My 91 F150 (straight 6, manual) started acting up the past week. While driving along (at no specific time interval) the engine will start studdering on and off. Eventually I'll get a service engine light on and off and then the engine will finally die, I can restart it but it stills runs rough and will die again. This has happened twice 2 days apart. It drove fine the day in between.

Pulled the codes, the first time and got the following #'s 112, 117, 122, 327
These are low voltage codes for ACT, ECT, TPS, EVP.

Pulled the codes, the second time and got the following #'s 112, 117, 122, 126, 327, 556
These are the same low voltage codes for ACT, ECT, TPS, EVP and new codes for MAP/BP sensor out of test range, and Fuel Pump circuit Failure.

So it looks like I am getting codes for all of my 5 volt transmitters, Checked TPS and ECT supply voltage with meter and it is bouncing around. Not too sure about the fuel pump circuit failure?

I am pretty sure the 5 volt power is coming from the computer, right?
Is there another potential problem other than my computer?
What do i need to do to replace the Computer, just disconnect battery and pull it?

Thanks for any help.

 

Had the virtually same symptoms on an E150. Shop told me it was the computer because of all of the codes. Waited a week for the computer to come in only to have it act the same. Friend told me that it sounded like a bad MAP sensor. Replaced MAP sensor and van ran great. Still is a year later!

 

I've answered some of my own questions now. I missed a section on fordfuelinjecters.com when I was reading it earlier. The Computer has a voltage regulator that steps down the voltage to 5V for several sensors. Since I am getting codes for my sensors that operate on 5V and since the VREF wire going to the sensors had a bouncing voltage I am going to assume that the computer voltage regulator has crapped out and I need to replace the computer.
Would a bad ground on my EEC (computer) cause it to have problems generating the 5V referance voltage.

Any remanufactures to stay away from?
Any problems I may run into installing a new computer?

 

Make sure you get the ECC from the same year vehicle, with the same engine and tranny combo or you could have trouble.

You can use the code on the ECC to help if you need to.

Your very best bet will be a scrappers for a new ECC. Many people have very mixed results with computers from parts houses, but it's a good last resort.

Also, you could run into trouble with a bad ground. Make sure all your cables are in good shape and your grounds are clean and have good contact. You don't want to swap a non-returnable ECC in and find out your harness is toast or you had a dirty ground contact.

 

Since computers so seldom go bad, I would check elsewhere first. The likely suspects are all grounds, battery cables, under hood connectors and bad 5v sensors or rubbing wires, pulling the 5 volt supply down. This means taking things apart and cleaning and reconnecting them especially around the battery area. The only good connection (for your purposes here) is one that is perfectly clean and making strong mechanical contact.

 

Ok thanks for the input. So it sounds like there is a decent chance that one of my VREF lines (5 volt supply from EEC to Sensors) is grounding out somewhere and pulling the supply down. Sounds like a reasonable problem to me. Would I notice a dip in my 12 volt system if this is happening? (Asking because my gauge is stable when truck is having problems) I checked several of my grounds and they were fine. Can/Should I check voltage readings on pins on my EEC. Also how could a bad sensor pull down the voltage for the rest of the 5 volt system?

 

Try unplugging all of the sensors that use the 5V reference and see if there is any difference in the voltage. If not, keep looking for a short to ground possibly, but if not, plug the sensors back in one at a time until you see the voltage change again.

 

Problem right now is that my truck has run ok the last 3 times I have driven it. No codes no voltage problems with my sensors.
Today I started it up and started wiggling wires to see if I could get the problem to occur, but no luck. Truck was idling for about 20 minutes while I was doing this. I shut off the engine and when I tried to restart it it acted like the battery is dead. This is a problem I had in the past, truck would not start with hot eninge sometimes.
This was a problem i had that I thought I had solved. I had a termostat that was going bad and I would stop getting heat in my cab. So I thought I fixed this "hot restart" problem when I replaced my theromstat. I thought my coil was getting too hot with the bad thermostat but now I'm not sure.
I just remember something else that has happened to me about 3 times in the past 2 months. Sometimes when I try to start my truck I get nothing when i turn the key, just dead silence. It ry it 3-4 times and eventually it starts up no problems.
Not sure if either of these two problems are related to my shuddering and voltage problem. Wish the problem would occur more often to troubleshoot it.