Engine died during dyno and won't restart!
 

Got on the dyno for the first time with my new motor last Sat. Made a couple of pulls, tuner was working on the tune, then... car dies after the third pull and won't restart.

Car will crank but not fire - AND - the PCM won't communicate with LS1edit. Other electronics are working, i.e. lights, chimes, etc. I'm thinking that the PCM ground may have come disconnected.

Also, before the car died the fuel pump was doing some funny things, almost like voltage spiking. I'm thinking that the ground was coming loose, then came completely undone and killed the power.

Where is the PCM ground? Thanks!

pretty sure its on the back of the cylinder head.

I have seen Edit cash in more than one PCM in the past...

Yup at especially in the LT's, I havent had that happen with the LS's, Dam I shouldn't of said that!!. Anyway I was the tuner, First off its not the PCM, I tried another and still the same results, No start, No communication. Also what is happening is there is no fuel pressure, At first I thought it was the fuel pump, but I decided to read the pcm and no luck so I thought the same, Dam pcm fried that is why I installed the other PCM. After all that the Dyno operator told me on the last pull when it was coming down to an idle the engine just shut off. ( I didnt know that until the end). Now this is what the car did. There was a rich dip at app the 4000-5000 RPM range, in the low 11's, the rest was good at app 12.9 across. so I leaned it up a little just in that area and the next pull was around 14.2 across the board, thats when the car died....And yes I did check the fuses for the PCM and Lighter...Thanks for any advice...

I forgot to ask, did any DTCs pop up during the dyno runs that could shed any light?

This weekend I'll check the ground on the back of the head. I'd had been messing around back there addressing a suspected manifold leak, maybe I inadvertantly loosened something up?

Sounds like a shorted wire.On Z's I've found wires cut above the PCM from rubbing on the windsheild frame.

Nope, No codes at all...

Thanks, I'll check that too.

Hey Moe,

The PCM tanking that I witnessed happened during a write and the tuner guy knew it as soon as it happened (error msg I assume, as the room was filled with colorful language:))

I had a car battery totally die out of the blue on the dyno a few years back and act somewhat similar.

Yea true, as you know even at 99% write and then a disconnect will cause language to be disoriented. Been there with the LT's. When I uploaded the last tune it did say complete, turn key off, then after that it did not start. This is why I thought it was the PCM. But then the dyno operator said it died on the last pull. You can key on and not hear the pump prime, same with the backup PCM, No read, No pump??

This ^^^

Also, have you checked all of the fuses? Sometimes the smallest things get missed when hit with a no start.

Don't forget the grounds near the upper radiator support on the body.

Check the fuel pump relay.

You might also want a spare fuel pump relay, if you
dropped to low enough line that it was chattering
the pump load current might've burnt the contacts.
Maybe see if jumpering the contacts, makes the
pump go. That would narrow you down to relay guts
or intention (coil drive, VATS or PCM).

Bus / comms misbehavior might have also messed
up the VATS - PCM, with a working PCM try the
"relink VATS"?

Bus hangs can sometimes be recovered by pulling
PCM fuses, I don't remember which one (there are
two) did it for me, back when.

Yup, Man were stumped, I checked all of the fuses, swapped out relays and still nothing....??? Just cranks with no fuel pressure..

Can you see the fuel pump relay coil voltage? If you jumper the
relay contacts, does the pump light up?

I will have to let the customer do that since the car is back in his hands..Thanks for the advice, I'm sure he will try that...

Yes, I'll try that - thanks.

It's most likely the grounds on the back of the D.S. head. Turn the key on, and go out and stick your hand behind the head and start wiggling shit. I bet you'll hear relays start clicking.

sounds like the crank sensor to me