Hey everyone I just recently recieved my dad's old 93 f-150 2x4, auto with the 5.0L. During the 15 years that he's had it it has never given him a problem and he's only had to replace the radiator, a driver's side exhaust manifold, rebuild the tranny, 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 one day. 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 swapped it. 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 the local dealer 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. Then I replaced the sparkplugs cause they where looking a little worn. So now I'm getting a code 11, which means the system checks ok, but still having the issue. I know it has to be something simple I just don't know what, it might even be a clogged cat cause it's still the original but my entire exhaust is welded together. So no easy way of checking minus getting a shop to cut it out and welding on some flanges incase it isn't the problem I can put it back in.

Just to review here's a list of things I've checked:
1. EGR solenoid = good
2. EGR = clean and working
3. EVP = replaced and good
4. Vacuum lines = good
5. Brake Booster = good
6. Ground Wires = cleaned and good
7. PVC = good
8. Altenator = good
9. TPS = good
10. IBV = cleaned and good
11. EGR pipe = good
12. Fuel Filter = good
13. In tank fuel pumps = good and problem isn't related to just one tank
14. Fuel tank vent = good
15. Sparkplugs = changed
16. FPR = good
17. O2 sensor = good

Any help would be great cause I would like to be able to make this my daily so I can take my 300zx down.

 

Well, you checked all the sensors, took care of fuel and spark. The only things i don't see you mention here are the air filter (wich would be rare to cause such problems, as the truck seems well mantained) and the coil (maybe it's dying, just an idea). You could also replace the rotor and distributor top, and check the timing.

But i tell you this: usually these "greemlings" are caused by loose grounds or vacuum (wich you already checked). Well, good look in your hunt, do report back.

 

Already checked the coil, it's good, and even though the air filter is a little dirty I wouldn't say it's bad enough to change. Might check the cap and rotor before looking at Cat cause if it isn't them I don't know what it could be. Would like to solve this cause it sounds like a fairly common thing from what I've been reading.

 

What are you using to check the codes? Your truck should have 3 digit codes. It would be rare to find a '93 still giving 2 digit codes. Ford phased in 3 digit codes around '91-'92.

 

My experience with a Cat is it slowly gets worse and then plugs. It is not really an intermittent problem.

You have checked a lot of sensors, vaccum lines, etc, but what about your MAP sensor?

 

Other than checking to make sure the vaccum line wasn't cracked I haven't checked the MAP. The problem is intermittent but it does seem to be happening more often, like right now if I can even get it to stay running I'm always getting the motor to buck and surge while driving. Plus it's the original cat and has 186,000 miles on it.

And I'm following the way from fordfuelinjection.com to get codes and from what I've read Ford didn't go to 3 digit codes till 94. But either way the truck gives 2 digit and it's the original computer.

 

My current '92 F-350 and both my previous '93 Lightnings read out 3 digit codes. Just checking to make sure you were not getting false readings.

 

It's cool. Thanks for the help.

 

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.
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May have found the solution to the problem. After looking through the wiring diagram and mulling over what the dealership had said about the MAP sensor sending 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?