Surging and dying problems

I tried to search the forums before I posted this but couldn't find what I was looking for.

This is the issue:
My brother has a 2006 Chevy Tahoe 2wd 4.7L

His truck was surging real bad going down the road and it would intermittently stall out also and then at times die. He'd let it sit for a bit and it would start up and get him home but would continue to do this intermittently.

We both at the same time thought it was the fuel pump. So we dropped the tank and put a new one in. It still did the same thing and found that it was indeed getting gas but no spark... So, we changed the crank shaft sensor and it started back up but the surging is continuing and it still dies. Also it's getting starting to get worse.

We are both pretty baffled by it and can't seem to figure it out. Any suggestions?

Try cleaning your throttle body!

any codes?

Fuel pressure regulator ? Clean the IAC seats ? Gauges normal ? VAC lines good ?

Thanks guys.. We cleaned the throttle body out real good and it ran great since my last post until yesterday and he called me up with it doing the same thing. Today we were going to take it down to get an OBD II reading and it just died going down the road. We could only coast into the court house, (made me nervous, had my Sig P220 on my. lol). We tried to get it running but it just wouldn't start. I checked the fuel pressure and it had plenty; used the release valve (didn't want to but had to know if there was pressure with it cranking), didn't have a pressure gauge there. But it could be the FPR like delta said, just have to get my tools over to my brothers later and I'll check that.
I have a good friend that's 1600 miles from me and he mentioned the Alarm system can do that also if the system is going out. Anyone ever hear of that? I know it's all based upon resistors providing the right amount to send the output to the engine, or something like that. The truck ignition key system is not OEM so that might make some sense as it doesn't have a resistor in the key and if when it was replaced and they put in a cheap resistor to bypass the system, like they do for remote starters, I could see how that could be the problem.
Anyways, I appreciate all the input you guys have given. All I've worked on my whole life is Chevy and Volkswagens and I thought all this ECM stuff was supposed to simplify the problems.
Wish I could just rip all that crap out and put in a real engine that didn't require so much computer input to complicate locating the diversified criminal ailment in the copper striated multicoated polymer resistant rubber outter shell that should just simply be called a wire...

Yes, I have heard of after market alarms causing all kinds of problems. Good call by your friend. Also the crank sensor may be going out as the symptoms you describe can be that too. If this is the case. Be mindful when you remove it if it has any shims with/on it. Sometimes they can be finicky and require 2-3 shims to get the right magnetic pickup from the crank. Hope this helps.

alc5m said:

any codes?

Click to expand...

P1516 was the code. So we replaced the throttle body itself and it still did it. So, I'm guessing now, that it's either the TAC or TPP? It's just starting to get expensive to narrow it down.

We put a fuel pressure gauge on the pressure valve and it read with the key on, no start, 55psi, with the engine started 55-65psi. I though that it's supposed to stay steady at 55psi but it is fluxuating... Is it supposed to fluxuate?

With that code, p1516, is there any other inherent problems that could cause the code to read?

Thanks guys for all the help.

---------- Post added at 02:06 PM ---------- Previous post was at 02:03 PM ----------

delta579 said:

Fuel pressure regulator ? Clean the IAC seats ? Gauges normal ? VAC lines good ?

Click to expand...

Delta, I've tried to research where the dang fuel pressure regulator is on this model and I've come up with nothing on it's location, cause that's what we thought as a possibility (read previous post). Any suggestions for schematics?

Thanks

---------- Post added at 02:11 PM ---------- Previous post was at 02:06 PM ----------

delta579 said:

Yes, I have heard of after market alarms causing all kinds of problems. Good call by your friend. Also the crank sensor may be going out as the symptoms you describe can be that too. If this is the case. Be mindful when you remove it if it has any shims with/on it. Sometimes they can be finicky and require 2-3 shims to get the right magnetic pickup from the crank. Hope this helps.

Click to expand...

Just read this one... hmmm.. my nephew change this part and he's about as helpful as an a**hole on an elbow at times though his arms were skinny enough to fit up there. I wasn't around so my brother had him change it.

My brother is disabled so I'm trying to do whatever I can to help him out. He's helped people out all his life and then had health issues that disabled him. No way I can let him down after the heart he's had for others. Sorry, not trying to air laundry here it's just breaking my heart I can't get it going for him.

---------- Post added at 03:07 PM ---------- Previous post was at 02:11 PM ----------

OK.. It's probably a part of the aftermarket alarm system. I found a button underneath the dash that when held, with the key turned to the on position, lights up. The truck immediately started and ran for a few minutes then died again. I shut the light off, turned it back on and then it started again. I did this about 4 times with the same result but then it would start at all. I think this could be it but was wondering what everyone's thoughts/experiences are with this? Is there a way to bypass the whole system itself?

Fuel pressure reg. is on left side fuel rail, in the middle. It's VAC actuated, so it will have a hard VAC line running into it from the manifold. That wobbly of a fuel pressure reading my be a concern. There is a fuel pressure check valve at/in the fuel pump assembly. Normally this only comes into play when engine is first started, otherwise the pump would run continuously with key-on engine off. Like most electric motors, it may be developing a "flat spot" like on old starters. It will start fine, until the starter would stop on the "flat spot" then nothing. When the starter would stop in any other area, it works fine. So a fuel pump change out may be in your future. Hope this helps.

Once again, thanks guys.
We've narrowed it down to the VATS. It has an aftermarket system in it and when I played with it a bit, and did some research, I'm pretty confident this is it.
Logic behind it:
Fuel Pressure Ok.
Starts fine but then constantly dies.
Not getting spark after it dies.
No OBD II readings
I'm getting ready to check the cranking RPM's and I'll post those as well. Sure hope this helps someone who's also having/had the same problem(s).

It's still doing the same thing and this is becoming a hardcase. lol Anyway, anyone ever heard of cmp and ckp needing timed with eachother? It's my brothers thoughts but I'm thinking if the ckp was merely replaced then there shouldn't be any problem after resetting the ecm because anything out of sync would then be a mechanical problem.. correct?