1985 Eldorado Engine Stumble & Surge

[Elwood]

I'll give that a shot too, but I've been able to see the miss on #4 & #8 with a timing light at idle if the car is hot enough (20+min drive time & >85 degrees ambient temp) and disconnecting the EGR had no affect, with that test anyway. I've also manually stroked the EGR stem with a hooked piece of metal and the tubes into the intake are certainly not plugged. Even when the car is hot as mentioned above I can "cure" the symptoms just by selecting a gear that runs the RPM up over 16-1800. And I think this actually "cures" the miss because the fuel information display stabilizes at reasonable numbers too.

[carnut]

The service manual talks about spark plug wires that can be too close to the HEI lead ins at the distributor causing an inductive miss. Also two cylinders side by side could be getting an inductive miss from the each others wires as well. Are the plug wires routed by the book and all in their respective retainers? I agree an EGR wont cause a miss at idle but you say its RPM related above idle. By verifying the miss with a timing light, describe what you see and how you arrive at that conclusion. Also this question regarding torque converter lock up can be verified by the orange icon in the climate panel as driven in diagnostics. Its either engaged or not by the lights illumination. Also 3 or 4 years after this year of car, there was a GM bulletin stating that a worn distributor drive gear could cause erratic performance. Something never looked at during diagnostics. There was an issue with dissimilar metals, camshaft to gear, causing the wear. An improved gear was issued to correct this.

[steelybill]

We talked about grounds early in this thread, and tonight while removing my oil pan, I saw the other grounds that I forgot about earlier. There are a few bolted to the engine block just to the right of the starter. Don't know off hand what they are for, but they are worth mentioning , since all grounding points are important in these cars.

[83CADMAN]

I experienced a similar condition with my 83 Eldo. Went though all the same troubleshooting with some results after replacing all the vac lines.
I finally discovered the problem was in the EECS (evaporative emission control system). Try checking the vacuum at the charcoal canister. There is also a filter element located in the bottom of the charcoal canister that may need to be replaced. On mine I found a hole in the side of the canister. I located a replacement at my local U-PULL yard cost me $3 and now no idle stumble or surge. Go figure!

[steelybill]

That's really interesting Cadman. That canister is ignored by most people ( including me) It's worth a look for sure. I'll have to give mine a peek too.

[cadillac_al]

I think I read somewhere that the plug wires shouldn't be routed near the heater blower motor because of some interference. Anybody else remember reading that somewhere? #4 and #8 are in that area.

[Elwood]

Sorry for not getting back in here for a few days, been busy. I really appreciate the continued support, and hope to get an hour or two this weekend to give it another once over while everyone else is out whooping it up. I’ve been pinging any other source I can get to listen and an old buddy of mine who worked at a GM garage years ago suggested that I try replacing the pick-up coil in the distributor as long as I’m pretending its Easter (looking under every rock) so I ordered one on-line and it showed up yesterday. As I mentioned up near the top of this thread, the connectors (and seals) in the distributor were in rough shape when I started this and he thought there could be something down in the bottom of the cup there that might be shorting out those two adjacent contacts intermittently, or a broken coil wire that only opens when it is hot. As I said, I’m open for anything so with any luck I’ll have that replace this weekend. I also plan to check everything else that has been suggested lately, in order of post. Thank you guys again for the help!

[Elwood]

Well, I’ve proven again that you cannot assume anything based on someone else’s word. See my 6/9/09 post where I wrote off the suggestion that the distributor could be the source. My “virgin” two owner Cad with 84,000 miles apparently ran the first 30,000 or so on the factory oil. I checked all the grounds, and the evap can charcoal filter first and then pulled the distributor to R&R the pickup coil. The first clue was the need to use a pair of pry bars to extract the distributor. When I finally got the shaft out of the housing the top bushing was visibly egged and the pickup coil points for #4 & #8 were visibly daubed over from contact with the star wheel on the shaft. A quick trip to my favorite salvage yard and $25 (exchange) scored a serviceable replacement distributor and my first test drive seems to indicate a home run! My youngest daughter finished the install so I had to go back tonight and crank the base timing up several degrees to restore some lost power but I am optimistic that the mystery miss has been solved. I have to thank the 4 or 5 of you who have continued to offer help and advise, just wish I had listened a month ago. I’ll try to post a final summary once I’m convinced the gremlins have been banished!
Thanks again!

[steelybill]

Great to hear you have found something other than the usual ailments, and can likely get it fixed. Like you said about the oil, the sludge finally caught up to moving parts. Usually the camshaft is a victim of ignored oil changes. Is the distributor gear OK?

[Elwood]

Thanks Bill, the gear that came out looked good but the annular spaces up the sides of the distributor housing were plugged with clinkers and the top of the shaft looked like it hadn't seen oil in a long, long time. I just couldn't make myself believe a car in otherwise nice condition could have so much gunk in the engine with so little mileage, but "maintenance" is a relative term I guess.
Driving it on several trips today confirmed the need to reset the ECM if you change the timing as it did a couple very strange things after a couple starts, but it looks like I've picked up a couple MPG and the "hot, low RPM miss" is gone. Still notice the hot stumble off idle once in a while but hoping that the ECM will figure that out in another day or two.
Thanks again everybody.

[steelybill]

You may be right about the ECM fixing itself and the miss. Mine used to do that, and it just went away finally.