Occasionally running very lean

[Beej '86 325es]

I've had a strange issue recently where the engine is running extremely lean. I can monitor this with the wideband O2. The engine is a high compression NA motor and nearly all components on the engine are new, fuel filter is new.

It usually occurs when the car is first started, but every once in a while it will occur while driving, but just for a period of about 5 minutes.

Sometimes just turning off the car for 10 seconds and restarting fixes the issue. I'm thinking it may be something with fuel delivery or the O2 sensor.

Any thoughts on things I can check this weekend?

Thanks!

[328ijunkie]

Fuel pump/O2 sensor.

[M-technik-3]

filter

[FredK]

I'm pretty sure Beej has all new pieces.

Are you getting a CEL? Your O2 sensor might be getting 12V backfed.

http://www.r3vlimited.com/board/showthread.php?t=192533

[M-technik-3]

This wonderful gas that has methanol is great at spewing crude into the filter.

[Beej '86 325es]

I'm pretty sure Beej has all new pieces.

Are you getting a CEL? Your O2 sensor might be getting 12V backfed.

http://www.r3vlimited.com/board/showthread.php?t=192533

Although I've only got 1000 miles on it, it's always run like shit when cold and smoothes out once it's been running for a while. I've been reading about this lately, I wonder if this applies to '86 cars...

My code reader only seems to work when it wants to, but last time I had it in the shop, Reggie said it wasn't spitting any codes.

[328ijunkie]

Engine coolant temp sensor?

[Beej '86 325es]

I'm pretty sure Beej has all new pieces.

Are you getting a CEL? Your O2 sensor might be getting 12V backfed.

http://www.r3vlimited.com/board/showthread.php?t=192533

The more I read on this issue, it seems like it's just a problem for guys with late E30's. I may check if I'm getting 12V at the O2 heater wire anyway.

[Jszy25]

What kind of AFR's are you seeing during cruising and WOT?

[Beej '86 325es]

What kind of AFR's are you seeing during cruising and WOT?

Cruising 16-17, WOT as high as 18 or so, Idle 18-20.
This is intermitent and only recently happening with 1000 miles on the motor.

[Jszy25]

Cruising 16-17, WOT as high as 18 or so, Idle 18-20.
This is intermitent and only recently happening with 1000 miles on the motor.

Yea, definitely super lean.

O2 sensor could be suspect. Know any locals you could borrow their sensor for testing?

Also, whats the condition of your FPR? Is that new also?

[Beej '86 325es]

I'm pretty sure Beej has all new pieces.

Are you getting a CEL? Your O2 sensor might be getting 12V backfed.

http://www.r3vlimited.com/board/showthread.php?t=192533

I tried this rewire experiment, but no change and the O2 heater wire isn't getting 12V either way of wiring it.

On a cold engine (70 degrees outside), I get 12V at the switched ground (green/gray), 12V at the power wires (red/white), but 0V at the O2 heater wire (green/blue).

Shouldn't the O2 heater wire get 12V at startup?

[Beej '86 325es]

OK - I checked fuel pressure after the fuel filter (which I relocated next to the under-car fuel pump.
I'm getting nearly 50 psi, which is right on-par or better.
Anyone know what fuel volume rate I should see after the FPR?

I also checked voltage at the injectors, and all are pulsing with the same readings.

I think I forgot to mention something else weird happening...
I took heat readings at all of the header primaries right after starting. Cylinders 1, 2, and 6 are running a little cooler than the rest. After the engine is running for a while it evens out, but may just be due to heat transfer.

[Beej '86 325es]

As a followup, I solved the problem. The MAF was bad. It's probably one of the first things I should have checked, but I didn't suspect it since it is only a few months old. I wonder what could have caused it to crap out so fast!?

It got so bad that I couldn't keep it running more than 5 seconds, but I unhooked the MAF and voila!

[FredK]

That's weird that it died so quickly. Are you running an oiled air filter? Was it a new Bosch MAF?