, engine begins to "chug". If I attempt to give it more gas, it will stall and it has never stalled on these hills before. If I shift down, the engine will run faster and be "OK" but auto or manual shifting should not be necessary on these hills. Recently changed plugs, electronic ignition module, and fuel filter. I removed one plug wire at a time and each one affects engine idle. Car starts up immediately.

On level highway, engine sounds OK and ride feels OK. Used to get around 19 mpg. Now it seems to be getting around 15.5. That is more freeway than city driving.

Anyone have any hints? I do have the service manual. During the past 22 years I've replaced lots and lots of parts (camshaft and lifters at 98,000) on the car as any long time Eldorado owner would know. But I can't seem to figure out what else to do this time. I was thinking of buying a fuel pressure gauge to check that. My guess is that it is a fuel issue, but not even sure of that. (fuel pump? injectors? O2 sensor? valves?)

Body is in perfect shape. I would like to make 200,000. (100,000 was my original goal)

Thanks for your interest!

Frank

Do you have trouble keeping up with traffic at a light?

Probably a fuel issue. Check your fuel pressure first (very easy)--tape a gauge onto your windshield. Should read between 9-13 psi all the time.

Sounds like it's just not getting enough fuel.

Did you ever have intake gasket/head gasket issues? I had to replace the cam on my 85 Deville with only 38,000 miles on the clock because the previous owner drove it for a while after the intake gasket blew. Now, it runs just fine, although I had to use Seafoam about 6 times (no joke) to clean the antifreeze residue off of the exhaust valves which were sticking open.

I had similar problems until I got the GM top-end cleaner treatment as well, which is why I asked about performance from a dead stop

Thank you for the replies folks!

I do not have a problem keeping up with traffic at a light as long as it isn't heading uphill. If I tried, I believe I could keep up with them going up a low incline if I remained in a lower gear than normal. I did try one time to just let it shift normally from a light in traffic on a slight incline. Traffic ended up going around me and I had to pull off to the side of the road.

I'll get hold of a gauge today. Need to buy some hose as well to get gauge to windshield. Perhaps 1/4" copper is the appropriate size and material (?) I will bring a fire extinguisher with me..... hmmm....

It has never had intake manifold or head gasket problems. I replaced the cam because one lobe was completely gone. Never had water in oil. Car ran fine for 80,000 miles after cam replacement until now.

I thought about replacing the two injectors until I discovered the price. If the pressure is OK, do the injectors somehow become clogged, or would the problem be much worse if that were to happen? And does the filter in the tank get clogged or would low pressure most likely be caused by a bad fuel pump? And how likely is it that the fuel pump could have gone bad? These are the issues that have been running around my head but I had no one with experience to ask.

Another strange thing that happened was that just a couple of months ago, when I was working this "fuel" issue, the ignition module died. (It failed previously 2 years ago). I replaced it and figured, OK, this will fix the other problem. It didn't. But the bad module was tested - it failed perhaps 6 (all) tests. I've wondered whether the new module could cause this problem if it were to fail one of the tests (it wasn't tested).

Again, thanks for the support!
Frank

It's unlikely it's the injectors. But you can check it by visually checking the spray pattern with the engine idling and the air cleaner off.

Like others have mentioned, do a pressure test. The fuel pump on my 88 Eldorado went out at 220k miles. I did not loose any power beforehand. It just suddenly died and the car was inoperable. Yes, the filter in your tank or your in line fuel filter could be clogged. The inline fuel filter is a $10 item so you might just want to change it out anyways and see if it fixes the problem.

Thanks!

I replaced the in line fuel filter yesterday. I had big hopes. But car runs no differently. (and of course, that is good news too). It was a lot of work to replace that filter. I'm glad you agree that it was worth a shot.

To check injectors, I suppose you look for a nice spray of fuel from the injectors as you mechanically work the accelerator. And I assume both injectors should spray equally. I'm dissapointed to hear that the fuel pump didn't slowly fade on your Eldorado. It sounds like the motor in yours just burnt out (?)

I suppose it does seem reasonable that less fuel is needed to travel 70 mph on level freeway than what is required to travel 40 mph up an incline. I did notice that the instantaneous fuel consumption was around 10 mpg or less while going up the incline. And when doing 70, it may have indicated well into the 20's.

