Annoying misfire...
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Annoying misfire...
I've read through many posts but still have a couple particular issues that I am hoping may help someone narrow down my possibilities.
I am having a misfire occur on my 1993 F150 5.0L that only happens under light load, usually after the trans has up shifted but then I lightly press the pedal to go up a hill or something. It will either buck for a few seconds and then "pull" out of it or I can mash the pedal, make it down shift and it does fine. The strange part it is it doesn't seem to do this much when the truck is cold but as it warms up it tends to get worse.
It may have a slight misfire at idle as well but I swear it doesn't do this until it gets warm (still figuring out the problem). The plugs, wires, cap, rotor, IAC, EGR sensor, TPS and a few others have all recently been replaced.
One thing I read about was this plug wire 7 & 8 being to close to one another. Is this an issue even with new wires? I plan on going down and checking my routing on those today. I have not checked my fuel pressure yet but it doesn't seem like a fuel pump issue.
Any other suggestions? Thanks in advance for any help.
-Ryan
I am having a misfire occur on my 1993 F150 5.0L that only happens under light load, usually after the trans has up shifted but then I lightly press the pedal to go up a hill or something. It will either buck for a few seconds and then "pull" out of it or I can mash the pedal, make it down shift and it does fine. The strange part it is it doesn't seem to do this much when the truck is cold but as it warms up it tends to get worse.
It may have a slight misfire at idle as well but I swear it doesn't do this until it gets warm (still figuring out the problem). The plugs, wires, cap, rotor, IAC, EGR sensor, TPS and a few others have all recently been replaced.
One thing I read about was this plug wire 7 & 8 being to close to one another. Is this an issue even with new wires? I plan on going down and checking my routing on those today. I have not checked my fuel pressure yet but it doesn't seem like a fuel pump issue.
Any other suggestions? Thanks in advance for any help.
-Ryan
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Well I am about at a loss...
The truck has and holds good fuel pressure (~30psi vac on, 40psi vac off), has new plugs, wires, cap, rotor, EGR sensor, TPS, IAC (I believe), fuel filter and air filter. When I apply vacuum to the EGR when the truck is idling it stumbles, as I understand it is supposed to. And I can't find, don't see or hear any obvious vac leaks. I've separated plug wires 7 and 8 and don't see any arcing from any where when I look under the hood in the dark.
What else am I missing to check here? Could it be a bad O2 sensor? I would expect a code with that though. The only code I get when I scan the ECM is 11 (everything is OK).
Obviously I am missing something... any additional thoughts?
Thanks,
Ryan
The truck has and holds good fuel pressure (~30psi vac on, 40psi vac off), has new plugs, wires, cap, rotor, EGR sensor, TPS, IAC (I believe), fuel filter and air filter. When I apply vacuum to the EGR when the truck is idling it stumbles, as I understand it is supposed to. And I can't find, don't see or hear any obvious vac leaks. I've separated plug wires 7 and 8 and don't see any arcing from any where when I look under the hood in the dark.
What else am I missing to check here? Could it be a bad O2 sensor? I would expect a code with that though. The only code I get when I scan the ECM is 11 (everything is OK).
Obviously I am missing something... any additional thoughts?
Thanks,
Ryan
Cargo Master
Joined: Mar 2010
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From: Laramie, WY
Check compression. Really doubt that would be the issue, but I have seen it. My oil ring expander ring (the wavy one) was cracked, so I was burning tons of oil in #8. So much carbon built up on the #8 exhaust valve that it couldn't shut. Compression test showed 55psi with 160 or so on all others. This took alot of miles to build up that much carbon...
I know thats a bit of a freak thing, but wierd chit does happen sometimes.
My misfire was constant, so I doubt you have this serious an issue. Just sharing some thoughts.
Probably more likely is a sticky injector? I've tested these by pulling the injectors and fuel rail, then reassembly the unit outside the intake, turn key to on and watch the fuel spray pattern. Just don't have a cig in your hand.
I know thats a bit of a freak thing, but wierd chit does happen sometimes.
My misfire was constant, so I doubt you have this serious an issue. Just sharing some thoughts.
Probably more likely is a sticky injector? I've tested these by pulling the injectors and fuel rail, then reassembly the unit outside the intake, turn key to on and watch the fuel spray pattern. Just don't have a cig in your hand.
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I have not checked compression but might do that if I can't find anything else and end up pulling all the plugs/wires back off. I haven't seen any sign of oil consumption though. And I have wondered if an injector could be the problem but didn't know a good/easy method to check this. I have a set of 19# injectors around somewhere so I could swap those in if necessary. It just seems like injectors rarely go bad and I would also think I would get a code related to that,,, but maybe not.
I can't say with 100% certainty that it isn't the TQ converter but it doesn't exactly feel like that. As I said above, it shows no codes at all which is the other thing that has me stumped a little. I've purposely continued to make it buck/jump for 10-30 secs at a time trying to get it to throw a code but no luck.
It does seem to get worse as the motor warms up though. I drove it yesterday after messing with some stuff and the problem was almost non-existent for the first 3-5 minutes but then it started to get worse. And on the 3 hr trip I took in it last weekend by the time I got home it was running horribly.
Thanks for the suggestions guys, keep 'em coming.
-Ryan
It does seem to get worse as the motor warms up though. I drove it yesterday after messing with some stuff and the problem was almost non-existent for the first 3-5 minutes but then it started to get worse. And on the 3 hr trip I took in it last weekend by the time I got home it was running horribly.
Thanks for the suggestions guys, keep 'em coming.
-Ryan
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