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rough idle and high bank 2 fuel trims

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Mar 1, 2019, 9:39 AM

Post #1 of 3 (600 views)
rough idle and high bank 2 fuel trims Sign In

Hello Forum, seeking diagnosis advice!

Vehicle: 2005 Explorer, 4.0L SOHC non-Flex V6. 155K miles.

-hard start (sometimes need to depress gas pedal)
-rough idle
-very rough idle when put in gear

Error codes (from a old cheap handheld scanner)
-P0174, which I understand to be “too lean (bank 2)”, and bank 2 = drivers side, where cylinders 4/5/6 are.

1st thing I did: some general maintenance, some of which I have been delinquent on and some of which didn’t think would cause my issue, but was already in there so replaced to rule out. Did the following:
-cleaned throttle body
-replaced spark plugs
-replaced spark plug wires
-replaced ignition coil
-replaced fuel filter
-replaced pvc valve
-replaced mass airflow sensor
-replaced fuel rail pressure sensor
-replaced air filter
-replaced intake manifold gaskets
-replaced left (driver) upper O2 sensor
-replaced right (passenger) upper O2 sensor

**No change in behavior.

2nd thing: built a smoker and checked for vacuum leaks. EGR valve (original) was leaking some.
-replaced replaced EGR valve

**No change in behavior.

3rd thing: Evap purge hose going to top of intake is pretty sketchy looking. Removed from intake and plugged intake port, in case either hose or the purge solenoid is bad.

**No change in behavior.

4th thing: bought a Bluetooth OBDII scanner (amazon, BAFX scanner) and loaded FORScan on a laptop – maybe it doesn’t take much, but I’m really impressed with what one can do with $23 and free software!
-scans show long term and short term fuel trim on Bank 1 to be +/- 5% - and stay that way as a crank RPMs up
-scans show long term and short term fuel trim on Bank 2 to be very high, LTFT2 pegged at 25%, STFT2 near 20%, and increases with higher RPMs
-data looks something like this (importing data into excel and plotting) (attached the jpeg if the insert doesn't work...):

5th thing: with the STFT2 and LTFT2 staying high as a increased RPMs, I concluded that this didn’t look like a vacuum leak, or at least if it was it was a really really bad one, which my smoke test didn’t show. So I thought maybe we’re looking at clogged or dead injectors. Put a mechanic’s stethoscope on the injectors I could get to (easy on bank 1, bank 2 harder) and all seemed to be clicking away. So I cleaned them and swapped them
-removed injectors, noting cylinder position
-cleaned with carb/throttle body cleaner (attaching a tube to the injector, putting cleaner in tube, putting 20 lbs of compressed air on tube, actuating injector by manually pulses the leads with a 12v battery
-all injectors fired
-reinstalled injectors, but put bank1 injectors in bank 2 and vice versa
-new o-ring seals
-before completely installing, test cranked engine with the fuel injectors hanging off the fuel rail. All injectors fired.
-put everything back together

**No change in behavior.

**note, while doing this, went ahead and pulled the valve covers to check out the timing chain. Bank 2 chain is tight, no visible signs of cassette failure. Bank 1 chain had a little slack, no visible signs of cassette failure. new gaskets used when re-installing the covers.

6th thing: scan again. STFT2 and LTFT2 still high. Bank2 is high with what was bank 1’s injectors. So I think I can say the injectors are ok?

So now I’m scratching my head a bit – what to check next….

1-exhaust leak before O2 sensor? take my smoker and put in my exhaust and see what happens

2-injectors? double verify that injectors, fully installed, are injecting? Pull plug wires, crank, and see if plugs are wet?

3-fuel pressure? This explorer don’t have a test port on the fuel rail. Could there be a clog in the pressure rail at/before the bank 2 side? Would weak fuel pump cause this kind of behavior? How best to test fuel pump pressure? Don’t really want to just replace fuel pump.

4-vacuum leak – double verify no vacuum leak? have the laptop plotting LTFT2 and STFT2 and spray propane around intake, brake booster, vacuum lines?

5-timing – double verify bank 2 cassette didn’t explode and timing is whack? Best way to do this? Pull off oil pan and look for chunks of plastic?


Soooooo…..thoughts? Comments? Suggestions?

Tom Greenleaf
Ultimate Carjunky / Moderator
Tom Greenleaf profile image

Mar 1, 2019, 12:15 PM

Post #2 of 3 (587 views)
Re: rough idle and high bank 2 fuel trims Sign In

? What did plugs look like on that bank?
OK, so the part cannon isn't enough it's picking on that side would check plain compression of a couple and a couple on other side. If off then why.

Timing chain plastic teeth if so you'd see those in oil pan or maybe draining oil but not so fast it wouldn't pick on one side. That's smoother even low compression or lower over time till out of spec a lot.

I'd sooner think intake has a crack you just didn't happen to find.

Old tricks maybe - propane torch not lit AYOR, non flammable brand BraKleen (brake parts cleaner) should stall it totally with a vacuum leak other brands may be flammable read before you pick one. OMG, don't let that stuff get on anything you can't target it will destroy paint like nothing.
Touching gas pedal really should make any difference or confuse it but seems it help this should smack clearly as a leak or lack of compression why compression one side only not sure yet still thinking,


Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

Mar 1, 2019, 3:01 PM

Post #3 of 3 (581 views)
Re: rough idle and high bank 2 fuel trims Sign In

WOW, you win the parts cannon prize.

Looks like you through everything at it but what may actually need.

Now, lets do some actual diagnostics

What is the fuel pressure?
Does the fuel pressure hold when the key is shut off?
What is the TPS voltage at idle?


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