Random lean conditions

[macipusy]

So the past 3 mornings, after 10 minutes of run time, my AFRs increased all of a sudden. They went from normal up to over 17:1 at idle and cruise.....I didn't try anything in boost for safety reasons.

After shutting the car off and then on a few times, the AFRs returned to normal for the rest of the day, until almost exactly 10 minutes after startup the next day, for the last 3 days straight. Turn the car off and on a few times, and it goes away everytime, sometimes sooner then later.

I hooked up a fuel pressure gauge last night and this morning when I was expecting to lean out, it happened. The fuel pressure did not change...32psi at idle and slightly higher at cruise. This rules out the fuel pump and FPR....I would think.

My next thought would be to replace the MAF....anybody got an extra good one for sale?

Also, could it be an injector problem? Any way to test this without removing injectors?

I still need to hook up the lap top to the PP6 and see if there is a deflection problem while the lean condition is happening.

I am running a PP6 with 550cc injectors and a walbro 255lph pump on E85.

Any suggestions are appreciated.

[gijonas]

I thought you already had a thread going about this??

[macipusy]

I had a thread about hunting AFRs...got that fixed with a narrow band O2 replacement. Everything was good for a couple of weeks.

This is a separate problem....AFRs will lean out across the board and stay there...no hunting.
I am guessing it might be a MAF problem now, maybe sending a wrong voltage during some stage of its warmup...I don't know.


Always seems like its 2 steps forward and one step back with this car. I guess its all part of owning a 20 year old car with 250K miles

[gijonas]

Well i did have a similar problem and it did turn out to be a bad MAF.If that helps.

Are you on a stock MAF or JECS?

[macipusy]

Stock MAF.

I guess I'll try to see if anyone has one for sale.

This is the third lean out problem I have had that is totally isolated form the others....I'm glad I got my wideband when I did.

[Legacy777]

Does the problem ever go away without shutting the car off?

If the problem happens about the same time after cold startup every time, I'd say it's possibly a warm up enrichment table that's out of whack. When you replaced your O2 sensor, did you reset the ECU? If not, I'd suggest doing that.

[gijonas]

^^^ good call, hes always on top of things...

[macipusy]

Good point....I cannot remember resetting the ECU, so I will do that today.

As far as going away on its own, I am too paranoid to drive it around long enough at 17-18:1 AFR to find out.

[macipusy]

I reset the battery, and it still happened this morning. It would not go away by itself, only when I shut off the car for 10 minutes.

I also floored it a couple of times, and the AFRs seem to only freak out in idle and cruise. At WOT all is good.

[Legacy777]

Do you have access to a laptop to run Vikash's scan tool? I'd be curious to see what the ECU parameters are showing during this lean condition.