93 ranger 4.0 crank no start. Then backfires

[JonH]

93 ford ranger xlt is a frankenstein of a truck. Engine and 5 speed trans are stock. Not much else is. Built for offroading. Doubler dana 44 9 inch on 41.5s

Wheeled all day on the trails. Started and shut off(turned key off) at least 15 times. Drove on to trailer. Started, drove off trailer. Turned key off. Hosed off mud on body and underneath. Did not hose Engine bay. Started. Parked in driveway and locked up. 2 days later crank no start.

Pulled out Chilton book to troubleshoot.

Hooked up timing light to check spark.
No spark.
Verified fuel pump makes noise when key on.(also fuel smell if I crank and crank)
Has 12 volts to coil pack with key on.
Ohm tested coil pack. Passed. (Installed new anyway cause I had one)
Verified trigger signals to coil pack from EDIS
Checked ohms of crankshaft position sensor and wiring. Sensor had 15.48 M ohms.
Replaced crankshaft position sensor.
Still crank no start.
Verified ohms of new sensor (and wiring) passed.

Proceeded to test EDIS (ICM)
Checked power to terminal 8 pcm relay. Good
Checked continuity of terminal 9 and ground. Good.
Checked resistance of crankshaft position sensor and wiring (again) good

Tried another known good EDIS. No change.

Book says check circuit from ignition module to spout connecter terminal 3. (I think is typo) suppose to say pcm?
Have not checked that yet.

No OBD1 codes present. Does have the all good 111 code.

Check engine light turns on with key on and shuts off when cranking.

All fuses and relays test good.

While cranking, have noticed a few times with timing light hooked up no spark while cranking but as soon as I turn key off 1 flash of timing light followed by backfire.

Any help greatly appreciated.

 

[JonH]

Forgot to say engine is 4.0 OHV

 

[SenorNoob]

Maybe I missed it, but did you try checking to coil pack? That's about the only thing left at this point I think.

Edit: I've also seen spark plugs foul enough to cause this on small engines. Seems a little unlikely on a 4.0 though.

 

[JonH]

Maybe I missed it, but did you try checking to coil pack? That's about the only thing left at this point I think.

Edit: I've also seen spark plugs foul enough to cause this on small engines. Seems a little unlikely on a 4.0 though.

Yup checked coil pack. Step by step. Power to plug. Signal from EDIS while cranking and ohms across all terminals (with Chilton directions) all passed. I had a new one in box so I swapped it out anyway. No changes

 

[SenorNoob]

That's just weird.

 

[JonH]

That's just weird.

Back tracking a bit. I was using a multimeter to check 3 signal wires to coil pack. Voltage was fluctuating so I assumed it was good. But Voltage was not dropping below 11 volts. I tested with an L.E.D. test light and no flash at all, not even a flicker. Went over every chassis ground and ohmed and checked and cleaned everything that didn't look shiney. Trouble shooting steps said if ICM and crankshaft position sensor are good (and I ohmed all the wiring between ICM and PCM) to replace PCM.
Replaced the PCM with a reman. No changes. Either PCM is identically bad or not PCM issue.

Kind of back to square 1.

Compression good
Fuel pressure good

Ohms to and back from crankshaft position sensor at ICM plug about 580

ICM is from a running vehicle. What else could make coil pack signal wires not cut Voltage to spark?

 

[SenorNoob]

It sounds like the coil pack is never pulled to ground to make a signal. Isn't that done at the ICM?

 

[JonH]

It sounds like the coil pack is never pulled to ground to make a signal. Isn't that done at the ICM?

Yes. And kept running in circles starting back at square one at least 30 times. Kept asking what am I missing. Everything. Literally everything tested perfectly.

Is fixed now.

Brand new out of the box autozone crankshaft position sensor 580 ohms through harness to ICM and 1.2 volts ac while cranking through harness to ICM. (First part I replaced)

Every similar and parts throwing forum post I found a resolve to was mostly crankshaft position sensor.

Took one off the junkyard motor I bought to rebuild (forgot it had a sensor on it)

Fired right up. Is alive again.

I still don't understand. But happy to done with the headache. This was a tough one.

 

[RobbieD]

More and more, I hate having to remove original parts. I don't know why "new" parts have gotten so crappy these days.

You did good working through that head-scratcher.

 

[SenorNoob]

Congratulations! It's a truck.

 

[DPDISXR4Ti]

FWIW, I've heard the after-market EDIS ICM modules are often crap out of the box. That said, the original ones seem NOT to be failure-prone. In fact, I can't ever recall seeing a replacement one in a junked vehicle.