Stumble/hesitation when cold
05-10-2014, 01:45 AM
#1
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Location: Billings/Missoula
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Stumble/hesitation when cold
So I did a whole fuel system clean on my 87 22re. Cleaned tank, new pump, filter, lines and rail blown out, and new flamethrower injectors. One thing I know for sure is that after doing all this, the truck is MUCH improved in terms of power and mileage... number 4 injector was totally clogged.
However, immediately after it developed a stumble or hesitation when the engine is cold. Before it is warmed up, if I give it just a little bit of throttle and hold, the truck will buck and stumble and be generally unhappy. Apply a little bit more throttle and it snaps out of it and revs happily and freely. Just the first few percent of throttle or simply taking off from a stop causes this problem.
The good news is it goes away once the engine has warmed up. Still, I'd like to track it down.
I've considered the tps as a possible culprit but feel that operating temp wouldn't affect that. My other thought was maybe I damaged the fuel pressure regulator with brake cleaner when I was cleaning the fuel rail. But I don't know what symptoms of a messed up regulator would be either.
One last piece of info. The truck seems to idle where it wants to on any given day. Sometimes it will be at 1200, others at 800. If you turn the idle screw down you 800ish while it's up at 1200 or so, the next day it might idle too low and want to stall. Not sure if that's relevant, but it's what I'm dealing with. I appreciate any help I can get!
However, immediately after it developed a stumble or hesitation when the engine is cold. Before it is warmed up, if I give it just a little bit of throttle and hold, the truck will buck and stumble and be generally unhappy. Apply a little bit more throttle and it snaps out of it and revs happily and freely. Just the first few percent of throttle or simply taking off from a stop causes this problem.
The good news is it goes away once the engine has warmed up. Still, I'd like to track it down.
I've considered the tps as a possible culprit but feel that operating temp wouldn't affect that. My other thought was maybe I damaged the fuel pressure regulator with brake cleaner when I was cleaning the fuel rail. But I don't know what symptoms of a messed up regulator would be either.
One last piece of info. The truck seems to idle where it wants to on any given day. Sometimes it will be at 1200, others at 800. If you turn the idle screw down you 800ish while it's up at 1200 or so, the next day it might idle too low and want to stall. Not sure if that's relevant, but it's what I'm dealing with. I appreciate any help I can get!
Last edited by Latigo; 05-10-2014 at 01:47 AM.
05-13-2014, 05:14 AM
#3
Sounds like you might be running lean or rich when cold.
1st place I'd look is the cold start injector. Try unplugging the connector to the cold start injector and see if it improves the starting cold. If it gets better then you are likely running rich
If it doesn't get better then plug it back in and verify the injector actually works and is not plugged
1st place I'd look is the cold start injector. Try unplugging the connector to the cold start injector and see if it improves the starting cold. If it gets better then you are likely running rich
If it doesn't get better then plug it back in and verify the injector actually works and is not plugged
05-13-2014, 07:20 AM
#4
Registered User
Doesnt hurt a thing to calibrate the tps. Free stuff there...lol. I would do that right off the bat to eliminate.
Diagnosing isn't about finding out what it wrong....its about finding out what does work, eliminating possibilities until the issue comes to light.
Diagnosing isn't about finding out what it wrong....its about finding out what does work, eliminating possibilities until the issue comes to light.
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