76 Eldorado Hesitation/Skipping Problem

[dcrews1969]

Hi....I was wondering if any one might have any suggestions? I have a 76 Eldo with the 500 cu 4 brl carb. I have recently had the engine rebuilt and still have the same problem as before of an unexplained hesitation with the car before and after it has reached operating temp. The hesitation is more of a dead spot in the acclerator travel. It occurs about mid range ...kind of a bog feel.
If you floor the car it will pick up and move like it should...The gas tank has been cleaned,the carb replaced twice, 3 fuel pumps,new distributor,new plugs twice, new plug wires twice, new ignition module twice, fuel pressure has been checked, all vacuum hose replaced, all fuel hoses replaced,strainer inside tank has been removed and in line filter installed due to deterioration of strainer and lack of availability either new or aftermarket. Doesnt seem to be a fuel delivery problem. Also the engine vacuum has been check by the factory shop manual and all checked out the way it should. The intake manifold has been checked for leaks at the gasket.
The car also runs poorly at idle, seems to be worse after it has reached operating temp...more of a skipping, as you can hear it in the exaust.
Thanks for any input you may have...signed out of money and ideas.

 

[MAC1]

Did you check the vacuum advance on the distributor? It sounds like a timing problem. Was the distributor installed correctly? Also, I would make sure all vacuum switches are working properly. In other words, find out what is suppose to happen when the engine reaches normal operating temperature. For example, is the A/C & Heat Control Switch located in the cylinder head suppose to activate. Is there any other sensor that is suppose to monitor water temperature and activate vacuum effecting timing that may be malfunctioning?

 

[dcrews1969]

reply

Hi..thanks for the reply...i did forget to mention that i have replaced the vac adv on the distributor also. The only vacuum type sensor on the engine is the thermo vacuum valve located on the head which as you say monitors the water temp had also been replaced but is now disconnected because the only function it served was to open and close the heat riser valve in the exhaust while the car initially warms up.The heat riser is still on the car for originallity but it is in the full open position so that the exhaust is not restricted in any way. As for the timing, i thought the same thing, i took the car to a certified mechanic to double check myself. He could not find any thing wrong with the timing, as it was set to factory specs. I was still not satisfied so i removed the engine from the car once again, and pulled off the front timing cover to check the chain for alignment being that it could be possible that it was off by a tooth or more..Nothing here either ...timing chain and gears were in perfect alignment.

 

[MAC1]

How about the EGR valve? Is it functioning correctly? I suspect you checked it but just in case. Is it hanging open or stuck, which is causing vacuum problems?

 

[dcrews1969]

The EGR valve is the original and has been checked and seems to hold vacuum fine. At the time of the engine rebuild i replaced the egr valve with an after market one since the orignal type seemed to be no longer available. This new one came with these washer type spacers that had to be sized to the hole in the manifold. Needless to say, it didnt work. I cleaned checked and did a vacuum test on the original EGR which all checked out fine. So i reinstalled it on the car, but it seemed to make things even worse. so it has been disconnected (still on the car). No vacuum is supplied and blocked off, so that it is not functioning at all.

 

[MAC1]

OK...You said you replaced the ignition module--Are you referring to the ignition coil? If you haven't already, I would replace the ignition coil. I would also do the nighttime wire arching check. You know, open hood when it's dark out to see if there's any electrical arching. I would also ask someone to give it some gas and see if any arching occurs. Actually, I would first check for arching before considering replacing the coil since you may find the answer is wire arching.

 

[dcrews1969]

Yes, I have replaced the cap, rotor,coil, igntion module,wires and plugs. I think this thing is possessed...LOL. Most of each more than once.
The strangest thing to me is that this is the same exact problem that was occuring before the rebuild of the engine..
As for checking for arcing, i have done this too...i have even run my hand over each wire while the engine was running(DUMB IDEA HUH?) but thank goodness it wasnt arcing. Just to add...i have removed the cat converter just to see if this may have any effect....but as with everything else i have tried ..nothing. Again thanks for any suggestions or ideas.

 

[MAC1]

Here's a link to CadillacOwners.com to a thread entitled 1970 Eldorado Hesitation that my help, particularly the following quote:

This is a common problem with quadrajet carbs. Usually this is a combination of weak accelerator pump and weak secondary air valve spring. You may be able to fix it by tightening up the spring but eventually the accelerator pump should be changed.Quadrajets also had a problem with the power valve getting stuck because if the car backfires is can send soot up into the power valve. It's relatively easy to tighten up the spring so that is where I would start.A quadrajet is made up of 3 main pieces. The air horn which is the top piece, The floatbowl or main body which is the middle piece,and the throttle plate which is the bottom piece.These pieces are separated by gaskets so it is easy to see which part is which when you look at the carb.To tighten the spring: look on the airhorn at the passenger side near the back. You will see 2 large roundish plates on top of the carb.These are the secondary air valves. There is a piece of linkage hooked to the passenger side of these valves. There is also a small flush mounted straight screwdriver slot next to the air valve shaft.That is what you turn to tighten up the spring. You will also see an allen head screw going upwards into the air horn which locks the adjuster slot. Loosen the allen head screw and then turn the slotted one 1/4 turn clockwise then test the car for hesitation.If it helped but not completely solved the problem then try another 1/4 turn. If that doesn't work you will have to rebuild the carb. Make sure that the secondary air valves rotate freely and if they don't,spray the shaft with carb cleaner and work the valves open and closed until they are free.In addition, the piece of linkage that hooks to the secondary air valve shaft hooks to a vacuum can at the other end.If the linkage is mis-adjusted or if the can leaks vacuum that could cause your hesitation. Quadrajets are not bad,just picky .

I know you said that you replaced the carb. but was it a rebuild or brand new? If it was a rebuild maybe some parts were not replaced that should have or the power valve is stuck, which makes sense.

 

[dcrews1969]

Thanks ..i will definately look into this over the weekend.