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Posted this originally in PCM tuning but think it's better suited for forced induction.
I am seeing and feeling a choppy RPM signal and trying to diagnose. Combo is 5.3 single 7875 turbo, Terminator X DBW, t56 magnum. Junkyard d585 truck coils with brand new AC Delco 9748CC plug wires. NGK BR7EF plugs. KW7 170 amp alternator from 2020 Silverado powered by PWM signal generator set to constant 14V. Every wire in the car is brand new. Entire combo has less than 20 miles on it. Car runs well otherwise.
Verified both coil grounds on Holley harness to back of heads are tight. ECU power and ground are direct to battery terminals.Two 4 gauge grounds- one from engine block to frame and another from same spot on block direct to battery. No other grounds. Log that shows the RPM chop (2nd gear pull):
Not sure what to look at to diagnose. My first thought is the junkyard coils or plug gap?
Perhaps EMI noise from something?
Need more grounds?
Plugs are gapped at .026, could that be too large? Running 12 psi. What else to look at? Help please
Posted this originally in PCM tuning but think it's better suited for forced induction.
I am seeing and feeling a choppy RPM signal and trying to diagnose. Combo is 5.3 single 7875 turbo, Terminator X DBW, t56 magnum. Junkyard d585 truck coils with brand new AC Delco 9748CC plug wires. NGK BR7EF plugs. KW7 170 amp alternator from 2020 Silverado powered by PWM signal generator set to constant 14V. Every wire in the car is brand new. Entire combo has less than 20 miles on it. Car runs well otherwise.
Verified both coil grounds on Holley harness to back of heads are tight. ECU power and ground are direct to battery terminals.Two 4 gauge grounds- one from engine block to frame and another from same spot on block direct to battery. No other grounds. Log that shows the RPM chop (2nd gear pull):
Not sure what to look at to diagnose. My first thought is the junkyard coils or plug gap?
Perhaps EMI noise from something?
Need more grounds?
Plugs are gapped at .026, could that be too large? Running 12 psi. What else to look at? Help please
A few things to check:
Remove/land all of the plug wires again on each spark and coil pack. Two clicks at the coil, one at the plug
Pull the plugs. Is there clearly a cylinder or 2 that isn't firing properly. (ie. more black plug). For troubleshooting, I would switch to a TR6 plug gapped at 0.025 to see if it clears up. BR7's are more cranky about indexing and gap.
Check the grounds. Odd things happen when the grounds aren't adequate - the ones at the back of the head, and sides of the block. To troubleshoot, possibly, divide them up so they aren't sharing a landing point. Make sure the copper landing point isn't overly oxidized. The ones at the back of the head can be particularly finicky about ground quality and sharing a landing point with something else.
Is the setup's crank or reluctor arrangement as it was from the factory or is it modified. If the crank has been messed with in any way, the reluctor run-out is important and tough to diagnose.
Last high rpm break-up issue I went through was a weak/damaged coil 6. There was a bad connection at the plug that ultimately damaged the coil. Problem eventually showed up as a darkened #6 plug. Changed the coil and things cleared up. I also, stopped using the BR7 plugs. With the MAST heads, they were just more cranky (occasional miss, poor signs of plug clearing, etc...) then I wanted to deal with.
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Rpm stutter/choppy 
