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1958 Series 62, 1985 Eldorado
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Discussion Starter #1
I recently purchased an 85' Eldo w/ 84,000 miles, HT4100 gas engine. After a month of effort can't cure my last drivability problem. Symptom is an off-idle stumble (most noticed from a standing start) and low speed cruise surging (25-40mph). I have replaced: cap, rotor, ign. modual, plug wires, plugs, dist. cap harness, throttle possition sensor and harness plug, catlytic converter, exhaust resonator, and various and assundry other minor items. Most recently I have removed and cleaned the EGR twice. This effort has eliminated several other issues but still have the stumble and surge, only after the engine is at full operating temperature (i.e. >12-15 minutes drive time). Also observe erratic "Fuel Info" display with "instant" mode selected, display will rapidly indicate low single to high double didgit numbers and occasionally display various alphanumeric combinations along with intermittent lighting of the "Range" mode light or going blank for up to 1 second, also only at temperature and only when surge is present.
The car averages 18-19mpg on my commute and >22mpg average highway.
Thoughts anyone?
 

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1958 Series 62, 1985 Eldorado
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Discussion Starter #2
Oh, and I forgot to add, after a 45 minute mostly highway drive on our first 80+ degree day and 10 minute shut down I started the car and put the trans in drive but the car would not move. I then noticed that in the left side "information center" the top left and bottom right red lights were lit. I did not have my reading glasses and couldn't read the errors so I shut the car off and left it over night ( I was home and wanted to move it but didn't need too). The next day everything worked as before and have not had this problem reoccur, but haven't tried to start and drive it hot.
 

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'85 Fleetwood FWD
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728 Posts
One thing I would add to what you have already done, is check the fuel pump pressure. There is a capped-off port in the fuel line, not far from the TBI where you can plumb in a gauge. The book sez the pressure should be between 9 and 12 lbs at that test point, in all speed ranges.
Some mention is made of the port in the manifold that the EGR valve is mounted on, for a build-up of "stuff" in that port.
Also hoses to the MAP sensor and really, all vacuum hoses for visual condition.

The spray pattern of the injectors can also have an effect.. In a throttle body, with the air cleaner off, the spray pattern from the injectors can usually be seen to some degree

Hope this helps.......

BILL
 

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'87 Coupe DeVille 4.1L FWD(New engine '08) 1981 F100 '03FXDL
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879 Posts
You posted nothing about trouble codes being present in diagnostics.
 

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'85 Fleetwood FWD
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728 Posts
Like Dave mentioned, you posted no trouble codes.. If you can get some codes it will be easier to help you. Do you know how to enter diagnostics??
with the ignition on, engine off, press "off" and "warmer" buttons both at the same time, momentarily. First is the seganment check, then status will begin with codes "E", and after it runs thru them, "F" codes , if any, will come up. When those are through, .7.0 will show it;s ready to go farther into checking the system.

The system in these cars can check just about anything when the right sequences are used. I know only the simple things that I had to learn about it to fix mine.

BILL
 

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1926 Model T street rod, 2000 Jaguar XJ8, 1999 Corvette.
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You say you've replaced the throttle position sensor. I presume you adjusted it to spec?? Thats the varible resistor that determines fuel delivery and how much. I agree with having you get the fuel pressure reading first. If at spec, I suspect TPS is out of range.
 

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'85 Fleetwood FWD
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728 Posts
The book says to make "sure the TPS pick-up lever is located ABOVE the tang on the throttle actuator lever". This info in the book suggests that maybe it's possible to get it wrong. Just thought it was worth mentioning that.

Vacuum leaks are also mentioned. Hoses from 1985 could be deteriorated. They were on mine
 

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1958 Series 62, 1985 Eldorado
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Discussion Starter #8
Thanks for the input guys. The TPS replacement was done due to a previous group of problems including a TPS fail error code (I don't have my book here right now so don't have the code number). The tang is possitioned correctly and the sensor was zeroed at 0.65 vdc (mid range of the requirement). Since my last attempt, cleaning the EGR twice, I have logged no error codes but the loss of power when I reset the ECM. I'll see if I can find a fuel pressure gauge and check that this weekend.
Does anyone have an instrument cluster out of a car who could look and see what the upper left and lower right indicators are on the left side "Information Center"?
 

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'87 Coupe DeVille 4.1L FWD(New engine '08) 1981 F100 '03FXDL
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I have logged no error codes but the loss of power when I reset the ECM.

