1999 Tahoe will bot run... please help

[chevyracer8262]

My 99 Tahoe that I did a 383/4l80e with 0411 pcm was running good and I was able to put about 700 miles on it then it just shut off and would not crank, after sitting for 5-10mins it would crank so I thought coil so I got a used coil and ignition module from my uncle put it on and drove the crap out of it for about 700 miles then Saturday I was driving back from church and it backfired and shut down and hasn't had any spark since, I replaced the ign coil, crank position sensor, cam pos sensor, ignition module and distributor cap and still no spark, I just double checked the distributor and it's set dead perfect according to the service manual but still no spark, replaced the ignition switch and still no change. I had an issue with the crank position sensor earlier and found out it was too far from the triggerwheel because that blocks been line bored and honed so I checked my scanner and I'm getting rpm signal, u habe 12v power at the crank and cam pos sensors, coil and ign module, can someone please help me figure out this thing because I really need it get to work right now I'm having to share my daughter's truck with her

 

[Schurkey]

My 99 Tahoe that I did a 383/4l80e with 0411 pcm was running good and I was able to put about 700 miles on it then it just shut off and would not crank, after sitting for 5-10mins it would crank so I thought coil

If it won't crank, it's not the ignition coil. It's a problem with the starter/starter wiring/battery, or starter solenoid circuit.

If it cranks but won't start, it might be the ignition coil.

drove the crap out of it for about 700 miles then Saturday I was driving back from church and it backfired and shut down and hasn't had any spark since, I replaced the ign coil, crank position sensor, cam pos sensor, ignition module and distributor cap and still no spark,

Do you have power and ground to the ignition coil and module?

still no spark, replaced the ignition switch and still no change... ... I checked my scanner and I'm getting rpm signal, u habe 12v power at the crank and cam pos sensors, coil and ign module

Where are you testing for spark?

IF the distributor main shaft turns, (beware Vortec distributor gears) about all that's left is the ECM and the ignition system wire harness.

 

[chevyracer8262]

Sorry I guess I need to clarify my rushed post from last night. The engine spins over but has not fired since the backfire Saturday, when I was building this truck I continuity tested every wire and every connector and repaired anything in need of repair, after the backfire I replaced the crank and cam position sensor, coil and ignition module with all brand new delphi units, last night I checked the distributor timing which was spot on as well as the rest of the mechanical parts of the engine and everything is in perfect working order, I even replaced the ignition switch and wiring and still no spark. I checked all of the power and ground circuits all of which are what they should be even added another body to engine ground strap I had laying around and still no spark.

 

[Schurkey]

Do you have power and ground to the ignition coil and module?

Where are you testing for spark?

IF the distributor main shaft turns, (beware Vortec distributor gears) about all that's left is the ECM and the ignition system wire harness.

The engine spins over but has not fired since the backfire Saturday,

Cranks, doesn't start 'n' run.

when I was building this truck I continuity tested every wire and every connector and repaired anything in need of repair,

Do you have power and ground to the ignition coil and module NOW, not weeks ago?

last night I checked the distributor timing which was spot on

You clearly aren't testing the timing with a timing light since there's no spark. HOW are you "checking the distributor timing"?

 

[chevyracer8262]

I checked Power and grounds at all of the sensors, coil and ignition module all have power and ground and all ate brand new right out of the boxes, I'm checking for spark at the coil with a spark tester, and the distributor is an alum housing aftermarket 96-02 vortec 5.7 distributor which the rotor is pointing to the correct casting of the distributor dead at the no 1 terminal of the distributor cap with the engine at TDC of the compression stroke per the service manual directions

 

[Schurkey]

You have an RPM signal at the computer.

You've checked for power and ground "everywhere".

You've replaced multiple ignition parts with respectable brand-name components which "probably" are not faulty (although that's a possibility, especially given the Communist proclivity to make crappy and outright counterfeit parts.)

Seems to me the more-likely issue is a failed computer, or a failed wire harness between the computer and ignition module, or between module and coil.

 

[chevyracer8262]

Ok I followed the directions an advanced ignition diagnostics section of the service manual and every input and output required has power measured between 12.25 and 12.4vdc and every ground in the entire harness registers between 64 and 75 ohms to a clean engine ground, checked the signals from the cam and crank position sensors all pulses the led test light at the pcm and the output from the pcm to the icm pulses and from the icm to coil pulses. While testing yesterday it started to fire but would not start then when I went back out to work on it today it wouldn't fire again.. so any ideas on what it could be?

 

[Erik the Awful]

every ground in the entire harness registers between 64 and 75 ohms to a clean engine ground

You should have less than half an ohm, preferrably 0.1 ohms. Since "every" ground has 64-75 ohms, I'd grab a battery brush and clean the negative post and terminal on the battery. Then hit every ground point and the ground terminals themselves.

 

[Schurkey]

I'm checking for spark at the coil with a spark tester,

WHAT KIND of spark tester? Photo? Link?
Does this spark tester have an actual gap that the spark has to jump, or does it flash a stupid light-bulb? The light-bulb kind are USELESS.

While testing yesterday it started to fire but would not start then when I went back out to work on it today it wouldn't fire again.. so any ideas on what it could be?

It CANNOT "start to fire" without spark.

What are the chances you've fuel-fouled the new spark plugs? Pull 'em out, crank the engine to blow-out liquid fuel. Let the plugs air-dry, or better yet, heat 'em with a propane torch to burn-off any fuel residue. After they cool, put them back in and make sure the correct plug wire is attached to each plug.

 

[cc333]

It could be the computer.

Back in early 2020, we were driving our '94 K2500 and parked to talk to someone. When we finished, we tried to restart the truck and move on, but nothing happened. It turned over but it wouldn't start. Eventually it did start, but this happened again later on and was effectively permanent.

The most peculiar aspect of it, which led me to believe it was the computer causing the no-start condition, was that the Service Engine Soon indicator was dark with the ignition in the on position and the fuel pump wasn't activating. So I decided to try replacing the computer. It wasn't terribly expensive, fortunately, so I didn't have much to lose.

And it solved the problem!

I noticed that the computer I was replacing actually wasn't the original part– it had been replaced before, possibly for the same reason.

Are ECM failures like this common??

c