Engine cut out / ECU torque limit ?

[jml911]

Hi chaps

We have an ongoing issue with our Boxster race car.

We've done a lot of mods and it's significantly more powerful (I'll go into the modifications at some point when we've ironed out all the issues).
But for now the ECU has been remapped

Basically the engine cuts out when you come out of a corner and out of pitlane if pushing hard.

I'll try to explain how this happens.

You'll go into a corner as normal. Hit the apex and as soon as you're heading to the exit point and getting on the gas (not even flat) RPM is probably 3500- 4000 + the engine suddenly will go into limp mode (effectively it cuts out. 1000rpm and it won't actually move and will stall). Switch off the ignition and re start it and it will reset. Once over 4500-5000 rpm there's no issue. You can head off the straight at
full revs, foot flat to 7000rpm no problem

It's very much like driving a turbo and blowing off a pipe. You have power and then there's nothing as you come on boost.

Basically accelerate hard from low revs in 3rd gear (it doesn't happen in first or second as far as I can remember nor 4th)

If I ride the clutch a little coming out of the corner then there's no cut out but I'm also not going flat out. I don't think I'm even really engaging the clutch - ie it's not slipping.

To me this seems like I'm hitting an electronic torque limit.
Has anyone heard of something like this before ?

[Qmulus]

The diagnostics built into the ECU/DME is the place to start. If you have a driveability issue that severe it will have faults in the ECU. It is also helpful to know what year/engine/injection system you have.

[jml911]

Originally Posted by Qmulus

The diagnostics built into the ECU/DME is the place to start. If you have a driveability issue that severe it will have faults in the ECU. It is also helpful to know what year/engine/injection system you have.

Well it's a 2000 but we've changed a lot
it's not a 3.2 anymore put it that way - bigger injectors - the lot

We can't read any faults at the track. Our machine for some reason isn't picking up the fault. It's a "soft fault" for sure as it's reset by turning the ignition on and off.

[BYprodriver]

Fuel pressure?,pump?, level?

[jml911]

Originally Posted by BYprodriver

Fuel pressure?,pump?, level?

That's a good suggestion
We've upgraded the pump - but perhaps there's something else going on.

We've tried running with a fuel tank and it didn't make any difference.

[BYprodriver]

Originally Posted by BYprodriver

Fuel pressure?,pump?, level?

I forgot to add my 2000 S has 116,000 miles all original (fuel injecters & pump,DME) engine, except for 99mm sleeves & pistons. The 3.6L easily break tires loose thruout 1st gear with no torque limiting. Traction control was optional & PSM stability control became available in 2001 for USA.

[jml911]

We're pulling about 200 pound-feet of torque at 3,000 RPM rising to 310 at 6,500 at RPM. That is a lot more than a standard 3.2 early 986 which I think peaked at 226 lbs/ft

I don't know if there's such a thing as an electronic torque limit but as mentioned earlier we need to hook it up and see what error codes are produces.

Oddly - this never happened on the dyno and it was run multiple times over 3 days.

Waiting on our tuning guru to become available to look at it. In the meantime we also need to find the cause of the ABS failure.

Not having a great time of it at the moment !

[jsceash]

I don't know what happened to my car at the track last year. But it has some similar issues. My configuration is a 3.6 and 5spd with a remap, 987 air intake, and sport exhaust. While running out 4th gear 5000 to 6000 When coming out of one turn to another (Esses). it would go to limp mode. I could quickly switch the key off then on and it would come back full power???? Suggestions were to replace the fuel pump and the filter, which didn't help but cost me about $500. I could run 2nd or 3rd gear to 7000 no issue. I could not reproduce the problem off track. I was at the same track 2 time earlier in the year with no problem the only change between was I had changed the front motor mount to a Wevo Semi solid. I went back to the 987 front mount and the last 2 track weekends I had no problem at all.

It was amost like the motor vibration + the G's reversing in the turns shut it off. Just like your problem there was no code saved or current able to be read by Durametrics or my Dyno Scan software.

[jimk04]

knock sensors?

Think they can be coded out..or just undo them from the block and fasten out the way!

Would explain the 'soft' fault, as they are just doing their job, albeit rather more drastically than a normal timing pull.

[jb92563]

High G's and transitions make me think of loose wiring connections/shorting as the computer is going into limp mode.

It also makes me think of the crazyness I had going on with my MAF. It was intermittent in nature.

I took the MAF cleaner to it and the wire harness/plug connectors and that fixed it up.

I also pulled the filter and inside the filtered side of airbox in the drain I found bits of loose paper that looked like a parts number label, maybe from the filter element?

Since I cleaned all that out all the codes went away and it runs like a champ.

Since the computer is only responding to inputs that don't register as sensor faults, yet drastic enough for limp mode, but intermittent with the G's, I would also suspect the connections/shorting somewhere.

[jml911]

It can happen coming out of the pits though.

Hopefully I'll have the car on the diagnostics tomorrow and it will show some errors after the engine cuts out.

[thstone]

Here are a few of my thoughts;

Engine sensor - knock sensor, cam position sensor, crank position sensor, etc.

Blocked intake - I had similar symptoms ultimately found to be debris in intake. Take it apart and check everything!

ECU - check the re-map.

Variocam - make sure that the variocam system is operating properly

[jml911]

Here's the code
It's a P1508 Function Monitoring Torque Comparison

From what I can see online the most likely issue is that I'm hitting the torque limit - so hopefully it's just a matter of raising this limit in the map.

The lesson here is always get the codes but it's actually exactly what I thought it would be. Waiting to hear from our tuner to when he can look at the car next.
It is a possibility that it could be a MAFF issue. But we've replaced that and with have a new CDA airbox on the car - so it's unlikely. I'll update you when I know more

[jml911]

Just to close this off. The measure mass flow wasn't able to compute the throttle angle and throttle position. It was happy enough at full throttle because it was close enough to what it was expecting but at half throttle it didn't like it.

So it's been re flashed and calibrated and it's superb now. Smooth power throughout the range and no cutting out.