Trouble idling on cold start
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Trouble idling on cold start
Hello,
I am in need of a bit of diagnosing with an idle issue.
1991 300 I6 w/ 121,000
The truck runs GREAT other than starting when the motor is cold. When I turn it over for the first time, the motor with crank through, but not start. Turn it over for a second time, then it will start but act like its missing very bad or running on a few cylinders. And at this time, it will not respond to me pressing on the throttle. It will eventually die after a few seconds. Then when I turn it over for the 3rd time, it cranks and idles perfect. The truck runs absolutely flawlessly other than the idling issue. After doing some research, I replaced the IAC, but the problem still exists. I checked the TPS with the voltmeter and its perfect. Timing doesnt seem to be an issue because its only when the motor is cold, and runs perfect when it actually gets running.
At this point, I dont know where to turn next. Any help would be greatly appreciated!
I am in need of a bit of diagnosing with an idle issue.
1991 300 I6 w/ 121,000
The truck runs GREAT other than starting when the motor is cold. When I turn it over for the first time, the motor with crank through, but not start. Turn it over for a second time, then it will start but act like its missing very bad or running on a few cylinders. And at this time, it will not respond to me pressing on the throttle. It will eventually die after a few seconds. Then when I turn it over for the 3rd time, it cranks and idles perfect. The truck runs absolutely flawlessly other than the idling issue. After doing some research, I replaced the IAC, but the problem still exists. I checked the TPS with the voltmeter and its perfect. Timing doesnt seem to be an issue because its only when the motor is cold, and runs perfect when it actually gets running.
At this point, I dont know where to turn next. Any help would be greatly appreciated!
FTE Legend
Joined: Nov 2015
Posts: 30,912
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From: Angier, NC
What if you turn the key on for say 5 to 10 seconds, then off, back on for 5-10 sec. like 3 times then see if it starts.
After codes as posted I would look at fuel PSI when cold and will not start, then when not running good, then when it is running.
Just throwing it out there but thinking it is not building fuel psi when cold.
I had a EFI tractor that would surge after about 1.5 hours of running. Turned out to be the in tank fuel pump would fail when hot and only found that using tractor with a gauge taped to the hood.
Dave ----
After codes as posted I would look at fuel PSI when cold and will not start, then when not running good, then when it is running.
Just throwing it out there but thinking it is not building fuel psi when cold.
I had a EFI tractor that would surge after about 1.5 hours of running. Turned out to be the in tank fuel pump would fail when hot and only found that using tractor with a gauge taped to the hood.
Dave ----
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Thanks Dave,
It very much seems to be the case because after I do get it idling correctly after a few tries, I can shut the motor off and then it will start up just fine (after building fuel pressure). Say this is the case, are we looking at fuel pump failure or something else?
Thank you
It very much seems to be the case because after I do get it idling correctly after a few tries, I can shut the motor off and then it will start up just fine (after building fuel pressure). Say this is the case, are we looking at fuel pump failure or something else?
Thank you
What if you turn the key on for say 5 to 10 seconds, then off, back on for 5-10 sec. like 3 times then see if it starts.
After codes as posted I would look at fuel PSI when cold and will not start, then when not running good, then when it is running.
Just throwing it out there but thinking it is not building fuel psi when cold.
I had a EFI tractor that would surge after about 1.5 hours of running. Turned out to be the in tank fuel pump would fail when hot and only found that using tractor with a gauge taped to the hood.
Dave ----
After codes as posted I would look at fuel PSI when cold and will not start, then when not running good, then when it is running.
Just throwing it out there but thinking it is not building fuel psi when cold.
I had a EFI tractor that would surge after about 1.5 hours of running. Turned out to be the in tank fuel pump would fail when hot and only found that using tractor with a gauge taped to the hood.
Dave ----
FTE Legend
Joined: Nov 2015
Posts: 30,912
Likes: 4,123
From: Angier, NC
Well...........The pump builds the psi but if the pump(s) are not getting the needed voltage, if any at all on cold start, would need to be looked at before going and replacing $$ pump(s).
Now I do not know the fuel system that well but guessing it is EFI?
If so and it is like some of the others posted on here there is a relay and 2 I think it is safety switches.
A bad relay would not let power out to either switch to make the pump run.
1 switch is the oil psi switch - no oil no fuel.
The other I call a "roll over" switch, if in a bad accident the switch opens to kill power to the pump(s).
So you can see I would first pull codes as it may give you a path to follow, bad crank sensor maybe? That would not tell the ECM the motor was cranking.
If no codes then I would do the fuel PSI test. If you find you have no PSI when cold you would need to find why, no power to pumps? If so then why could it be a bad oil psi switch and cranking it a few times gets it to close?
I think it is fuel but do pull codes first.
Dave ----
Now I do not know the fuel system that well but guessing it is EFI?
If so and it is like some of the others posted on here there is a relay and 2 I think it is safety switches.
A bad relay would not let power out to either switch to make the pump run.
1 switch is the oil psi switch - no oil no fuel.
The other I call a "roll over" switch, if in a bad accident the switch opens to kill power to the pump(s).
So you can see I would first pull codes as it may give you a path to follow, bad crank sensor maybe? That would not tell the ECM the motor was cranking.
If no codes then I would do the fuel PSI test. If you find you have no PSI when cold you would need to find why, no power to pumps? If so then why could it be a bad oil psi switch and cranking it a few times gets it to close?
I think it is fuel but do pull codes first.
Dave ----
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Harte, it read code 128 (MAP sensor).
I cant seem to find any vacuum leaks. Possibly a faulty sensor? Would this cause the trouble idling during cold start issue?
Thanks
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Joined: Sep 2014
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From: like subarctic, brrr man!
MAP Sensor tells the computer stuff about the air so it can compute how much to open the fuel injectors. MAP=Manifold Air (Absolute?) Pressure Sensor.
It's kinda important.
I'm not sure where or what it looks like, mainly because I'm using GM parts from a Jeep in mine (DIY EFI).
It's kinda important.
I'm not sure where or what it looks like, mainly because I'm using GM parts from a Jeep in mine (DIY EFI).
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