Engine missing when I let off the gas??
Thread Starter
Le Mans Master
Joined: Aug 2007
Posts: 8,735
Likes: 412
From: WV
Engine missing when I let off the gas??
I have had this miss for a few weeks on my 89, at first just slightly,but it just started getting worse.. Last night coming home from a cruise in I started to really notice every time I was going down a hill with my foot off the gas or cruising with my foot just barely on the gas traveling at a steady speed I had a miss, it almost felt like a plug was fouling out and this made the car buck..When I was on the gas accelerating or had my foot into it hard, the car ran great with no miss or bucking.. On every car I have ever had before if I had a miss it was always under acceleration and turned out to be a plug, plugwire, coil, or a Ignition control module.. What would cause a car to miss only when decelerating or just moving at a steady speed???...Any help would be greatly appreciated...WW
Last edited by WW7; May 29, 2011 at 10:28 AM.
Thread Starter
Le Mans Master
Joined: Aug 2007
Posts: 8,735
Likes: 412
From: WV
My egr and air are eliminated and have been tuned out of the chip. I have also sprayed at least a full can of carb cleaner at the motor and found no vacuum leaks. I also put a vacuum gauge on it and have 17 lbs vacuum. The Bosch 3 injectors I got from FIC are only a year old and went in with the new 383 last year, I know that doesn't mean I couldn't have one that went bad so I will check them..Thanks for the reply...WW
Last edited by WW7; May 29, 2011 at 10:20 AM.
Melting Slicks
Joined: Nov 2008
Posts: 2,765
Likes: 5
I am not positive from here but it sounds like the engine is going lean when you are off the gas.
If you have a Wideband O2 setup to use it may help out troubleshooting greatly.
Or you can pull each spark plug & look at & read each carefully.
Ignition misfires always show there ugly heads at WOT.
There are several very steep 30-38 degree grades and some 1 mile long I used to troubleshoot engine misfires while test driving.
In my hotrods I wound test & tune and try to reach over 100MPH before cresting to the top & braking very hard for a stop sign 800 feet away.
If you have a Wideband O2 setup to use it may help out troubleshooting greatly.
Or you can pull each spark plug & look at & read each carefully.
Ignition misfires always show there ugly heads at WOT.
There are several very steep 30-38 degree grades and some 1 mile long I used to troubleshoot engine misfires while test driving.
In my hotrods I wound test & tune and try to reach over 100MPH before cresting to the top & braking very hard for a stop sign 800 feet away.
Last edited by 87 vette 81 big girl; May 29, 2011 at 11:09 AM.
Melting Slicks
Joined: Aug 2003
Posts: 3,399
Likes: 394
From: Lakeville MI
Might be DFCO (Decel Fuel Cut Off) or a transition out of DFCO. Sometimes when the fuel is restored, this can be felt as a minor jerk right when going from engine braking without fuel to free rolling in gear with fuel.
Thread Starter
Le Mans Master
Joined: Aug 2007
Posts: 8,735
Likes: 412
From: WV
Well I found the problem... One of the plug wire boots was backed off the spark plug..I guess this was letting it get spark when I was on the gas by jumping the gap, but with the reduced spark when off the gas wasn't letting the plug get spark...Im positive I pushed all the boots all the way on when I did spark plug about 6 months ago because I always listen for the "Click"..Could the heat have cause it to back off?? I also notice the plug wire boot was real soft, and when I looked at the box for the Accel wires it said they would handle up to 400 degrees. When I just checked the temperture of my headers when I got back from a test drive they were at or slightly above 400 degrees 6 inchs down the header.. I just ordered a set of Taylor wires that are good to 600 degrees and I may also put thermal sleeves on my wires to protect against the high heat...Thanks for the help guys....
..WW
..WW
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