99 Tahoe 0411 backfired and will not start please help

[chevyracer8262]

I have a 99 Tahoe with a 383 stroker 4l80e swap that I was running using an 0411 pcm with the 02 express 3500 calibration. This thing ran great once I got the calibration close to where I wanted it then Saturday it backfired through the exhaust and died and has not fired again since. So far I've checked for powers and grounds, replaced the cam and crank position sensors, coil and ignition control module with all brand new delphi components, check the distributor phasing which was perfect per the service manual, still no fire. I habe rpm signal on the scanner so I think the crank position sensor is working and I've also verified the pcm has power and grounds can someone please help with figuring this thing out because since my transmission went out in my other truck this is my only transportation

[blindsquirrel]

99 Tahoe - Engine Cranks But Does Not Run - Document ID 403280.pdf
99 Tahoe - Enhanced Ignition System Diagnosis - Document ID 403698.pdf

[chevyracer8262]

Ok I followed the directions in the attached files 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?

[SiriusC1024]

Skipped timing chain?

[chevyracer8262]

Already check that, when I pulled the distributor cap the rotorpointer was dead perfect with how I set it at TDC when I had ot running

[reubone]

Check injectors to make sure they are spraying. Check rocker arms to verify valve travel. Check exhaust/intake systems for obstructions. Check for cracked or broken intake manifold Spray starting fluid or do a compression test. Verify spark at the plug.

[chevyracer8262]

Already checked all of that, injectors are firing, I already readjusted the rockers because their full roller and I had one start ticking so I already pulled the covers and readjusted all of them and they are moving correctly, I've verified 55-58psi fuel pressure on my gauge, the intake is a world product motown alum efi intake and I know it's not cracked, also done a compression test and am certian there is nothing mechanically wrong with this engine which is brand new (less than 2000miles) with all topshelf parts that I blueprinted, flow tested and assembled myself.

[SiriusC1024]

Have you verified spark with a timing light?

[Pitbull]

Was it raining? Lol I know how retarded that question sounds but if you're using the vortec style distributor from that vintage, I literally kept a spare cap and rotor at all times because they would corrode so bad and quickly that it would do exactly like you describe and almost always when it was or had been raining. No amount of scraping and cleaning would revive them either..... It would show spark, just not even remotely in time.. I finally made a suck line with a pcv valve that pretty much fixed it.

[chevyracer8262]

Checked for spark with a spark tester at the coil and at the plugs. I've driven through some very heavy rains but when backfired and shut down it was a dry sunny day and since then I've replaced the cap and when I replaced the rest of the ignition components but it was one I had lying out in my shop that gets pretty humid

[reubone]

Checked the exhaust for obstruction? Fuel spark and timing verified then it has to be airflow.

[chevyracer8262]

Yes I'm certain the exhaust has 0 obstructions because it has headers to a custom offroad 2.25" wye toast 3" single so I see no way possible for it to get obstructed

[Pitbull]

I had spark too, it just wasn't in time.... Those caps are notorious for cross arcing.

Have you looked at the harness portion going to the crank sensor? I seen one that had chaffed against the power steering pump or metal line and finally just barely ate through.

Are you using the updated Spider that puts an actual injector in the intake runner or something else?

[chevyracer8262]

Im picking up a new cap and rotor on KY way home, I've ohm and visually inspected every wire in this entire harness first then proceeded to other parts. This engine has aftermarket heads and a world products 4bbl flange individual injector intake and I'm running the 36lb flex fuel injectors

[horsepowerguru427]

Whats your MAF reading, also whats your MAP reading. since it wont run the KOEO should give you some insight as to what theyre doing or if theyre reading correctly at all. cranking data is helpful as well when it comes to diagnosis.

[TheMechanic]

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

Every ground should be near or at zero ohms.
Close off your brake booster vac line.

[bk2life]

any updates?
i cant see a backfire caused all of this..

[SiriusC1024]

Backfire can make a the timing chain jump a tooth or two. That's why I mentioned it before. I still think that's the real problem, despite what the distributor says. One tooth is hard to eyeball sometimes. Gen 3 doesn't have a tensioner.

[Fast4.7]

My van did this a few weeks back. Started running rough, lost power, let out a huge backfire. It still had spark but it seemed weak. Turned out the rotor had a hole burned through it that could not be seen from the top of it.

[chevyracer8262]

This is not an ls motor this is a 96-98 vortec truck based roller 383 stroker with a bullet performance timing set which I verified is still dot to dot where I degreed it to and the distributor is still set dead on per the factory service manual, this engine is mechanically sound. Last night I built a new grounding harness and replaced every chassis wiring provided grounds all of which read 0 when continuity tested using my fluke multimeter, I also replaced the distributor cap and rotor with the blue streak upgraded components along with all of the delphi components, new iridium autolite plugs, custom msd 8.5mm super conductor wires and still no spark at the coil or no1 plug location using the oem brand spark tester so I'm thinking it's probably the coil driver in the pcm