951 Running Lean Under Boost- HELP

[tchudy]

I've been fighting a lean fuel issue this year and I am looking for some advice. I have a 1986 944T. Lindsey dual port wastegate, MBC, 3BAR FPR, Stock DME, Stock injectors, Wideband Air/Fuel Meter (2 years old). Fuel pump is original. Engine was completely rebuilt about 3,500 miles ago. All vacuum lines new. Everything on the engine is new or rebuilt.

Last winter I replaced the fuel rail with a used stock one and put new seals and screens in my injectors (injectors had been cleaned and flow tested after the engine rebuild). I cleaned inside the fuel rail as well as I could. I have a fuel pressure gauge under the hood that confirms that I have the correct pressure in the rail at idle and while reving the engine. I tried swapping out the DME but no change. The only other thing I did last winter was to add a Lindsey catch can off of the AOS.

At idle my A/F ratio is between 13.5 & 15. During normal acceleration (no WOT or boost) my A/F ration is about the same as idle. When I go to WOT and at about 3,000RPM boost starts kicking in. A few seconds after boost my A/F ratio drops to the bottom of the gauge, lean at 11 or below. If I let up and come off of boost the ratio is again, same as idle. At boost when the A/F drops there is no loss of power. I tried lowering the boost but no change. Spark plugs all look good. I did a compression and leak down test...all good.

I ordered a new fuel pump to rule out low flow. Not sure what else I should be looking at. I am assuming that my wideband O2 meter is not faulty since it is so new. Any help would be appreciated.

[Derek C.]

Replace the fuel filter while you're in there, and it's cheap and easy to re-clean and seal the injectors. Maybe check/clean the airflow meter?

[tchudy]

I bench tested the airflow meter and it is good. I'll change the fuel filter also.

[tchudy]

Thought I should mention that the turbo is a K26/8

[rick13]

Shouldn't you have "chipped" the DME with a better tune? What kind of boost are you running? Bad gauge...?

[soxnail]

To be clear, the gauge shows lean after the boost kicks in and not right at WOT ?
If so is there a number (PSI) at which it happens and is it repeatable ?
Sox

[tchudy]

Soxnail, you are correct...the gauge shows lean after boost kicks in, not at WOT. It goes lean a few seconds after boost kicks in, no matter the boost setting. It does this every time. I did try a "Euurochip" (came with the car) but no difference. I didn't have this issue last year so that is why I am stumped. I'm going to invest in a stand alone system later this year.

[kdjones2000]

FYI, "11" is a RICH condition, as it should be while on boost.

You want to be running 11-12's while on boost to ensure that you are not at risk for pre-detonation.

What you describe sounds like how it's supposed to work.

If you didn't chip your DME/KLR and are running stock injectors with a K26/8, 3bar FPR and a MBC, then you are going to be off optimal AFR at some point(s) in your RPM range.

It sounds like a blown headgasket waiting to happen....

[soxnail]

Keith is correct. I totally missed it 11 is rich and right for boost.
See mine pasted below.
Sox

[tchudy]

Guess I need to educate myself on AFR and my boost gauge. According to the instruction sheet the low end is lean. I still have much to learn. Thanks for all of the info.