Again, thanks for the support.
Frank

The spray pattern should be even at idle and when you rev the engine up. When you turn off the engine, the injectors should not drip. Yes, both injectors should spray equally.

My fuel pump completely died without warning.

It takes a lot more power to go up inclines and to accelerate the car.

Thanks for the reply and the answers to my questions.

I am just leaving to head to Advance Auto Parts to pick up a fuel pressure meter. In preparation for that trip, I took the brass cap off of the fuel line service fitting so that I would have some sort of idea of what fitting and tubing to buy. In the fitting, is what appears to be a small plastic plug. I don't know if perhaps it is a check valve of some sort. I hate to pull it out without knowing, because the cap does not appear to be of a type that would seal the fitting. Can you provide some advice as to what to do with that fitting?

Thanks,
Frank

Get a bottle of Lucas fuel treatment ("Tune-Up In A Bottle") and add that to a full tank. If you have injector problems, it will clean them out pretty good.

I'll pick up a bottle of the Lucas fuel treatment when I head back into town.

I have a pressure gauge now, but not sure how to connect it to the fuel fitting on the gas line. The fuel pressure gauge kits had fittings to work with what must be a valve core similar to the type used for a tire or refrigerant system. But my fitting appears to have a plastic piece that doesn't appear to be set up to have something inserted into it. Is that normal?

Also, the fellow at the auto parts place told me that he was surprised that all I needed was a gauge to measure up to 15 psi. He showed me that the pump was rated at 45 psi or something like that. I assume the reason you would have a 45 psi pump and a pressure of only 12 psi is because the return line allows the fuel to return back to the tank and therefore the line pressure is much less than the pump pressure. (?) I think the return line is a little smaller than the supply line and that is why there is some pressure in the system.

Thanks,
Frank

Another thought... Is it possible the "plastic piece" that is coming out of the main fuel line pressure fitting (shraeder valve type fitting) actually some hardened fuel residue that has oozed into the dust cap over the past 22 years? Is that something than anyone has seen happen? There is no way to check pressure unless I remove whatever that is.

Thanks!

Don't these cars have a diagnostic mode? any codes? It's starting to sound like another catalytic problem but you should check that fuel pressure first. There shouldn't be anything plastic in the schraeder valve. It might be some rubber gasket from the cap; just guessing. I have to check my fuel pressure tomorrow so maybe I can clarify some more then if you haven't got it checked by then. Good luck

Hi there, thanks.

Yes, it does have codes that can be read. I'll run through them to see if any help can be found there. When I was looking at the the fitting before, I didn't realize it was actually similar to a shraeder valve. So I didn't want to forceably remove the "plug" inside it. But now it seems I need to get that stuff out of there. It sticks out of the end of the fitting by about 1/8" and is quite hard and stuck pretty good. But I'll get some pliers and clean it up. Seems there is just one surprise after another when working on that engine.

Thanks again.

hmmm, the fuel pressure on any throttle body motor is always under 15 psi (at least, GM vehicles). the test fitting is on the driver's side of the engine. follow the fuel line from the throttle body down by the distributor. you can't miss it. you need to unscrew the cap. once you do so, you'll see the fitting and the nipple (looks like a tire valve stem). screw on your pressure gauge.

i agree with the above post--it may also be a catalytic converter issue. in any case, the engine probably is fine, just something minor.

The catalytic converter does have 176,000 miles on it. I don't know how long they are supposed to last. I haven't checked fuel pressure yet. Had a little set back yesterday -- had two hernia repairs. So I am laid up for a few days. Changing the catalytic converter now would be either overly expensive or extremely difficult.

I have found the fuel pressure fitting, and I appreciate your advice regarding it being similar to a tire valve stem. I couldn't see that since there is a hard black substance filling the fitting and is shaped such that it fills the inside of the dust cap. I didn't know what it was, but I am now sure I need to clean that substance out of there to gain access to the valve stem. Unfortunately, I imagine the substance fills the entire valve stem and I may have difficulty getting it cleaned out. Then I figure pieces will end up in the injectors and mess those up. Any advice in that respect? I suppose I should disconnect the main line, then clean the valve out, then connect a plastic bag on the line and turn the ignition on to allow fuel to flush out the hardened varnish or what ever it is(?) I wonder if the valve core will be destroyed in the process.

