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?

 

Any black smoke out of the tailpipe when this happens?

 

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.

 

If the air bypass valve you are referring to mounts at the throttle body, then he has already replaced it. It's official name is IAC valve or Idle Air Control vavle.

 

Check the TPS sensor. I had to replace this on my 89 302 as well as my 93 302. They need to be replaced after a certain amount of years.

 

Don't have any black smoke. The IAC valve has been replaced within the last 6 mo's. The TPS has also been replaced within the last 6 mo's.

 

It seems as though you have a high resistance problem created by the engine heat, check the engine harnes. As for the tps and iac being replaced in the last 6mos, I have seen them die quicker.

John

 

How do your plugs look?

1989 F-150 : 5.0, shorty headers, Flowmaster cat-back, K&N filtercharger intake, March pulleys, MSD-6T, soon to be Mass-Air...doesn't know she's not a Mustang

 

Plugs are brand new as well as wires, dist cap and rotor button. Have run diagnostics on all replaced sensors and electrical parts and they all check out good. No codes. Just runs like crap

 

i would really check the fuel pressure regulator. it sounds just like a problem my buddy had on that exact same truck. he replaced all the crud you've replaced before he finally figured it out.


1990 F150 Custom 2wd
300 straight-six, Mazda 5 speed

1971 F100 2wd
360 FE, C6

"It doesn't break 'til I fix it"

 

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.

 

Thanks for the info. I hope to get it looked at this weekend. It has passed my knowledge so I'm getting some outside help.

 

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.

 

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.

92 F150 XL 4x4, 5.0L AOD, Headers, K&N Air Filter, 3.55 Gears, LT235/75/15 Tires.

 

Automatic? Maybe the CV cable....especially if it doesn't have trouble in Park.