Violent Bucking '86 C4 problem
Thread Starter
5th Gear
Joined: Dec 2007
Posts: 5
Likes: 0
Violent Bucking '86 C4 problem
Man, this was a wild experience. Have an '86 C4. Only mods were removal of air pump and modifying MAF. has been running great for years. I was on a 300 mile run when half way though on a flat road going about 62 mph the car bucked so violently that my body was being whipped back and forth. I noticed that all the power to the instruments went dead. Since I was in heavy traffic, I flored it. It contined to buck, but eventually caught and i was able to get off the road. All was back to normal til i needed to punch the trottle. Then it started bucking again. Now, I can cause the bucking by flooring it hard in any gear, but it won't happen with slow acceleration.
i checked for vacuum leaks, MAF seal, ground wires, etc.
Any ideas guys....this raised hell with the car. it banged the rear end everytime the engine caught and then shut down, just to bang again. Not a cool feeling.
i checked for vacuum leaks, MAF seal, ground wires, etc.
Any ideas guys....this raised hell with the car. it banged the rear end everytime the engine caught and then shut down, just to bang again. Not a cool feeling.
Race Director
Joined: Jan 2006
Posts: 10,039
Likes: 0
From: CA
The symtoms you indicate lean toward fuel delievery,other than your gages going dead.That seems like an electrical problem.Sounds like the car is just shutting down intermittently,or going into a limp home mode.But in limp home,your insturments shouldn't go dead.You checked the grounds,it must be on the + side.That's all I can think of.This can be frustrating.Check all battery positive connections,good luck.
Race Director
Joined: Jun 2005
Posts: 17,640
Likes: 1
From: Lenoir City TN
St. Jude Donor '08-'09-'10-'11
Check the idle air control valve, smptoms similiar to my 86. You can clean them and reassemble make sure the pintle is restored to the correct dimension upon assembly. They can get dirty.
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Pro
Joined: Dec 2004
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From: Daytona Beach Florida
Man, this was a wild experience. Have an '86 C4. Only mods were removal of air pump and modifying MAF. has been running great for years. I was on a 300 mile run when half way though on a flat road going about 62 mph the car bucked so violently that my body was being whipped back and forth. I noticed that all the power to the instruments went dead. Since I was in heavy traffic, I flored it. It contined to buck, but eventually caught and i was able to get off the road. All was back to normal til i needed to punch the trottle. Then it started bucking again. Now, I can cause the bucking by flooring it hard in any gear, but it won't happen with slow acceleration.
i checked for vacuum leaks, MAF seal, ground wires, etc.
Any ideas guys....this raised hell with the car. it banged the rear end everytime the engine caught and then shut down, just to bang again. Not a cool feeling.
i checked for vacuum leaks, MAF seal, ground wires, etc.
Any ideas guys....this raised hell with the car. it banged the rear end everytime the engine caught and then shut down, just to bang again. Not a cool feeling.
Le Mans Master
Joined: Sep 2006
Posts: 6,050
Likes: 147
From: Phoenix AZ
2021 C4 of the Year - Modified Finalist
bucking bronco
check the connectors on the ECM. check the grounds on the dash and lastly, it really sounds like a bad ignition switch , turning the engine on and off.
