1991 f150 4.9l i6 efi 5spd 4x4
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5th Gear
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1991 f150 4.9l i6 efi 5spd 4x4
I have an intermittent rpm/idle issue going on. Occasionally the idle will stick randomly at around 1500-2000. Sometimes at idle it will sit around 1200. Occasionally it will at an idle will rise and fall all by itself from about 1000-1600, then just randomly stop doing that. It also jerked with light throttle. I’ve replaced IAC valve, tps, map sensor, and 02 sensor. I unplugged vac like to EGR and that stopped the jerking and felt like I had more power with it unplugged too. Generally I got 230mi out of a tank before I unplugged the EGR, now it’s about 175 till I fill up. Plugs and wires are good. I’m kind of at a loss of what do next. Thanks for your help guys.
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From: Angier, NC
Welcome to FTE
One of the first things to do is see what codes the computer has and fix them in the order they are listed as 1 can fix others.
Have you checked for vacuum leaks? Bad vacuum hoses can cause a vacuum leak that the IAC valve is trying to correct. This leak may happen as the motor moves when running / driving.
When you changed out the IAC did you check the port if it was clear?
Als have you cleaned the throttle valve? What if it or the cable is holding the idle up that the IAC valve cannot control?
How many miles on the motor, compression good, maybe a plugged cat?
Just thinking out loud.
Dave ----
One of the first things to do is see what codes the computer has and fix them in the order they are listed as 1 can fix others.
Have you checked for vacuum leaks? Bad vacuum hoses can cause a vacuum leak that the IAC valve is trying to correct. This leak may happen as the motor moves when running / driving.
When you changed out the IAC did you check the port if it was clear?
Als have you cleaned the throttle valve? What if it or the cable is holding the idle up that the IAC valve cannot control?
How many miles on the motor, compression good, maybe a plugged cat?
Just thinking out loud.
Dave ----
FTE Legend
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From: Angier, NC
I dont know what them codes mean maybe you can Google them to see what they are?
Sometime in the 60's all motors started using PCV systems and it pulls clean air through a filter breather.
Dave ----
Sometime in the 60's all motors started using PCV systems and it pulls clean air through a filter breather.
Dave ----
FTE Legend
Joined: Nov 2015
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From: Angier, NC
Ok I am thinking out loud here and really dont know the computer trucks that well but .........
If the new O2 did not fix the lean code I would look at the EGR side as that can make it run lean and the idle go up & down.
I am thinking the EGR valve might be held open at times and why the lean and idle problem and the lack of flow would also show there could be crap holding it open at times.
Again thinking out loud but look at the EGR as that having issues can cause all the other things you got going on.
But lets see if anyone else has something to say.
Dave ----
If the new O2 did not fix the lean code I would look at the EGR side as that can make it run lean and the idle go up & down.
I am thinking the EGR valve might be held open at times and why the lean and idle problem and the lack of flow would also show there could be crap holding it open at times.
Again thinking out loud but look at the EGR as that having issues can cause all the other things you got going on.
But lets see if anyone else has something to say.
Dave ----
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5th Gear
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So I replaced the EGR valve. Upon initial start up it runs and idles perfect. But once I start driving its jumps and sputter while picking up speed. Going to check codes again tonight see if anything different appears. Thank you for your help thus far!
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FTE Legend
Joined: Nov 2015
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From: Angier, NC
When you changed it out did you clean the port the best you could?
The valve may not be hanging up now but if the exhaust flow is not right that could lead to problems I would think?
But good to hear I could help, just old school thinking what could make it run lean from the codes you gave.
Dave ---
The valve may not be hanging up now but if the exhaust flow is not right that could lead to problems I would think?
But good to hear I could help, just old school thinking what could make it run lean from the codes you gave.
Dave ---
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5th Gear
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Yes I checked the exhaust port before install and it was clear. I checked the fuel pressure and pressure reads about 47 psi idle and about 50 under some load. It seems the pressure regulator is working as well. So then I checked fuel filter, which was not in great shape. Replaced it but still getting lean code and drivability seems the same sputters and jumps and loss of power. I’m thinking maybe injectors at this point might have some issues. Let me know what you think
FTE Legend
Joined: Nov 2015
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From: Angier, NC
Could be injectors I guess.
I would add a can or 2 of Seafoam to the tank and run that and see if that helps.
I know some like Barry Man 12? over Sea Foam so what ever one you want to get cant hurt.
Maybe someone has something else to look at?
Dave ----
I would add a can or 2 of Seafoam to the tank and run that and see if that helps.
I know some like Barry Man 12? over Sea Foam so what ever one you want to get cant hurt.
Maybe someone has something else to look at?
Dave ----
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