Do you have to buy the full gauge kit to connect to the fitting? I mean the gauges are around $18. I had planned to buy an appropriate fitting to work with the gauge but that was before you good folks explained that I was dealing with a shraeder type valve. Now, it seems the only fittings I can find to fit it are the ones that are in the full kit. Those are around $40 I suppose.

Thanks for the support and advice!
Frank

Use a needle to remove the plastic substance from the valve stem. I would not worry about plastic getting inside and messing your injectors. There is a filter before the injectors. Once you get as much plastic out as possible, turn on the key to let the fuel pump build pressure and push the middle of the valve stem to let pressurized fuel out to clean things out.

I believe you can also use a tire pressure gauge to measure the pressure. You might need someone to hold the gauge on the valve stem and another person to turn on the key. But overall, the proper gauge is the way to go since you can monitor the pressure while driving as well.

I have 240k miles on my 88 Eldorado and the CAT is still fine. A classic symptom of a bad converter is the transmission will also want to hang up on lower gears and not want to upshift. Do you have this symptom?

Great idea of using needle and then using the gas pressure to shove pieces out. I really didn't want to remove the fitting and to remove the two gas line clamps just to get to where I could read pressure. Thanks for that idea. You mentioned there is a filter before the injectors. Does that filter get clogged?

I found a fuel pressure gauge at Harbor Freight for $13 (HF # 92699). I believe it has the correct shraeder fitting. It appears I will have to buy some rubber fuel line to get the meter up to the windshield while driving.

Glad to hear you have 240k on your cat. How is it you know it is fine?

My transmission has never hung between gears. My transmission slips between 1st and 2nd. It has been doing that for 8 years probably. Without thinking about it, I let up on the gas a little just as I know it is ready to shift into 2nd. People riding with me wouldn't notice the slip. If I don't let the gas off a bit, it can really slam into 2nd. I've always wondered if there is an adjustment for that other than replacing the transmission.

Thank you for the help.
Frank

I believe if you remove the injector, you will find a screen filter. It's been a while since I did that. You might want to remove your injectors and clean out the junk.

"Glad to hear you have 240k on your cat. How is it you know it is fine?"

I have no symptoms of a clogged CAT. Symptoms would include low power and excessive throttle to get the car moving or to go up hills which would cause the transmission to hang up in lower gears.

"I've always wondered if there is an adjustment for that other than replacing the transmission."

You might want to change out the transmission filter. If it is clogged, the transmission would not be developing the pressure it should and this would cause excessive slipping. You could also try tightening up the TV cable a bit. This is the transmission cable that hooks up to the throttle.

Sorry I didn't get back sooner but i see you are on the right track. That plastic stuff shouldn't be there so it should work once you get it cleaned out. I don't know about adding any hose to read the fuel pressure while driving. It probably can't be done becuase it isn't a universal type of hose. That funky 1-2 shift could be a problem with the vacuum modulator or a small leak in the line. Let us know how you make out.

OP,
IMO, this sounds like ignition failure under load. How old are the wires, cap, and rotor? You noted that you had replaced the plugs at one point. What brand did you use?

You might want to try throwing a MAP sensor at it...should be easy to find at a junkyard, or you can use a T-fitting and a suitable length of hose to allow you to place the vacuum gauge inside while you drive. Any Haynes or Chilton manual can assist you with interpreting gauge readings. If this problem only occurs under heavy load, it could also indicate a problem in the vacuum circuit used by the MAP sensor to control the mixture. Check for cracked hoses, loose connections etc. before/while replacing the unit. There might be fault codes, or failing that, even electrical problems with the MAP sensor.
If the mixture is too lean, the resulting heat buildup may be causing too much current to be drawn from the ignition module, causing its failure as you've described. I'm not aware of any fuel-line fittings which do not use Schrader valves; if your fitting looks at all like a tire valve, then make sure you depressurize the fuel system, (pull the fuel pump fuse, crank engine for 10-15 seconds) and have a Schrader valve tool handy before you attempt to pull out the plastic cap.

Thanks for replies and advice friends.

I've been laid up for a few days, but I do have a fuel gauge kit now and I will clean the shrader valve and check pressure today. Thanks for the encouragement that indeed I am looking at a shrader valve with some sort of build-up inside. I still have to buy some fuel line and couplers to extend line to windshield.

