How to fix the lean condition CEL codes on a supercharged VX?

[VehiGAZ]

I generally run 93 octane - only occasionally do I get stuck with 91 - but it's always "high test" since I supercharged...

The new MAF went in last night and it sort of seems to run a little smoother and stronger. I'll see if I pop any CELs in the next couple of weeks before monkeying with the fuel system (other than changing the filter).

[Hotsauce]

Our stock fuel pressure reg is adjustable.

Its just not a factory approved adjustment.

In the top of the FPR is a tamper resistant torx screw that adjusts fuel pressure. Its factory set, and secured with loctite.

Clockwise increases pressure.

John C.

[VehiGAZ]

Thanks hotsauce! That's a pretty valuable piece of info!!!

No CELs since the new MAF went in on Wednesday, and I think my mileage has improved, too. We'll see what tale time tells...

[AlaskaVX]

I'm having the same problems I think... also some smell of fuel on startup. Let me know if that fixed it!

[VehiGAZ]

Alaska,

Yes, I was also getting a noticeable gas smell in the exhaust on cold startups. It lasted for a minute or so until the ECU switched over to "warm" operation mode. I thought it particularly odd that I would be getting lean codes when the smell of gas suggested it was running rich! Anyway, it is not gone since I replaced the MAF.Anyway, I'm not saying I'm cured just yet, but I haven't gotten any more CELs since replacing the MAF last Wednesday, and I also think the engine is running a little smoother and stronger since. And although I haven't finished a full tank yet, I think my mileage has improved as well.

So here are my lessons learned...

1) K&N filter oil can gunk up your MAF elements and throw off its operation.

2) Be careful if you buy a rebuilt MAF and make sure you can return or exchange it if it doesn't work well.

As my mechanic explained to me, they will rebuild the MAF, test it, and if it is anywhere within spec range, they will sell it. That may be fine for stock engines, but my supercharged engine may not be happy with a MAF that operates at one end of the spec range or the other.

Btw, if anyone is reading this and wondering what the heck an MAF is and what it does, here's a quick explanation... the Mass Air Flow (MAF) sensor is located on the air intake piping and tells the engine control unit (ECU, the engine computer) how much air is being sucked into the engine. The ECU uses this measurement to decide how much fuel to spray into the intake in order to have the right fuel-to-air ratio for the given operation of the vehicle (e.g., idling vs. wide-open throttle acceleration).

If the MAF is under-estimating the amount of air going into the engine, then it will mix in too little gas, resulting in lean codes P0171 and P0174 (as has been my case). Conversely, if the MAF is over-estimating the amount of air, then it will mix in too much gas, resulting in rich operation. Neither one of these is good for your engine and may pop check-engine lights.

Good luck Alaska!

[VehiGAZ]

Two weeks and no CELs!!! Whoo-hooo!!!! No more stuttering throttle, the smell of gas on startup is gone from my exhaust, and my mileage has improved about 1-2 mpg (although that last one might be because of the warmer weather). I'm considering myself in remission for the time being - if this keeps up for another 2-3 months, I'll call my CEL problem fully cured.

In the meantime, I ordered a Scan Gage II from Amazon which just came in. I'm going to use it to display instantaneous mileage, which will hopefully cure the S/C-induced spasms in my right foot. ;Dr;

Thanks for the winning tip, Ldub!

[Jolly Roger VX'er]

Our stock fuel pressure reg is adjustable.

Its just not a factory approved adjustment.

In the top of the FPR is a tamper resistant torx screw that adjusts fuel pressure. Its factory set, and secured with loctite.

Clockwise increases pressure.

John C.

I did this too when I replaced my FPR....the tamper-proof torx bits were available at Advance Auto when I bought them...I bumped mine up a little (rich=clockwise). Been running great!

Just bear in mind that cat's don't like overly rich conditions!

[USMCvxOFFROAD]

Any one have a problem with their vx running way to rich with out miss fires? because i do and have no idea whats going on, and it was fine till i had her smoged here in cali and a new exhaust put on. idles at about 1000 rpm too. oh and buy the way anyone have an extra electric radiator fan laying around for a 99

[FelixFisher]

I did this too when I replaced my FPR....the tamper-proof torx bits were available at Advance Auto when I bought them...I bumped mine up a little (rich=clockwise). Been running great!

Just bear in mind that cat's don't like overly rich lingeries conditions!

Pretty nice thought yes cat's dont link overly rich conditions