Rough running Cadillac 1966 conv Eldorado

[Roy Nash]

Please can someone help me with poor running 66 429ci caddy.
I have a long standing issues with poor starting and very rough running engine.
I could not get to the bottom of its poor running, after replacing all the ignition system components and check the carb, timing and mixture, so the engine was removed, thinking camshaft was worn, on stripping the engine nothing was broken or worn, but new shells, piston rings, timing gear set, camshaft/followers, valve spring were replaced.
The valves clean and refaced into the head, but still running just the same as before the engine was rebuilt.
Double check and replaced ignition items again, tried 3 carburettors, checked the distributor for wear. Checked for servo/ air vacuum leaks. Checked cylinder compression ok. The engine is running rich, check co which is a 4.0% but HC is very high at 1500- 2000 ppm, inlet manifold has no cracks, car has only does less then 40,000 from new.
Would the chock tube in the right side of the centre heat riser port, be cracked inside to cause this bad running issue, or has anyone else had a similar problem or can help.
Roy

[cadmium]

In what city do you live?  Maybe someone nearby can help out.  It's virtually impossible to diagnose stuff like this here.  It could be anything.  You slapped on three carburetors.  Were any of them cleaned and rebuilt?  Did you try tuning or adjusting any of them?

[cadillactim]

Simple way to check for vacuum leak is gradually cover top of carb with your hand and see if engine smooths out . If it does, there is excessive air being drawn in. Do you have the correct base gasket on the carb, and also the stainless steel,shim that was sometimes used? Also make sure bakelite base where pcv hose attaches is not cracked.

Of course bad plug wires can be an issue, but you have probably checked that.

Tim

[James Landi]

Oh Roy... yours is a very sad narrative.  These engines are so well designed, durable, and can run well over 120K miles with tune ups, and nothing more.  Because of the piston rings, they will begin to burn oil, but truly, you should not have any problems.  I'm only guessing, but since the problem exists AFTER you';ve done all of this work, I would suspect the intake manifold... have you put a vacuum gauge on the it?  Vacuum gauge can give you tremendous insight into what is wrong.  They cost around 40 dollars, and they come with diagnostic instructions about what might be wrong IF the gauge is NOT steady at idle and what a low or high reading can tell you.  That;s where I;d start Roy... so sorry to hear you;ve encountered so much heartache.  James

[35-709]

Be sure the vacuum check valve at the power brake booster isn't leaking/bad. 

[savemy67]

Hello Roy,

Your post implies that you have the ability to analyze the exhaust from your car, and you say it is running rich.  I can think of a limited set of circumstances that cause a car to run rich.  One circumstance would be a mal-adjusted carburetor (including choke) that does not allow the carburetor to establish the correct stoichiometric ratio of air to fuel.  As cadmium asked, were any of the three carburetors you installed adjusted properly?

A second circumstance would be incomplete combustion of the air fuel mixture in the cylinders.  This could be due to an ignition problem, or an engine condition problem.

Regardless, having a few diagnostic tools can be very helpful when trying to diagnose engine trouble.  I strongly second James's recommendation about procuring a vacuum gauge.

It seems like you changed a lot of components without firmly establishing the most likely cause.  This is akin to a doctor performing surgery to find the source of a cough.  Please consider focusing on one system at a time (fuel, engine) based on what the diagnostic tools indicate.

In the case of vacuum issues, in addition to Tim's suggestion, you could pinch off or block off all vacuum connections to the engine and see what a vacuum gauge reads.  If the gauge is unsteady, you probably have a manifold vacuum leak.

Do you know if the heat riser valve in the exhaust manifold is open or closed?  A valve stuck in the closed position will force all the exhaust from one bank of cylinders back into the cylinders and through the exhaust crossover in the manifold to the other bank.

Was your compression test done with a compression tester or did you use a leak-down tester?  If a compression tester was used, what are the readings for all 8 cylinders?

As cadmium noted, it is difficult to diagnose issues like this from afar.  The take away is to acquire some diagnostic tools, and use a methodical approach.  Establish a baseline, and change one factor, and see what changes.  Good luck and keep us posted.

Respectfully submitted,
Christopher Winter

[David Greenburg]

Also check the fuel delivery; a clogged filter or forgotten filter that was added on some time in the past, or, as is common with an old car that has sat for extended periods, crud that builds up in the fuel tank. Test the fuel pump, and if that’s good, try starting the car with known fresh gas out of a gas can.  If there’s big improvement, you’ll know the issue is with your tank or lines.

[bcroe]

One thing I have done, is use a wide band OX sensor gauge on my car,
which tells a lot about how the mixture is doing at any instant. Some
owners have also done this. It should have a moving indicator, as any
digital display will be only a blur of segments on a fast transition (just
when you need it). Take a look at eBay item number: 302603190756

APSX V2 Anti-Glare D2 Digital Wideband O2 AFR Gauge & Sensor Kit

These can be inserted in the tail pipe if there are no air leaks, mine
are permanently installed by the engine.  I use these on both carb
and EFI cars to see what is happening, no guessing. 

Another thing I have done is move the timing light pickup down 4
cylinders from the usual place.  If the distributor is not wobbling,
the timing should read exactly the same.  Bruce Roe

[Eldo66]

Roy,

First question - does your 429 have the air injector reactor system (installed on 1966 Cadillacs delivered to California)?

Second question - try replacing all of the rubber PCV lines and clamps, and check the entire PCV system carefully for leaks.  Carefully check the PCV line connection to the valley pan cover and ( as cadillactim suggested) the nipple insert on the carburetor base plate that connects to the rubber PCV line.  Since you've recently reassembled the intake manifold, you have probably been through the PCV items. 

Last question - Is there still a vacuum supply line connected to the car's original level control compressor?  If so, try capping off that vacuum line.  My car came with its original compressor connected to the vacuum supply line-  but the internal components were seized, creating a massive vacuum leak.  I cured it first by capping off the vacuum line, and eventually for good after my brother repaired the ALC compressor. 

For years, my 429 baffled me with a rough idle and emitted an odor of partially burned hydrocarbons.  I tried checking and replacing all of the obvious fuel supply, ignition, vacuum, and AIR system items to no avail.  Turned out that the PCV line that runs down to the valley pan was the original, and had cracked open from heat and old age.  Since the connection is underneath the manifold it was hidden from view.  I installed a new line and clamp, and the engine idle improved immediately. 

Good luck,
P. Nesbitt