Bad idle, engine sputtering and missfire under WOT
01-17-2024, 09:06 AM
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Bad idle, engine sputtering and missfire under WOT I recently bought a 1994 Pontiac Firebird Formula
it has many mods, cams, ported AFR heads, an MSD box, Holley Throttle body, and more...
Anyways first of all it runs without the MAP sensor;
-> It sometimes goes into a 2000rpm idle but them drops to 800-1000rpm back and forth, like i said inconsistent.
-> iI runs great at light Throttle but if you WOT it starts sputtering at 4000-5000rpms and won't accelerate properly, almost seems as if it's rev limiting.
-> When its cruising and i let off the throttle it dropps to 1000 rpms and it starts bouncing off that to 1500 rpms or so, like it wont stay there, but when I press the throttle a bit it starts Acceleratinghen as normal.
When i plug the MAP sensor it corrects the 2000rpm idle but stalls out
Some Master LT1 Tech help me out, appreciate it
it has many mods, cams, ported AFR heads, an MSD box, Holley Throttle body, and more...
Anyways first of all it runs without the MAP sensor;
-> It sometimes goes into a 2000rpm idle but them drops to 800-1000rpm back and forth, like i said inconsistent.
-> iI runs great at light Throttle but if you WOT it starts sputtering at 4000-5000rpms and won't accelerate properly, almost seems as if it's rev limiting.
-> When its cruising and i let off the throttle it dropps to 1000 rpms and it starts bouncing off that to 1500 rpms or so, like it wont stay there, but when I press the throttle a bit it starts Acceleratinghen as normal.
When i plug the MAP sensor it corrects the 2000rpm idle but stalls out
Some Master LT1 Tech help me out, appreciate it
01-18-2024, 01:43 PM
#3
I would get a scanner and look at all the air sensors. IAT, MAP, MAF. Check the TPS sensor and see if the MAF is dirty.
These symptoms sound like the engine is cutting fuel because the air calculations are off and the engine is not seeing the right volume or density of air coming into the engine.
Your high RPM symptoms feel like MAF problems I have had on other engines. My guess is that unplugging the MAP sends the computer to an assumption of sea level (denser) air than the system is reading otherwise. I expect that the MAF readings are out of the idle speed equation, though.
If your engine has a tune, then going to a tuner to sort this stuff out is probably the best route and the only way to untangle things. If it is stock, you can read the Factory Service Manual or get a 3 day subscription to it and read the emissions/sensor descriptions to see how these are supposed to work and when they go in and come out of the loop.
These symptoms sound like the engine is cutting fuel because the air calculations are off and the engine is not seeing the right volume or density of air coming into the engine.
Your high RPM symptoms feel like MAF problems I have had on other engines. My guess is that unplugging the MAP sends the computer to an assumption of sea level (denser) air than the system is reading otherwise. I expect that the MAF readings are out of the idle speed equation, though.
If your engine has a tune, then going to a tuner to sort this stuff out is probably the best route and the only way to untangle things. If it is stock, you can read the Factory Service Manual or get a 3 day subscription to it and read the emissions/sensor descriptions to see how these are supposed to work and when they go in and come out of the loop.
01-18-2024, 01:49 PM
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I would get a scanner and look at all the air sensors. IAT, MAP, MAF. Check the TPS sensor and see if the MAF is dirty.
These symptoms sound like the engine is cutting fuel because the air calculations are off and the engine is not seeing the right volume or density of air coming into the engine.
Your high RPM symptoms feel like MAF problems I have had on other engines. My guess is that unplugging the MAP sends the computer to an assumption of sea level (denser) air than the system is reading otherwise. I expect that the MAF readings are out of the idle speed equation, though.
If your engine has a tune, then going to a tuner to sort this stuff out is probably the best route and the only way to untangle things. If it is stock, you can read the Factory Service Manual or get a 3 day subscription to it and read the emissions/sensor descriptions to see how these are supposed to work and when they go in and come out of the loop.
These symptoms sound like the engine is cutting fuel because the air calculations are off and the engine is not seeing the right volume or density of air coming into the engine.
Your high RPM symptoms feel like MAF problems I have had on other engines. My guess is that unplugging the MAP sends the computer to an assumption of sea level (denser) air than the system is reading otherwise. I expect that the MAF readings are out of the idle speed equation, though.
If your engine has a tune, then going to a tuner to sort this stuff out is probably the best route and the only way to untangle things. If it is stock, you can read the Factory Service Manual or get a 3 day subscription to it and read the emissions/sensor descriptions to see how these are supposed to work and when they go in and come out of the loop.
I have a 94 V6 camaro to Daily and I've fixed most of its problems, it also had the "Missfire and Sputtering when WOT, at 4000 to 5000Rpm", turns out the MAP was unplugged but it the TAs case if I plug the MAP in, it runs baaaad, barely accelerates and stalls if I don't hit the gas
Also I took out the MAF sensor and the car just turned off, do i just unplug it before turning it on?
01-20-2024, 03:47 PM
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exactly, I've been digging up in countless forum posts, narrowed it down to a Timing advance issue, that can be corrected with a tune(guy described all my symptoms, except he didn't have no MAP sensor problems and lso fixed them with a tune) or the Coil going bad
05-27-2024, 06:23 PM
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Getting there Changed out the cam, adjusted the valve train, the motor was timed correctly, so yeah, anyways I still have a ways to go but the car runs much better now, also it had 1 ground, had to connect 2 other grounds, previous owner built that car with his eyes closed and fumbled it big time