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.
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.