Truck doesnt start right every once in a while.

[6.0vortecchevy]

Well every blue moon my truck wont start correctly, Ill go to fire it up and it will fire for about 2 seconds and then die. then ill go to start it again and it wont fire at all. I will have to wait about 30 seconds to try and start it again and usually it will start up perfect after that. The motor has a gmpp hot cam,Lt and intake. what could it be making this happen. Today I had to drive almost 10 miles and shut it off to have it run right.

[Gregs]

crank relearn maybe?

[6.0vortecchevy]

no that was done a long time ago.

[Taz]

Hello 6.0vortecchevy,

Intermittent issues can be a pain to diagnose … as you well know. Can use post your current tune and list the modifications to your vehicle ?


Regards,
Taz

[6.0vortecchevy]

i have my tune posted somewhere in this forum ill have to find it.

[6.0vortecchevy]

http://forum.efilive.com/showthread.php?11421-ac-wont-work-at-idle&p=99674

And all i have for mods is a gmpp hot cam intake long tubes and full exhaust.

[Taz]

The thread linked to a tune that was posted in July 2009. You are still using this exact tune, with no changes ?

That tune had an “out of range” parameter warning – B4348. The parameter itself looks OK - the file just may not have saved properly - prior to being flashed. Will need to fix that – could be causing an issue.

The tune itself appears highly modified from stock. I realize the issue is intermittent, and difficult to predict when it may happen, but logging what is happening when the problem arises will be necessary to narrow down the parameters – or a lot of trial and error on your part !

Try reflashing the tune with the out of range parameter warning corrected – may or may not help.


Regards,
Taz

[6.0vortecchevy]

Yea idn whats up with that it doesn't come up in my dtc codes. what table is it, im on my mac so i cant look at the tune right now.

[Taz]

Fixed the out of range parameter warning ... tune posted below ... may or may not make any difference.


Regards,
Taz

[nevinsb]

When mine was doing this, I had one of the temperature tables backwards in the tune.

[GAMEOVER]

Hows your fuel pressure?

[6.0vortecchevy]

Hows your fuel pressure?

Fuel pressure is good, Im almost starting to think it could be a faulty cam sensor. What do you guys think.

[6.0vortecchevy]

Ok just install the fix tune, i will report back to see if this problem arises again. thank you vary much for your help. If it continues to happen i will replace the cam sensor.

[joecar]

Fuel pressure is good, Im almost starting to think it could be a faulty cam sensor. What do you guys think.Yes, this is a possibility, faulty cam and/or crank sensors.

[6.0vortecchevy]

Yes, this is a possibility, faulty cam and/or crank sensors.

Iell I know it cant be the crank sensor because i replaced that not to long ago.

[6.0vortecchevy]

Well still does it, more then ever now. Im going to replace the cam sensor and see if thats the problem.

[joecar]

Yes, try the cam sensor.

Also, after that, if it still happens when hot, there is the possibility that the crank sensor wiring is partly melted (the wires are very thin)...
the wire insulation is fusing the 3 wires together, if so then separate the wires and insulate them (this is what I found on my TA).

[nevinsb]

Can the cam sensor signal be checked from the V2, or do you need a logging scanner, like the Snap-On red brick? I've seen the cam sensors inside the distributors fail quite frequently, but usually they either don't start at all, or start and idle horribly with a check engine light.

[6.0vortecchevy]

well i verified my fuel pressure today, and the gauge read 55 at idle and 40 when sitting for about 20 mins. So next im going to replace the cam sensor and see if that dont fix my prob.

[joecar]

Do you have the manifold referenced FPR (located at the fuel rail)...?

[6.0vortecchevy]

Yes i do why, I was also considering that going bad also.

[joecar]

Measure the rail pressure with the hose removed, it should stay steady at one value.

If the inside of the reference hose is wet with fuel then the FPR diaphragm is punctured, this is a problem; this is easy to check and eliminate as the source of your problem.

[6.0vortecchevy]

Ok well i just wet out side and I took the line off the FPR liek you said, and i started the truck and I noticed gas was coming out of the port. And liek you said i dont think it supposed to leak like that. So is that my problem? and also i have a crack in the boot that slides onto the FPR.

[joecar]

Fuel coming out of the vacuum/reference port on the FPR: yes that's the problem;

(this causes two things to happen: failure to regulate pressure and excessive fuel)

[6.0vortecchevy]

Ok thank you for the advice, ill change it after I get out of school and see whats happens.

[6.0vortecchevy]

Ok i switched FPR today and so far no bad starts. i will let you guys know tomorrow if anything occurs. That little sucker cost me 58 bucks.

[6.0vortecchevy]

Well its still doing it, so I think I'm going to change the cam sensor.

[joecar]

Let us know how it goes.

[6.0vortecchevy]

Well replaced the cam sensor today and that still had no effect, but one thing i did notice that i didn't before is that every time before i have a bad start i hear a relay going off. Its like i have a dead battery but it not. So every time i don't here that relay go off i have perfect starts. And that would explain why im having crapy starts. Every time i disconnect my battery to work on my truck it would start up like that.

[6.0vortecchevy]

I wonder if I have a loose ground somewhere.

[joecar]

I wonder if I have a loose ground somewhere.Check for this anyway.

[joecar]

Do you have access to anyone who has and knows how to use an automotive oscilloscope...?

If you do, get him to capture CKP and CMP signals, and if he has a 4 channel, then also #1 primary/secondary/trigger.

The waveform will show if the CKP and CMP signals are correct and in phase wrt to each other.

[joecar]

You replaced the CMP sensor, and no change. This leaves the CKP sensor.


But, first, swap your starter relay since it is cheap and easy to do (what vehicle is this...?).

[6.0vortecchevy]

Yea my friends dad is a master tech at gm so if swapping the relay don't do this then ill have him take a look at it. But one thing i replaced the CKP sensor liek a year ago.

[6.0vortecchevy]

OK guys im going to feel really dumb, but i got a hold of a battery tester and it read 12.12 and 41% battery life. Technically its a bad battery. but it cranks fine. Another thing i got in my truck about half an hour ago and i went to start it, and everything just went dead. then i went to start it again it it fired up sooo im leaning towards that bad battier.

[6.0vortecchevy]

Ok FINALLY found my problem, after all the hassle I went through it turn out to be a bad positive battery cable. Thanks for all your guys help on this one.