P0171 & P0174 System Too Lean

Sierra54 · December 18, 2008

After seeing this code come up on my truck and searching the forum I've seen several posts on this topic. I didn't feel comfortable spraying throttle body cleaner around the intake manifold to find the leak however I did try cleaning the MAF sensor and the codes came back after being cleared. Already purchased new intake manifold gaskets and will be ready to tear into it when I get back in town from Christmas vacation, will be driving the wife's car. Before I dive in does anybody have any bits of wisdom or advice? I do have a Chilton manual for reference. Also, are the felpro gaskets I picked up descent quality?

D&SYukonDenali · December 18, 2008

How many miles. Around 100k, I would guess the sensor (MAF) needs to be replaced. Might as well do the pre-cat O2's also.

dlstewart01 · December 18, 2008

You are on the right track. Iv'e had these codes twice. Both times my tube between the air filter and throttle body came loose at the throttle body. But most of the time on trucks with some miles it is the intake gasket.

have a good one,

Don

Sierra54 · December 19, 2008

I have about 193,000 miles on it. The air intake is snug. I disassembled it when I took out the MAF sensor for cleaning. Also while the intake tubing was off I cleaned the plate and what I could reach around the throttle body. Also tried removing the oil cap with the engine running as suggested in other posts, but didn't notice any changes.

Will replacing hte precat o2 be a PITA since they've had 9 years to rust in place? I don't have a torch or anything to heat them up with.

D&SYukonDenali · December 19, 2008

I had the exact same codes on a different vehicle for a while (2001 BMW 330xi with 140k miles). I parts chased it for months. Replaced everything from the air intake boot to the little seal on the oil dipstick tube. When it came down to it, it was the MAF sensor itself (held off doing that one til last since it was the most expensive part out of the list to replace).

The pre-cats O2 (on that car) were not too bad; they were in place for 7 years. I have a large torque wrench and borrowed a special tool from AZ to remove them. The hardest part was just getting the tool positioned to reach the damn thing. Given these truck should have more room, I would think it should be slightly easier.

Sierra54 · December 19, 2008

SES did not come on this morning. The temp outside was about 30 F a little warmer than usual. Is there a way to test the MAF to see if that's the culprit. I'd like to avoid replacing the gasket if possible but this the high miles it may be time anyway. Either way I'd like to resolve of this myself, if possible.

Thanks for the suggestions thus far.

Sierra54 · January 15, 2009

Finally had time to replace the intake manifold gasket and low & behold the service engine light came back on the next day. Fuel pressure is at 60 with the key on and 52 running. Is there anything else I can do to rule out the MAF sensor, pre-cat O2's or possibly the fuel pump even with these numbers? I'm not terribly upset replacing the gasket with high miles but I don't want to throw money at parts that don't need replaced. I also don't want to let this go for too long and burn up the catalytic converters.