1970s 1978 Eldorado idle/smooth running issues

[joeinbcs]

Howdy all,
I currently have possession of a '78 Eldorado Custom Biarritz Classic that was donated by Jim Caffrey's brother John, on behalf of Jim's estate.  The car will appear in a Charity auction on Bring a Trailer as soon as I can get everything sorted. Proceeds from the auction will benefit "Honest John's Texas Legends", a 501(c)3 Charitable Corporation named in honor of John Foust, to benefit young victims of drunk drivers.
It's a 18,300 mile car, but running poorly.  John told me the car had brake and carburator issues, but knew little of its condition, as Jim had about 40 cars, and this one had been kept in Florida where Jim spent winters.  So, I have no records at all.  I replaced the master cylinder and the brakes now work well.  I know it has a new copper and brass radiator from US Radiator because I called them and they found that Jim ordered it in Feb of 2021.  The Carburetor looked new as well.  I tuned the idle mixture screws using vacuum, but it still did not run right.  Also checked the timing, which seemed to be within tolerance.  Then, I became convinced that the carburetor had been improperly rebuilt, so I bought another.  Put it on last night and it ran just as rough as with the previous one.  I've also changed the plugs and the oil.
Looking for ideas on what to try next.  I'm picking up a new EGR valve this morning, and I ordered a new distributor cap and coil.
I'll have a virtually new car and empty bank account if I ever get to the end of this.
Anyone who has thoughts on what could be wrong, please send 'em my way.
Oh, one last point...the car has a spacer under the carburetor, about half an inch thick.  I reused it when I swapped carbs, using only the spacer and no additional gasket, as it was before.  Could this be an issue?
Thanks, Joe

[joeinbcs]

I just took the EGR valve off.  It seemed like it was stuck on the car, but pressure on the bottom will expel vacuum off the car.  Maybe this is OK?

[TJ Hopland]

I'm not sure what you mean about egr pressure?  At idle it should be closed and if its an original you can usually reach up inside it and operate it and if you do that at idle it will either stall or at least make it run really rough. 


A assume you have a manual and are using the correct procedure for timing?  I don't remember details but I do remember 78 had what seemed to be an unusual process with some extra steps and settings at a fairly high RPM. 

The carb being changed kinda raised my eyebrows.  General exchange carbs have never been a good thing in my opinion even 40 years ago and today when it seems like almost everything is junk I'm really suspicious of that carb.  I think the 77-78 Cadillac carbs were unique to Cadillac and were 800 cfm vs the usual 750 and the tune was not usual so you really had to go my the book to set one up, kinda like the timing that just wasn't typical. 

Since this should have the hydro boost brakes is the brake booster vacuum port on the back of the carb capped?  I'm assuming the Eldo's got the electric level ride pumps like the other cars so there are no vacuum lines related to that.

I don't remember having EGR valves themselves leak, most of the time they would get plugged up and not work which could cause other issues but they didn't tend to leak especially at idle.  Occasionally I remember finding them with a burnt out gasket but that too was rare.  Most of the time people replaced them because they were just guessing and hoping and often introduced new issues because the replacement wasn't quite right.

Base gasket thickness I would not think would be a big deal since this has an electric choke and I don't remember any extra passages or odd things in the intake or bottom of the carb.  I do sort of recall that there are some very thin areas on the intake where there isn't much surface area so would  be easy spots to have a gasket especially a used one not seal up properly so it may be worth another look there. 

I'm thinking it may be worth the time to do a compression test just to make sure you mechanically have 8 fairly matching cylinders.  With this low of mileage this thing has had to do a lot of sitting so it could easily have stuck rings or valves plus something must have happened to the original carb that someone thought wasn't easily fixable, what ever killed that could not have done the rest of the engine any good.  This is one time an Eldo is an advantage sitting higher and with this cad engine design and the plugs kinda pointing up and out it doesn't get much easier.   