The plugs I bought were cheap ones - Delco perhaps. I can check. I didn't realize that could be a bad thing. And I have assumed that they were OK since I just did that a year ago or so. Plug wires are perhaps 10 years old; again they were the cheapest ones I could find. The cap and rotor are original... 177,000 miles on those, but they "appear" to be in sound condition - no apparent cracks, square metal corners...

I can monitor "instantaneous fuel mileage" as I drive. I have always assumed that was actually the result of a vacuum measurement. It doesn't get ridiculously low... say around 9 or 10 when the engine begins to struggle. I have looked for vacuum leaks, but haven't found one. And the rubber hose seems to be in pretty good shape.

It is interesting that you mention ignition module failure due to too much current draw. It happens that when it failed a couple of months ago, it was during a time when the engine was "chugging" badly as I going up an incline at 35 mph +/- in high/4th gear. I was just sort of "playing" with the car's condition to learn more about it, when all of the sudden, the engine just died. I was able to "coast" up the incline (an overpass) and back down onto a side street before stopping. While there seemed to be a link between the struggling engine and the ignition module failure, I couldn't come up with a reason for it. You are saying that, in effect, a lean mixture could result in heat buildup, which could result in a heavier than normal current draw by the ignition module (?) That certainly was what it seemed! And that is why I try to back off the load to the engine when it begins to stall since ignition modules failures leave you stranded. Would you explain why the ignition module draws more current when the mixture is lean?

Another factor I think is valid: This condition started suddenly. It didn't worsen over time and it hasn't worsened since it happened. It seems to be more of a device failure than a gradual system degradation.

Thanks for the help!

Frank

An excessively lean mixture will burn much hotter, as well as faster, and presents very little resistance to the spark plug air gap. When air is compressed, it heats; adding fuel causes a bit of quench, as well as electrical resistance. A lean mixture will cause the temperature in the cylinders to rise; the ignition module itself will then heat up because there is now too much current flowing. It's possible also that too much resistance, caused by deteriorated cap, rotor, wires etc., would mean that the spark is not hot enough to burn the mixture. Pull one of the plugs and have a look at the electrode; this will tell you a lot about the combustion process. I'd recommend you also replace the cap, wires and rotor: no matter how they look from the outside, the carbon tracks forming on the inside will also add resistance. It sounds like you may have overloaded an already struggling engine. Don't be afraid to use 3rd gear for going uphill. I've found 4th to be suitable only for freeway cruising, and if you downshift between 50-55 you'll be fine. I've had a few arguments on this, but never a transmission failure. Gasoline engines produce torque toward the middle of the RPM band. Remember, they were going for economy. But keeping RPM low by using too high a gear results in overloading ("bogging" or "chugging"). Additionally, the proper heat range plugs are essential, and it's worth the extra bread to buy at least the mid-grade wires, since cheap ones will only last about a year or two. 10 years is a bit much, IMHO, even for the premium ones. You can also use a can of carb cleaner to find vacuum leaks; spray it on each fitting while the engine is running and listen for any change in idle speed. They're not always visible to the naked eye.

thank you for the explanation regarding how a lean mixture can cause ignition module stress.

I checked fuel pressure while driving. From the time the key is turned on, the pressure stays within a pound of 13 psi. That includes the few miles I drove up inclines, etc. Turning the key off allows the pressure to drop, but it drops slowly and stays at around 6 pounds for some time. I suppose that all means there is no fuel supply problem. I looked at the injector spray and it "seems" to look OK.

So now... I suppose I should replace plug wires, plugs, distributor cap, and rotor... (??) I figure I'll pull a few plugs first to see how they look. As many of us know, at least a couple of the back four are miserable to change. I was thinking I might pick up a rocker arm cover gasket and remove the rear rocker arm cover, That makes changing the plugs a little easier and would allow me to be sure half of the camshaft lobes are OK.

With the engine in idle, I have removed one plug wire at a time and each one affected engine idle.

Haven't really figured out whether this is an ignition or fuel problem. Feels like a fuel problem, but not sure what else to check in that regard.

Should I do some checking on the O2 sensor or anything else first? I checked trouble codes. There is none that is related to this type of issue.

