Hello,

I recently purchased a 1990 F350 chassis cab, 5 speed 4x4 that's spent the last ten years on a farm. I've spent a tremendous amount of time working on the exterior and interior to bring it back to life. Polishing paint, fixing rear fuel pump, fixing running light wiring, ect.

The last issues on the list is with the engine. When I bought the truck, the Map sensor was plugged in but the vacuum line had a bolt stuck in it. This forced the computer to dump fuel, giving it decent power on acceleration but ran very choppy at idle.

With the Map Sensor fully installed, the truck runs very smooth at idle but hesitates under acceleration. With the vacuum line blocked, it idles like it's cammed but runs great under acceleration.

I have already installed a new rear pump, the previous owner said they had already checked the fuel pressure, but I believe I should do it again just to be sure. I tried installed a new map sensor but that did not solve the problem.

Any suggestions of where to check next?

Thank you!

 

Hey, Welcome to the Forum. Nice truck. First thing that I would check, would be the throttle position sensor. You can test it with an ohmmeter.

 

Fuel pressure and check codes. Does the Check Engine light work? Check the sensors and such that don't set codes. You need a book, vacuum pump and volt/ohm meter.

Catch it up with the maintenance schedule.

 

What he said, first step is *always* codes and fuel pressure.

Vacuum leaks would be just as important in this case, it sounds like you have some.

 

Would not hurt to clean the Idle Air Bypass Valve, and replace with new gasket.

 

I'll begin this evening by checking the codes and ohmmeter on my tps. The check engine light isn't on, but did come on while the Map was unplugged completely, so I know it does work. I have ordered a fuel pressure tester and will check that this week as well.

Even with a new pump on the rear, is it possible I'd still have fuel pressure issues? Would there be a fuel pressure regulator or sensor that could be causing the truck to run lean?

Thanks

 

Yes it is possible. I believe you have two in tank pumps, an inline pump and a switch over valve. If the inline pump was weak, or the switchover valve wasn't actuating properly, you could be loosing pressure. However, with a dead inline pump you probably wouldn't be able to run.

 

1990 was the first year for the in-tank high pressure fuel system. No frame mounted high pressure pump or switching valve.

 

A few updates.

Fuel pressure is good, no codes relevant to the problem (A few regarding the rear pump that I recently replaced.)

TPS seemed to be on the verge of incorrect during testing, it's been replaced. This seemed to have helped *some* but the truck still struggles to pull its own weight.

The engine will run fairly smooth on idle and when feathering the accelerator just right, but any sudden change to the throttle and it will bog out horribly. Putting my foot to the floor, even for a few seconds, will bog and not accelerate.

I have a replacement fuel pressure regulator arriving tomorrow, although I dont feel that it's the problem. What else do you recommend I look at?

 

edit edit edit

 

Your truck is looking good and it's good to hear an update. I think I missed something. Why are you swapping the regulator if the fuel pressure is OK? What is the pressure anyway? What were the codes you pulled?

Some people on this site have a wealth of experience and factory documentation to troubleshoot these problems. If you are just going to throw parts at it they can't help you.

 

Codes were 11 10 22 33 41 87 95. Fuel pressure stayed between 35-40 psi.

Thanks for your time!

 

After speaking with a friend about the problems, he believes it's possible that the marks aren't lined up where they were from the factory and that I'm not actually in time. Has anyone experienced this?

Anyone?

 

 

After days of testing and diagnosing, I'm still lost. The engine only revs / pulls the weight of the truck without severely stumbling if I have the MAP sensor vacuum line disconnected and plugged up or spray something flammable in the throttle body. The fuel pressure is great, however the computer is running the engine too lean to drive it.

The truck has not displayed any codes since clearing the codes. 22, 87 and 95 were all corrected prior to the reset, though I'm surprised I haven't seen 41 come back, as the truck is still running too lean to drive.

I spent last Saturday swapping parts from a friend's 1991 460 F350 and eliminated quite a few sensors and parts from the list of a potential culprit.

As of today, I have either tested, swapped or replaced:

TPS
IAC
EGR
MAP
FPR


The timing was set with a light, but I also played around with it by ear to verify the balancer hadn't slipped, showing a false timing reading. No help.

The rear tank was completely empty, then filled with fresh fuel. The rear tank also has a brand new pump, as well as a fuel filter. I have tried testing on both tanks, no difference with either one,

I also ran a test today on the vacuum, I'm running around 18 at idle and 20 with a slight rev. Again, the only way to drive the truck is with the MAP plugged in but vacuum line plugged. I now have the truck home, so I wont need to force the truck rich anymore. I'm going to replace the plugs tomorrow (they're nasty from the truck being forced to run rich) and beat my head against the hood some more trying to diagnose this issue.


What else is left to try?