WingChun

I'm starting to think the MAF is causing an issue in my Turbo but to be honest I'm not sure and would welcome advise from anyone familiar with the symptoms.

Car is stock and it will boost fine and quickly upto 0.8bar from low rpm just over 3000 and this will hold until somewhere between 4600 and 5000.
From there it starts to drop to 0.7 and before it reaches around 6000 its at 0.6bar. Car feels like its holding back.

I know the turbos are fine because when I ran it with the MAF disconnected it boosted full and felt REALLY strong all the way.

Ok running without the MAF is not the smartest thing to do, especially since my son sitting beside my informed me that the analogue boost gauge was approaching 1.4bar, at which point I stopped.

So is this normal behaviour, the drop in boost, or should I be forking out for a new MAF?
Any other checks I can do?

DiegoR

What's the milleage or KMS in your 993tt?

I kinda have the same problem, I said, kinda, because my OEM boost gauge reads 0.8 BAR above 4500 RPM at WOT always, however soemtimes the car accelerate strong and you feel the "kick" putting down the desired torque that a turbochargd engine usually develop but sometimes int e same gears that use to feel this kick (2/3 gears) it doesn't punch you against the seat or just doesn't feel the explosive/torque to the red ine going WOT and just feels that pull like a naturally aspirated engine with out any hesitation though....

My car has 30k mile or 49xxx kms on the clock, toally stock, no 02 sesnors/CATS from factory recently serviced and I even cleanded carefully the MAF with a spray MAF cleaner can but this problem still persist.

Sometimes cleaning the MAF's solve some issue, mainly power loss, but most of the times the MAF's get worn internally and just need to be replaced with a new one and you can really feel a new behavior of the engine power. I just don't know if replace mine and will fix this small issue.

OverBoosted28

I don't see how your car would run anything close to normal once the MAF is disconnected. The DME needs that input to tell the other systems what to do (air/fuel ratios etc...). If you think the MAF is actually your problem, buy a proper cleaner and clean it. These sensors don't regularly fail. The oil type reusable filters have been shown to foul the film element. If this is not the case and you are not to far into mileage on the MAF, I would look elsewhere for your lack of boost. These cars are quickly approaching 2 decades of existence. ALL of the rubber items (hoses) should be replaced. Even stock motors impose a lot of pressure on these systems. Under hood temps just add to their degradation. Good luck

WingChun

Guys, thanks for your comments.

The car has covered 112,000 miles now but the engine itself seems fine, turbos were rebuilt only 4000 miles ago and wastegate actuators operate ok.

I reckon the Motronic program is pulling the boost for some reason and this is why I suspected the MAF.
The stock air filter is installed and I did clean the MAF recently with electrical contact cleaner but this made no difference really.

WingChun

RESULT!

I removed the MAF from the car again and pulled the sensor completely out from the body, soaked it in contact cleaner and thoroughly cleaned all the parts with a small brush.

I also noticed, whilst using the Durametric earlier, that the IAT sensor was reading 6 degrees C too high, which would not help matters in warm ambient conditions as the ECU may retard ignition timing too early.
Since this is merely a thermistor, I soldered in a 500 ohm resistor in series (after first establishing the correct value with a variable resistor) to bring the temp reading down to an accurate level.

Net result is engine now pulls strong and clean at 0.8 bar most of the way, with a slight dip to 0.7 and then rises to 0.8 again to the redline. No hestitation.
On/off throttle response is also now much smoother.

The bottom line is that just spraying the MAF with cleaner was not good enough in my case.

Hope this is help to others who maybe suffering hestitation, low boost etc, although there can be other causes of course.

dombeau

Thanks for sharing. At one point if everyone explain how they fixed it or we get input from other Rlisters we might end up with a super DIY library! Let us know after long term driving!

Felix

Curious how you concluded it was off by 6 degrees?

I think boost/timing is pulled after 50 deg C IAT.

WingChun

The car was in the garage with a stone cold engine and it was reading 26 degrees on the Durametric, which I knew had to be way out.

I removed the IAT sensor from the IC and compared it to three other reference points:
Cylinder head sensor - 20
Car outside air sensor (dash) - 20.5
Normal thermometer - 20

I didn't realise that 50 deg was the threshold for ECU interaction but based on that my engine could have started loosing power at maybe 44 deg.

DiegoR

WingChun, goo d to hear you found the problem. I will check mine as I have as well the Durametric tool. So basically what chnaged the behavior of your engine is the mod you did to the IAT sensor because just cleaning the MAF wouldn't do any better for your past issue right?

DM993tt

Interested in this IAT sensor mod. That sounds like some advanced tech, or some good MacGuyvering.

/I have a new in box Bosch MAF for sale if anyone is interested. $350.

DiegoR

I might be interested on it. Just to be clear, that "Bosch MAF" is just bosch brand or is a genuine Porsche/Bosch MAF?

WingChun

I think the thorough MAF clean did the trick to be honest, the IAT was just something I noticed that was reading too high, so I decided to see if I could improve its accuracy.

Like I said before, the difference is night and day.
Ok the car is only stock but to feel and hear that lovely flat 6 pull strong and clean through the revs with no hiccups.....man that is sweet!

All I need now is more power.

DM993tt

is there a difference? THe porsche maf is a bosch part # unless I am missing something (which is entirely possible).

WingChun

I'm not going to recommend that anyone do this, better just to buy a new one if it is inaccurate.

What would concern me is folks trying this, not making a good solder joint with the risk of the resistor coming loose/falling off and getting dragged into the motor.....not good.