Terrible bogging, no codes*

[truegearhead]

Originally Posted by The Radium King

i think the sensors involved besides o2 sensors and maf are throttle position (there are several - on the throttle, in the pedal) engine speed (rpm - tach) outside air temp and engine temp. not sure which ones stay in play when in limp mode. i have a bosch motronic manual i can email you if you pm me your email address.

Thanks again!

[truegearhead]

I spent the morning over at a Porsche Specialist and between two techs and a another Boxster to compare values to no one has any ideas. I could have bought a Boxster for what I've spent on resolving this problem. Frustrations starting to come through. For some reason the MAF reading and predictive table values are off from one another, but the MAF appears to be working correctly and showing correct values.

Symptoms
-bogs when hot, the hotter it gets the more it bogs
-runs great with the maf unplugged
-no codes (verified by Porsche shop)
-engine temp correct (verified by Porsche shop)
-maf reading and predicted table reading are off
-tps 82% at full throttle..odd


Parts replaced this week (all oem)
-maf
-O2 sensors (front)
-fuel filter
-air filter


Things I've checked
-fuel pressure 3.1 bar (correct)
-vacuum leaks sprayed everything down with carb cleaner.


Something is making the car adjust its MAF values away from the predictive values. But all systems seems to be working properly.

[The Radium King]

will affect maf readings:

the new maf is bad?
the new maf is wrong part number?
the new maf got fouled by oil from your filter (same as previous maf)?
vacuum leak (but would be more obvious at idle than wot, and you've already checked that)?

is intake system stock other than oiled filter?

[911monty]

Something that affects the MAF is air temp. Is your air temp probe mounted correctly or is it by chance up against the radiator?

[truegearhead]

Originally Posted by 911monty

Something that affects the MAF is air temp. Is your air temp probe mounted correctly or is it by chance up against the radiator?

Air temp probe? That's a new one, I did get an air temp sensor fault at one point but was told it was from pulling the maf. It's behind the radiator? I just cut the plastic out behind my radiators

Edit: can someone confirm the intake air temp is not a part of the MAF? My understanding was they were both integrated.

[911monty]

Originally Posted by truegearhead

Air temp probe? That's a new one, I did get an air temp sensor fault at one point but was told it was from pulling the maf. It's behind the radiator? I just got the plastic outbehknd my radiators

The air temp probe should be in a grommet in the driver side intake to the radiator. Since you have done so much in such a short time and may not have known it's possible it is now where it shouldn't be?

OOPS Passenger side intake.

[911monty]

Originally Posted by truegearhead

Air temp probe? That's a new one, I did get an air temp sensor fault at one point but was told it was from pulling the maf. It's behind the radiator? I just cut the plastic out behind my radiators

Edit: can someone confirm the intake air temp is not a part of the MAF? My understanding was they were both integrated.

Well I just checked in the Bently manual and it says "Hot film mass airflow sensor with intake air temperature sensor" Learn something new, I thought they were independent in the early cars.

[mikefocke]

Might want to read the last few paragraphs here. Explains a bit about how the MAF works.

[truegearhead]

Well despite the problems the car made it to the track! I ran the first day in open loop (MAF unplugged) and the second day in closed loop. The bogging is gone, I think it was poor stored values. An overnight battery reset did the trick. However the car is much slower in closed loop with the MAF connected, I ran it four sessions so I think it had enough time to establish expected values. I think the problem may be the throttle position sensor, its currently reading 82% at WOT. Does anyone know if it should be reading 100% on a non-e-gas car?