Hey all. I have an 89 F1 with a 302 EFI system. My problem is: When I start the truck, it runs fine until it warms up. Going down the road everything is great until I have to stop. It starts loping big time and sometimes dies. It's even worse with the A/C on. Sometimes just bumping the gas a little corrects the problem, other times I have to sit and hold the gas a little to keep it running. I thought it may be a vacuum leak, but I got the truck up to operating temp and with it running sprayed some carb cleaner all around the intake and vacuum lines and it never changed the Idle. I have replace the O2 sensor, IAC valve, EGR valve, throttle position sensor, changed plugs, wires, distributor cap and rotor button and even had my catalyic converter checked just for the heck of it and nothing is helping. Wondering if it could be the mass airflow sensor or just something internally. Also, when I am stoped and it runs rough and lopes, the oil pressure drops or dances back and forth. Any ideas?
You might check the fuel pressure regulator, and the air bypass valve. The regulator smoothes out the flow of fuel from the pump, so it might be clogging up, especially if it is original. I don't know if temperature affects it or not, but temp does affect the air bypass valve.
Just a thought.
Hey, dont know if your question was answered but, I have the
89 f150 and had the same problems. What I found out the #5 or #7 piston was burned out,rings and all. Had a major head job also. Found out that the 5.0 motor had problem passing EPA standards so they were run lean to pass.Have you had exhaust
manifold trouble,mine cracked twice both sides. Now I use Headders easy flow cat and flowmaster muffler,K&N filter,Chip
and RV cam. Try copression test all cyclindes dry and wet.
If you can hear any ticking noise thats Valves/lifters. So hope this is helpful to you and Good Luck.
It is NOT going to be anything like stated above (granted that you do not have a Major power loss). Do you have an exhaust job on your vehicle???? the reason why I ask is because I have seen problems with idle related to backpressure with the exhaust. Especially if you have removed the CATS and have BIG dual exhaust.
Just a thought but I would NOT begin tearing the heads off Etc.
1988 Ford F250 4x4, 5.0 liter (soon to be Roller 5.0), AOD tranny, 2.5 Dual exhaust, Headman Shortyheaders, 33" BFG's Mud Terrain
1980 Ford F100, with 1988 5.0L Roller (carburated), T-5 five speed Borg Warner World Class Transmission, 31 spline 9" 3.73 posi , and a bunch more!! 13.78 quarter mile.
1985 Ford F150 2wd, Brand New Roller 5.0 with GT40P heads, AOD tranny.
I had an idling broblem for a long time before I figured out what it was. I ended up frying an O2 sensor bacause of a bad IAC solenoid. I had a bad IAC solenoid but replaced the O2 sensor first not knowing. The problem persisted and a month later replaced the IAC solenoid. Problem still persisted. After that I replaced practically everything that could be replaced. I later re installed my original 02 sensor (keept all used sensors) and the truck has run fine since. I believe that the O2 sensor failed due to the soot and unburned fuel going through the exhaust from running really rich. This was causing the truck to sputter and stall.
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