Topic: Engine Misses leading to stalling
in Forum: C3 Engines
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Any ideas why our engine is suddenly stalling? It has been a joy for the past few months until now.
1977 Corvette with Edelbrick Cylinder Performer heads, 8.5:1 compression ratio, (1.5 years old), is suddenly experiencing a rough miss at idle and eventually leads to stalling. We have checked the timing. adjusted the idle air mixture, cleaned the spark plugs, replaced the Diestributor Cap, Coil, Rotor, and Ignition control module. We have disconnected all vacuum accessories and the vacuum reads 18 inches of mercury. The idle cannot be maintained @ 900 RPM ( jumps around) and when auto trans is placed into DRIVE, the car stalls. Exhaust sounds like spitting and missing. When throttle is opened, jets of fuel are visible and fuel is visibly drawn into the venturis.
When we pour Redline Fuel System cleaner down the throat of the carburetor @ 3000 RPM, (our idea was to remove carbon in the cylinders) the engine runs great afterwards for about 5 minutes. It has a steady idle, idles at 500 RPM in DRIVE without stalling, and exhaust sounds smooth and steady.
After 5 minutes, it then starts missing again, and stalls with the auto trans shifted into DRIVE.
We were spectulating maybe a head gasket leak or problem?
Thanks for taking the time!
Anni and her red stalling Demon 
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Duncanville, TX - USA
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Wow...lot of variables here, but I'll give it a shot...
How old is the fuel in the tank?
Really sounds like either bad fuel, or a carb issue. Could also be a plug wire problem, as it takes more electricity(spark) to fire bad/so-so fuel. With the Redline, the fuel fires easier.
Can't see a head gasket being the cause of this...maybe an intake gasket, but not the head gaskets.
What about an EGR valve? Does your engine still have one?
What does the vacuum gauge show at 2500rpm, compared to the idle reading?
How much voltage is at the red/pink wire on the distributor with the engine running, AND engine off?
How old is the fuel in the tank?
Really sounds like either bad fuel, or a carb issue. Could also be a plug wire problem, as it takes more electricity(spark) to fire bad/so-so fuel. With the Redline, the fuel fires easier.
Can't see a head gasket being the cause of this...maybe an intake gasket, but not the head gaskets.
What about an EGR valve? Does your engine still have one?
What does the vacuum gauge show at 2500rpm, compared to the idle reading?
How much voltage is at the red/pink wire on the distributor with the engine running, AND engine off?
Joel Adams
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Vette(s): 1977 Black T-Top ZZ4 5Sp 16in Wheels
I think I would be checking the harmonic balancer, as Joel suggested with your bird chirpping.
Just thought that I would give an update to the progress of our 77 vette.
Today we spent all day doing checks to see if we could find the problem of him being very sluggish when driving and having a bad idle in drive.
We did a compression check of each cylinder and they all met within normal specks.
The fuel pump is working perfectly.
We did a gas cap off test and found no difference.
We tighten down the intake manifold since some of the bolts were a little loose.
The carb. was flooding so we took it apart and adjusted the float so now its no longer flooding.
We looked at the spark plugs and all looked great but two of them had a little oil on them. No antifreeze. Nor any antifreeze smell coming from the tail pipes. So we are ruling out a head gasket problem.
Good news is that we finally got him to idle in drive and my husband just took him out for a test drive and to fill him up with premium gas since he was very low.
He called and told me that when cold he ran super then as soon as he warmed up to temp he started to stutter again, he just does not seem to have the power that he had before. When you press the gas pedal from a stop he hesitates and stutters before he gains speed. He used to just purr and you would get that seat of the pants feeling.
If you have him in drive and you put the ac on he stalls. AC on in park he is fine.
Maybe the spark plug wires are bad even thought they are brand new. We have put 3000 miles on the car since the rebuild of last year. Even though the carb. was cleaned up perhaps it's still the problem.
This is just frustrating but I know that we will eventually find the problem. When cold he seems great but when he warms up to temp that's when the problem starts up.
I took him a couple of weeks ago on a long highway trip about 120 miles round trip. I kept the speed to around 70 which is our legal limit. After that trip he started acting up.
Also not that this could be the cause but he has started an annoying bird chirp that sounds like it's coming from perhaps the harmonic balancer or one of the pullies in front. It's not a bearing. The AC compressor, alternator, water pump and power steering pump are all brand new and running just fine. Belts are tight. All the pullies are also brand new. Seem's like the Demon is living up to his name.... it's like he is possessed. LOL
Just were to look next.
Anni
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Mounds View, MN - USA
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Vette(s): 70 LT1 coupe, 69 350 HP coupe, 69 390HP 427 coupe, 71 LS5 convert, 85 coupe, 93 coupe
A simple check is to rev the engine to at least 3,000 RPM, then slam the choke shut until the engine almost dies. Do that several times. Sometimes there is just a little bit of dirt in an internal passage that gets sucked out by the high vacuum. No promises, but it is simple and free to try it.
Larry
Larry
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Oak Creek, WI - USA
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Vette(s): 1981 Great White Shark. Red Interior, 350/190 hp. PS, PB (SS), A/C CC, T-Tops. Served three years in Active Duty Army, then Retired Air Force after 34 years! Badger State Vettes Car Club. 175,000 Original miles!! Now own a 1998 C-5!
77 Red Corvette: Seems like I am having the same problem(S). My 81 has been in the shop for about a week now. Two weeks ago I went to Effingham to have new carpets put in, ran great. Coming back to Milwaukee, going in Chicago, she started running like crap all of a sudden. When we looked at it in the shop, took off the Distributor cap and the rotor fell out !! Never se3en that before. Engine still missing and no power. My corvette guy thinks that there is something in the carb, or some needle valve gasket gone to hell so that is the course of action I am taking now, rebuilding the carb. I will keep everybody posted. When the Red Corvette runs fine, let the white one know about it!!
Dan
Hello to all that have replied,,We think that we have found the problem but won't know until we can start working on the car later this evening. Looks like the ceramic socks that we used to protect our spark plug wires did not do a very good job. The spark plug wires are brand new and looked good until we decided to remove the socks and that's were we discovered damage to several of them. So we have another set of the same which we will put on to make sure that was the problem. If so I will be so HAPPY! We have ordered a set of the 135 degree plug boot type to avoid this from happening again.I will post hopefully great news sometime tonight or tomorrow.Thank you very much for your response,Anni
We finally fixed the beast!
5 spark plug wires were burnt out. Those ceramic socks just could not stop the heat from getting to the wires. So that's why he was missing as soon as he warmed up.
So we put on some new ones and he ran like a charm. Lots of power!
Thanx to everyone that responded to my help request!
Anni and her Demon back on the road 
PS....
As for the chirping sound I think that might be from the ac compressor since we just had that recharged. Once the engine stopped jerking all around from the bad idle we could sort of see the ac compressor moving a little. So we tightened it down and put some belt dressing on and you could still hear it a little but it was not as bad. So maybe it needs to be driven for the belt to wear in properly. If not then the search will continue :)
When you fuel or oil fowl spark plugs even if you clean them they are no good, toss em, always get new ones, when you mention the cherping sound, I thought a loose Alternator belt might be a problem, if the battery is not putting out enough voltage to the ignition, that will cause a misfire, when you rebuilt the motor did you repaint the pulleys, make sure that you don't have a lot of paint down in the grooves that might cause the belts to slip, clean off the paint, rough up the grooves with maybe 80-100 grit sand paper.
in Forum: C3 Engines
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