Any additional advice would be appreciated.

Thanks,
Frank

It seems you're dealing with a combination of problems. Start by eliminating them one at a time:
1. R/R cap, wires, rotor, plugs. A ratchet with a swivel head, or perhaps just a "wobble extension" may save you the trouble of removing the valve cover. Check timing and idle speed too. (It's worth the extra effort; you're "already there!")
2.Check the oxygen sensor (It should fluctuate between .1-.9 mV rapidly after warmup.) A static value or one which changes but does not exceed any value below .9 mV means a defective oxygen sensor.
3. Have the catalytic converter tested. You'll need a smog/tune shop for this of course...
4. Have another look at the MAP sensor. Without accurate readings from this device, your fuel mixture will never be correct. It's possible that a lean mixture, caused by the failure (or even partial failure) of this device, could have taken out your ignition module. OBD-I is not as likely as OBD-II to set fault codes for oxygen or MAP sensors. You'll still need to "sniff it out."
Edahall is onto something too...if your converter has failed, of course you'll need an exhaust shop. Consider his advice...depending on the smog check program in your state, perhaps ordering a pretest will help you narrow it down to this...without having to annoy your neighbors! (i.e., sawing off the exhaust to see if there's any improvement!)
It's likely your converter failed, due to the old cap, wires, plugs and rotor. This could also have damaged the oxygen sensor. Change 'em all, then have your converter looked into. It will be money well spent. If the CAT is OK, THEN the MAP sensor is suspect...

I was afraid you would say that -- a combination of problems, that is.

If you feel that the odds of a failed camshaft causing this problem is remote, then, like you say, it would be far easier not to take the cover off. a universal joint or swivel head would allow me to get all 8 plugs changed.

I can measure the voltage on the O2 sensor without a lot of trouble. Can the MAP sensor voltage be measured as well? If so, would you tell me what the acceptable voltage range and change pattern would be?

I believe you are saying that it wouldn't make sense to replace a defective O2 sensor until I know that the cat is OK. Because if the cat is bad, I would stand a good chance of destroying the O2 sensor again (?)

I am not sure that a "Pretest" is something available in Kansas, but I will find out -- that would be a great idea if it works.

I suppose, depending upon the cost of a "pre-test", it might not cost a whole lot more to just change out the catalytic converter if its being bad is a strong likelyhood. Advance has them for $60. Two questions in that regard: If something else is wrong, could it destroy the cat again -- like before I get the "something else" fixed? And is there an analyzer to check the catalytic converter that would be loaned out, say from Autozone or somewhere? I am assuming you measure the mixture of the exhaust content to determine whether the cat is OK.

I checked current/history codes again today. There is none relating to engine performance.

Thank you for the ongoing support.

Frank

Frank,
You're dancing around an obvious issue. Change the plugs to whatever Delco plugs the OEM spec calls for. Change the wires, cap and rotor using AC Delco or another quality item. Your symptoms are so typical of failed ignition that this is the logical place to start.
As far as the difficulty of changing plugs, you'll need various extensions, swivels, etc but it is doable. No need to pull the rocker cover. Change the wires at the same time, plug by plug.
This is hard but not complicated. It is basic. Post back when you have done the work. My bet is that your car will be running fine then.

Thank you NickySantoro!! I sincerely appreciate your confidence that this will be fixed. I've chnaged the plugs three times I believe. And they were changed one time, the first time by the dealer. But I never enjoyed it!! I'll get wires, plugs, distributor cap, and rotar -- probably tomorrow. Had eyes dilated today, so things are blurrier than normal right now.

Glad to hear your opinion that the symptoms I've described are typical for failed ignition.

You folks on this forum are great and I truly appreciate your guidance with issues like this one that I just haven't seen before.

Thanks!

