I have read many topics on this within this site and "think" I know where to go with this issue, but am looking for additional opinions.

Truck run good, the NV3500 in it started to goto heck, dropped transfer case and tranny, installed new cluster gear, input shaft gear, bearing seals, etc. Reinstalled tranny and transfer case. I wanted to be sure that all rotating parts were as they should be, so with no driveshafts or exhaust hooked up, I started the truck and let run for a few to be sure nothing was out of the ordinary. All good! i disconneceted the battery and finished the completion of this job.

Was getting ready to drop the truck down off the stands and thought, heck, start it up and let it warm a bit since its 20 degrees out! Went to start the truck and ......nothing. It will turn over but not fire off.

About 5 mths ago I put a new ECM in it due to a complete failure of it. Fired right up after it was installed.

This time around.......Engine will not start. so i let the truck sit for a few days so i could have a "cool down" period. LOL! Went out today to start trouble shooting it. Put key in and it fired off.....for about 1 second then dies. did this several times. finally it said "nope, aint gunna fire". Disconnected battery for a few minutes and retried...still nothing. Put the cheesy code reader on it and it shows a fail to read.

At this time.....I have no voltage to the coil. Fuel pump turns on and stays on, but sometimes decides to shut off after a few seconds of the key being on. Checked ASD relay..It is good. However, I pull the relay and reinstall it and it closes contact then de-engergizes within a second. Occasionally on cranking I get a smell of gas...

The last time it fired off for a second, it backfired before it died. I was very careful not to disturb the wiring for the Crank sensor or anything else when the bell housing met the block.. The truck originally had a automatic in it, and that wiring is tied up out of the way.

The truck is a 96 4x4 ex cab with a 360.


Thoughts and ideas gentlemen?

Thank you!

 

Pump should fire up, run for a few seconds, and then shut off when you just turn the key to on. Coil should also be powered during this time, but, after like three seconds, if the pcm doesn't see a crank/cam sensor signal, to indicate the engine is turning, it will trip the ASD relay, and fuel pump, and coil, no longer get power.

Most of the time, when this happens right after a trans swap, the crank sensor is the culprit........ they tend to get beaten up as the trans goes in/out.......

 

crank sensor was my thought on this... especially since the fuel pump runs "erratically" at times. I have read that the only way to go is with a OEM hall effect sensor. Not sure if this is the right way to go as opposed to a 50 dollar sensor from oriellys...

Any others have thoughts and ideas on this issue?

And thank you Hey you for your reply. I wont be one to leave without a response as to the turn out of this situation.....So many places have folks that dont follow up, hence the final culprit is never know. I hope for others to learn from this as well.

 

From what I have seen, there have been more problems with aftermarket sensors, than success stories........ so, its a crapshoot, with long odds..... Go for the dealer part. Yeah, it costs more, but, we KNOW they work.

 

Go OEM...thats what I have heard and read. As for the root cause of the problem, anyone else have any other input on this issue? Or other things I might check for? I have a few bucks, but aint rich, so dont wanna throw money at this thing unless its a really good educated guess! LOL!

 

pull the sensor and check it to see if its damaged...

 

update.....

Been busy so aint had time till yesterday to work on this truck. Using the factory service manual i tracked down the wires leading to the PCM. Voltage to the sensor is 5.2 volts during crank. Ground wire is at 1.2 ohms, and the ouput from the sensor does show a reading. I used the frequency function to detedt any pulses from the sensor. It showed 18 Hz during crank. Another interesting thing, now the fuel pump and coil relays are not energizing at all, even within the first 3 seconds of key on. Of course the PCM is not triggering the ASD relay...

Could this still be a crank sensor issue? And was the way I measured the output of the sensor correct?

Boy I miss driving this truck! At least we have several other vehicles to drive so we arent truckless LOL!

 

Have you checked voltages at the asd relay, to see if the pcm is requesting, and the relay is just telling it where to stick it? (or, you could just swap around a couple relays..... see what ya get.)

According to popular theory, even with a failed sensor that would trigger an ASD event, you should get 3 seconds worth of fuel pump/coil.... unless cam/crank sensor harness is shorted/grounded out somewhere?

 

Im in the shop now...wireless internet is a beautiful thing!...Right now I have 12 volts at both pin 30 and at one side of the coil for the relay in the box. Pulled relay and bench tested it with a power supply. coil energized, pin 30 and 87 show .3 ohms...it is good. Gunna get a light and inspection mirror to try and see the crank sensor and wiring...wow what a location!

 

inspected wiring from crank sensor to the main harness. All appears fine. I was careful when reinstalling the tranny so as njot to damage it or anything else....but ya never know. I have an older Di-log Auto meter. I cant remember what setting to use to measure the hall effect sensor for output? Is it frequency, ms pulse....? Also could the cam sensor be a possible issue?

Thank you