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1991 F250 DTC Problems

Hello all,

I have an issue with my truck that I am hoping you can help with. I have posted in forums like this before and not had very good luck.

I have a 1991 F250, 5.8 L, 125,000 mi. I have owned the truck for about 8 months and would actually like to be able to drive it. I bought it with a check engine light on (almost a death blow in CA because it causes an automatic failure when it is SMOG tested). I ran codes with a jumper wire in the test port. I got a Code 63-TPS low voltage and Code 98-Hard Fault. On the recommendation of a mechanic firend I changed the TPS and IAC Valve. No change. I then went out and bought a tester at the parts store and ran the test again and got the same codes. I tried to complete the code reset procedures and the codes would not clear. I have also read that the Code 98 could also mean that the Neutral Safety Switch could be bad.

I have taken it out on several short test drives (around the neighborhood) and it seems to shift hard into second gear when moving from a start. When I bought it I had it towed home because it would not stay running when put into gear. When I started digging around I found that it was low on tranny fluid. I filled it with about 1.5 gal of tranny fluid and corrected that problem. Hoping that the hard shift is not because of the lack of tranny fluid. Previous owner had stopped using the truck and only drove it a couple of miles from home to service station that I picked it up from.

J
 

blacksnapon

Moderator
Staff member
concentrate on the "63".Problems with a non responsive tps can upset the shifts. The trans shift scheduling relies on the information sent by the tps sensor. Wiring/connector/sensor/pcm is what you need to look at.
 
Last edited:

blacksnapon

Moderator
Staff member
You'll need to check the reference voltage, and continuity of each wire from the sensor to the pcm. My wiring diagrams are thin older than 10 years. You might try google.
 
Hello all,
Hopefully there is somebody out there still watching this forum. I finally had some time off to test my TPS. I tested the TPS voltage- 0.03v; getting power from PCM-5v and have good ground. TPS was installed brand new. Thinking I got a bad one. Gonna take it off and swap it out at the store unless somebody out there has some pearls of wisdom.

J
 
Got the TPS problem taken care of. Got a defective one from the parts store. After I put the new one in the CEL went off. Took it for a test drive and CEL came on less than a quarter mile from the house. Ran codes again and got a Code 33; EGR not opening properly. So I guess I am chasing problems now. Hopefully this will fix the problem(s) once and for all.
 

blacksnapon

Moderator
Staff member
There's an egr sensor. It will have 2 vacuum lines going to it. Generally, it will be on the driver side. About 1" by 2" and black.
 

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