fordmechanic

The truck starts fine, but will not accelerate, just falls on its face and dies. It only has 45,000 miles on it. Truck idles and works fine (sometimes). Sometimes it idles poor. There are no codes in the pcm. Was brought to me with this condion last week and it ran flawlessly no matter what you did. I tuned it up and drove it 5 miles and it was perfect. Tk returned with the same condition except now I can duplicate it. I have tried an Iac, coil, tfi module. Fuel psi is 55. I even pinched off the return to jack it up to 70ish and have the same condition. I have perfect spark right up to the last revolution of the engine before it stalls. I checked and cleaned the MAF. I unplugged the spout and no difference. I unplugged the DPFE, the egr vr and all other solonoids not necessary for the engine to run just to eliminate them from possibly being or shorting something.............same problem. I have called the Ford hotline, I had
another mechanic helping me and both of us can't come up with the problem. I am starting to suspect the pcm but don't have one to try.

ejiii

Even though the MIL is not illuminated you might take a manually triggered snap shot with your scan tool when the truck is failed then review all the serial data and see if something is out of spec. Since this is an early OBDII vehicle I'm not sure how "tight" the rationality (part of comprehensive component monitoring) monitors are. You could have a sensor giving wrong information to the PCM for the actual operating condition (like TPS giving a closed throttle position signal when the throttle is actually open)

Either way, you will either see the problem in the data or you will have eliminated a bunch of components and systems.

Just call me Sean

iTrader: (1)

You say no codes in the PCM, did it enter diagnostic mode? Several Fords I've worked on that failed to enter diagnostic had fried computers. Of course the owners didn't believe me and took them to the dealer where they told them it was the computer. Also, you could have a PCM power supply problem. Truck runs then dies because of no PCM power and this would erase codes before you can retrieve them. Have you done an engine running test or wiggle test? My truck had PCM power problems, it was a loose and corroded connection at the starter solenoid. Truck would die and fail to restart, the computer would draw from other circuits and blow fuses.

fordmechanic

Yesterday I decided to check timing. I maked 10 degrees on the crankshaft, pulled the spout and started truck. The mark is nowhere near close (like 40 deg btdc?. I loosened the distributor and turned it to get it to line up and it got even worse. I then turned it back where it was. I plugged the spout in and out several times and it makes no difference in the timing. I am really starting to think pcm. I have a used one ordered.

I also substituted a new contour? tp sensor, it plugged in and gave me the same readings but no difference in performance. Naturally I couldn't mount it so I had to manually turn it and operate the throttle at the same time to do this.

Doug1969

I have the same issue(s).
Mine's a 1993 300 4.9 inline six. Idles just fine, even revs up nice but soon as I go to take off it bucks and sputters. Almost Every sensor has been replaced including distributor and fuel pumps.
Any thoughts ??

Steve83

A '93 is not the same as a '96. Fill in your signature:


(phone app link)

...and either post in a thread about an '87-93 4.9L, or start a new thread. Either way, be specific & thorough. "Almost every" is vague. List each part that was replaced, when (time/miles), why (symptoms, diagnosis), with what (brand, PN, source), and whether or not the replacement passed the same tests the original failed.