Frank

From "Automotive Service" by Tim Gilles:
[CATS] can become plugged after running for a prolonged period of time with an ignition system defect. A rich air-fuel mixture can also result in a plugged converter when it overheats and melts internally...might also experience harsh or late shifts due to the resulting faulty vacuum signal or increased throttle pressure in the transmission.
By doing all the ignition system work, you will likely be correcting the problem which fouled your converter. Since you ran it for so long with the ignition system in such poor condition, I'd strongly recommend you replace both the oxygen sensor and the CAT.
If you don't have a vacuum gauge, MityVac sells a plastic one for around $35.
You can check for a restricted exhaust by using a vacuum gauge, too:
With engine at normal operating temperature:
Connect vacuum gauge to manifold vacuum source. Note in-Hg reading at idle. 16-22 in.-Hg is considered normal below 1000 ft.
Increase engine speed slowly to 1500 RPM, then release.
Note what happens to the gauge, not necessarily the value. It should return to the idle value quickly; you're looking for a delay.
The needle should also be steady. There is a page of vacuum gauge readings/interpretations in almost every service manual.
Snap the throttle open quickly--to 2000 RPM, then let it go, all while watching the gauge. Repeat as necessary.
A restricted exhaust is indicated if the needle returns slowly, or it "hunts" for the value first obtained at idle. There should be high vacuum available as soon as the ISC contacts the throttle (this is part of the emissions controls.)
Though an exhaust gas analyzer can tell you a lot about where to look for engine troubles, it is not an exact science so much as an interpretive one. Best to leave the MAP sensor for last. NickySantoro is dead on. (+ Karma UU, dude!) Only thing I'd add to his advice is: to put the new cap (oriented properly of course!) next to or even atop the old one. Pull the wires off one by one (i.e. CHANGE #1 plug, then pull off the old wire...attach the new wire to the new plug...) Then, attach the new wire to the new cap, checking as you go. Repeat for all the others. So long as you detach only one wire from one plug at a time, you can't get the wires mixed up. When you're finished, you'll just have to remove the old cap, change the rotor, and pop the new one back on. Make sure you gap those plugs properly too. When installing the new plugs, you can use either an old spark plug boot (you'll have plenty of those!) or a 6" length of 3/16" tubing as a wrench to get the threads started...
Having done all this, if the vacuum gauge test indicates a faulty CAT, once this is all done you should be back to normal...if not, THEN it's time to wonder about the MAP sensor. But I couldn't think of the vacuum gauge test in time or, for that matter, symptoms of clogged exhaust. Funny because I reconditioned a vehicle in '06 with the same problem. Time flies!

Thanks for the guidance hthorn. I believe I have a vacuum gauge, not sure, but if not, I will get one, borrow one, or get mine back and test to see whether the cat is bad. You describe an interesting procedure to make that determination. I plan to better understand why the vacuum reacts the way it does depending on the condition of the cat.

I'll advise of the results I find.

Thanks again!

Frank

Cool--just remember that if the exhaust has too much backpressure, it stays in the cylinder too long, thus displacing the fuel/air mixture. To develop vacuum (since an engine is, essentially, a vacuum pump) there are many interdependent factors. The fact that your transmission has been shifting late as you describe indicates a faulty vacuum signal, as the vacuum cannot build to a sufficient level to allow the transmission to shift. It's being kept low by the exhaust gas which cannot escape fast enough.

Thanks again hthorn. I appreciate that explanation. Reminds me of two other factors that may contribute to that discussion.... One is that there has been some black smoke coming from the exhaust pipe for perhaps 100,000 miles. Not hardly enough to notice, but there is more than there should be. (A friend, who was following me one day when the car had perhaps 75,000 on it, commented that some black smoke was coming from exhaust. Car has 177,000 miles on it now). 2nd: Brake pedal goes too low. I have bled the brake lines a lot... like I've bled more fluid at one time than the lines can hold and there is no leaks. Perhaps something else going on there besides low vacuum, but, just thought I would throw that in.

Another issue I have been curious about is the auxillary vacuum pump that starts up when the ignition is turned on. I assume the vacuum from the pump helps the power brake unit and other vacuum dependent accessories. Are the two vacuum systems kept separate somehow? Perhaps there is no connection between the power brakes and the vacuum created by the engine.

I know this is a difficult question, but, if a new cat would have perhaps a 2" diameter passage way for exhaust through it, how small could that capacity become and still allow the engine to run as well as mine does? Say... 1", 1/2"...? I hadn't realized how these symptoms could tie back so readily to a plugged cat. It would be interesting to bypass or gut the cat just for a test.

I have to heal for a few days from two hernia repairs, but am anxious to get back out there to replace ignition components and test for defective cat.

Thanks again for your continued support.

