1986 Vette won't run right
Thread Starter
3rd Gear
Joined: Oct 2014
Posts: 3
Likes: 0
1986 Vette won't run right
My 1986 Vette is having an issue with running. I put the Accel 24 lb. high flow fuel injectors and the Edelbrock high flow tubes on it and now it won't stay running when the MAF is connected. We adjusted the timing a little to get it to idol right and currently have it set between 8 and 10. We changed the plugs, wires, cap, rotor, and the coil on top of the cap. We disconnected the cats and there are flames coming from the manifold. It seems like it's starving for air.
Any advice?
Any advice?
Racer
Joined: Aug 2009
Posts: 496
Likes: 4
From: Cordova TN
My 1986 Vette is having an issue with running. I put the Accel 24 lb. high flow fuel injectors and the Edelbrock high flow tubes on it and now it won't stay running when the MAF is connected. We adjusted the timing a little to get it to idol right and currently have it set between 8 and 10. We changed the plugs, wires, cap, rotor, and the coil on top of the cap. We disconnected the cats and there are flames coming from the manifold. It seems like it's starving for air.
Any advice?
Any advice?
Race Director
Joined: Apr 2002
Posts: 10,036
Likes: 346
From: Anaheim CA
Sounds like you have run up against the minimum injector pulse width problem. This is quite common when you go to injectors (and/or fuel pressure) that are too large for the engine.
The ECM calculates the injector pulse width and then compares that number to the minimum pulse width. It then uses whichever is LARGER. With large injectors that will cause the engine to run very rich. On my '86 the minimum injector pulse width is 1.8ms and I usually idle at 2.2ms with 22lb injectors. You'll need a scan tool to determine what pulse width the ECM is using.
The ECM calculates the injector pulse width and then compares that number to the minimum pulse width. It then uses whichever is LARGER. With large injectors that will cause the engine to run very rich. On my '86 the minimum injector pulse width is 1.8ms and I usually idle at 2.2ms with 22lb injectors. You'll need a scan tool to determine what pulse width the ECM is using.
Thread Starter
3rd Gear
Joined: Oct 2014
Posts: 3
Likes: 0
Thread Starter
3rd Gear
Joined: Oct 2014
Posts: 3
Likes: 0
Sounds like you have run up against the minimum injector pulse width problem. This is quite common when you go to injectors (and/or fuel pressure) that are too large for the engine.
The ECM calculates the injector pulse width and then compares that number to the minimum pulse width. It then uses whichever is LARGER. With large injectors that will cause the engine to run very rich. On my '86 the minimum injector pulse width is 1.8ms and I usually idle at 2.2ms with 22lb injectors. You'll need a scan tool to determine what pulse width the ECM is using.
The ECM calculates the injector pulse width and then compares that number to the minimum pulse width. It then uses whichever is LARGER. With large injectors that will cause the engine to run very rich. On my '86 the minimum injector pulse width is 1.8ms and I usually idle at 2.2ms with 22lb injectors. You'll need a scan tool to determine what pulse width the ECM is using.
Thanks. Didn't think of that.
Will this cause it to run crappy at the low RPMs and run good at the High RPMs? I only ask because it sounds like this might be the issue.
Drifting
Joined: Aug 2010
Posts: 1,704
Likes: 8
Does the car run like crap in closed loop? do you mean bad idling ?
in closed loop the car uses the O2 sensor to calculate the target AFr.when you change to larger injectors you need to retune the injector flow rate in the tune,as Cliff said.Usually you end up with a richer mixture than needed, at light throttle , in closed loop, the ECM tries to meet the 14,7 ratio and she fights continuosly cuttin injectors pulse width.When you floor the gas pedal and go WOT the engine enters in open loop and PE comes on ,no more 14,7 AFr ,no more O2 sensor,just a richer mixuture 11.5 and plenty of air
in closed loop the car uses the O2 sensor to calculate the target AFr.when you change to larger injectors you need to retune the injector flow rate in the tune,as Cliff said.Usually you end up with a richer mixture than needed, at light throttle , in closed loop, the ECM tries to meet the 14,7 ratio and she fights continuosly cuttin injectors pulse width.When you floor the gas pedal and go WOT the engine enters in open loop and PE comes on ,no more 14,7 AFr ,no more O2 sensor,just a richer mixuture 11.5 and plenty of air
Melting Slicks
Joined: Jun 2013
Posts: 3,065
Likes: 39
I'm pretty sure that 86 does not take 24 lb injectors. I think it's supposed to use 22 lb. 24 lb is for the 85. You can either get a tune to correct that, or go back to the original size injectors.
More fuel does not always mean more power.
I'm pretty sure that's your problem.
More fuel does not always mean more power.
I'm pretty sure that's your problem.
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