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88 2.9L Misfireing/backfireing issue


88 XLT Ranger

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1988 2.9L Misfiring/Popping issue

Hey guy's

I am at a loss here on this 2.9L my issue is it misfires like its running on 5 cylinders. At start up cold it pops/misfires a few times than calms down idel's at 800rpm's. As soon as I give some throttle on the road it starts misfiring I can feel it through the throttle as it feels its pushing the peddle back. I changed the Ignition module,coil,plug wires,spark plugs,high valume fuel pump, fuel filter, checked the fuel pressure it good, it acted like it was going lean I changed the MAP sensor to a Napa one now it seams to do it a lot more than before:dunno:

The one thing I haven't checked or changed is the Dist cap and rotor. With my old Ford MAP it would run ok for a few miles than start misfireing now its all the time with the new one. Any help is very much appreciated on this issue
 
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88 XLT Ranger

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"I GUESS NO ONE KNOWS" :dunno:

I see 40 views no help on this issue I searched found one other post like mine. He had no reply's I guess this is just to hard for anyone to figure out. The Napa parts guy's there Chevy/Toyota die hards told me you all knew nothing I wanted to prove him wrong. I guess my day in the sun proving him wrong is gone?

I changed the MAP back to the original one it fired up fine idled down to 800 rpm's no misfire as soon as I got on the highway starting up the grade 5 miles it ran at first up to 65mph than started slowing to 45 than the same issue misfire/ popping in the intake. Its back to running like shit
 
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Hagan

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Wait...Napa didnt "know how"???

I don't know...did you check codes?
 

88 XLT Ranger

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Wait...Napa didnt "know how"???

I don't know...did you check codes?
Thanks Hagan

These Napa boy's are rubbing my face over the coals hard :-( I have a code checker I tried 5 times with key on it checks ok all passes. I fire it up I get brake on and off not detected code 74. Maybe I am not doing it right? I got the book on it and it is a Actron Code Scanner for domestic Ford Mercury with EEC-IV or MCU engine computer

I wish I could get the codes I never get past that brake deal
 

Hagan

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I'm terrible at diagnosing efi problems so I may not be able to help much or steer you in a wrong direction unintentionally. But, I wonder how likely it is to be a computer problem? I had a '92 Bronco that had a couple capacitors in the computer leak. Caused all sorts of issues...but the main thing is I was unable to pull codes.
 

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I'm terrible at diagnosing efi problems so I may not be able to help much or steer you in a wrong direction unintentionally. But, I wonder how likely it is to be a computer problem? I had a '92 Bronco that had a couple capacitors in the computer leak. Caused all sorts of issues...but the main thing is I was unable to pull codes.

"I appreciate your help very much"

I just did a test again key on all pass fired it up running real rough let it run 2min at 2000rpm's. I shut it off waited 10 seconds fired it up put scanner on test I seen code 87 (Fuel Pump relay circuit failer) only once than it smoothed out running like a kitten no rough idle or misfire. I re-tested again running I got code 74 brake on/off switch not detected and code 77 operator error during dynamic response portion of engine test. I did give it wide open throttle once before testing. This kinda gets you stressed out
 

Hagan

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Sounds like code 87 is where you need to start. Kind of sounds like an intermittent issue. Maybe a short or even a bad fuel pump relay? Possibly check the inertia switch so you can rule that out.
 

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Sounds like code 87 is where you need to start. Kind of sounds like an intermittent issue. Maybe a short or even a bad fuel pump relay? Possibly check the inertia switch so you can rule that out.
The truck when it runs rough misfire and popping its like its running to lean or running out of fuel. I can hear it through the intake plenum like a tick stumble. Thus no power I changed the fuel pump now with your help the "Fuel pump relay" might be the issue. I just checked O-Reilly has a Master Pro in stock $12.99 its in town. I will check the wires to the relay I think its on the drivers side inner fender well. Its worth a shot at this point where is the inertia switch? again thanks for the awesome help
 

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Yeah the fuel pump relay is on the passenger side fender. I can't remember if it was green or brown. I remember reading somewhere you could swap relays around with another one or you could test it. Relays are relatively cheap so it's worth a shot just replacing it to see what happens

The inertia switch is mounted inside the cab on the passenger side where the passenger would rest there feet. It's mounted against the firewall usually at the edge of the carpet/vinyl flooring. I'd test to make sure there is continuity going through it.
 

