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Spark plugs and wires changed about a year/4k miles ago (work started a van pool and my usage went way down...)
The truck wouldn't start the first try last night. Tried to catch, stumbled and died. Shut it off, and tried again and it started, but high idled at around 2k rpm for 10 seconds or so before settling down. On the drive the truck kept trying to stumble and die at idle/traffic lights. If I ran the AC it would keep running but the idle did fluctuate a bit more than normal. I let it idle in the driveway when I got back and it would shut off after a few minutes of idling. Ran the DTC codes and got codes for both banks lean (P0171 and P0174). Idle with the AC on is around 600 rpm, with AC off around 500 rpm in gear, 150 rpm or so higher out of gear.
I figured the Fuel Pump Control Module was bad as it has never been changed. Picked up a new Dorman module from OReily's. The old module was corroded on the back, but not all the way through and was not cracked. I pried the plastic top off and the circuit board looked intact, but couldn't see the back of the board. The truck fired right up with the new module, but is having the same stall and shut off at idle issues. It hasn't shut off on me while driving at speed and seems to be stable everywhere but at an idle.
DTC codes are now:
P0171 System too lean bank 1
P0174 System too lean bank 2
P2195 HO2S11 not switching correctly, Sensor indicates lean
P2197 HO2S11 not switching correctly, Sensor indicates Lean
The truck is sluggish responding to the throttle/fee rev and slow to return to idle speed if rev'd, both while out of gear. Power seems more or less normal if you get on it hard while driving. I sprayed carb cleaner all over looking for a vacuum leak and could not find one.
Did I just get a bad module? Is the fuel pump now bad? Are the O2 sensors bad (they may be the originals, so probably due to be changed anyway)
Any other hints or troubleshooting tips? I guess I could go borrow a fuel pressure gauge and see what the fuel pressure is doing, but what else? Old Fuel Pump Control Module Installed Old Fuel Pump Control Module Back Side
P0171 and 0174 are typically vacuum leaks or the maf sensor needs to be cleaned or replaced. Since you checked for vacuum leaks next thing I'd do is go get a can of cleaner for mas air flow sensors and take it off the truck and follow the instructions on the can to clean it. You can get the cleaner from Walmart in a dual pack with throttle body cleaner and do that at the same time if you like for extra good measure but I don't think the throttle body is your issue.
The o2 sensor codes could be a hint though about what's going on. Maybe you had a rodent chew on the o2 sensor wiring since the trucks been sitting and maybe it's causing all the above mayhem. Though typically I think the engine ignores the 02 sensors until it's warmed up and goes into closed loop so I don't know if they would affect your idle at a cold start?
Maybe you do have something going on with fuel supply. Can you monitor fuel pressure via obd2?
What about your fuel trims long and short term?
Last edited by needsmoarturbo; Aug 28, 2020 at 07:14 PM.
MAF first its easy but be careful not to touch the wire, its fragile. You may need a security type torque's screwdriver
Check fuel pressure (most auto parts store have these as loaner tools)
Change fuel filter, change air filter
The above should get you on the path to solve this issue
Cleaned the MAF and the throttle body, no change. Spent some more time digging and it looks like there is a vacuum leak around the back side of the intake manifold, maybe where the power brake booster ties in or there are a couple of other small connections back there. They are very difficult to get to even with the throttle body off. I haven't had time to fight with it since Saturday. I used carb cleaner to spray around until the rpm picked up. It would be unusual, but it could be an intake gasket as well. Need to dig out by borescope and poke around back there and see what I can find
There was a small vacuum line at the back of the manifold that came unplugged. Was a first rate MF to fix. Couldn't get my hand back there, so had to use a mirror, borescope, small pry bar and some long, bent needle nose pliers to finesse it back on. Runs fine now
Thats why on the 05 they did away with that passenger rear vac connection its too hard to deal with . They put a metal fitting in drivers side on vac hose to brake booster with a wye on it . Some 04 guys have already modified theirs and plugged passenger side hole . If you get a new intake manifold that hole is not drilled out on passenger side . To find a vac leak I prefer to have the homemade smoke machine ,much easier to deal with.
But you did get some good maint done in the process . if you leave truck sit much watch out for rats , put some green mouse bars in and around truck .
Stalling At Idle
