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Cycling Valve / KLR Fault Diagnosis

EddySpaghetti

New member
Hi there,

I have a problem with my 'New' '90 Turbo. It is only boosting to about 1.2 Bar

Had a read through Clarks garage webpages and a search on here and it looks like the most likley issue is the cycling valve. - I have checked the pop-off valve and the wastegate exhaust for leaky wastegate issues.

Actually When I tested the pop-off valve there was no flow between the pipes, but blowing into the top one did cause the air to leak out of the vacuum tapping on the top, is this correct operation?

I have a pipe clamp on order so I will test the cycling valve operation when that arrives, if it does turn out to be a problem of wastegate control, does anyone have suggestions on how to trace the fault to either a poor signal from the KLR or a faulty valve itself? - I didn't really 'get' the instructions on Clarks about listening to the valve with a stethoscope

Thanks for any suggestions, need my booooooost back :)

Eddy
 
Do you mean that youre only achieving 3psi of boost? Remember that one bar on the boost gauge is one atmoshpere and two bar indicated is one bar of boost...
 
That's right.

If I understand it right then the guage in the 944 reads pressure relative to atmospheric pressure, so in normal driving the needle is below 1, as the manifold is at vacuum. I think the boost should reach abuot 1.8-2.00 on the guage at about 3000rpm, once the turbo is getting going (so positive 0.8-1 Bar above atmospheric pressure). Mine is only reaching about 1.2, and all the urgency is gone...

Cheers,

Eddy
 
The in-dash gauge reads absolute pressure which is atmospheric + boost. So when driving off boost it will be below 1 bar and when on boost it will be 1 bar + boost pressure. I cannot see how it is the cycling valve. The cycling valve can only deliver whatever boost pressure is being provided by your turbo. 1.2 bar of pressure i.e. 0.2 bar of boost wont be enough to open the wastegate against the spring within the wastegate. Sounds to me like you've got a leak. Have you done the simple stuff yet like checking your intake hoses are intact and havn't sprung a leak or been blown off?
 
I have looked for leaks, and I can't find anything obvious, its going to be pretty hard to find something like a hairline crack, afterall, the ducting is probably a good three metres all told, and often partly hidden. Any tips welcome though, can you use washing up liquid like for bicycle tires ? :)

I've been reading the Clarks garage website and it mentions ways to test the cycling valve. I think I understand the logic of testing it by clamping off the line to the wastegate: I think 1.2 Bar would have to be enough to open the waste gate if it was let into the diapragm chamber by the valve no? - otherwise the valve wouldn't be controlling anything, the wastegate would just automatically open when the boost in the manifold reached some threshold (max allowable) value.

What I don't get from the Clarks guidance is how to diagnose whether the valve is physically broken or just getting a duff signal from the KLR. Does anyone know what the signal should look like from the KLR? Haynes manual, as someone commented on one of my other posts, is a chocolate teapot if you have the Turbo, despite what it says on the inside cover...

Cheers,

Eddy
 
the wastegate should be opening at 1.7-1.8 bar (approx) - a weak wastegate will open much earlier. Has it always been like this since you picked it up?

have you done anything? (mine usually breaks only when I try to "improve" it [:)] )
 
No I haven't done anything to it, not deliberately anyway.

It wasn't like this when I picked it up, it happened after about a week of 'driving it like I stole it'...[:D]

Also happened pretty suddenly, I didn't notice any gradual loss of oomph, was there one minute, gone the next. It still boosts a bit, and the turbo 'rush' starts, with some boost showing on the guage, but just doesn't get anywhere near as powerful as before. That's why I was thinking it might be an electronic issue (signal to the valve), but I realise it could be a leak that developed very quickly too.

I'm just thinking that an electronic signal issue may be easier to diagnose than trying to find a leak in all that piping...

Cheers,

Eddy
 
One way of checking for leaks is to spray WD40 or carb cleaner or something equally as flammable in and around the areas you are testing. Any of the stuff sucked in by the partial vacuum at idle will result in a momentary rise in RPM.

Also at the point your boost flattens off do you hear a whooshing noise? Try to listen out for it because once you come on boost and the intake is pressurised above 1 bar then instead of air being sucked in through any crack, it will blow.

I wasn't 100% sure what the operation of the cycling valve was so looked at the Clark's Garage explanation:-

"The cycling valve is controlled by the KLR Unit (Knock Regulator Unit). The KLR receives signals both directly and from the DME Control Unit to determine how the cycling valve should be controlled. The chips in the KLR have a boost limit which comes preset from the factory. When the actual boost reaches the computers preset limit, the KLR sends a signal to the cycling valve to close which allows exhaust pressure to open the wastegate. If the cycling valve fails, loses power, or a problem occurs in the KLR unit, the cycling valve will fail fully closed. In this mode boost is limited to approximately 1.2 bar. This is essentially the boost at which the force of the exhaust pressure will overcome the wastegate diaphragm spring pressure."

So I can see how you come to your conclusion. Maybe check for leaks one more time then replace cycling vavle? They are pretty cheap from a breakers I should imagine.
 
ORIGINAL: EddySpaghetti
Also happened pretty suddenly, I didn't notice any gradual loss of oomph, was there one minute, gone the next. It still boosts a bit, and the turbo 'rush' starts, with some boost showing on the guage, but just doesn't get anywhere near as powerful as before.

I've had the same symptoms a couple of years ago on a summer track-day in mine, the car went into overboost protection (limp-home) mode apparently. I let the car cool down for half an hour in the paddock & it was fine again.

If the vacuum pipe that controls the recycling (dump) valve has come off or the recycling valve diaphragm tears it'll give the same symptoms.
 
I had the over boost problem with mine and it will limit it to 1.2 bar, but it was like someone had but the brakes on hard if you went past 1.2 bar. This was due to a hose not being fitted back on from the ISV, hard to sport as its under the manifold. If your not getting any whooshing sound than it could be the cycling valve or the feed to it. Sometimes the plastic pipes that the hose attach to the cycling valve snap off.
 

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