[bcroe]

On a car this old an original timing chain is
suspect regardless of low miles.  The OEM
has plastic teeth on the cam sprocket which
can crack and fall off without warning.  I
do not tolerate this time bomb on my cars, I
ALWAYS change out the original.  I have
changed enough front drivers to know the job
is a pain.  Bruce Roe

[joeinbcs]

Thanks for the replies.  I'll respond below to each question:
1.  By pressure on the EGR, I meant how much force it takes to push the diaphragm up while the device is mounted on the car.  I could not move it, took it off, then got it to move, expelling air as I push it up.
2.  I bought a manual, but it turned out to be the "Supplement", as there is no 1978 manual.  This only covers diesel engines.  I would normally buy a full FSM, but I didn't think I would need it.  Now I wish I had one on hand.  I do not know anything about the peculiar timing method for this car.  If anyone can help, I'd appreciate it.
The carb I ordered and installed is the correct number for this car:  17051958.  The seller's (US Carburetor) page contained this language:"From core to finished product, this carburetor was rebuilt to factory pre-set internal and external settings. In addition, this carburetor was tested on an engine simulator to ensure OEM specs are met or exceeded."
3.  There is no vacuum port at the back top that needs to be capped on this unit, only the outlet farther down that goes to the AT kick down.
4.  I'll clean up the EGR valve, which seems to be functioning, and reinstall.  Maybe a stuck valve was the problem, or part of it.
5.  I'll see if I can find any faults with the spacer, maybe take it out and replace with the gasket that came with the carb.
6.  Yes, I was thinking it might be time to do a compression check.  I think I have the tools to do that.
7.  I suppose the timing chain could be the culprit.  Thanks for the suggestion.  Hope it is something less invasive, as that's far beyond my modest capabilities.
Thanks a lot for your ideas/guidance.
Joe

[TJ Hopland]

I have to go do a few things at the moment and don't for sure know where my 77 manual is, I would have expected the supplement to have the tune up section it it still since that would be something that changes year to year.  I can't remember 77 is mostly white with a blue border?  And the 78's are brown?  Or Dark blue?   If anyone knows let me know that may help me spot them in the stacks of crap I have everywhere.

Sounds like the EGR may have been stuck shut which would not be causing your issues.  Shut is the default position with no vacuum signal.  Air rushing out when you move it sounds normal.  If you move it and hold it then put your finger over the port then let go it should more or less hold that position till you open the port again.  I'm not thinking egr has anything to do with your issue unless its hooked to the wrong place on the carb and running at the wrong times.  Till you get the idle issues worked out it should not hurt to disconnect and plug the vac line.

Seems like a goodish sign that there isn't a brake booster port on the carb, at least it was the right one at one time.  Who knows if the innards are right but getting the right body seems like a good start. 

I always forget about the timing chain.  Quick check is to pull the distributor cap and rock the crank back and fourth and see how far you have to rotate after you change directions before the rotor changes directions.  If you have one that is almost gone its super obvious because you end up rotating an inch or two on the pulley before the rotor catches up.  Slight problem is Cadillac didn't include a crank bolt on this engine family so there isn't any easy way to rock it unless its a really loose engine with the plugs out and its a model with a solid fan.  If you are going to work on more of these engines picking up a bolt and washer for your tool box may not be a bad idea. 

Im thinking the thin area on the intake is maybe between the big and small bores like where the 2 different circles meet?  Its only a couple MM's wide right there so not a lot of area to grab a gasket.  I doubt the intake is warped but would not hurt to run a straight edge over it when you have it off just to make sure there isn't a blob of petrified gasket there you missed.  Also run the edge over the carb base, those are easy to warp because people think you have to torque them down to a few hundred foot pounds.  The front bolts you just damage the whole carb but those back ears will just bend.

For a compression test I would usually pinch off the fuel line and run the carb out of gas so you don't end up flooding it in the process.  Prop the choke and throttle fully open.  Pull all 8 plugs after blowing any loose crap out around them first.  Disconnect the fat B+ wire off the distributor cap so you are not shooting random sparks all over.  Hook up a battery charger and wait the same amount of time(ish) between tests so that the battery voltage will be similar for all cylinders.  You don't have to have a stop watch or anything just don't do 3 in a row then wait 10 mins because after the 10 mins the battery will have more of a charge.  If you don't use the charger the battery may get weak and slow down so your later tests will be lower.    You can kinda rush it the fist time and see what happens.  If they are all close don't worry about it.  If they are all over the place is when you want to be more careful and consistent to give it the best chance of accurate readings between cylinders which is what you are really looking for vs an absolute number.   

[joeinbcs]

Thanks a lot for the time you took to help me get the car running right,
The real problem, which you alluded to, was tha vacuum port to the (nonexistent) brake booster.
I thought the brake booster line should have been at the top rear, as the carb I replaced had a capped port there.
However, today a friend brought a smoke device over and we realized (Duh) that the brake booster outlet (rear bottom) had no plug.
Once we swapped the plug from old carb to new and adjusted the timing the car ran beautifully.
Thanks again for all the help.
You zeroed in on the problem, but the extra port through me off.
The car runs great now!