No the knock sensor is not going to do this. Adam is not running the stock CV, so the KLR is not controlling boost. At worst, a bad knock sensor could signal the KLR to pull 6° ignition timing.

 

OK...SO THERE'S THAT.

 

Hi Adam,

I have had this EXACT same problem for a few years now - really hope you find a fix !

Unless I have missed it, no one has suggested spark plugs - high boost may cause sparks to fail if plug gap is too wide or plugs old/dirty. Also Coil?

Mind you - didn't help me!

I have replaced coil, plug leads, plugs, dizzy cap, rotor arm, DME, KLR, engine earth. Always the same - 16psi is ok, 18psi - violent cut out under full load most of the time. Can push through it by keeping throttle down and letting car buck, or if back off throttle engine will come back instantly - ignition does not need resetting like the normal "limp mode" control.

The cut out is so sudden it must be an instantanoeus event, therefore generated by one of the computers, or a sudden loss of ignition? I even tried disconnecting the vac line from the KLR so it can't measure the boost but it made no difference. Surely this means it can't be the DME deciding that boost is rising too fast and triggering any protection?

One thing we have in common is the Seimen's 55's.....but you say this is a new problem whereas I had it as soon as I had all the mods I needed to go to 18psi.

Keep the ideas coming guys !!!

 

I've tried to tell some of you before. It won't be the engine ground. It will be the hot lead from the battery to the starter.

 

ehall,
i replaced the hot lead from the battery to the starter ,
but makes no difference

 

This man talks great sense! You can spend months replacing parts trying to discover a boost leak and be sure you've covered everything, then pressurise the system and find it it 5mins flat (ask me how I know!).

I didn't know that's how the overboost was triggered, but its definitely the overboost you're hitting. I know that feeling well, you'd also be amazed how many well cared for, seemingly fine 944t's have boost leaks so that would definitely be the first place I'd start before wasting time doing anything else.

p.s. if its an earth fault I'm pretty sure the rev counter and dash gauges bounce around like crazy when it cuts out/in. So you'd see it.

 

I checked for Boost Leaks with a pressure tester , but no leaks
( besides small leak at the throttle body shaft )

 

Blimey Ben, haven't seen you for so long and now I'm bumping in to you everywhere!

I've checked for boost leaks, plus mine doesn't have an AFM anymore - it's a MAP conversion so measures pressure straight from the inlet manifold and gives a voltage signal direct to the DME.

Could still be that the DME thinks that boost is rising too fast though. edit - actually it probably doesn't as I think that I have tried to sneak up to 18psi by accelerating gradually. Adam, have you tried that?

Regards

Graham

 

Hello. Love your wheels! Did you have those when I last saw you?

Just a quick check on this boost issue. Can you get it to accelerate to full force if you trick it by easing on and off the accelerator in short gentle cycles? The boost cut in my example was being triggered by sensing too much boost for 2secs or more so if I eased on and off the throttle in waves I could get it to accelerate very hard for a second and then ease off before the cut came in. Leaving your foot down for too long or going off and back on boost again too quickly without giving it time to re-set was met with a violent loss of acceleration.

 

I don't know - I had them at the last dyno day but I don't know if you were there - I think that was the one when WUF and MarkK both passed 400.

Not tried the on/off thing - when I get the car back together I'll give it a go, but that won't be for a few weeks now. Which car did you have this problem on, and did you fix it??

 

Mine was a 'Ben' related issue. I fitted a Lindsey boost enhancer the wrong way round in my first turbo my first experience of turbos and no idea what boost I was running but it was lighting up the back wheels at 110mph and that was the first and last time I've ever hit the rev limiter in 5th in a 944! (I was a lot crazier at 18years old) I don't dare do it in WUF even though I know logically she must be able to.

 

Hi Rogue, you seem pretty confident about this and I know from previous threads that you know your stuff - if it's a limitation of the chips, is it something the vendor can eliminate by raising the limit/allowable rate of change in the chips?

Bearing in mind that it can't be anything to do with the CV, KLR pressure or boost leaks with my MAP system - can it?

 

What chips are you running?

The KLR/CV isn't the problem.
With your MAP system, you shouldn't have to worry about boost leaks mis-representing airflow.
And yes, your chip vendor should be able to raise the overboost limit map on the chip.

 

I am running stock chips ( PCA SP3 class Race car , it has to be stock )
If i go above 10.5 ponds it starts acting up.
After you stay of boost for half a lap it works fine again for the other half a lap without shutting the engine of .
The CV is by passed and using a Boost controller to limit it to 11.8 pounds

 

What year is the car/DME? The 86-87 DME (24pin) have a lower boost limit than the 88-89 DME (28pin).
The overboost limit for the 24pin DME is right around 12psi (depends on RPM), but it sounds like your hitting the overboost limit.