New to this forum. I have a 91 F250, 4.9l-6 4x4 that I've had since new. Haven't really had any problems of note (broken window motors, door locks, wiper motor) until now. Now the truck was my daily driver until 2005. Then I gave to my father in law to use as occasional use truck for work around his property. SO the truck probably has been run once every couple of weeks for the last 5 years, unless me and the family are visiting and then its used daily. The truck performance has gone down over the last few years, although it ran good enough...until now. Went to fire it up and its running really bad. Changed pugs, rotor, cap wires. Spark is good on all cylinders. However, the truck is running on 3 cylinders (#2,4,6). Cylinders 1,3,5 are dead. I can pull the plug wires on 1, 3 and 5 it makes no difference but they do spark. If I pull 2, 4, or 6 the engine dies. When I spray carb cleaner in the intake the engine smooths out (all plug wires connected). Compression is 140-150 on all cylinders. I read on this forum that the ground (?) side of the injectors are tied, in banks, to the EEC (ECM?) and that's what provides the pulsing of the injector. That would explain how I might get 3 injectors to die (I think). I measured voltage on good and bad injectors (key off both sides 0v, key on both sides 12v) So before I run out and try to find a new ECM, are there any simple tests that I can run that will verify the problem area. Also, if you agree the ECM (or EEC) needs to be replaced, how do you get it out. Thanks

 

It does sound like the Tan wire with Orange stripe wire going to pin #58 is not going to ground by the EEC (PCM) Computer.

It could be a pushed out pin at the computer plug or an open wire #96 (Tan wire with Orange stripe to pin #58).
You need to unplug the computer and check to see if the pin #58 has an complete circuit to any of the injectors (1-3-5) on bank #1.

The computer is located in the drivers kick panel and is unplugged from under the hood.
I think in 1991 the computer comes out from inside the cab after unplugging it.

If the wire and pin are OK then it does sound like a bad computer but you might try unplugging it and plug it back in and see if that fixes it.



/

 

Thanks, I'll try to take a look at this tomorrow. You're just suggesting that I pull the plug and verify continuity from pin 58 to the connector at any of the 1,3,5 fuel injectors? If I have continuity, then its likely the computer. If I don't then its the wire. Do I have that right? Thanks

 

Yes you have it all right.
But some have reported that they just unplugged the computer and plugged it back in and then everything work again (pins in plug not making contact). Maybe not the same problem as yours but the result is the same.
Also make sure no pins are pushed out.

 

I checked it, had continuity on pin58. I also put a test light on the tan wire to see if there was any pulsing on the line when cranking and go nothing, so I think it is the ECM. Ordered a reman today, should be here tomorrow. We'll see if that fixes it, I sure hope so. Thanks for your help. I'll let you know the results when I get the reman ECM installed.

 

Subford, Thanks for the help. Got the remanufatured ECM and installed it. Truck runs like a charm. Hopefully good for another 20 years.