2003 Tahoe, Losing Fuel Pressure, Fuel Pump has been Replaced

[ivin74]

Gotcha yea Delphi is my next go to option if I replace the pump again. I'd like to test the pump, but I don't know where I would find an adapter to attach to those quick connects at the fuel rail. It's 3/8 flare right? I remember there's two types of flared fittings but can't remember which type this is.

You don't have to buy any fittings, disconnect the fuel line from the fuel rail. Put a jumper hose on the ends with clamps.

After reading your other posts I believe it maybe the either the cam or crank sensors. Non OEM are junk, I have run into this in the past. Also the Dorman intakes DONOT seal. I don't think this is a contributor to your problem but the vehicle might run rough at times.

 

[tahoefix]

You don't have to buy any fittings, disconnect the fuel line from the fuel rail. Put a jumper hose on the ends with clamps.

After reading your other posts I believe it maybe the either the cam or crank sensors. Non OEM are junk, I have run into this in the past. Also the Dorman intakes DONOT seal. I don't think this is a contributor to your problem but the vehicle might run rough at times.

Thanks. Thats good info about the cam and crank sensors. Going to replace them next weekend and will report back.

I have read a lot about the Dorman intakes leaking. Are you talking about leaking where the runners meet the heads or at the seam where the intake halves are joined? To remedy any potential leaks at the seam, I completely sealed the joint running around the circumference of the manifold, with plastic welder epoxy. My seams won't be leaking for sure. It could be possible for a poor fit at the heads though, is that what you were referring to?

 

[rockola1971]

I dont think I would hang my hat on the Crank or Cam sensors. I didnt catch any info about how the engine runs after its started? Typically a Cam or Crank sensor will get worse when they are warmed up. I would expect a code to be thrown then. I also would expect the engine to be running like hell or not at all.
As for fuel pressure loss, there's the injectors (believe you replaced and assume good), all fuel line fittings/seals, Fuel Pump and its check valve and the rail itself. After a thorough inspection of a pressurized fuel system to check for leaks and I mean every inch of it, not just fittings. Pay close attention to areas where fuel lines come near frame, etc and are in retainers. If nothing shows up, could be the fuel pump check valve or FPR.
How many miles one engine? Timing chain getting ready to jump time on you? Have a look at real time data for ignition advance? Is it all over the place at idle?

 

[tahoefix]

I dont think I would hang my hat on the Crank or Cam sensors. I didnt catch any info about how the engine runs after its started? Typically a Cam or Crank sensor will get worse when they are warmed up. I would expect a code to be thrown then. I also would expect the engine to be running like hell or not at all.
As for fuel pressure loss, there's the injectors (believe you replaced and assume good), all fuel line fittings/seals, Fuel Pump and its check valve and the rail itself. After a thorough inspection of a pressurized fuel system to check for leaks and I mean every inch of it, not just fittings. Pay close attention to areas where fuel lines come near frame, etc and are in retainers. If nothing shows up, could be the fuel pump check valve or FPR.
How many miles one engine? Timing chain getting ready to jump time on you? Have a look at real time data for ignition advance? Is it all over the place at idle?

Thank you for that Mr Rockola
I understand your point about cam or crank sensor performing worse as they warm up. As I understand it though, the cam sensor is ONLY used at startup, to find TDC in the firing stroke. Ive read the engine will start and run without the cam sensor, but not the crank sensor. If the cam sensor is not plugged in, or bad, the PCM will test for misfires and then flip the timing 180 degrees to get the engine started. I did have a period of time where I was getting backfires through the intake at startup, but that has gone away after improving the PCM ground. There are no engine codes being thrown whatsoever.

I've done a thorough visual inspection of all fuel lines and joints, and see no leaks. Also I dont smell any fuel, which is a good indication the leak is in the tank, return line, or injectors. You are correct, injectors and fuel pressure regulator have been replaced(and pump too). The injectors I purchased are these: https://www.ebay.com/itm/403135354521
They are supposed to be AC Delco, and they look like it too, but I've heard some say that inexpensive injectors like this can be leaky. No drivability issues however. I'm thinking the leak is likely the injectors or the check valve.

Theres 240k on the odometer, and the engine runs quite well after getting started. The only thing to note is that I have very poor manifold vacuum, 10-12 in Hg at idle. I've replaced anything I could think of which would cause intake leak or exhaust restriction. The only things I can think of which could be causing the low manifold vacuum are:
-something in the evap system causing the purge solenoid to stay open. Is the purge solenoid supposed to open at startup? If I do the key on engine off fuel prime, I can hear the purge solenoid opening.
-leaking rings, but I dont know if poor ring seal can cause this large of a change in manifold vacuum. Stock cam.
-leaking intake valves. I also dont know if valves in need of a valve job could cause this large of a drop in manifold pressure.
-something retarding the timing

Timing is around 3-5 degrees at startup, and gets up to around 17-20 after it warms up (at idle). Not as jumpy anymore (it used to be really jumpy) but still roams a little bit. It jumps back and forth a few degrees every couple seconds. Could be the timing chain for sure.

 

[ivin74]

I have read a lot about the Dorman intakes leaking. Are you talking about leaking where the runners meet the heads or at the seam where the intake halves are joined? To remedy any potential leaks at the seam, I completely sealed the joint running around the circumference of the manifold, with plastic welder epoxy. My seams won't be leaking for sure. It could be possible for a poor fit at the heads though, is that what you were referring to?

That's correct the leaks are normally at the runners, I read on another forum that they put a strip of permatex to keep them from leaking. You can check for leaks spraying carburetor cleaner on the runners.

 

[tahoefix]

Here is some interesting information, the crank relearn procedure doesnt impact the running of the engine, it only impacts the setting of DTC's.
From https://ls1tech.com/forums/pcm-diagnostics-tuning/1264257-crank-relearn-p1336-how-do-2.html

Once again guys and gals, IT'S FOR MISFIRE PURPOSES ONLY! Once you modify an engine, specifically an aftermarket cam, you disturb what was a SMOOTH ROTATION of the crankshaft. The case relearn is there so the computer can "learn" the small idiosyncrasies in crank to cam timing. It uses this information to better detect small misfires. There is no credible evidence it's used for anything more.

 

[tahoefix]

That's correct the leaks are normally at the runners, I read on another forum that they put a strip of permatex to keep them from leaking. You can check for leaks spraying carburetor cleaner on the runners.

Gotcha. Leaking at the top, bottom, or sides of the interface where the runners meet the heads?
or run a bead all the way around the gasket piece?

 

[ivin74]

Gotcha. Leaking at the top, bottom, or sides of the interface where the runners meet the heads? View attachment 360901
or run a bead all the way around the gasket piece?

From what I have read its mostly on the bottom and on the inner runners, I would still put a bead all the way around on every runner to be on the safe side.