OK Lel me start off by saying that I have an 03 base model Z51 50th Anniversary. It has a lot of aftermaket parts. The motor is a 383 built by 21st century. Originally it was a heads and cam package that was then turned in an A&A V2 blower setup with blower cam on a 3.4 pulley, which happened about 7 months

The no start Issue happened randomly one day. I drove to my apt. Everything was fine. Then I saw a closer spot so I moved my car to that spot. Right after I moved to that spot I tried to start the car after and it instantly wouldn't start. It acts like it wants to start but it feels like it just can't get over that hp to start. First I figured maybe its a bad battery, red top optimas are known for that so I figured why not. Still didn't work... So since it was almost starting, I figured well maybe fuel is an issue. I checked it - it primes so Im assuming fuel pump still works (255walboro walbros with Kenne bell BAP). Now its leading me to believe it may be a wiring or electrical issue. So I cleaned all grounds, checked all fuses, and tried to check all relays. i actually had a tuner come over and hook up scanner to connect to them to see if they could find maybe a reading that was off. When he hooked up to the computer everything read exactly how it was suppose to but when u tried to crank it withthe key - it lost communication with the pcm. Before cranking it it streamed data to the reader just fine but as soon as u tried to crank the car it would loose communication with pcm and show an error.

Has anyone ever experienced anything like this. We still don't know why my car won't start. Im gonna really need the help of the Corvette Gods to figure this one out. Bill Curlee help
I've also cleaned ignition switching as well too.

!!!Need help ASAP!!!

 

Bump. Need help fast.

 

the tech here, that scanned it.
additional points, checked with a gm tech I know, jist of things..

YES, pcm fuse maintained power with a test light throughout all cranks.
No, it didnt act like a bad ground or security error.... (security doesn't ever shutdown the entire PCM during cranking on a GM. )
I had added a body ground and additional engine ground during cranking.
Also one additional positive at engine bay fusebox +.

The ONLY time out of twenty attempted cranks that the PCM stayed 98% online and talking to scanner through cranking was when I sprayed a contact cleaner on pcm contacts.
It stayed online through the crank only that was one time right after I sprayed contact no ox on contacts.... after that, back to offline when cranking.

 

ThX for r chiming in Will. We tried a lot of different things but to no avail. I just got off the phone with Bill Curlee and we need to check the voltage at the pcm fuse while cranking. That may give an indication to why the pcm is going offline. I am going to have to see if its looking power at crank.

 

did you tell him I had a huge F350 diesel with dual 1000 amp batteries hooked up to your car with two sets of ultra heavy duty 2 gauge jumper cables ( one set on your cars body at fuse box and one engine )

plus a heavy duty batter charger maintaining the entire jumper circuit .

Heard how FAST the car cranked ?

that was the first thing I did, add some grounds and take "enough" volts & amps to crank the car, then over double it. that assures a clean data scan.
a weak power or ground wire AT the pcm plug can do the rebooting / crashing thing ( so can 42 other things )

so far im sticking with my original personal diagnostic flowchart of first send the pcm out to get checked, then if its ok, rebuild the female pcm connector pins, all of them. not just power and pcm ground.
when I go with this personal diag flowchart please keep in mind how many more variety of pcm issues ive seen than most folks.
for instance - one chip is cooked in pcm, it gets fixed - then plugged in, then car runs for an hour to weeks etc = you have an intermittent engine wiring short that feeds directly to pcm.

know anyone with a megasquirt you can borrow and test on your car ? im positive that pcm is more fault tolerant and stout.

only other thing scanner read was at totally flat gas pedal the pcm read the gas pedal was 18% down already. ( floored it read 99.8% down ) sounds like a chip telling it to run rich, can anyone confirm thats what the chip changes.

 

Bump for some input u guys. Ill chime in with voltage readings on pcm fuse 16 during crank at around 7 or so tonight.

 

William

I responded to Joe's PM request for assistance. I had limited info on your troubleshooting efforts.

Sounds like you have ventured a LOT deeper than most people do! WELL DONE!

Yes, I listened to it crank over the phone. Initially it was DEAD and required jumping to get it to turn the engine over. Turns over fine but I did not detect any cylinders firing.

Joe indicates that the battery dies pretty quick when the car is shutdown. Sounds like there is a SIGNIFICANT Parasitic key off current draw. Not saying that is your issue but, that need to be researched and tracked down.

If the PCM goes off line, initial thoughts would be that its losing power in the ignition switch " HOT IN RUN AND START but you have indicated that you have already checked that.

I would have to say that the PCM is the correct diagnosis and should be checked. YES,, I too have seen quite a few very strange PCM & BCM related issues.

Whatever the issue is, the PCM thinks that it is being SHUT DOWN in a normal manor because it is not throwing any sub system DTCs or internal memory DTCs.

I go pretty far proving that ALL the EXTERNAL PCM requirements (POWER&GROUND) are good because I hate to throw PARTS at a problem and troubleshooting is easy and free.

Please let us know what you find was causing the issue. Sounds like a pretty unique issue.

Take a look at the BCM total SLEEP CURRENT DRAW and see if you can find out what is preventing the BCM from going to sleep. Total Sleep current draw should be 20 milliamps. It will help prevent killing the battery.


Bill

 

I had a similar problem last month. First I replaced my red top, no help. Sometimes it would start, other times nothing. When I got it started, took it to the dealer. They did the diagnostics and found out that it was the ignition switch. $750.00 later, all was fine.

 

I wish it was that simple. I rebuilt the ignition switch thinking maybe that was the case

 

what he said.
also, the symptoms did not match a flaky ignition switch.
usually they work a percentage of the time when they are failing.
and, he already serviced it. so tis not the case.

I mentioned to him I spoke with two of my senior GM tech friends and have a few things to try if im booked for another appointment shortly.
Im a professional mechanic, none of that is free advice or service.
one of the reasons I stay out of forums usually.. too much noob hearsay.
professional, experienced troubleshooting aint' free.

I hardly take any wiring pics and pcm screen grab photos. only if somethings unique.
https://www.facebook.com/WilliamSven...00000686899395

 

bump / word ?
this is why real techs aint in forums...what we do is over yalls heads :-)

 

Hey maybe you can help me ... when I set my alarm the lights will flash because that's the selection I selected .... Now what has me confused is that when I unlock my car using the fob ... no outside lights just inside lights come on ... why won't my security lights come on and stay on for a min or so???? Plesase Help

 

Thx Vette8 U da man ... gettin old I guess forgot all about that ... I almost scheduled a appt at da dealer (stealer) ship ... Thx again and Happy Turkey Day

 

bump / word ?