Overboost Protection?

[Hairyarse]

Just following on from a statement I made recently on 'what did you do today' (On the 'other' forum []) I have a reoccurring issue with my Turbo.

Went for a spin after, had the 'overboost' type problem rear it's head again, the second time it did it (whilst overtaking a lorry - scary!) shortly after I had to stop for a car in front turning right. As soon as I stopped the car stalled. Very weird! Will take a look tomorrow to see what's up, if I can find it

I had this happen again yesterday. I was full throttle, near to rev limit and the 'overboost' type problem happened again (i.e. the revs cut right back like someone has turned off the power.) I backed off, then back on the throttle and all was ok. However, like the scenario above, within a short time - half a mile or so - I had to stop at a junction and the car stalled when I came to a stop. It restarted and was then fine again.

The layman in me was thinking it could be the TPS. However, I've done the checks listed on Clarkes Garage already for the DME, KLR and TPS and all comes up ok. I've not put air in to the vacuum circuit to check for leaks, so guess that's next step but having replaced most hoses I think it's ok.

To be clear, it only ever happens when I'm full throttle and very close to the rev limit, if slightly off full throttle it never happens and it doesn't happen every time these circumstance are met.

Any clues anyone? I'm stumped! [&:]

Thanks in advance.
Andy

 

[steve 944t]

Do you have a Promax/Lyndsey boost enhancer fitted? If so, try adjusting it. Maybe it was set up in the summer and the colder denser air is now allowing too much boost occasionally?

 

[Hairyarse]

Hi Steve. No, I should have added that my Turbo is completely standard.

EDIT: ...Also the issue has always been present - not often though. It stopped after fixing the vacuum lines, but at the beginning I never had the stalling issue, which is why I'm stumped, otherwise I would think it's just another vacuum leak.

 

[Hilux]

The car will stall in limp mode if stopped and off the throttle

Restarting resets normal mode

Maybe it was set up in the summer and the colder denser air is now allowing too much boost occasionally?

My 944T was "tweaked" as the seasons changed - cool dense air makes a massive difference to power/performance

 

[Hairyarse]

Didn't realise that there was a limp mode! Would that be the case as after the power cut, it drove normally before I stopped and the engine stalled.

 

[homesea]

My old one did the same, promax found the boost leak. It was the hose under the inlet manifold, think it went to the ISV.

So check for boost leaks.

 

[amrbose14]

When I had an over boost problem it turned out that the small bit of hose where the boost enhancer was installed had perished. It's fairly exposed, on top of the engine.

Chris

 

[Hairyarse]

Thanks for the tips guys, will take a look at boost leaks.

 

[Frenchy]

Andy,My 220 when standard could easily hit the KLR Overboost protection, all that was non standard was a Promax Boost Enhancer, as said previously cold damp conditions will hike up the boost considerably.
Jim.

 

[Lowtimer]

Definitely a leak somewhere.

 

[Hairyarse]

Just read on Clarkes about the pressure line from the wastegate leaking being a common problem - must have missed that one before. Looks like next one for checking

 

[944Turbo]

Overboost protection on a standard car kills the boost and then allows you to run with tiny boost, it doesn't usually stall, though you have to reset it (igniton off and on) to get boost back. My turbo behaved similarly not long after I first had it when the coil was breaking down, replacing the DME relay and rotor arm improved it for a while but the coil was the final culprit. Somehwere in the workshop manuals it tells you what the resistance should be between the terminals, mine was a bit out.
tony

 

[Hairyarse]

Oh thanks Tony, will check that as would never have considered the coil!