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Thread: Missfiring

  1. #11
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    Pulled plugs again and checked the o2's? Checked plug wire order after the opti change?
    Last edited by donfrye; 02-06-2018 at 08:39 PM.
    95 Mystic Z28, 17x9 FR, 17x11 RR ZR-1's, Pacesetter LT's and Y-pipe, Borla adjustable, Moroso CAI, 2800 Stall, AC Delete, and Cracked Dash/broken lid Mod.

  2. #12
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    Quote Originally Posted by stevenrogers89 View Post
    believe it or not but i had some issues like yours and i put a coolant sensor on mine and it fixed mine my car wouldnt even run because the coolant sensor was bad but just a cheap idea may fix it
    Had that issue on a TBI truck and chased it for months.
    95 Mystic Z28, 17x9 FR, 17x11 RR ZR-1's, Pacesetter LT's and Y-pipe, Borla adjustable, Moroso CAI, 2800 Stall, AC Delete, and Cracked Dash/broken lid Mod.

  3. #13
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    Quote Originally Posted by maximumvelocity View Post
    After being stupid busy, I had about an hour to jump back on the car again. After pulling the fuel rail off and replacing a fuel injector o-ring that wasn't seating properly, I spent another 15 minutes or so looking for a vacuum leak that didn't exist. Then I ran across my high idle culprit. The IAC was unplugged. Now it's back to normal rpms, but I suspect it's still running pig rich on the driver side bank as the exhaust was still rich with unburnt fuel that burned my eyes, and it wasn't revving smoothly. Still no codes for the short duration it was running.
    Was the injector o-ring not "seating properly" on the driver side? Was it possibly causing a vacuum leak on the manifold end? If so, the PCM would have jacked up the long term fuel corrections. That's what I was getting at in post #5. After you replaced it, how long did you run the engine? Long enough/hot enough to get it into closed loop? At any point did you clear the PCM to reset the long term fuel trims? If not, it may run rich until you do.
    SOLD - GONE TO A (VERY) GOOD HOME ! - 94 Formula A3+1: 381ci forged stroker - Callies Stealth, Oliver 5.85 billet rods, BME nitrous pistons / CNC LT4 heads / CC solid roller / TH400+GearVendors OD / 4.11 Strange 12-bolt / 300-shot N2O / Spohn Suspension / roll bar / MoTeC M48 Pro engine management system /a few other odds 'n ends.

  4. #14
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    Like stated above you need to reset the pcm if you were running it with problems like that.

  5. #15
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    Quote Originally Posted by Injuneer View Post
    Was the injector o-ring not "seating properly" on the driver side? Was it possibly causing a vacuum leak on the manifold end? If so, the PCM would have jacked up the long term fuel corrections. That's what I was getting at in post #5. After you replaced it, how long did you run the engine? Long enough/hot enough to get it into closed loop? At any point did you clear the PCM to reset the long term fuel trims? If not, it may run rich until you do.
    Ok, yes it was driver side. It may have been leaking, no way to tell now. Yes I did reset pcm. It goes into closed loop somewhere after a minute of running. Ran the engine long enough to get it all the way to operating temp and a few minutes after that. Still blowing black smoke with gas. When the car is warm and I hold the throttle down to a fixed position, say 3000 rpms, the rpms will drop to about 2700 and go back up every 2-3 seconds or so. It kind of reminds me of a sine wave.

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    Ok, started it warm again and it was in closed loop. When I bring it up to 3000rpms it'll hold for about 30 seconds and then drops down to about 2500, and then starts toggling between 2500 and 2300rpms. The ignition doesn't seem to be retarding but maybe 1-2 degrees between the rpm fluctuations going from 30 to 28 at the lower rpms...if any of this info makes a difference. The rpm numbers are based off of the factory gauge, which reads a few hundred below actual.

  7. #17
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    Not likely ignition timing retard. The advance is programmed as a function of RPM and engine load (MAP). If you change the RPM or the throttle, RPM is going to change, which changes the advance. The higher the RPM, the more advance is needed, lower RPM less advance. Only way to see if there is knock retard is to monitor it with a scanner.

    Are you saying you are revving it in neutral, you hold the throttle steady with the tach at 3,000 RPM, and even though the throttle is not moving, after 30 seconds the RPM drops, and is swinging back and forth between 2,300 and 2,500 RPM? Can your scanner show the IAC counts? Would be interesting to see if the PCM is tweaking the counts in synch with the RPM changes. When the engine RPM elevates, the PCM increases the IAC counts to prevent the engine from stalling if the throttle blades suddenly close. The RPM variation may be the result of minor IAC count adjustments.

    I don’t think either of the above is indication a specific problem, unless it actually misfires causing the RPM to vary.
    SOLD - GONE TO A (VERY) GOOD HOME ! - 94 Formula A3+1: 381ci forged stroker - Callies Stealth, Oliver 5.85 billet rods, BME nitrous pistons / CNC LT4 heads / CC solid roller / TH400+GearVendors OD / 4.11 Strange 12-bolt / 300-shot N2O / Spohn Suspension / roll bar / MoTeC M48 Pro engine management system /a few other odds 'n ends.

  8. #18

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    Not going to lie didn't have ttime to read entire responses. So I don't know if the o2(s) were changed or monitored with a scanner.. sounds like a bad o2 sensor to me.. they degrade and it goes pig rich.. computer tries to correct situation but cant as to why engine can't hold a steady rpm in neutral.. I've also seen them be bad and not throw a code.

  9. #19
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    Also when you hook it up to a scanner look at the map sensor reading, tps voltage, O2 readings, MAF reading, and CTS/ECT reading at both cold idle and warm idle. Had a TBI truck that would show 12% throttle(even though no throttle was applied) at idle and it ran peg rich. Do a compression check as well. Go through every check to rule out as much as possible. Also make sure you are not carbon tracking on the opti high voltage side.

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    Also look at knock counts. I would also check inputs and outputs of all sensors with a Fluke DOVM with sqaure wave capibilty. Also when has the coolant been flushed or serviced? It could be running hot and not showing up on your gauge and causing spark knock in which timing will be pulled and enrichment of fuel will be added, so I would use an infra-red gun to check against what the gauge shows and the scanner shows.

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