Hoping for some help here, I bought a 91 F-150 4.9L 5spd manual for my son as a first car. It has 170000 miles on it but it is rust free and is unmolested. I bought it with no exhaust other than the y pipe because the seller said it had a clogged catalytic converter. I replaced the exhaust from the y back along with a new emissions tube. The truck doesn't run horrible but it surges when you first start it and if you step on it there is a flat spot. Also the check engine light is on. It runs a little smoother as it warms but never completely smooth. I started with a tuneup and I replaced the IAC from Advance Auto. No change. I scanned it and got 5 codes, the first two were 117(bad ECT) and 122(bad Tps). They were cheap enough so I replaced them both, no change. The next codes are 513 (Pcm Internal voltage fail), 553 (Air management circuit 1 fail) and 565(canister purge solenoid circuit fault). I pulled the vacuum hose on the fuel regulator and theres no fuel seen and the engine kept running and I disconnected the egr valve electrical connector and it made no difference in the way the engine runs. I also checked the diaphragm in the egr to see if it moves and it does. I hate throwing parts at a truck so im open to suggestions. I usually tackle the codes in the order they come out but I have no idea how to test a pcm. Any help would be appreciated

 

1991 was the first Ford started to use 3 digit codes on these trucks. Since yours is 4.9L with a 5 speed I would have expected 2 digit codes.

Regardless if it is 2 or 3 digit codes you need to warm up the engine before running the KOEO tests and CM display. If not you will probably trigger false ECT and/or ACT codes.

How did you pull the codes? count flashes or with a code reader?

If the codes are truly 3 digit then you may as well start looking for a replacement PCM. Code 513 is usually a fatal error that is not repairable.

 

I had the truck running for about 15 minutes before I ran the test. I used a code reader to pull the codes.

 

Thanks for clarifying how you got the codes. A code reader can be a handy tool.

Code 513 is a very ominous issue.

My Ford Service Manual states this:

Key On Engine Off:

• Replace PCM

Key On Engine Running:

• Replace PCM

Continuous Memory:

• Replace PCM

It is becoming quite to common for the capacitors to leak on the PCM circuit board but it usually exhibits different symptoms than yours. It might be worth a shot pull yours out, open and inspect it for signs of leaking capacitors.