Frank

The CAT has very small honey comb passages. They can easily become clogged.

If you live away from the city, you could certainly unbolt the cat and drive the car with a pair of ear plugs.

You can either bypass the CAT or use the gauge--my guess is your neighbors will appreciate it more if you use the gauge! It will tell you definitively. Much simpler. Maybe once before you do the ignition work, and once after. Then after the exhaust work is completed, you should be able to feel the difference. But if you can find your earplugs, and not your vacuum gauge...
Black smoke could mean incomplete combustion, i.e. unburned fuel, which makes it now 99% likely that your CAT is defective.
...Auxilary vacuum pump? Not unless you have a diesel. You might want to check your master cylinder. Low vacuum would cause a "hard pedal". Also, if you're not bleeding the system properly, you might not be getting all the air out.

Thanks guys. Yeah, I live in a neighborhood that would not appreciate muffler removal. It is hard enough to live here with an '86 Eldorado. I can't find a vacuum gauge in the garage, but Harbor Freight has them for around $13 with the fittings and hose. So I plan to pick one up tomorrow.

hthorn... My car does have an electric (14v @ 8 amps) vacuum pump. It is located under the battery tray. While I never had a car with one before, I just assumed that all the Cadillacs had one. I would think the pump would affect the vacuum test regarding the cat. Indirectly, it is tied to the brake booster, cruise control, egr, transaxle modulator, MAP, etc. Might make one wonder whether that could be a source of transmission problems. The pump is noisey.

The brake pedal isn't hard. It just goes a long way down. And I did follow the bleeding procedure to the point that I really don't think there is still air in the line. I have wondered whether the master cylinder is bad. But, I figured if it was allowing fluid to get passed the seals, the pedal would slowly go clear to the floor with pressure. But it does not do that -- once the brakes are set, the pedal goes no further down.

The plot thickens.

Thanks for the help with this!

Frank

Only pump I know of on those is next to the battery, for the suspension. That's a new one on me...
Next time you've started it up, pump the brake pedal several times after you've shut the engine off--then stand on it. (Literally!...) If it starts to sink after 30 seconds, the seals could be leaking.
The pump shouldn't affect the vacuum test, since its purpose is usually to supply additional vacuum at idle or under low vacuum condidtions. The test as previously described should not be affected because the conditions are changing too rapidly.

Hi hthorn,

Thanks so much for the master brake cylinder test procedure. I'll give that a shot.

Here is a link to the vacuum pump if you are interested...
http://www.partsamerica.com/ProductDetail.aspx?MfrCode=A1C&MfrPartNumber=641502&PartType=540&PTSet=A

I bought a vacuum gauge today, so I am ready to test for a defective cat. However, Midas Muffler today, at no charge, connected a pressure gauge ahead of the cat and measured back pressure. I was dissappointed to find out that they felt the cat was OK. They suggested that perhaps the timing chain had jumped a tooth. I do have a timing light, so I can check timing. They also told me that the 14 psi I measured should be more like 44 psi. I explained that the system uses a return line and that 14 psi isn't the direct pressure of the pump and that pressure in excess of that amount is allowed to release into the return line by a regulator within the TBI. Didn't seem as though they bought that.

So... it seems I need to check for vacuum leaks and to replace the wires, plugs, dist cap, and rotor. I'll also do the vacuum check for the cat.

Also need to buy a bottle of Lucas fuel treatment as mentioned by ehall.

I've learned a lot through this event! Thanks for that!

I'll let you know.

thanks,
Frank

Your engine is TBI so 14 psi is correct not 44 psi. The newer cars with PFI use much higher pressures.

Sounds like your CAT is OK from the test that was done.

Next step should be to replace wires, plugs, dis cap, and rotors. Make sure you use AC Delco parts especially for the wires and plugs.

Thanks Edahall.

I figured checking the timing would be an easy chore. I can't find any source for what the timing should be. I can't find the VECI label... perhaps it has fallen off. I did set it before. I can jumper pins A&B of the ALDL connector, but can't find what the timing should be.

Anyone know? 1986 Eldorado 4.1L, 87 octane fuel. I believe it should be 10 degrees but not sure.

