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

[tahoefix]

Hi Guys,
I'm having a problem that I could use some expertise in guiding to a solution. The 5.3 non-flex fuel engine starts hard. Usually takes two cranks to get it running. I did some fuel pressure tests - I'm losing fuel pressure, there's a leak somewhere. Here's the data
Key On Engine Off: ~53-55 psi
After 5 minutes the pressure drops to 32 psi
After 15 minutes it drops to 22 psi

Next, started the engine. Fuel Pressure idling: 46 psi
shut the engine off. within 3 minutes its down to 36 psi
within 10 minutes of shutting off the truck, down to 20 psi

So, I'm losing pressure somewhere. I've done a visual inspection of the lines, fuel pressure regulator, fuel filter, and injectors, and cannot find any leaking fuel. Here's the parts that have been replaced already:
Fuel Pump (AC Delco MU1615)
Fuel Injectors (AC Delco 17113553)
Driver Side Fuel Rail (GM 17113696)
Fuel Pressure Regulator (ACDELCO 2173299)
Fuel Rail O-ring Kit (GM 17113552)

I'm thinking it is unlikely the fuel pressure regulator is at fault. It is brand new, and there's no fuel in the vacuum line. I'm thinking either the injectors or the Fuel Pump, and leaning towards the pump. The fuel trims don't suggest a leaky injector. The trims are less than 5%, and closely matched between both banks. So I think its the pump. But I'm open to further tests to perform. Unfortunately there's no easy way to test the fuel pressure at places other than at the fuel rails. I'm ordering a set of hose pinch off pliers to pinch off the return line, that should rule out the fuel pressure regulator.
Next weekend I'm pulling the manifold and will test the injectors for leaks.

I'm wondering though- brand new fuel pump, why is it loosing pressure? Its ridiculous, a brand new Delco part leaking? Are there any alternative fuel pump assemblies that would guarantee I never have to redo this job?
Thanks for any words of wisdom

 

[ivin74]

I have had brand new fuel pumps be bad out of the box, they were not AC Delco though. Have you tested the new pump? If I was you, I would disconnect the fuel line from the fuel rail, make an adapter to test from there. This would rule out the pump. I'm currently running a Delphi FP, and has been great for 3yrs.

 

[MassHoe04]

Delphi was probably the second most recommended on the Jeep forum. I had a pump fail on my 05 4.0L. I could not wait for MOPAR fuel pump and NAPA had Delphi available from the closest warehouse next day.

The Delphi looked, fit and performed like the factory pump in every way.

If I ever need a pump for my 04 Tahoe and Delco was not an option (or just too expensive)... I would not hesitate to go with a Delphi.

 

[Fless]

The fuel pressure seems to be just out of spec. Read this post carefully and see what you think:

Crank No Start After Driving

Well it's time to bring out the big guns (that's you guys). Last year I swapped in an LQ4 into Fat Konnie (Yukon XL). Specs are in my sig. I have a very strange, but not unheard of, starting issue. When I did the swap I put in all new AC Delco sensors on the motor) with the exception of the MAF...

www.tahoeyukonforum.com

 

[Joseph Garcia]

Welcome to the Forum from NH.

Lots of knowledgeable folks here who freely share their knowledge, experiences, and perspectives. Knowledge is power.

I hope that you will become a participating member in the Forum's discussions.

Pics of the truck, please.

You are already receiving sage advice from the knowledgeable folks on this Forum.

 

[tahoefix]

I have had brand new fuel pumps be bad out of the box, they were not AC Delco though. Have you tested the new pump? If I was you, I would disconnect the fuel line from the fuel rail, make an adapter to test from there. This would rule out the pump. I'm currently running a Delphi FP, and has been great for 3yrs.

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.

 

[tahoefix]

The fuel pressure seems to be just out of spec. Read this post carefully and see what you think:

Crank No Start After Driving

Well it's time to bring out the big guns (that's you guys). Last year I swapped in an LQ4 into Fat Konnie (Yukon XL). Specs are in my sig. I have a very strange, but not unheard of, starting issue. When I did the swap I put in all new AC Delco sensors on the motor) with the exception of the MAF...

www.tahoeyukonforum.com

Gotcha thanks very much for that. Perhaps the fuel pressure is not the root cause. The root symptom I am trying to resolve is hard starting. Sometimes it will start in 1 crank. More often it takes 2-3 cranks. If we assume fuel pressure is acceptable, the only other things I can think of which would cause hard starts would be bad/intermittent cam or crank sensor, or their associated wiring.

 

[Fless]

It wouldn't hurt to do a crank - cam position relearn procedure, just to rule it out.

 

[tahoefix]

So to recap- the main problem is the hard starts. With fuel pressure being close to within spec, perhaps low fuel pressure is not the root cause. The behavior of the hard starting is this: one in 10 times it will start as soon as I turn the key. Most of the time it takes 2-3 turns of the key to get the engine running. When it takes 2-3 times, it doesn't happen as soon as I turn the key the second or third time. It cranks, then fires, then stumbles, then finally catches and runs. Going back to basics, if fuel pressure is acceptable, that leaves air or spark. The possibilities I'm considering are:
crank sensor
cam sensor
MAF
MAP
coolant temp sensor

Throttle body is brand new, has been cleaned, and is also AC Delco. Has new Delco plugs and wires. Already replaced the intake and intake gaskets.

Something of note:
I've already replaced both the cam and crank sensor once. They however are NOT Delco parts. They are whatever was available at the local Oreillys, I think they were Standard Ignition or something like that. I haven't been able to find any store which has the AC Delco Cam Position Sensor in stock. Recently I purchased an AC Delco crankshaft position sensor (213-354), and NGK camshaft position sensor. I haven't installed either of these parts yet though. That's next on the agenda.

Also:
I have been monitoring the engine performance with a VCX Nano. The ignition timing was jumping around quite a bit (like 10-15 degree jumps at idle). I cleaned up the ground at the front frame rail and it significantly improved the timing jumping around. So perhaps there is a ground issue contributing to this. I've already cleaned up the grounds at the back of the driver side head, and at the block behind the oil pressure sensor. I think I need to do the passenger side head yet.

One last thing:
Monitoring the MAP sensor, I'm seeing 10.5-12.5 in. Hg at idle. Which is low, and should be up around 17-18. I've replaced the intake with new Dorman intake, and religiously checked all vacuum lines. MAP sensor replaced, and get the same reading. I can find no leaks. Initially I suspected clogged catalytic converter or exhaust, so replaced both of them. Fuel trims are good and it idles fine, not like it would with a huge vacuum leak. Purge valve has been replaced as well. Although, I do notice that the purge valve seems to cycle at Key On, Engine Off. (I noticed this when priming the fuel pump). Is it possible for poor sealing valves or rings to cause this poor of intake vacuum? If I'm giving it throttle, vacuum rises to 20-30 in Hg

Any thoughts or advice is welcome

 

[tahoefix]

It wouldn't hurt to do a crank - cam position relearn procedure, just to rule it out.

Sounds good, I'll do it again. I have done it once already, but for sure it can't hurt to do again!

 

[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.