Tallchevy, btw it doesn't ever seem to backfire, but it does buck a little after cold start while still in open loop. I call it more cutting out than bucking, but could be the same. On occasion it will surge for just a second after a stop light of somethin, but its very short and I think it could be that negative timing spike showing up.

 

I dont think its the plugs or it would be backfiring or idling poorly. my guess is still the fuel pump. But just to keep this going what is your IAT reading at?

 

Is your scanner capable of showing live missfire data???

 

Plugs usually cause a hesitation just off idle or they just miss all together. However if the not gapped properly they can cause driveability issues. Injectors usually leak and don't close all the way or the don't open properly but usually you get a check engine light for that cylinder. Same with a sensor if its not functioning properly...

For it to not have a check engine light for any thing and still pull timing underload leads me to believe that either something is malfunctioning and the computer is not registering it or the computer has something wrong with it causing it to pull timing...
This is just based on the info I have in front of me of course.

 

I don't know for sure if my scanners show random misfire.

What's weird is, it might go a whole day without acting up, and then the next day act up every time.

I was getting it to act up pretty good yesterday and again the first thing that come to mind was that feeling of running out of gas. You know when your running out of gas, it may idle fine and run fine from idle to 75% throttle, and then a moment later only run fine from idle to 50%, idle to 40%, 30%, and so on till it dies…… well that's what this does of a cold start except in reverse order. It always idles fine, but only runs good from idle to 25%, then the next second 35%, 45%, and so on for about a minute. Then eventually runs good all the way to 100%. When your in the bad area, it acts just exactly like there's not sufficient fuel. But it could be it pulling all that ridiculous timing too.

I want to see if I can run a fuel gauge into the cab and watch it as I actually drive. As of now all I can do it watch from the engine bay and rev in park and see that the fuel pressure is good, but it doesn't act up in park anyway, so im not gettin the whole picture.

Question: before I eliminate fuel problems, is there any way my pump can be putting out proper pressure but insufficient volume? Even momentarily?

 

Yes It could be the pump on its way out. You need to monitor the fuel pressure when this problem occurs. I think There is also a fuel pump relay. You might want to swap it with another one from something like the AC....

 

i went through the same deal and it ended up being bad wires.
you can check resistance,but thats a bunch of BS,i have been through that once before.
took my DIG6 box to a local shop and put it on their "TESTER".
they said O your box is bad...
so i buy another Dig6 box.
same problem as before when i get home and swapped out the box.
So i had the local shop test 2 new boxes.
same bogus results. I got my money back, tested the plug wires.
resistance was good but i was still having the same damn issue.
So i bought some cheap Autozone wires and fixed my problem.
my truck was doing the same as yours so i started freaking out and started doing the basics,replacing stuff 1 at a time and ended up being my wires.
$30 fix for my 5.3.
good luck
Ed

 

I haven't read thru the whole thread but just reading thru this page it sure sounds fuel related to me. I would surely see if you can run a fuel pressure gauge into the cab with you so you can see what's going on there.

 

i agree with the fuel gauge testing,but really.
symptoms as such,the pump would either work or not.
would not be intermittent .
just my .02

 

FastBrick, I would be willing to ship you that ECU that i bought that ended up being locked, if you could ship me one of your unlocked ones back. I would send mine with an extra shipping label to send yours back so no cost to you. That is one easy thing to change before i get into the more expensive things. The truck has 160k miles and I dont know if the fuel pump has ever been changed. I wonder if the prefilter inside the bucket could be dirty.

I might even change out the mass air sensor with a new one, even though its not really reading abnormally. Is there a good one to get? Like SLP or something?

Looks like Ill change out the ECU, and then either fuel pump or mass air. I have no other leads to follow so ill be shooting blind.