If you 'reset' the ecm by disconnecting the battery....bad idea. Doing that: erases the RAM(learned library) and reverts the system to the PROM. That ROM programming was used for a brand-new vehicle/engine/sensors. Trying to get a 29yr old engine system to run on the values of a brand-new engine/sensors isn't the way to go. Put miles on the engine and let the RAM rebuild.
May I suggest you buy a Cadillac Factory Service Manual(not a haynes/chilton) for your car? ebay always has a slew of them...$25 and up. Having one to use is 'handy'
 

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1958 Series 62, 1985 Eldorado
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Discussion Starter #10
Thank you Dave, I just bought a book on e-bay so I'll have some reading to do next week. I did reset the ECM by lifting the negative this time. I haven't had the will to drop the panels under the dash and look for the fuse, and I've had to disconnect power a couple other times since I got the car anyway so I'm hoping the drive time I do have on it (~1000 miles over all) since I started fixing things is enough to restore the RAM. It probably has 200 on it since the last reset and still have the drivability issue at full operating temperature.
 

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'85 Fleetwood FWD
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728 Posts
I dropped both under-dash panels off until I was done fooling with the problems. It's also a good time to get familiar with what's under there while it's accessable, for the relay center etc.. Your manual has a parts locator page, and a fuse block page etc.
 

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1958 Series 62, 1985 Eldorado
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Discussion Starter #12
Okay, I bought the 1985 final edition Cadillac service manual and have read it cover to cover, run all the diagnostics and still have the stumble and surge drivability issue with no failures detected through diagnostics other than one occurrence of a soft error #23 which seems to have registered during my normal commute. The “mystery “ information center indicators I documented earlier were due to the engine dying immediately after hot start, which has now occurred 3 or 4 times (had the radio too loud and miss-diagnosed the first instance). The surge condition seems more engine RPM than throttle position related, i.e. if cruising at 30-40MPH and experiencing “significant” surge/pulse/hunt conditions along with extremely erratic “fuel information” data a change to “drive” (3rd gear) from “overdrive” with no adjustment in throttle position immediately cures the symptoms. Similar response is observed at 15-25MPH cruise in “drive” when the transmission is shifted to L2 (2nd gear). The car still runs great in all other conditions and is still getting “typical” fuel economy (~19 city, ~23 highway). One other significant observation is that upon release of throttle to coast down from nearly any cruise speed, and even if above conditions are occurring, the fuel information display stabilizes at “reasonable values” for 5-8 seconds and then reverts to rapidly changing blank/numeric/alphanumeric values and random lighting of the “Range” mode indicator. The book doesn’t seem to have a cure for these symptoms so I’m all ears.
 

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1926 Model T street rod, 2000 Jaguar XJ8, 1999 Corvette.
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I think the biggest clue is the blanking out of the displays. I would suspect either the climate control head or the mileage display head as faulty. I.E. loosing the ground signal. On this early computer system, I've never found it necc nor have I seen an issue with it relearning parameters after an ECM disconnect, unlike my later 91 Allante which requires a structured idle learn procedure. I think it would be a good idea to drive this vehicle with the fuel pressure gauge positioned to be able to confirm steady pressure when this surge, stumble occurs. One other thing, check and adjust the TV cable at the throttle body to the trans. Early upshifts cause cause a surge to be felt. You can monitor torque converter lock up thru the orange dots in the climate display as driven as well. Is it locking up too early??
 

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'85 Fleetwood FWD
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728 Posts
If in fact one of the display heads is faulty you may not be able to get the info you need. I've seen those on ebay, but luckily didn't need one (yet). Mine goes nuts occasionally. I just tap the buttons a bit and the display seems OK again. Must be the switches on the PC board in those that act up.
 

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1958 Series 62, 1985 Eldorado
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Discussion Starter #15 (Edited)
Thanks again for the feedback. I didn't mention that I was able to get a fuel pressure gage on the car a couple weeks ago and pressures were well within the acceptable range at all RPM's, however I didn't try piping the gage into the cabin for a drive test. Also confirmed that the injector spray pattern was correct. Given the symptoms I think I'm still chasing something other than the fuel system. I also believe the display heads are probably functioning correctly since I was able to run and properly read all the diagnostics listed in the service manual and erratic displays only occur in conjunction with the erratic engine function. The time to onset and severity of this condition has increased with our increasing temperatures, and the dying upon hot start is routine now so my guess is that something is going to start setting error codes soon. The new "die on hot start" is odd to me also. The car starts easily but dies as soon as the key is released to the run position when hot. I can then immediately restart the car and it will run fine, accept for the stumble and surge. I noted in another thread a suggestion on testing for EGR tube blockage by manually stroking the EGR valve stem at idle and confirm that idle quality diminishes. Worked perfect. I could easily kill the engine with a small opening of the EGR.
The transmission functions perfectly with converter lock occuring properly for both throttle possition and speed. As noted, this surge condition is displayed at lower speeds in 3rd gear which should disable converter lock.
 

