eaunatural

Can anyone please shed some light on where the ECU is pulling the Boost Pressure Sensor values from? It's more complex than just reading off the MAP sensor, right?

I have been trying to troubleshoot some fault codes and in the process, has prompted me do to some maintenance work as well.

P1136 Porsche fault code 440 - Pressure Sensor Boost Pressure
P0236 Unknown fault code - Google points to intake boost pressure related

Car through a CEL one day, felt like it went on semi-limp mode, not as responsive. I noticed right away that the boost gauge started showing 0.1 when at idle/coasting or when car is off/ignition on. Normally, it would display zero under these conditions.

Parts I've replaced/checks performed:

• MAP sensor
• Checked for boost leaks via lower IC hoses. Found 2 small leaks: F-hose to dv connection (fixed) and venturi tube (see below)
• Venturi tube
• #16 Check Valve (read this was a common fail item so replaced it since I was in the area of work)
• 710N diverters
• N75 valve
• Coilpacks/plugs
• Fuel filter
• Checked wastegate rods to see if they were snapped, pushed, they seem to move freely with very firm pressure
• Cleaned MAF
• Removed and cleaned throttle body
• Reset battery and throttle body adaptation
• Checked for boost leaks again via lower IC hose, held 20psi for over 30 seconds
• Durametric Readiness indicators all PASS
• CEL hasn't come back on but fault codes still there

After all this, car has seemed to have gotten it's juice back but with a very big however. The car still has it's hiccups. Car will run fine under normal conditions without WOT but after a few WOT runs, car will get a stutter and feel lethargic again. At this state, may also stall when coming to a stop.

So it was suggested that it may be a failing MAF so I went ahead and replaced with new part, reset the ECU and fault codes. Tested and drove about 70 miles over the weekend and nothing has really changed.

Values below when at idle or car off/ignition on:

Boost pressure sensor - 1148 hPa
Setpoint boost pressure - 1019 hPa

I believe these two values are supposed to be closer together after confirming with 2 other 996tt owners. Boost pressure sensor is higher than usual. I suspect the large disparity is why the boost gauge reads greater than 0 at idle or car off/ignition on.

One last thing - not sure if related to the above but I've seen another fault code previously but it has not come back since clearing the codes.

P0444 - Porsche fault code 98 - Tank vent valve

I've activated the EVAP purge valve on the Durametric and I hear the audible clicking which indicates that it is functional. *Edit* Just Replaced this part as well 6.17.17

Apologies for the lengthy post but would really appreciate anyone's insight on issue and next steps? Thank you in advance!

eaunatural

Has anyone experienced or have any knowledge on the causes when seeing 0.1 bar on boost gauge when car when car at idle or engine off/ignition on? So odd but it's throwing off the whole system...

I know the value is absolute and cannot possibly be boosting. Do you think this is a wiring issue that is causing the MAP sensor's value's to be out of wack?

Appreciate any insight on the possibilities!

T10Chris

P0444 can be caused by gas cap not being fully tightened, just as a heads up and should be unrelated to your other issues.

Does the boost gauge read 0.1 bar before you crank the engine, or does it read 0.0 until the engine is started and then goes to 0.1 at idle and after shut down?

eaunatural

Hi Chris - The boost gauge reads 0.1 the moment you turn the ignition on. It also stays at that value when at idle and when coasting. The car will still boost but after heavy foot the car will seem to go on failsafe mode and the boost gauge will read 0.0. I have verified on durametric that when this happens the boost pressure and setpoint values go static.


Would really like to know what other variables could cause the boost pressure sensor to read 0.1 in this scenario aside from a bad MAP sensor (replaced already). Too much intake manifold pressure or something else is off?


Thank you

Tanks95

OP...any resolution on this?

eaunatural

Yes, it was resolved shortly after my post. It was the MAP sensor and resolved after disconnecting battery for a few hours. My mistake was being impatient and replacing everything I can think of when I didn’t immediately see a change and not disconnecting the battery long enough. Lesson learned but at least my car got an over the top tune up as a result lol.

Are you experiencing similar issue?

Tanks95

yes i am. and no, i haven't started to make it rain on the problem yet, but i BELIEVE i have it narrowed down to the MAP, MAF or N75.

I am in the education phase right now. I am learning as much as i can about HOW the components work together (makes trouble shooting soooo much easier)

so to be clear, for me the new guy, it was the Manifold Absolute Pressure sender? Not the Mass Air Flow.... Just making sure it wasn't a typo MAP / MAF.

And you replaced the MAP or just did the ECM learning reset?

Interesting note about the battery (ECM Reset), i just learned after a long search session on the forums.

After being disconnected for a few hours, turn key to position 1 for at least 1 minute. (don't touch throttle)
Turn off for at least 15 seconds
Then start

Cal me crazy, but this is the fun part for me....learning all of these little quirks and nuances.

Thanks for the reply and your time.

eaunatural

Yes, I replaced the MAP and when it did not immediately fix the problem, I put the old MAP sensor back on and started exploring other solutions aka 'parts replacing' lol. I also replaced the MAF but it wasn't until I put the new MAP back on and did a long battery disconnect and drive that it cured the problem.

Call me crazy but I somehow thought the new MAP sensor was defective at first. I also didn't drive the car a lot during all the parts replacing. My theory is sometimes you have to give it time for the car/ecu to relearn everything when you replace parts. I hope this helps.

Curious, what symptoms are you experiencing? Is it exactly what I had experienced. Side note, I should have updated this thread 2 years ago w/ the solution!

Tanks95

Not the exact symptoms, but similar. Car runs phenomenal up to WOT application. Any attempt at WOT, it’s almost as if limp home mode starts, it will not go beyond .4-.5 bar, stumble, stumble, buck buck pop, pop.

Done boost leak down test, all good.
Removed Y pipe, did a good visual touch/pull inspection
Disconnected vac lines from actuators and feed them pressure, all good.

Somebody is not communicating well, I am thinking its maybe: electrical fault in the N75, MAP, or MAF

*don't know if this counts for anything, but i FEEL like i am getting close to solving it.

Dock

Was it doing this when you first got the car?

Tanks95

Hard to answer Dock. Because i didn't do any WOT pulls when i first got it. As you know, it had a torn CV boot that was slinging slop everywhere, therefore, i did more of a kitty kat shake down run to make sure it got to operating temp, changed gears smoothly, Oil Pressure stable, voltage, etc... no race car stuff.

Dock

At what RPM does the problem first start if at WOT?

Tanks95

want go past 5k..with heavy throttle application

starts to kick and jump around 4k.

if i very slowly apply throttle it will climb above 5k

Tanks95

...when boost kicks in is when things seems to get wonky. which is what leads me to believe its a communication issue as in either the ECM is not seeing the correct correlation between boost pressure and AFR or one of the key components is sending incorrect data.

Dock

So it appears to be RPM related and not boost level and/or throttle position related?

If you apply just enough throttle (no boost commanded) to allow the RPM to reach +5000 does the problem show up?

Do you have any roads with hills/inclines in you area?