Hey guys, got a problem and I'm stumped. Any help would be appreciated. Got a 90 model 5.0 coupe with mass air. Drove it one day and it ran fine, got in the next and it had a miss. It misses at low rpm 1500-2000 and especially under load. If you put it in this exact condition ( uphill, 5th gear at say 1800 rpm) for any period of time it will start popping through the intake. All wires were spark tested and ohmed. All plugs checked. Compression test showed 115-120 on all cylinders. Cap and rotor look fine. Coil ohmed out fine and is getting 12 volts. I have a fuel pressure guage mounted to the regulater and it's getting good fuel pressure. Ran balance test and it passed twice then give me a fault for cylinder #5 and the engine immediatly shut off. Don't know why. Fired it back up and ran the test 3 more times and passed every one. Ran the codes and got a bunch of air diverter and egr faults cause all that is off the car. The only faults I got that I'm not sure about are 54 ACT sensor open and 96 Fuel pump secondary circuit fault. I replaced the ACT only a couple months ago, could this be causing the stumble? And I'm not sure about the fuel pump fault cause the car has fuel pressure. Please help.
low rpm miss under load
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87WhiteStang1
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- Dec 19, 2007
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I have been having the same problem for a few months now. I have done everything i could think of or that has been suggested to try to fix it. I even took it to a performance shop for them to look at and they worked with it for hours and said the only other thing they could think of was a short in the cpu. so i replaced the cpu and had the same problem. I am at the point now where i am about to replace the whole under hood wiring harness because i have no other ideas. If you get it fixed let me know what ya did.
check the bolt holding down the distributor. my came loose and the distributor over time would move and the timing was off. this caused the same problems you had.
that's the only time you will feel it. it woud buck horribly under 2k rpms regardless of gear unless I rode the clutch. turned out my timing was off due to a loose hold down screw.
Ok, I replaced the plugs and wires just to be sure and they didn't help at all. Anyone have any other ideas. I'm really starting to get frustrated. I'm replacing all the injectors tomorrow. I've got an extra set in the garage and I just want to rule it out. If that doesn't work then I'm going to buy a leak down tester and start looking at maybe a valvetrain issue. Please shoot me any ideas you may have, I'm desperate.
87WhiteStang1
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sounds like the same exact thing mine does. I thought for a while could be something in the heads/ valves but i replaced with gt40's and same exact issue.
hmm
Same issue after swapping heads huh... I have no clue then I guess. Maybe it's time to pull the motor and have it looked at. I'm no stranger to troubleshooting / wrench turning but I have not been able to figure this one out. 2 different reputable shops have not bee able to nail down the issue either.
I've also done a compression test and all were decent and within 10% of each other.
Same issue after swapping heads huh... I have no clue then I guess. Maybe it's time to pull the motor and have it looked at. I'm no stranger to troubleshooting / wrench turning but I have not been able to figure this one out. 2 different reputable shops have not bee able to nail down the issue either.
I've also done a compression test and all were decent and within 10% of each other.
Changed cap and rotor today. No help. Swapped out tps and mass air sensor, no help. Ran it first thing this morning, ice cold and had same problem so in my opinion that rules out O2 sensors. As you said I'm not a newbie to troubleshooting, been wrenching for years and this thing is driving me crazy. I'm changing out the coil and injectors tomorrow and if that doesn't fix it then I'm pulling the heads. I have another set in the garage and we'll see if that helps. I promise one thing, I WILL fix this car. Hopefully my problem will be your problem and it will help us all.
87WhiteStang1
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I have been looking around trying to find an injector and ecu wiring harness and i'm hoping to get one soon. Thats the only other thing i can think of at this point. i know that it could just be one little wire not getting a connection or somthing that would do this. plus i don't have any other ideas at this time. If that doesn't do it then idk what will. i guess i would just have to drive my car with a missfire for the rest of its life... We'll see
FIXED IT!!!!
It was an injector. Relaced all injectors and it runs smooth as silk now. All the injectors I removed worked but on a couple of them the little plastic tip had crumbled and I think this was disrupting the spray pattern. If you haven't checked injectors yet I would. Only took about 30 min to change them out. Thanks for all your input, I'm gonna go do some burnouts now.
It was an injector. Relaced all injectors and it runs smooth as silk now. All the injectors I removed worked but on a couple of them the little plastic tip had crumbled and I think this was disrupting the spray pattern. If you haven't checked injectors yet I would. Only took about 30 min to change them out. Thanks for all your input, I'm gonna go do some burnouts now.
87WhiteStang1
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Well i recently swapped in some 24# injectors and they were used but seemed to be fine. And it had the same exact miss as before. It would be really weird if these injectors and the ones i had on there had the same exact problem.
87WhiteStang1
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- Dec 19, 2007
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87WhiteStang1
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- Dec 19, 2007
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