2.9 stumbling, not revving

[aball4620]

Hoping to get some fresh eyes on this problem. 2.9 starts up and then stumbles and surges while idling. Won't rev past about 2k. Fuel pressure primes to 36 and then sits at 29psi, increases when tapping the throttle, and bleeds down to almost nothing over 24 hours. I have an old, noisy high pressure pump and swapped it back in wondering if the high pressure pump was failing, but no change in symptoms. FPR is new and line is dry. Injectors are fresh remanufactured and I checked the spray pattern before installing. As for codes, the only one that shows up is 63 in KOEO continuous memory, which is TPS voltage out of range (brand new TPS).

Any help is very much appreciated - if you have any questions please ask. I've replaced a ton of pieces but I find that if I start listing them nobody responds to the original post.

 

[sheep herder]

TPS may be new but have you checked the voltage on it?

 

[Dirtman]

In the words of Ron Burgundy....

New just means not tested.

 

[gaz]

aball:

Because you fuel pressure bleeds off, I would relook at the seal between the FPR and the rail. Dry line or not, the pressure should hold on the rail so it is leaking.

If it isn't the there, go back through and examine each injector, could be just 1 O-ring.

 

[aball4620]

aball:

Because you fuel pressure bleeds off, I would relook at the seal between the FPR and the rail. Dry line or not, the pressure should hold on the rail so it is leaking.

If it isn't the there, go back through and examine each injector, could be just 1 O-ring.

It’s there but no harm in replacing it. I’ll go through and check the injectors too - shouldn’t I be getting a fuel smell in the engine bay if there was a leaking o-ring? Or could it somehow be leaking past an o-ring into the upper intake?

TPS may be new but have you checked the voltage on it?

In the words of Ron Burgundy....

New just means not tested.

Yes, it has been tested. It's been a couple months so I don't remember the exact readings, but something like 0.71 - 4.9 with no weird jumps on a smooth curve. When I did it it matched spec. That is part of the reason I'm so at a loss with this single code that only shows up in continuous memory. I also checked continuity on the entire injector harness thinking maybe there was a ground fault somewhere but haven't found anything.

 

[aball4620]

Well, in an act of desperation after running through a few other electrical ghost diagnoses and coming up empty handed, I decided to pull the harnesses off the injectors. I'd already gone through and checked o-rings on the rail and the lower intake with no obvious issues. I turned over the engine to clear out the cylinders, re-primed the fuel pressure, and then let it sit for a couple hours. Jumped back in with the fuel pressure at about 20psi, hit the key, and it tried to start up. With no electricity to the injectors.

So, these are rebuilt - I'm not going that route again, or at least not from this company and not Bosch. I know lots of people have a very low opinion of Bosch injectors. What would you recommend instead?

 

[gaz]

aball:

How did the seal between your fuel rail and the FPR look?

The lower intake manifold is done in 5 steps and it requires a re-torque after it's warmed up.

 

[aball4620]

aball:

How did the seal between your fuel rail and the FPR look?

The lower intake manifold is done in 5 steps and it requires a re-torque after it's warmed up.

Everything looked good. o-ring was new with the new regulator and was installed correctly. There is no leakage. Everything on the engine was torqued to spec, including the re-torquing of the lower intake - but this issue predates the re-torquing. It was present from the first firing after the head gasket replacement.

 

[aball4620]

aball:

How did the seal between your fuel rail and the FPR look?

The lower intake manifold is done in 5 steps and it requires a re-torque after it's warmed up.

So after stepping away for a couple weeks I did pressure testing last night. I rigged up some fuel line components to test for pressure at the end of each component. Straight out of the pump pressure hits almost 100 psi. After the filter before hitting the rail pressure gets to about 65 psi. Blocking off the return line exiting the fpr I get about 65 at the rail but no more than 36 when the return line is open. I also cycled the pump probably a half dozen times without starting and pulled the plugs. They were all dry. Pressure had dropped a little down to about 55, and when I let it sit overnight the pressure had mostly bled off (return line still blocked off). The plugs are still dry so a couple questions - is there a more effective way to try to isolate a leaking injector? The gas should seep past the rings and clear the cylinder, but how long could I expect it to be present in the cylinder - would it still be there overnight? And would this even wet the plug or do I need to get our the boroscope?

