Thanks in advance,

I have an 05 express 2500, 4.8, with about 125k miles. I drove about 3 hours, stopped for maybe 30-40 minutes, and within 5 minutes of driving in pretty heavy traffic the check engine light came on. My scanner said Po171 bank 1, but the O2 sensors are fine. They are also fairly new. MAF is new and fuel pressure was fine about a year ago when last measured. A few months ago it had a random misfire problem that I thought was resolved. It is running normally as far as I can tell. Anyone have advice on how to proceed?


thank you

How do you know the O2 sensors are fine?

It would be good to know the fuel pressure today, but not critical yet.

MAF is new, what brand is it?

My scanner has a IM monitor and it at least says the o2 sensors are fine.

The MAF is from auto zone so duralast.

I think I can get the fuel pressure tonight, figured I’d also see if I can fine any vacuum leaks.

The fact that it’* on bank 1 made me think perhaps a leak on that side?

thank you,
Edward

Just checked the fuel pressure, 60psi

spent some time looking for vacuum leaks with propane but without luck, though it’* hard to get to the engine in a van, so I could have missed it.

then I happened to notice the oil dipstick wasn’t quite seated all the way in, maybe 1/2out. After a quick google it’* possible this caused the code? Could it be that simple?

I don't think it would do that. The dipstick tube leads to the lower crankcase, not any part of the intake tract or combustion chambers. A P0171, if caused by a vacuum leak, would probably be something leaking on the intake manifold or the intake manifold gaskets.

Has this ever had intake manifold gaskets replaced?

Still original intake manifold gaskets as far as I know.

Edward

Still original intake manifold gaskets as far as I know.

did some more tests tonight. I got a scanner that could read live data which has given me more info that I’m having a hard time understanding

so LTFT are about 12-15% at idle with b1 about 2% higher on average. And maybe 15-20% revving.

STFT are within -5-5%. All the time.

the free frame data from when the code appeared had the LTFT as high as 25%.

Also, I’m 7 hours away from home. Should I drive home and fix it or go to a mechanic.

thanks
Edward

If the check-engine light isn't flashing (indicating severe misfires), it'* probably okay to drive home.

Regarding the intake gaskets: Over time, they lose elasticity and start allowing vacuum leaks in little bits here and there. Several years ago it was like clockwork that the weather would get cool and then folks would have lean misfires and stalling because of this. Same cars were okay in warmer weather and/or regions, but eventually were also affected.

Where are you now, and what'* the weather like?

currently in western North Carolina, it’* been beautiful weather, 80 for the high and 50 lows. All seems to be happening as it’* warming up.

is there anything I should watch for on the drive? Any number the fuel trims shouldn’t get to or something?

The only thing that confuses me about a Vacuum leak is that the LTFTs go up and down with rpm. I thought with vacuum leaks they would do the opposite, do vacuum leaks also cause this too?

thank you again, really appreciated your take the time to help and teach me.

Edward

50 could start to affect them, depending how old they are. 21 years is a long run without replacing the original set.

I would just watch for anything drastic happening.

Depends on throttle plate and loading and severity of vacuum leak.

You're welcome!