NZR Need help with 93 5.0L

[Amadeus]

Hey everyone I just recently recieved my dad's old 93 f-150 2x4, auto with the 5.0L. During the 10-12 years that he's had it it has never given him a problem and he's only had to replace the radiator and a driver's side exhaust manifold, and clean the EGR. The original owner before that kept impecable service records and both him and my dad have only used Mobil1 in the engine.

 

But here's where it gets tricky after my parents drove it a 1,000 miles up here I have it for a week and then it doesn't want to start. When I can get it to run it sounds like it's surging, stumbling, or running lean. I replaced the fuel filter and it seemed to fix it (altough I think it was more because I reset the computer). Couple of days later it starts to act up again so I pull codes from the truck and get 23 and 34, which are for the Throttle Postion Sensor (TPS) and the EGR Valve Position Sensor (EVP). So I first check the EVP, it reads good voltage but it's slightly low on ohms so swap it no change so put the old one back on. Then check the TPS and it's a little low on volts at idle, supposed to be .9v and reads .86v so swap it with a new one. By this time the problem corrected itself but came back the next day.

 

Took it to Performance Ford and they kept it over night to tell me the next day that they couldn't duplicate the problem and the only codes they could pull where the EVP and TPS. So basically nothing new, but they atleast could tell me that the O2 sensor, fuel pressure, and alternator where good. Drive the truck home and it does perfect for about a week and then it starts to act up again. Same problem surging and stumbling like it's running lean and sometimes dies when I step on the brake. So I'm thinking it might be a vaccum leak so I check all hoses and gaskets and nothing.

 

So then I read online from other peoples post that the problem could be caused by a clogged Idle Bypass Valve so I take it off and clean it with the EGR and put them back on. No change so now I'm back to square one the truck has trouble even starting and when it does it promptly dies. The thing that gets me is that it's random, even in one drvie it could come and go then not show up for a couple of days. So I'm almost positive that it's something easy and electrical, I just don't know what.

[jbehuniak]

On the distributor is a ignition module, disconnect the battery and pull it off, I think its a 8mm socket that has a really thin wall. Make sure there's no corrosion on the plug and it grounds itself on the distributor so clean both surfaces. I had the same problem with my 5.8 F250, it was stupid.

Hopefully that helps. I also had some grounds that had corrosion so cleaned those up. You might not get alot of replies sense this is a Z forum but good luck with the truck

[Amadeus]

Thanks for the reply I wasn't expecting a lot of replies here, but figured I would give it a try being as there are people here who've worked on 5.0l. Took the truck to a different dealer to try and figure out the problem. They came back saying that the EGR diagphram was cracked, the MAP sensor was reading high on volts, and the PCM was sending strange signals. Although they believe that the PCM problem was caused by the MAP sensor and suggested that the MAP problem be fixed before looking into the PCM.

 

So took it home and changed out the MAP sensor and PCM, and guess what, no change. So took it to the local AutoZone to get the codes ran and they no longer can do OBD1 so went over to O'Rielly's and they gave me the scanner to scan the truck myself. KOEO codes where 22 and 34, did the KOER got codes 22, 34, 63, and 98. Although I could never get to finish the test cause in the middle of the test the scanner would tell me that it couldn't read the computer.

 

So I'm thinking that I might have a bad PCM or a short somewhere in the wire harness so that's the next thing I'm going to look into. Unless anyone else has an idea.

 

Codes:

22-MAP/BP sensor out of self test range.

34-PFE or EVP circuit above the closed limit of 0.67 volts

63-TPS circuit has intermittently failed below minimum 0.6 volts.

98-Hard fault present.

[78 LS2 Z]

Then check the TPS and it's a little low on volts at idle, supposed to be .9v and reads .86v so swap it with a new one. By this time the problem corrected itself but came back the next day.

 

 

FYI, the TPS can be adjusted by loosening the screws and rotating. The best voltage is about 0.985 for these; performance wise. You can dremmel out the holes in the TPS slightly to give more adjustment. Probe the 2 voltage output wires and rotate it until you get the right voltage. You can usually get at least .40V of adjustment. The TPS was not bad at .86V and the car should run fine between .7v and 1.0 volt.

 

Ford computers tend to "stack" codes as a chain reaction to a single problem and they can be a bit misleading(speaking from my own personal experience). It's likely something very basic, make sure you did a good job with the throttle body cleaning. Inconsistent problems can be very frustrating. I would check for vacuum leaks again with some starting fluid in the engine bay. Good luck.

[RS Speed]

Fuel pump intermittently cutting out? When the car is stumbling is the fuel pressure reading correctly?

[Amadeus]

Don't know if the fuel pump is intermittently cutting out, but I may have found out what my issue was. After looking through the wiring diagram and mulling over what the dealership had said about the MAP sensor getting the wrong voltage, I wanted to see if it was the voltage going to or from the PCM. So tested the voltage from the PCM and it was within limits but when I tried testing the voltage coming from the MAP sensor I couldn't seem to get it to fluctuate with vaccum. So I looked in my Haynes manual cause I remember someone told me that the MAP, EVP and TPS all shared the same wiring, and found out that they all shared a common ground wire back to the PCM.

 

Anyways decided to rig up a temporary jumper wire from the ground wire to the negative terminal on the battery. Lo and behold the truck runs like a dream. Let it run for about 15-20 minutes while randomly taking the wire off of the terminal. And everytime I took it off the truck would start to act up, but when I put it back on it'd even out and start running right again.

 

So that means I have to trace back this wire and see where it's acting up at, and hope it isn't in the PCM. My question is does anybody know if this is a ground wire that is controled by the PCM that alternates the ground in relation to the voltage or is it just a normal ground wire?