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Yeah the fuel pump relay is on the passenger side fender. I can't remember if it was green or brown. I remember reading somewhere you could swap relays around with another one or you could test it. Relays are relatively cheap so it's worth a shot just replacing it to see what happens

The inertia switch is mounted inside the cab on the passenger side where the passenger would rest there feet. It's mounted against the firewall usually at the edge of the carpet/vinyl flooring. I'd test to make sure there is continuity going through it.


Update on the issue

I thought about all your great info than I was thinking maybe run it until it does its normal popping / misfire and than put the scanner on. I took and drove it up a back road its real steep but you can only go 35mph for 5 miles. The highway is 55 mph where it always gets me running at high RPM's. I fired it up sounds great went on the back road going up some 5 miles to the top once I got there water temp normal it starts popping/misfiring. I pulled over hooked the scanner up shut it off waited 10 seconds fired it up popping/missing once it went to high idle testing it smoothed out like last night. I still got the same two codes no help operator error and brake on and off deal. I than took the scanner off and the truck ran great no issues some 5 mile to town shutting it off twice than going home 6 miles :dunno:

I don't know maybe each time it acts up install the scanner test it until back to normal. Why would the scanner test bring it back to running normal for a while?
 

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If you shut the truck off and restart it without using the scanner, does the problem clear up as well? You have to test your theory before assuming it to be fact.
 

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If you shut the truck off and restart it without using the scanner, does the problem clear up as well? You have to test your theory before assuming it to be fact.
Thanks for helping

Once it starts popping/missing it stays for a long time its always been that way hot and cold. I shut it off a few times each time fire it up popping/missing no power. Now after talking with Hagan I went down fired it up after 5 hours sitting its popping/missing I shut it off put the scanner on fired it up popping/missing as soon as it went to higher RPM's with the scanner on test and came back down no popping or missing. The truck seamed to have more power like it should. I ran it again up the steep grade back road until it does its normal popping/missing pulled over shut it off hooked the scanner up fired it up popping/missing I turned the scanner to test it went to higher RPM's came down cleared up truck runs smooth and has its power back. This is the part I don't understand why would that scanner help the issue? It seams the high idle or higher RPM's on test mode part clears things up
 
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Spott

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So, the only thing that reliably and immediately solves the problem is to put the computer into test mode, and the problem always remains resolved for a period of time after returning to normal operation from test mode.

All the sensors and relays behave exactly the same during test mode as they do during normal operations, except for the computer itself.

I have to say, given all the other component replacements, it sounds to me like the computer may have developed some minor fault. Have you visually inspected the computer circuitry? I'd recommend second opinions on this suggestion, just because it's such a slim possibility, but maybe it's time to try a substitute computer.
 

88 XLT Ranger

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So, the only thing that reliably and immediately solves the problem is to put the computer into test mode, and the problem always remains resolved for a period of time after returning to normal operation from test mode.

All the sensors and relays behave exactly the same during test mode as they do during normal operations, except for the computer itself.

I have to say, given all the other component replacements, it sounds to me like the computer may have developed some minor fault. Have you visually inspected the computer circuitry? I'd recommend second opinions on this suggestion, just because it's such a slim possibility, but maybe it's time to try a substitute computer.

The computer the main brain where would that be located on an 88 Ranger? maybe find one at "Pick and Pull" to try. This issue has been a nightmare thus far maybe where pinpointing the issue is the computer
 

Spott

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It's to the right of the passenger's footwell behind a kick panel, just ahead of the passenger's door. You have to unbolt a large connector to get the computer assembly out, and then you can take a cover off and inspect it. IIRC, the entire circuit board is dipped in a gray epoxy-coat, so any overheating, cracking, or component damage should be easy to spot.
 

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