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Need some help to get rid of a mis fire gremlin

1K views 13 replies 6 participants last post by  93volpe 
#1 ·
I saw a while back that someone had a sorta similar issue, but was a 5spd car and not an AOD. I've posted this on my local fox club page with no for certain cures

So here's a rundown on what's been done to try to clear a low end stumbling/misfire along with excessive gas fumes at idle, and to add to it, during cruising 70 to 80mph on interstate there is an occasional pop/cough in the exh system, all of this occurs after warmed to operating temperature and in above 35 degree weather and tends to get worse the warmer the eng and weather temp get....... TPS changed, O2 sensors changed, fuel and a/c – WOT relays switched, plugs changed, IAC cleaned, coolant temp sensor changed, IAT sensor changed, distributor with new TFI module replaced (stock distributor), cap/rotor replaced, new fuel pump with new sock filter, new inline fuel filter, MAF meter cleaned , BAP sensor tested. EGR system has been cut and capped off, new coil. A cylinder balance test preformed with no faults, compression check done (all cyls were in the 90’s with about 6 psi difference). A water test(squirting water on the header tube at head) indicated #2 is where the problem lies. All header tubes immediately boiled off/evaporated the water, #2 took at least twice as long. Both times, when plugs were replaced and when the compression check was done, the plugs were burning good and were all consistent with the electrode/ceramic color. Fuel pressure checked (40 psi) No codes show during retrieval except pass codes most of the time, only exception is code 96 Fuel pump circuit, but disappears. it does not always show after the misfires



Specs for the car: a 92 GT 5.0 with an AOD trans and nearly 300k miles, NO MODS all original except for no cats and has Flowmasters
 
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#3 ·
I would change your injector as well. I had a 02 f150 that had a problem like this. Nothing helped, stuck in new injectors and bam! Ran like new!
 
#4 ·
I swapped #1 & 2 last nite. I'll check it tonite to see if the problem followed the injector. A quick test after swapping looked like it did but we didnt get the car out and heated up like before... I'll post the injector swap results later
 
#8 ·
Pulled codes a couple times with other minor issues.... 96 always showed up... fuel pump circuit. After changing #2 injector, i decided to check codes again just for the fun of it... code 11 ... pass code, then code 10 for switching to stored codes, there's ole 96 showing up again . SMH
 
#10 ·
Have you check the fuel pressure regulator on the fuel rail or the rail it self if the problem tracked for #2 to #1 when you changed #2 it may have disturbed gunk in the rail itself.
 
#11 ·
Yep, fuel pressure is at 40 give or take. I took an old antenna and with extreme dexterity, touched each injector, i can hear them they are all functioning. I'm wondering if it's a computer issue when it comes out of the "closed loop" (not up to operating temperature) to the warmed up mode. All the trouble seems temp related..runs great when just started
 
#12 ·
PSI in the 90's seems really low. Did you do this with a cold or warm engine? Fuel shut off and TB open? I'd recheck the compression and then calculate what your lowest number should be, if you're below that 15% range, that could be causing your stumbling misfire.
 
#14 ·
Yeah the compression check was done hot and I also sprayed around the engine and vac lines with starting fluid... no change. I think a burnt valve/head issue is my culprit considering we're less than 4000 miles from tripping 300k on an un modded, all original engine. Up until about 2 yrs ago we still had the orig plug wires and radiator hoses lol. I have a 79 351w I've been trying to sell but once we hit 300k I may raid the windsor heads and put on
 
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