sysiphus

Well, here goes:

1992 Custom SuperCab with the I6 starts intermittently running rough. Almost no power, no surging or bucking though. My first thought was that the front tank ran out of gas (gauge does not work for front tank), so I switched to the rear, goosed the throttle a bit, and was back to normal.

Next day, I started off on the 700 mile journey to take my son to college. Ran fine for an hour or so, then starts acting up again. Runs rough at low speed and will only smooth out if I put the pedal to the floor and let the engine speed up, then I can back the pedal off and it runs fine again. Until the trans shifts, then it's the same thing. Heavy white cloud coming out of engine, huge fuel odor. Do the old 'pop the hood and see if anything is glaringly wrong' trick and find a vacuum hose is disconnected. Connect the hose, start it up, and all is well for about 15 minutes. Pull off, do a quick internet search, and see signs pointing to the fuel regulator valve. Change that out and it runs fine for about 500 miles (interstate), then starts acting up again in town.

Next morning we do the final hundred miles with the first 25 or so being no problem, then it begins again. Starts using a lot of fuel, like 25 miles for a quarter tank. Alt. gauge starts creeping into the low voltages, and then craps out completely. Replaced alternator, and the charging system perked up, but the rough running situation is getting worse. Happening more frequently, with less response to putting it at WOT.

Was told that the fusible link from the alternator to the battery can cause some problems. Changed that out with no joy. Got to thinking that maybe it was a weak spark, so I changed out the coil and ICM.

Sadly, I'm unable to pull codes right now since I had to leave the truck there. I'm just wondering if someone has a shared experience, so I can have an idea of what to prepare for!

sysiphus

And if one wanted to blindly throw parts at it, where would you go next? MAP and TPS? Not even sure I can keep it running even if I were there to perform KOER tests...

Chris_1

iTrader: (1)

ICM and PIP could be going out on the ignition side, or fuel pressure could be an issue - only way to check that is with a gauge. Fuel pumps could be on their way out or your filter could be clogged up.
I'd start by checking the fuel pressure - I believe that in 92 the I6 required 45 (min) to 60 psi - cold and check again once the pump gets warmed up.
And a fuel filter and the tool to change it would not be a bad thing to bring with.

sysiphus

Makes perfect sense. Thanks! Of course now it will run fine while I have the means and the time to test the pressure! I have to wait until it is running rough, and just as sure as God made little green apples it won't crap the bed until the worst possible moment! I HATE intermittent problems!

Vette117

How many times have you refueled? Any chance you have bad fuel in both tanks? Otherwise, perhaps there is some sort of contamination stirring up in the tank under certain circumstances causing it to run poorly. Like mentioned before, check codes and fuel pressure and go from there.

sysiphus

Seems as it was a bad TPS. Backprobed and found ZERO change in resistance except for WOT. Changed it out a couple months ago (or so it seems), son says it is running fine with the exception of dying when cold. Hoping that is due to screws still being loose that hold TPS to intake, as I had to leave them a bit loose because I broke the top "ear" removing the old one, and had to JB Weld it back on at the last minute. He will drive it about 200 miles this weekend, and then I'll jump in and drive it 700 miles cold the next day. Hope my gamble pays off!

sysiphus

It was the TPS. 650 miles straight through with no issues.

forrest411

Keep in mind thay the TPS has 1 mounting hole that is oval so it is adjustable. If any problems creep back up you may have to adjust it slightly. I was told by a long time Ford mechanic to start in the middle of the oval and go from there. Hope it stays running strong!

Chris_1

iTrader: (1)

Somewhere in all the things I've posted is one called "testing the TPS". You don't have to do all the tests, just get a closed throttle voltage from the signal wire and make sure that it is at .9 volts.

sysiphus

Some are, and some are not (adjustable, that is). Neither the Motorcraft one I took off, nor the aftermarket one I replaced it with, were adjustable. No idea if it's related to the year, or just the level of parts that were on my truck. My assumption is that the adjustable ones match up to a TB that has some type of index mark on it, but that's just a guess.