I'm Baffled, Please Help
10-03-2020, 03:20 PM
#1
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I'm Baffled, Please Help I hope someone can help me. I've been trying to get this lq4 to run for 3 days. It's in a 2006 Chevy 2500hd, 2wd extended cab, base model work truck, vinyl floor, crank windows, base base.. I'm a pretty competent mechanic. For some reason that I cannot figure out I have no spark. Here's what I've done so far
- Verified >12v to pink wire of each ignition coil with key on
- Verified <1ohm resistance between each coil connector and battery negative on brown ground wire
- Verified pcm commanding spark through hp tuners
- Replaced all 8 ignition coils with known good coils
- Replaced all 8 plug wires with know good wires
- Replaced all 8 spark plugs with brand new iridium ACDELCO plugs
- Removed VATS and downstream O2's from PCM using hp tuners
- Check and filled all fluids
- Checked, unbolted, cleaned, and re-installed ALL grounds. Harness to engine, engine to cab, cab to chassis, battery to chassis, engine to battery, ALL OF THEM
I have everything else, Fuel, compression, air, but it won't spark and I can't figure out why.
The ONLY thing I can see in hp tuners that I can think MIGHT be causing no spark is the oil pressure reading. PCM is reading -0.3psi oil pressure with key on. Both when I'm cranking the engine and not cranking. It reads -0.3 all the time. But I thought the pcm would at least let the engine fire for a second before shutting down for no oil pressure. Is that not true and the no oil pressure reading is preventing spark and I need to figure out if it's a bad sensor or truly no oil pressure?
I really appreciate any help. I've been searching all day and tried everything I have been able to find and I still can't get any spark.
- Verified >12v to pink wire of each ignition coil with key on
- Verified <1ohm resistance between each coil connector and battery negative on brown ground wire
- Verified pcm commanding spark through hp tuners
- Replaced all 8 ignition coils with known good coils
- Replaced all 8 plug wires with know good wires
- Replaced all 8 spark plugs with brand new iridium ACDELCO plugs
- Removed VATS and downstream O2's from PCM using hp tuners
- Check and filled all fluids
- Checked, unbolted, cleaned, and re-installed ALL grounds. Harness to engine, engine to cab, cab to chassis, battery to chassis, engine to battery, ALL OF THEM
I have everything else, Fuel, compression, air, but it won't spark and I can't figure out why.
The ONLY thing I can see in hp tuners that I can think MIGHT be causing no spark is the oil pressure reading. PCM is reading -0.3psi oil pressure with key on. Both when I'm cranking the engine and not cranking. It reads -0.3 all the time. But I thought the pcm would at least let the engine fire for a second before shutting down for no oil pressure. Is that not true and the no oil pressure reading is preventing spark and I need to figure out if it's a bad sensor or truly no oil pressure?
I really appreciate any help. I've been searching all day and tried everything I have been able to find and I still can't get any spark.
10-08-2020, 12:32 PM
#2
Negative oil pressure??? Double check you have the Oil Pressure and MAP hooked up right. They have the same connector in the same section of harness. Can't remember which color wires go to which sender but they are different.
Have you pulled a plug out to verify spark? If you're getting spark, do the gas rag trick and see if it fires up and idles. That should tell you if PCM is triggering fuel cut.
Have you pulled a plug out to verify spark? If you're getting spark, do the gas rag trick and see if it fires up and idles. That should tell you if PCM is triggering fuel cut.
