Stumble/Hesitation AND stalling: *solved, fuel pump*

[Bill 1960]

So lately I've been chasing a couple of performance issues that I had thought stemmed from a common cause, but now I think not.

Problem 1: intermittent stumble at idle or hesitation when first accelerating from a stop. Sometimes won't happen for hours. Sometimes only a few minutes apart. Never misses more than a second or two and then resumes normal smooth operation.

Problem 2: stalled on the trail during slow speed operation in 4 Low. All the symptoms of low/no fuel pressure. Managed to self recover by letting it cool for a few minutes when it stalled and then restart. It always started right up after a cooldown, but would stall in another 1-2 minutes again. Cranking immediately after a stall it would not start. Once I got to a section of trail where I could let it cool down for a half hour, I scanned for codes.
P069E status $07E8 Fuel Pump control module requested MIL.
P0191 status $07 EB Fuel Rail pressure sensor circuit range/performance bank 1.
P0171 status $07E8 system too lean bank 1.
Reset the codes; after cooldown we departed at higher speeds and the problem has not repeated during normal roadway driving.

Diagnostics so far:
I ran two bottles of Techron through it with no change. Indicates to me it's not a sticky fuel injector causing the stumble.

Installed a fuel pressure gauge on the rail and drove it around (thanks to @Doubeleive for pushing me to do this). Seems exactly on spec 55-60 at start; 42-45 driving at any speed or throttle. No leakdown, and even more annoying no change in fuel pressure when the idle miss or stumble occurs. Which is what convinced me the miss and the stall are not a single problem.

I removed the electrical connectors from the FPCM and the fuel pressure sensor and cleaned them. No change.

Next up: fuel pump gets changed tomorrow. Even though the pressure is OK now, it certainly wasn't on the trail. I don't want to deal with dropping the tank in the woods and changing it so it's getting a new one while I'm in a place I can get it done. If I need to change a sensor or FPCM I can do that anywhere. Well, except for programming the FPCM.

After the fuel pump, I'll clean the throttle body to see if it affects the stumble. The MAF was cleaned a few months ago.

I also picked up a set of plugs and wires. I'm guessing they have never been touched, so I'll change those. Needs doing anyway, and maybe that's causing the stumble.

Let me know if you see something being overlooked. Otherwise I'll update this as the problem(s) are resolved to hopefully help someone else in the future.

 

[Bill 1960]

A comment about the circumstances to future readers: This rig was built to explore, so we're currently far from home, and hopefully going far afield from pavement, cell phone service and tow trucks. Which is why I am inclined to replace parts just because they might be bad.

It's also the post wuhan flu summer, so supply chains are stretched thin, and repair shops are booked. It takes me about a week of waiting just to get into a shop.

All of which is to say the circumstances are different than if I was at home, with the luxury of spare vehicles, my own garage to work in, and other things to do not requiring this vehicle.

 

[wsteele]

Based on what you saw on the fuel pressure, I personally wouldn't change the fuel pump or FPCM as they seem to be working fine. That is a lot of work to replace something that your empirical tests say are fine.

I could box up my Tech 2 and send it to a UPS store near your current or near term future location and you could probably do a lot more diagnostics in the field. Might save you some unneeded repairs.

 

[OR VietVet]

I would hate to be wrong but your symptoms in #1 are just like what I experienced with my rig when my D/S O2 sensor went bad and I could shift to neutral at stops and keep it from stalling and when I drove it I felt no problems. I took care of it at the very first signs and never got to the point where your #2 problem could have come in to play. I replaced all 4 sensors and problem solved and runs like a top.

If you do replace sensor(s), I would also, at first chance, check for possible back pressure problems with the cats.

 

[Bill 1960]

Based on what you saw on the fuel pressure, I personally wouldn't change the fuel pump or FPCM as they seem to be working fine. That is a lot of work to replace something that your empirical tests say are fine.

I could box up my Tech 2 and send it to a UPS store near your current or near term future location and you could probably do a lot more diagnostics in the field. Might save you some unneeded repairs.

That’s a generous offer, which I appreciate, but I don’t know how to use a T2 and at this time of year, the repair bill is not a concern. It’s not that money grows on trees, but we’re traveling, so every day the truck isn’t reliable is a day of summer lost, and the costs for accommodations don’t stop, so…

I need it ready and reliable for wilderness areas. And if it fails, and I have to pay for an off-road extraction, it’s $$$$.

The real danger to the budget is the time I can’t go exploring and I start looking at the new vehicle availability in the area LOL!

 

[wsteele]

A comment about the circumstances to future readers: This rig was built to explore, so we're currently far from home, and hopefully going far afield from pavement, cell phone service and tow trucks. Which is why I am inclined to replace parts just because they might be bad.

It's also the post wuhan flu summer, so supply chains are stretched thin, and repair shops are booked. It takes me about a week of waiting just to get into a shop.

All of which is to say the circumstances are different than if I was at home, with the luxury of spare vehicles, my own garage to work in, and other things to do not requiring this vehicle.

Another thought was if you had a dealership near your current location. In our neck of the woods, unlike the privateers, the dealers are bending over backwards to get trucks in the door for service work.

They have been limping along with reduced inventories, so they don't have all the normal work that comes with new car sales at full steam.

Pretty sure they will have somebody there who knows how to use the Tech 2. Maybe get everything you need done while you wait. in an air conditioned room with a TV.

 

[Bill 1960]

@PNW VietVet those are some good thoughts. I have monitored the fuel trims and O2 sensors with my Foxwell scanner, and I don’t see any anomalies or difference between the banks. I think that contraindicates an O2 sensor, yes?
On the cats, give it the boot and she’ll run right on up to triple digits, there seems to be no loss of high rpm power like I have seen with plugging cats in the past.

@wsteele we think alike. I phoned the dealership here 2x a week ahead, couldn’t get service to pick up. Left a detailed voicemail; no callback. I took that as a sign. Fortunately I know another shop in this town I’ve used before, and they’re installing a new Delphi pump tomorrow.

Unless some miracle occurs and the pump cures the stumble, I’ll change the plugs and wires next.

Friday I’ll have a new FPCM, one of the plug and play aftermarket units.

The major concern is what caused the total loss of fuel pressure and stall. No reoccurrence since that day to give any opportunity to diagnose it. My initial thought was overheat of the FPCM. Stay tuned…

 

[CaptainAmerica1]

vapor locked fuel lines?

 

[Geotrash]

At 42+ psi, you’re well above the RVP of gasoline, which runs 8-12 psi at 100°F, depending on the region and time of year. Given that the fuel pump is submerged in the tank and the entire fuel system is under positive pressure, vapor lock is unlikely. I know some folks have wrapped their fuel rails on these trucks, but Boyle’s law is pretty hard to argue with.

My money is still on the fuel pump for problem 2.

 

[OR VietVet]

I have to say that after all my years in the shops, I never saw a fuel line vapor lock on fuel injection. Not saying it cannot happen, like with the old mechanical injection systems and some of the early designs of the electronic fuel injection. I just never saw it happen. I would assume it can be more common in high heat areas in the southwest and then is more likely after shutting off the vehicle and then the hot soak takes place. Old mechanic told me once that in those areas and at those temps, if you have a fuel cap not venting and think you have a vapor lock, you just remove cap and then try the restart and then he said, "Then dammit, get a new fuel tank cap"!