Hello!

This is my first post after scouring the forum for information. I didn't want to start off asking stupid questions haha.

I Recently bought a 91 f150 L6 manual (w/ 2 gas tanks) with 130k miles. The truck is in overall good shape, and runs pretty well. I'm pretty good with working on cars, but most of my experience has been with import cars. Anyhow, my CEL comes on after driving for about 10 minutes.

I pulled the codes on the CEL engine off and got:

52: power steering pressure switch open
25: knock not sensed
42: No O2S switching detected
327: EVP/ ept circuit below minimum voltage
328: EGR valve voltage lower than expected
332: Insufficient EGR flow detected
542: Fuel pump secondary circuit fault

SO.....

My main question is where's the best place to start?
After reading for a few days, and looking at the trouble code definitions, and what different combinations of codes could mean, I think I should:

Check all the vacuum lines for leaks
check for vacuum at the evp sensor
clean the EGR
clean all the connections/check for grounded wires

am I headed in the right direction? I have no experience with vacuum lines whatsoever. I am assuming I just replace any cracked lines.

If all of these seem ok, what then? replace the EGR and the EPT?

As for the other codes, My steering seems fine, but researching code 52 tells me that there might be a nut loose behind the steering column?

The one I really don't get is code 542. Both tanks pump fuel just fine. However, the gas gauge is broken on the front tank. Rear tank shows up fine, but always shows E on the front tank. Research says one fuel pump might be grounded, but then it wouldn't work right?

Any help would be appreciated! Thanks in advance

 

You're gonna have to start over, its either going to be 2 digit codes or 3 digit but not both.

"91" I believe would be 2 digit codes but I'm not positive.

 

I thought it was weird. I looked it up and other posts have said that the OBD1 went from 2 digit to 3 digit in '91, and while they say its rare, some have 2 digit codes for regular codes and three digit codes that are in the memory. I just went out and checked it twice. and it throws the two digit codes, then pauses for about 10 seconds, then starts throwing 3 digit codes. both 2 and 3 digit codes all have .5 second between blinks, 2 seconds between numbers and 4 second pauses between codes.

 

52 is a KOEO or KOER.
25 is a KOER code. Key On Engine Running Self-Test only code.
42 is a KOER code. Key On Engine Running Self-Test only code.

So you are not reading something right.

 

ok yeah so I'm an idiot.
I dont know why I didnt realize this before. I was reading them wrong (as I was told). I got 52 25 42. when in actuality I was getting:
522 and 542. those are in KOEO. I am still getting 327 328 332 and 542 in CM.
sorry guys.

I pulled the negative cable to reset the codes, drove around again till I got the CEL, and got the same codes.

I did notice that this time when I was watching the codes, with the key on, it sounded like the fuel pump in the engine bay was running continuously. I unplugged the test wire amd turned the key again. same thing. what I dont get is that both tanks still pump gas ok, and the front tank fill gauge wont work. any suggestions? again, sorry for the idiocy.

 

Yes it sounds like you have a bad PCM Computer.
So I am not going to try and go in each code.
Open up the PCM Computer and check any caps for leaks.

I think with the caps replaced or the computer replaced the codes may be down to one or two.

 

ok will do. I head on down to the scrap yard this weekend. thanks for the help!

 

Thanks for the help guys! got a new computer from the junk yard and all my CEL's are gone! drove around quite a bit and nothing popped up. Have a different issue now but I'm gonna start a new thread for that