All three links worked for me as I just clicked on them.

 

Good info there Bill. After reading I too think the ECU is in limp mode. I had the same thing happen to my 84 F250 after I swiched to EFI. Another ECU fixed it.

If the PIP was sending out a 10x pulse train, I doubt the engine would even run, but back fire and stall out at ignition timing would be random in ref to engine RPM.

One test I do with a poor running engine is disconnect the SPOUT connector and let the engine run on base timing, That way I can see if its a ECU or TFI problem.

 

That is a good idea. I'll also see what the injectors are doing while cranking, to see what the computer thinks of the slower turning PIP.

Thanks guys,

Rick

 

With out a PIP signal to the ECU, the ECU will not fire the injectors. Check out the "noid" light to test injector wireing. Its just a lamp you hook to the harness in place of the injector. The light will flash if the ECU is fireing the injector. Constant light or none means ECU NOT fireing that injector.

As for a "noid" light, I use a dash lamp/socket and carefully insert the wires into the harness. I do that at night to be able to see the lamp flickering.

 

Thanks subford and eddiec1564,

Your comments, links and suggestions have been informative and very useful. I want you guys to know that your contribution is appreciated.

After reading up on the ignition system and performing some new tests, I agree that the computer is in limp mode. I observed the following:

* There is a 2.3ms injector signal shortly after commencing cold cranking. Apparently this is not enough to start, but choking the intake gets her to light off.

* There is no change in injector pulse while cold or warm cranking with the SPOUT connector in or out.

* There is no audible change in engine operation cold or warm with the SPOUT connector in or out.

* The pulse width is very narrow between idle, WOT and throttle shut (max=3.0ms, min= 1.5ms).

* The tachometer in the vehicle reads accurately. I think we can put to rest my 10x signal theory!!! Thank you for being kind to me and gently deferring! I promise to learn the proper settings of my Fluke 88 and to avoid tilting at windmills!

Ok, so I am down to a melted trans solenoid connector and harness and a computer in limp mode. I did sever the 9 wires to the solenoid pack, above the melted and fused wire connector. I inspected the harness from the tranny up back to the computer. I removed the battery cable terminal for a minute and reconnected it.

After doing that, it is still in limp mode. I did not remeasure the pins to the trans, figuring the damage is now limited to two (but very expensive) items: The trans solenoids and the PCM.

I am wondering about this conundrum: The pulse width is fixed at 2.3ms and below spec according to my info, but the HO2S sensor remains at .92v steady at idle. I observed the sensor readings fall below .1v when I shut off the engine and went to KOEO, so I believe the readings.

Some of the complaint about fuel economy can be explained: My neighbor knows very little about vehicles, especially these bigger American trucks. He thought it drove OK in limp mode. So you see my point about the fuel economy issue.

Typing this gave me an idea: I could watch the HO2S while revving the motor. since the pulse width is fixed; there should be a crossover when the engine volumetrics balance with the fuel being metered. I might be able to tease out a little more understanding of the failure by looking at this truck through the, uh, tailpipe!

What are your thoughts?

Rick

 

Melted tranny connector not good, I am not familer with the solenoid resistance of the tranny, best ohm them out. Sounds like the problem is a chain reaction type, 1st the tranny solenoid pack shorted or harness burnt out and took the ECU with it.

When the ECU is in limp mode, the injectors are at a fixed pulse width and fire at the PIP signal(all injectors fireing same time). This usually runs the engine pig rich so the engine is not melted with a lean burn. The O2 sensor will read rich all time also O2 sensor should be replaced after the ECU is replaced and wiring checked for any more dammage. They will clog up and read funny after running "pig rich"

Its probly time to check out the local U-pull-it junkyards for a ECU. Around my area the ECU usually cost around $50 with 30 day warranty from some of the yards.