Autothority MAF - lean run condition
 

My recently acquired '87 911 enjoys the services of one of these MAFs/K&N. Nice touch, I assumed during my pre-purchase inspection.

With title now in hand, I receive the news from greedy Porsche dealer that the poor thing is running brutally lean due to that "after-market MAF" and that I should cough up some serious coins for a genuine factory air-box and acutrements.

Nonsense, I think... it runs well with lots of power - but then it does kinda surge under load at lower RPM - pain in the butt around town.

Are these things tweak/calibrate-able and/or should I find a tuner-shop that can find their way around a MAF or customize a chip for my engine?

Advice would be appreciated.

Thanks

Ken

Your first step might be to get an adjustable fuel pressure regulator and increase the pressure a few pounds. Also check and make sure you have the correct chip for this unit. You can call autothority of confirm this. Look for any post by SteveW if you need a custom chip also since he does his own programming.

Seems to me you're getting yanked. No way should you spend real $$$ to replace an Autothority MAF for a stock set-up. Not sure about the surging though. Sounds like an unrelated problem. What kind of exhaust do you run?

"yanked" wouldn't be unheard of... but in this case I think that they really don't know from non-factory parts and this MAF is alien, hence it must be the root of all evil.

I'm running stock exhaust - am going to have to check on whether or not it has a chip installed. It's my understanding that the MAF comes with a chip...

Depends on where your lean running condition occurs. A MAF will not cause your car to run lean, and depending on how the chip is programmed, is capable of the contrary. Has the exhaust been replaced with something drastic like SSIs or headers? If so, then you will need a correspondly mapped chip, in which case I may be able to provide you. With the Autothority system, if your lean running condition only occurs at low/mid load/rpm, then it sounds like you need to adjust the tiny idle air/fuel trim pot enclosed in the adapter harness between the MAF and the stock harness plug. I believe it is a 15 turn, 10k trim pot, and clockwise will make it richer. Also, make sure you don't have any air leaks around your intake system, which will cause your car to run lean at idle and low loads.

Yes, the MAF comes with a chip and from what I understand, the car won't run for beans without it. I suppose it's possible that your chip is programmed for a different setup than your car has. Maybe the PO had a nice set of SSI's and a sport muffler that he pulled off before selling the car. Might be worth giving him a call to check.

If so, Autothority can reprogram your chip for your setup, or you can get a custom chip from Steve Wong for half the price. Not saying the chip is at fault (I'd be surprised if it was), but if it is, the fix is easy.

FYI...turning the tiny potentiometer on the MAF wire harness clockwise, leans the mixture. I had to lean mine substantially to smooth out the idle (especially when cold). Factory setting is 2.2k ohms...way too rich for my car. Now running at about 5.8k ohm and idle is smooth as silk. Worth a try as Steve suggests.

Thanks for the tips, gentlemen. I'll investigate further as soon as I can tear my beauty away from the dealer and get a call into the PO.

Now... is that clockwise for lean or rich?

Thanks again,

Ken