Engine randomly dies when coasting and won't restart

I couldnt think up a witty thread title so here we are. This is a new problem that I dont really know where to start. Truck is a 99 silverado with a 2002 avy 411 pcm running a 3bar OS on a forged 402 with a 2.3L whipple with 127 FIC injectors. It has been tuned for years and runs great, but this issue showed up last week. It died after the burnout at the track, but I was able to restart it fine. Made my run (testing new setup so not WOT yet) but after I let off when I was coasting down the engine completely died. I couldnt restart it so I had to get towed back to my trailer and I loaded up for the night with the winch.

Next day I go to mess with it and replace all the plugs although they didnt look bad. Start right up, backed off the trailer, then I made it 100 yards down the street and when I let off the throttle to coast to a stop sign it died again also. I tried for 10 minutes to get it to start, using the gas pedal to the floor for flood clear in case it was too rich, and even used my methanol kit test button (100% meth) as a semi starting fluid which has worked for me before. Nothing. Engine spins over fine just never fires.

It almost feels like both fuel and spark are being cut (or not activated), but I dont know what would do that. My only 2 clues are I dont have an RPM signal when cranking and it doesnt start, and the cluster immediatley shows "2" on the gear selection regardless of where the shift lever is.

I have checked all wiring and nothing appears burned or frayed. Replaced crank sensor but havent tried the new one yet and I have my doubts thatll fix it. NSS and both connectors to it are very nice, all wire connections are soldered.

I attached a couple logs, the first one is when it died at the track, and the other one the next day when it died and failed to restart. Anyone have any ideas? Thanks

Attachment 91871 Attachment 91872

Have you checked 5v reference?

Post the tune. I think I know why it is doing it but need to see the tune to be sure.

It will be this evening before I can post the tune, but I'm curious to what you may think it is. Ive been running essentially this tune for the past 5 years on multiple different setups and never had this issue until now.

Which 5v reference? The one to the crank sensor or something else?

Heres the current tune

Attachment 91886

I got a nice warm cookie for anyone that has an idea that leads to the answer for this one :D

Would adding a little bit to the throttle cracker help for the low rolling idle stall?

But I guess that doesn't really speak for the randomness of the issue happening out of the blue.

That still wouldn't explain the no restart though...

It's not really a rolling idle stall, the engine just straight turned off at like 2500rpm when I was coasting down from 90mph.

Alright here is a new development, had it idling peacefully in the garage while I poked around for exhaust leaks and it just cut off and same deal wouldnt restart. Getting pissed at this thing. Its not picking up the RPM signal when I try to restart it, so im not sure how that happens but has to be close to the cause.

Attachment 91928

Well did a write entire with the same tune as before to a spare PCM I had and it started and idled fine after the issue persisted with the other PCM, so I suppose that means the PCM is bad. I wish I had a better explanation than that though :/

Well, issue is still there with the different PCM. Idled fine in the garage for 10 minutes, backed it out of the driveway and put it in park on the side of the street then it stumbled and died. It acts like its a fuel issue, but I have good fuel pressure confirmed by 2 different gauges. 20 minutes later it started fine then I pulled it into the garage and got it as hot as I could (hood closed, no external fans, sitting at 3000rpm for a few minutes) to try and make it act up but nothing. Even did a few laps around the neighborhood and got yelled at by the neighbors. Im really at a loss on this one. I dont like issues that magically disappear because they will magically reappear at the most inopportune time.

lack of input rpm says crank sensor issue

Maybe check the fuel pressure when it dies. Mine done some crazy things like yours and it turned out to be a loose fuse on the fuel pump wire on the firewall. 1990 c1500

Yeah I am leaning towards the Crank sensor & fuel pump circuits
might be a cut in the wire or loose connection


theres very few things that will flat out kill an engine cold like that.
Others could be like,
Ecu plug is loose, power to ecu being cut, ...

I replaced the crank sensor with no change. I think the not reading RPM signal may be an hptuners glitch as it sort of does the same thing when it does start normally but kind of backfills the cranking time with data after it starts. When I replaced the PCM I obviously double checked the connectors to make sure they were tight. Fuel pressure is confirmed good by 2 separate gauges when cranking and running.

After my last post I took it to the track and beat on it all night without any issues and without really changing anything.

I can think of two possible causes.

1- The CAM sensor is having a problem and is preventing the engine from starting. Datalog CAM Sensor counts to see if it's working or not. Any Cam sensor DTC?
2- The MAP is triping a DTC. Disable "MAP/BARO Sensor Low" and set it to NO REPORT.

I have had the exact same issue with both scenarios being the cause.

I think if the cam sensor fails the engine still runs fine. It just has to 'guess' when you first go to start it, it may backfire once before starting.

I know when my cam sensor was unplugged the engine did that- backfire when it guessed the compression stroke, and ran like normal once started.

Any map weird behavior should be evident on the scanner log.

There are no extra DTCs besides the typical P0101-0103 for SD. The cam sensor glitching wouldnt explain it turning off, I was under the impression that was mainly used for starting only. I have pulled the plugs after trying a lot of failed starts and they were all dry. I figured that would at least be moist from fuel but nothing.

I hate to repeat myself but if you still have this issue with shutting off I would:
1. replace the cranksensor wiring (you said you already changed the sensor so all thats left is wiring)

2. have a fuel pressure gauge in front of your eyes when the issue appears so you can verify the fuel pressure isn't gone at that exact instant.

I've had fuel pressure drop unexpectedly from a failing fuse, it would drop long enough to kill the engine but when I went under the hood and looked at the gauge it would show full pressure. Later though I sat down and looked through my logs and saw that fuel pressure dropped and didn't move for a little while, traced it back to a small fuse I used on the fuel pressure relay wire (because the ECU throws a 12V signal to the fuel pressure relay which I found disturbing, most ECU use a ground to activate the relay.)