HELP: Car runs lean at WOT

sb_600 · 09-06-2011, 12:09 PM

Hey guys,

So at CMP yesterday my car was running lean at WOT.

Barrie came up and we added more fuel in the map and it was fine for around 20min, and then it would start to lean out again. we disconnected the battery, and then the same symptoms - fine for a while and then it would go lean.

Anyone seen this before? My innovate LC-1 AFR gauge would go back to calibration mode (would just flash like i had turned it on the first time) several times on track once it would start going lean again - but never when it was running fine.

I'm thinking it something electrical, but any help would be appreciated.

e30_kid89 · 09-06-2011, 08:56 PM

Are you sure the wideband is functioning/reading properly? id check into that first.

sb_600 · 09-07-2011, 02:05 PM

I'll look into it for sure, but i think it is ok - when I pulled the plugs, they were white... I'm thinking it may be a fuel pump issue as well

hawgripper · 09-09-2011, 06:46 AM

You could have low fuel pump pressure when the pumps cycles for a while and gets hot. Hook a gauge up and run it til she starts to lean and verify the pressures.

AlphasquadM3 · 09-09-2011, 09:03 AM

have you hooked up a fuel pressure gauge to the fuel lines to check fuel pressure?

sb_600 · 09-09-2011, 09:03 AM

Thx I'll check that too! I won't have time for the next week or so as i'm out of town on business.... i'll try and get to it next weekend.

AlphasquadM3 · 09-09-2011, 09:06 AM

i'm pretty sure there is a schrader valve along your fuel rail, by reading your actual fuel pressure from the fuel rail, that will point you towards the right direction for your problem. hopefully that would help.

BigD · 09-09-2011, 09:52 AM

When you say it ran lean, did it actually misfire or at least lose power? If not, I'm with Devon and would check the gauge, it's probably full of it (especially if it went off the scale, your engine would die at WOT long before you'd exceed a wideband's range).

sb_600 · 09-12-2011, 02:07 PM

no misfires, but a couple times the car would stutter (this wasn't at WOT - when getting back on the power after braking). I've been super busy lately, and haven't had a chance to diagnose this yet. I appreciate all the suggestions, and if you think of anything else it could be, let me know!

Next weekend i'll be able to get back to it - i'll keep you posted.

Thanks again,

sb_600 · 09-12-2011, 02:15 PM

What makes me think it isn't the gauge is that when i pulled the plugs, they were white. The car was running fine until I changed the headgasket. It's not a tuning issue because we retuned it and it ran in the 11.5-12.5 range during WOT, but then slowly started to lean out again. I reset the ECU and the same issue - would run well, but then would lean out again after about 15-20min on track.