1999 Tahoe will bot run... please help

[Erik the Awful]

ECM failures aren't that common. There's plenty to check out first.

 

[Schurkey]

REPEAT ECM failures--just like repeat ignition module failures--are likely due to not fixing the problem that killed the first one. In those cases, the ECM (or module) failure is a symptom, not a cause.

 

[df2x4]

While I would agree with Erik and Schurkey for the most part, I feel like ECM failures in these trucks are about to start (or perhaps already have started) becoming more common than they have been in the past. Reason being is that all the discrete electronic components (capacitors, resistors, etc.) are now 20+ years old at a minimum. It feels like I've seen 3-4 people in the past year or two reporting ECM/PCM failures here, which doesn't sound like much but is a pretty substantial increase compared to years past.

 

[chevyracer8262]

Here's a pic of the spark tester which is an oem brand that I set at 0.060" gap for the spark test, spark plugs are new autolite iridium no 26 plugs which were recommended by an engine builder I know because I have Protopline/early gen RHS 180cc angle plug heads that I did a little port work to. I just finished building a new grounding harness made from 5 leads of 16ga tefzel milspec wire that I ran from the 0411pcm and ign module branched with an engine ground and direct battery ground ohmed out as infinite after installation tested for spark at the coil and no 1 spark plug wire still no fire all plug wires are custm length msd 8.5mm super conductor wires that I built tested and installed after I found the no 1 plug wire had laid over in the header tube and burnt in half 2 days after I first got it running... I've changed the entire ignition system checked the distributor again and everything is set per the service manual bit still no spark... any more ideas?

 

[Schurkey]

Here's a pic of the spark tester

I see no picture.

which is an oem brand that I set at 0.060" gap for the spark test,

In open-air, you'd want a much larger gap. The spark plug is under ~150 psi during cranking, more than that when the engine is running. That's about ten times atmospheric pressure, although the fuel mixed-in helps the conductivity some.

I'd expect something beyond 3/8" gap for testing, more-or-less.

I just finished building a new grounding harness made from 5 leads of 16ga tefzel milspec wire that I ran from the 0411pcm and ign module branched with an engine ground and direct battery ground ohmed out as infinite after installation

"Infinite" resistance, or "Zero" resistance? Infinite doesn't make sense unless there's a wire broken in the harness somewhere. "Zero" resistance is what I'd expect from a new harness.

tested for spark at the coil and no 1 spark plug wire still no fire... ...I've changed the entire ignition system checked the distributor again and everything is set per the service manual bit still no spark... any more ideas?

TESTING for signal at the module would be the responsible thing to do.

If you're certain everything else is good, and you have RPM signal at the computer, but no signal to the module...I'd replace the computer. Apparently, it's not providing signal to the module.

 

[chevyracer8262]

My apologies the new ground wiring all toned out good and registered 0 resistance on my fluke multimeter I was worn out and rushed last nights post, attached is the spark tester and I was so frustrated that I even held a spark plug while spinning the engine to verify no spark