Regardless of the pressure drop the fpr is under spec. Should be at 41 according to Napa, and it is well under and still under warranty. It still seems like I might be losing pressure through the pump check valve, but that shouldn’t be causing any issues while running. I’ll know more after the part gets in this afternoon but any other ideas are welcomed!

 

[gaz]

aball:

I just popped the fuel rail relief on a rail that sat for 12 years; it sent a plume of old fuel vapors 6' feet in the air and surprised the bajesus out of me.

Are your gaskets all the orange/brownish fuel gaskets?

If your FPR is verified good and it's seal is not leaking then you should smell some fuel in the morning after being pressurized the night before. Because of the simplicity of this system if it isn't:

FPR gasket
Fuel rail
Injector gaskets

It has to be an injector issue. I do not fully understand the fuel return line other than the function that I thought that it performed; a loop for over pressure to return to the tank.

So you have no puddling or moisture on the injectors, lines or intake valleys?

Can you have anyone else smell under your hood in the morning?

 

[aball4620]

aball:

I just popped the fuel rail relief on a rail that sat for 12 years; it sent a plume of old fuel vapors 6' feet in the air and surprised the bajesus out of me.

Are your gaskets all the orange/brownish fuel gaskets?

If your FPR is verified good and it's seal is not leaking then you should smell some fuel in the morning after being pressurized the night before. Because of the simplicity of this system if it isn't:

FPR gasket
Fuel rail
Injector gaskets

It has to be an injector issue. I do not fully understand the fuel return line other than the function that I thought that it performed; a loop for over pressure to return to the tank.

So you have no puddling or moisture on the injectors, lines or intake valleys?

Can you have anyone else smell under your hood in the morning?

I haven't had anyone smell for the fuel but certainly can give it a go. There is no fuel escaping the system that I've been able to identify - so nothing breaching the injector or fpr seals. No puddling other than when I hit the schrader port or remove the rail or fpr. I've had two injector sets in - one ultrasonically cleaned of varnish and has black seals, and one that I cleaned with pressurized carb cleaner with a rebuild kit that has the orange/brown seals. No change in symptoms between the two, which makes me think check valve on the fuel pump. I'm also not noticing any fuel smell from the oil dipstick, so if there is fuel leaking past the rings it isn't much. I've considered jumping in a brass ball valve to the intake side to pressurize and then cut it off to let it sit. That would be the last piece to isolate with pressure and would give a definitive answer, albeit a pain to rig up.

Replacement fpr took an extra day to come in so that will be going on this weekend, and then I should also have my new computer in tomorrow, so I'll check symptoms isolating each component. Not that the computer would be causing the pressure loss, but there are plenty of other ways it could be causing these problems. \

Any other thoughts are appreciated

 

[gaz]

aball,

What I am saying is that if your rail is losing pressure overnight, just sitting, not running. It is an isolated subsystem; if that bleeds off, it does it by losing pressurized fuel or fuel vapors which changes to a liquid. It is depressurizing into the surrounding environment/air, not "into your engine". That is why I keep asking about the seals/gaskets which for fuel are not black. Black o-rings are not for fuel systems.

The only reason I suggested the FPR gasket is I tore mine down once and didn't use a new fuel o-ring when I put it back together and it leaked. I was fortunate I suppose as there were visible droplets while the engine was running. Easy to see.

A much harder leak to isolate is a slow bleed off over a period of hours, with no fluid evidence.

If your FPR is working properly and all your gasket are the correct type, properly installed and seated, then I suspect your fuel rail is deformed and not making a perfect seal with at least 1 of the gaskets in question.

 

[aball4620]

Everything installed at the moment are the correct fuel gaskets - nothing black. I hadn't even considered that vapor would release past a gasket when it wouldn't allow liquid past. Boy, that might have to send me back to the drawing board as I'm not even sure how I would go about addressing it. I suppose if the symptom is happening in isolation and otherwise things are running correctly - as they should if it was a slow vapor leak - then it doesn't seem overly important to address in a 32 year old truck.