Plesse help, truck won't stay running.
 

Alright so started adjusting some things in the tune and was almost done. We wanted to fix the idle surge and hiccup upon initial start up. Got the idle better but not perfect. Once we started addressing the start up it only got worse and worse, to where it would start but wouldn't stay running at all. Loaded back the tune that was on the truck before we started adjusting and the same thing. Would not stay running.

Details on motor, 5.3 with 100kish miles. Ls6 cam, longtube headers, cai. Nothing special.

First thing we think is its not getting enough fuel. New fuel pump and same issue. Getting pressure at the rails, getting spark, relays and fuses are good, its not throwing any codes, I swapped mafs from my other truck and that didn't change anything, Any ideas to what's going on here..? Also while he was tuning it wouldn't allow him to get to the timing.

I changed the cam position sensor with one I knew was good from a 5.3 we had in the shop. Now it starts but its just as crappy as before, the colder the weather is the more cranks it takes to get it running. When I get it running I have to feather the throttle for a while for it to get up to idle.

Re: Plesse help, truck won't stay running.
 

Here's a vid of how its acting right now. You can here some pinging/knocking like its misfiring but it stops once it starts to idle on its own.

https://www.youtube.com/watch?v=K4Rb...e_gdata_player

Re: Plesse help, truck won't stay running.
 

did this truck ever run right?

are you sure you have the "right" cam/crank sensors?

did it run proper before your cam swap?

need better details to help you out... its kind of vague

Re: Plesse help, truck won't stay running.
 

Bought the truck how it sits, had an issue with the idle when I first got it but not this bad. Had a buddy start tuning on it and this is what happened. Yes the "right" sensors are in the motor. Haven't been able to check the crank sensor yet, not sure how I was vague on everything done but okay.. there's a thread on it if you want more details on the truck.

Re: Plesse help, truck won't stay running.
 

seriously... no reason to be a doucher... how am i supposed to know you have a build thread for this truck somewhere else... i gave up mind reading and assuming things a long time ago...

so you modified an already poorly running engine... good luck

Re: Plesse help, truck won't stay running.
 

I posted everything that was relevant to my issue in the first post. And you asked the smart ass questions. Once again I have NOT TOUCHED this motor, only finding out what's wrong and I would like some help. Tuning was the first place to go seeing if anything looked off or if it were throwing codes which it was not, as I stated already.. I'm sorry I came off that way its hard to tell a "tone" on the internet.. just looking for some suggestions as I am stuck.

Re: Plesse help, truck won't stay running.
 

i did not ask a smart ass question... and i am not trying to be hostile... its real simple... details details details... because i am an engineer i start with the basics, and have to assume what your skill level may be... its not disrespectful... its the easiest path to the right answer. i did not mean to have tone... but its the internet and its hard to convey tone or not...

what is the actual fuel pressure reading?

is it drive by cable or fly by wire? for the throttle?

have you checked for any vaccuum leaks?

running that poorly i find it hard to believe that no codes are being sent... my suburban will set a code for fuel that only looks questionable...

are you sure the previous owner did not swap out ecm's?

since you purchased the motor modified and running poorly...you really need to check and verify every piece and sensor that was touched...or that you suspect was touched... that is why i wont buy someone elses project... its just a giant ? mark if it was done proper

Re: Plesse help, truck won't stay running.
 

Im not sure on the exact fuel pressure right now, I don't have a gauge. Its drive by wire. Going to be checking for vacuum leaks in the next day or so when I check the crank sensor. I also find it extremely odd there are no codes being thrown, in the video you csn see the CEL go off like nothings going on. When we had hptuners hooked up, it was not seeing anything wrong either. I'm fairly certain they didn't touch the ecm, but not 100%.

Re: Plesse help, truck won't stay running.
 

verify the fuel pressure and then check the idle circuit for obstructions carbon build up

Re: Plesse help, truck won't stay running.
 

You can have a bad cts or idle air control and not get a code. I have had a cts so bad the truck wouldn't pull itself on flat ground. On another vehicle the idle air control would not let it idle at all.
I suggest the basics first like check all grounds to make sure they are all in place and clean. Check fuel pressure and have your sensors checked.

Re: Plesse help, truck won't stay running.
 

I'd look closely at data stream for anomollies (sp) and pending codes for hidden issues.

cam swap? is it in time? test static and running compression. lab scope the CMP and CKP together and see if chain is slopping around at idle

a known good ECM with a stock tune would be required before I'd let it in my shop