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

Hooked up a noid light to the injector harness and spark tester. I have both spark and injector pulse. I'll pick up a fuel pressure gauge later today and start logging fuel pressure readings. Any other ideas now that I've ruled out injectors not firing or no spark?

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

Hooked up a noid light to the injector harness and spark tester. I have both spark and injector pulse. I'll pick up a fuel pressure gauge later today and start logging fuel pressure readings. Any other ideas now that I've ruled out injectors not firing or no spark?

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!