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HT4100 4.1, 4.5, 4.9 Discussion, 1986 Eldorado stalls under stress in Cadillac Engine Technical Discussion; The catalytic converter does have 176,000 miles on it. I don't know how long they are supposed to last. I ...
  1. #16
    FrankC's Avatar
    FrankC is offline Cadillac Owners Member
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    Re: 1986 Eldorado stalls under stress

    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

  2. #17
    Edahall's Avatar
    Edahall is offline Cadillac Owners Enthusiast
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    Re: 1986 Eldorado stalls under stress

    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?

  3. #18
    FrankC's Avatar
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    Re: 1986 Eldorado stalls under stress

    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

  4. #19
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    Edahall is offline Cadillac Owners Enthusiast
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    Re: 1986 Eldorado stalls under stress

    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.

  5. #20
    cadillac_al is offline Cadillac Owners Connoisseur
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    Re: 1986 Eldorado stalls under stress

    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.

  6. #21
    NickySantoro is offline Cadillac Owners Fanatic
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    Re: 1986 Eldorado stalls under stress

    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?

  7. #22
    hthorn is offline Cadillac Owners Member
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    Re: 1986 Eldorado stalls under stress

    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.

  8. #23
    FrankC's Avatar
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    Re: 1986 Eldorado stalls under stress

    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

  9. #24
    hthorn is offline Cadillac Owners Member
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    Re: 1986 Eldorado stalls under stress

    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.

  10. #25
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    Re: 1986 Eldorado stalls under stress

    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

  11. #26
    hthorn is offline Cadillac Owners Member
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    Re: 1986 Eldorado stalls under stress

    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...

  12. #27
    FrankC's Avatar
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    Re: 1986 Eldorado stalls under stress

    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

  13. #28
    NickySantoro is offline Cadillac Owners Fanatic
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    Re: 1986 Eldorado stalls under stress

    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.

  14. #29
    FrankC's Avatar
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    Re: 1986 Eldorado stalls under stress

    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

  15. #30
    hthorn is offline Cadillac Owners Member
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    Re: 1986 Eldorado stalls under stress

    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!

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