2013 GMC Sierra, stumble at first start, slow to start.

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10-05-2013
mekkis

2013 GMC Sierra, stumble at first start, slow to start.

Had a guy come in with a stock 5.3 4X4 truck, wanted DOD turned off. Not a problem, right?

After reflashing the truck, I go to crank it over and instead of firing right up it takes a half second before catching, and stumbles like it's running on four cylinders. This also happens on cold restarts, hot restarts are merely delayed.

1) Engine cranks for 0.4-0.7 seconds before turning on the injectors

2) I've only logged hot restarts, but typically the ECU commands ~4ms pulsewidth on both banks when it turns the injectors on. Sometimes it applies ~8ms on bank 2 for a moment - I ASSume that cold startups with more enrichment are doubling on bank two to cause the stumble.

I set the truck back to stock and it still starts up like this.

Any insight?
10-05-2013
mekkis

1 Attachment(s)

The cal info, if it helps.
10-05-2013
mekkis

1 Attachment(s)

Wow. VE airflow is toggling between reality and super high numbers, triggering fuel cut. A few seconds later in the log, before it smooths out and everything reads normal, it's dwelling on 0.000 lb/min most of the time.

Anybody have a stock cal? My gut feeling is something has become corrupted.
10-06-2013
EagleMark

Sorry I don't see anything for what you need... didn't you save the first read? Is it also corrupt? Has anyone played with this before you?

2013 should be under warranty? Heck most of the dealers will update the flash, even if you don't want it for an oil change...
10-10-2013
mekkis

A short timeline of events:

1) I always saved the stock read, I assumed it had become corrupt.
2) I hassled John @ TC, he said it was an odd symptom, sent me a stock cal (that was identical in WinHEX to the original read)
3) I took the battery cables free and touched them together, truck is fixed now.

I feel a ton better.
10-11-2013
EagleMark

Quote:

Originally Posted by mekkis

3) I took the battery cables free and touched them together, truck is fixed now.

I assume this drains power and clears PCM learn?

Forget what vehicle or where I read this is required to eliminate waiting minutes to hours on some?
10-11-2013
mekkis

Exactly.

It's a big thing in the German car world. I disconnected the battery on a 2006 TDI we were working on earlier this year, and out of curiosity stuck a DVOM across the cables. The electrical system had ~5 volts immediately after being disconnected from the battery, and it took a couple minutes to taper down to nothing. I imagine the meter itself could have drawn a portion of that voltage off. I haven't fooled with anything else by comparison, so I don't really have any frame of reference, but that seemed odd to me.