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1926 Model T street rod, 2000 Jaguar XJ8, 1999 Corvette.
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Check engine to chassis grounds. Should be one behind the alternator on a stud on the engine, one at the rear center hood bumper at the cowl and of course the battery ground. Loose, dirty grounds could be intermittant.
 

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'85 Fleetwood FWD
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728 Posts
Carnut is right, bad grounds can cause things you wouldn't believe. The factory manuals show all the grounding points, and there are a bunch, even one behind the corner of the back seat on some models. Mine has one near the battery, which was bad when I bought the car. It has multiple wires grounded there (all waiting to give ya a bad day):)
 

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1958 Series 62, 1985 Eldorado
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Discussion Starter #18
Again, I appreciate the continued support. Symptoms continue to get worse as the temperatures clime. I now notice a definite miss at idle now that it is “hot” (into the 90’s) and experimenting with gear selection can toggle the symptoms and can get the engine to miss at almost any speed with the throttle just off idle and very low engine RPM. The miss at idle is nearly un-noticeable unless you are obsessed with the problem. I got some time again this weekend (6/6/09) to do some more in depth troubleshooting and found the miss is certainly an intermittent, but possibly simultaneous, loss of spark to the #4 & #8 cylinders? (Note: the “entire” ignition system is new). I inspected, removed, inspected, cleaned, inspected, etc. everything from the distributor to the new spark plugs and all I found was some deterioration of the three connector ECM plug on the ignition control module in the distributor, which I cleaned, rebuilt and covered in heat shrink, to no avail. Measuring with a tachometer at ambient temperature of 70 and engine at full temperature there is no miss until RPM reaches ~1100 and the miss seams to disappear at ~1600 RPM, only missing on #4 & #8 cylinders????? I am all ears!
 

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'85 Fleetwood FWD
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728 Posts
The manual for mine also mentions intake manifold gasket leaks as something to check. In the old days we checked for manifold vacuum leaks by using a squirt type oil can with some gasoline in it, and dribbled some along the manifold gasket edges. If it was leaking, the RPM picked up.
Did you get a look at the MAP sensor hose ?, and the MAP hose fitting/opening in the throttle body?
My manual also mentions the HEI ground connection. I'm not sure where thats located on your car. There is a black wire on the coil in the distributor, which is the coil ground wire. Maybe that is what's referenced. The distributor schematic shows the grounds to be on/in the distributor housing itself. The black/red wire in the plug for the distributor is the reference ground to the ECM. Check that connector for loose fit on the pins etc. Mine was problem.
On mine, the ECM , the climate control, and blower motor ground is on the Alternator mounting bracket. You could check if yours is there, and it's condition/torque on the fastener.
Also, there is a junction block on the R/H shroud behind the panel (dash), sort of ahead of the door post area, with 26 connectors plugged into it.
Another one is located behind the panel, to the right of the steering column.

Some of my problems were fixed by simply un-plugging and re-connecting stuff, which likely helped make better contact in the connector pins etc.
That's how I made the cruise control problem go away.

The manual ground schematic shows splices in the ground wires (scary) They are usually in the wire bundles though, and well protected.

Hope all this helps a bit.......
BILL

Oh yeah, the ground at the jump-start junction block near the battery is also the ground for the fuel data center, and climate control panel (control head) That's worth a look too.
 

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70 Deville 77 Fleet 78 Seville 92 Deville 03 Deville
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I think it is next to impossible for the distributer to misfire only 2 cylinders. All 8 have equal access to the rotor. Now, since 8 and 4 are next to each other, there may be something to it. Maybe there is a defect in the cap, or the rotor may be wobbling pretty bad. I have never heard of this happening before though. I wonder what the plug gaps are on those cylinders. Sometimes I reduce the spark plug gap to .045 when the manual recommends .060 or .080 because I don't believe the HEI can fire .060 unless everything is perfect. When I changed the plugs in my deville they were all gapped at .030; must have been an old timer that put those in. I can't remember if I gapped my new ones at .045 or .060 but sometimes you can't change them that much without putting the electrode at an odd angle.
 
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