Engine running lean trouble code

**peperson** · 07-06-2009, 12:06 PM

The story - my fuel gauge suddenly started regestering only 7/8 after fill up. I wanted to see if it was the sending unit, or something was preventing it taking a full load, so using the trip odometer, I let it get as close to empty as I dared, and then fill up to see if it was taking close to the 16.8 gal it should. I cut it too close and it ran dry.

When I filled up, the gas gauge began working again as before (joy), but the service engine soon light came on (no joy). Filled all fluids, etc., (needed oil change anyway) and had them read the trouble code. They read the code first and said it indicated I was low on gas (not...had full tank). Light came back on shortly.

Went to another place and had them read the code and reset it again, and they said it indicated both banks were running lean and wanted to keep it overnight so they could check if it might be a leak in the intake manifold gasket, which would set the code right away, or if it was something else like an oxygen sensor problem, which would take a little longer to set the code again.

I have a feeling it's related to letting it run dry (talk about a lean mixture!).

Any advice on what I need to do next (don't really want the hassle of leaving my car overnight with someone...arranging rides etc.)?

**2001NBMZ28** · 07-06-2009, 12:24 PM

Welcome to the board. I'm guessing the codes were P0171 and P0174? If they keep coming back my opinion is it's something fuel related - not 02s, intake vacuum leak, etc. from trying to run it dry. First thing I'd do is replace the fuel filter (maybe picked up something in the bottom of the tank?). Might have hurt the pump - need a fuel pressure gauge to check though. If I'm correct on the codes look up the code diagnostics for your year at gearchatter.com Other codes can set too just from being close to running out of gas.

**peperson** · 07-06-2009, 01:40 PM

Thanks for the quick reply and info. Didn't get the codes, guess I'll get them read again. Might as well replace the filter and get the fuel pressure checked at the same time (got 150K on the clock, so probably good idea anyway). I haven't noticed any drop in performance, rough idle, or anything. Finding time is the hard part.

Haven't checked the price on code readers in a long time (when they were a little too pricey). Guess the 'tools' forum would be a good place to check for recommendations.

**SSTODD** · 07-07-2009, 07:49 AM

Buy some MAF spray cleaner and clean yours, and if it is not stock put the stock MAF back on the car as aftermarket ones cause lean issues.

**0rion** · 07-07-2009, 08:34 AM

I would also check fuel pressure. The pump uses the fuel to cool itself. Running it empty *could* have hurt the pump. I wouldn't tear the pump out without verifying fuel pressure to make sure you are low on pressure. The fuel filter could also be another suspect because when you ran it empty it may have sucked some crap up and partially clogged that filter. Just ideas.

**peperson** · 07-08-2009, 02:02 PM

Originally Posted by SSTODD

Buy some MAF spray cleaner and clean yours, and if it is not stock put the stock MAF back on the car as aftermarket ones cause lean issues.

It's stock. I'm bringing it to my mechanic Friday to let him check the fuel pressure, read the code's, etc.

I've reached the point a while back where it's stopped being fun trying to be a contortionist, busting my knuckles, etc., (not to mention trying to figure out these computerized systems). I'll take my old Norton out for a ride while he has the fun! Besides, someone has to pay for his kid's tuition!

Anyway, thanks all for the tips!

**Wesman** · 07-08-2009, 02:17 PM

Originally Posted by 0rion

I would also check fuel pressure. The pump uses the fuel to cool itself. Running it empty *could* have hurt the pump. I wouldn't tear the pump out without verifying fuel pressure to make sure you are low on pressure. The fuel filter could also be another suspect because when you ran it empty it may have sucked some crap up and partially clogged that filter. Just ideas.

Agreed. I don't think its coincidental that it started throwing lean codes on both banks only after running it out of gas. As mentioned, the fuel pump may have overheated and could be on its way out.

I'd replace the filter and definitely check the fuel pressure. Try turning the key to "On" and listening to the fuel pump - if it sounds like a dying animal, its probably gone south.

**peperson** · 07-09-2009, 11:18 AM

Originally Posted by Wesman

Agreed. I don't think its coincidental that it started throwing lean codes on both banks only after running it out of gas. As mentioned, the fuel pump may have overheated and could be on its way out.

I'd replace the filter and definitely check the fuel pressure. Try turning the key to "On" and listening to the fuel pump - if it sounds like a dying animal, its probably gone south.

I didn't hear any difference in fuel pump, and haven't noticed any performance change. No noticable change in gas MPG, although I heard the computer makes it run a richer mixture with those codes active.

But with 150K on the car, it may be time to replace the pump anyway. If I do, is there a better alternative than a stock GM replacement? The car is my commuter (my money pit is a '72 Vette), so I haven't done any mods that require anything special.

BTW, what would be a reasonable charge to R&R the fuel pump these days?

**0rion** · 07-09-2009, 11:26 AM

you can just swap out the pump out of the module using a racetronix pump and come in much cheaper than replacing the OEM module. I see $800-$1100 quotes for people getting the OEM changed.

**peperson** · 07-09-2009, 04:35 PM

Originally Posted by 0rion

you can just swap out the pump out of the module using a racetronix pump and come in much cheaper than replacing the OEM module. I see $800-$1100 quotes for people getting the OEM changed.

$800=$1100 -- YIKES!!

Do I need to do the wiring harness too because of more mower needed for the racetronix (as shown at http://www.racetronix.com/RX-F99-FPKG-2.html)? Or just the pump, like in the "howto" at http://www.j-body.org/forums/read.ph...37618&t=434889

**peperson** · 07-10-2009, 05:04 PM

Turned out to be a leak around the intake manifold. Could be gasket/seal, or warped manifold. Haven't pulled it yet to see. They had the seals, but not the manifold (if it needed replacement). Put it off for a week for a more convenient time. Seems unlikely, but must have been a coincidence that it happened after running out of gas. Strange.

**SteveC** · 07-11-2009, 11:18 AM

Originally Posted by SSTODD

Buy some MAF spray cleaner and clean yours, and if it is not stock put the stock MAF back on the car as aftermarket ones cause lean issues.

The only problem I see with this, is that if indeed the MAF, or the ends (no screen) WERE changed, and were dyno tuned for the new setup, installing any of the stock components back on would cause an extreemly rich condition.

I had my MAF ends replaced with ported de-screened ends, and when first put on the dyno tune my A/F ratio was 15.8:1. The dyno tuner set the A/F ratio to 13.5:1 to accept the new ends. If I went back to the stock MAF ends I assume I would be running pig rich.

SteveC