RPM spike on 5.0 mustang PNP

[BryceK]

Hello everyone I'm having an issue with this mustang that I need to sort out. luckily I was able to capture the issue in a log and hopefully with your help we can figure it out.

Basically I am getting strange RPM spikes that wreak havoc on WOT pulls in this mustang. Originally the car had an MSD TFI distributor in it that someone had messed with the ignition module and stripped out one of the mounting screws. In this case you could just wiggle the TFI plug and the car would shut off. No biggie so we got a NEW MSD TFI and put it in there. Now the car would miss and pop and fart all over the place and you could see it losing tach signal on the dash. Weird. so bad MSD out of the box we thought? Put a known good test distributor that we have in it and the car runs great. Awesome, Go to deliver car and when customer comes to pick it up its crap everytime he gets in boost. even in a rev the car sounded bad like it has a flakey RPM signal. Going through the wiring I found one of the main pcm grounds poorly done so i fixed that and the car is still running poorly especially on boost. Since then I have put the same brand new MSD distributor that we had bought for it back in and the car is working fine again however I can still see an rpm spike in the log at idle so i know that the problem is just not showing its face right now. I believe that the poor rpm signal is happening everywhere it is just very much more pronounced (of course) when it gets in boost and at higher rpm. This is the same car that I had posted a while ago about it not wanting to pull past 5500 rpm. which i feel we may be dealing with a lifter pump up issue. anyway here is a log of it idling and also a wot pull. please let me know if there is any other information I can provide to aid in finding the problem. thank you.

[Matt Cramer]

See if you can catch the spike in a tooth log.

Also, please post the MSQ so we can view your settings.

[BryceK]

I will work on the tooth logger thank you

[BryceK]

not sure if i captured whats needed here but ill give it a shot.

[Matt Cramer]

Yeah, you're reading some really tiny noise pulses. Try using "tach period rejection" under Noise Filtering, set to 10%.

[BryceK]

awesome. I actually was doing some digging in the search yesterday and i had actually applied that noise reduction and it was looking good but i wasn't sure. now seeing you post that I'm pretty confident. so noise reduction on and also tach period rejection? or just tach period? and leave it at 0.1ms? im not sure how to figure out the math. Thank you!

[Matt Cramer]

Yes, that should work fine.