Thanks!
Frank

I just set the timing to 10 degrees. It was at 8 degrees. Then I checked vacuum which is pretty steady at 17 at idle. A quick snap of the throttle took the vacuum to 0, but it came quickly back to 20 then dropped to 17 when the throttle was brought back to idle. If I slowly opened throttle, the vacuum didn't change a lot and the engine sped up normally. When I snap the throttle, the engine hesitates - sometimes enough to stop running.

I was surprised to see the vacuum stay at zero with the engine off but ignition on ... I was measuring vacuum at the tee to the air cleaner. I figured the vacuum pump would have produced some vacuum. I am wondering if it is bad.

Also noticed that one of the two cooling fans was full on when the other one was still. Wondering if the fan controller is bad. Engine was not hot when that happened.

I haven't checked the O2 sensor. I believe it is on the rear manifold. But there is no trouble code about fuel mixture if that makes a difference.

It seems the next step is to replace plugs, wires, dist cap, and rotor.

Thank You, Thank You, Thank You !!! To everybody that helped!

To summarize: Cad runs Can-Normal again!! No longer have to be afraid of going up inclines and such.

I replaced the fuel filter, but I am sure(?) it was OK. Also checked fuel pressure and vacuum, both of which looked good. I set timing to 10 degrees, which is what it is supposed to be, but the engine almost wouldn't start, so I backed it down to 6 degrees. Had exhuast back pressure checked and it was normal. Then I replaced the plugs, wires, rotor, and distributor cap. And the car runs fine. Seven plugs looked great. One plug (#6) looked as though it had not been firing. I have a bottle of Sea Foam for the fuel, which I will add next time I fill up.

It seems to me that it would have been more than one plug. Perhaps another one or two were intermittant(?) And should I assume it was the wire(s) or perhaps the distributor cap too. I did lose an ignition module just a couple of months ago and that was during the time the engine was running poorly. Perhaps the gaps between rotor and distributor and bad wire(s) cause stress to the ignition module(?)

I suppose I should bring the timing back closer to 10 now. Perhaps acceleration would improve a little.

Thank for all the help. I really appreciate all the support and guidance everybody gave. It was bad timing for me due to a couple of hernia repairs right in the middle of all of this. I wasn't supposed to lift and strain and such. And you can't own an Ht4100 engine without doing that at least weekly.

Thanks again!

Frank

Just in case... On the timing, you set it 10 degrees after you put the car into the set-timing mode. You don't just set it to 10 while the car is running.

Also, Seafoam does okay as a fuel system cleaner but it's nothing compared to the Lucas fuel treatment. Best use for it is to pull half the can through a vacuum line into the throttle body, and dump the other half into the oil, but you MUST change your oil and filter after 75-100 miles if you go that route.

Glad to hear you got it fixed......

As ehall pointed out, you have to set the timing while in set timing mode. Read in your manual on how to do this. 10 degrees is what the factory recommends but you often can get by with a little more advance than that. Keep advancing it until it starts to ping just slightly at low rpm's / high power (lugging). This is the optimum point and you'll get more power and fuel efficiency. My car is set at 14 degrees using low grade gas. If I used premium, I would be able to advance it even more.

I think you mentioned earlier that you had aftermarket plugs and wires. That likely could have been the problem. A/C Delco plugs and wires are more expensive probably for a reason.

Thanks guys for the tips.

I had planned to put the seafoam in today, but I will exchange it for the Lucas brand.

When I set timing, I did have it in the "set timing mode" or something similar on the display. I had jumpered pins A&B in the diagnostics plug. I haven't moved it up higher... closer to 10... yet. It just seems that there is something unusual in that the engine did not want to start when I had it at 10... granted I had the plug not firing. Normally, the engine starts within half a second. I had to crank it for perhaps 10 or 15 seconds to get it to finally start.... Almost as though the timing scale was off or the notch was in the wrong place (not possible). If it was off a tooth, however, I would think the engine would not run as nicely as it does. And it is just a 4 degree difference... (??) I'll move it up some today to approach the point of pinging as Edahall explains.

Incidently, the plugs I had were ACDelco plugs. And 7 of them looked perfect. The 8th one wasn't firing. But I don't think it was a plug problem, it was probably the 10 year old $22 set of wires or perhaps the original distributor cap or rotor.

Thanks again guys. You provide great advice in a great forum!

Frank