tommye

Listers,
My 951 cab has been running just great since replacing the KLR unit (thanks again George B for quick service!). In 5:th gear, I get 1.4 bar @2500 and 1.8 bar @ 2800, max boost sometimes gets up to 1.9 or so (as indicated by the dashboard meter).
However, twice now, I've had a new problem:
after a dash in 3:rd or 4:th with full bost up to nearly redline, the engine suddenly cuts out violently for half a second or so. After slowing down, it keeps cutting out everytime boost gets over 1.2-1.4 bar, even at lower rpm:s. This continues all the way home. Next time I take the car out, the problem is gone.
Also, the second time this happened, after slowing down to almost standstill and carefully starting again, the engine did not pick up at all at first. It felt almost like a lack of fuel.
Any good advice out there ?
Car is original except for a Lindsey boost enhancer.


Some other questions:
- boost does decrease a bit beyond 5000 rpm, at redline it's around 1.6 bar, shouldn't boost be constant on the 951S ?
- I have seen some oil film inside the intake tubes going to and from the intercooler. Is it worthwhile to clean out the IC ? What is the best way to do this ?
- Did the 951 originally come with a black exhaust tip ?

Thanks in advance,
Tommy

hosrom_951

You should hold boost better than the early 951's (running a k26/6 when your running a k26/8). Boost falling on high revs is just a way of the wastegate not doing it's proper job, which is common on ALL 951's.

Regarding the oil film, that is normal as well. I cleaned out my intercooler and both pipes with engine degreaser, a simple job (just make sure you cleaned the inside of the intercooler as well as the outside). But note, oil film will return after some time, that is the way the car is.

I am not sure of this, but i believe the 951 came with a chrome exhaust tip (unless if it was an option).

special tool

That is TEXTBOOK overboost protection. UNSCREW the LBE 360 degrees, and see if it stops.

Jake951

No, it's normal for the boost to drop at high rpm with stock turbo and stock wastegate. Even the factory spec on the 951S specifies reduced boost above 5500 rpm.

Jake951

If you are running the factory stock chips in the DME and KLR, then you shouldn't be running 1.9 bar. That will trigger the overboost protection. Maximum boost should be no more than 1.8 bar on the gauge. I believe the LBE comes preset for 15 psi (2.0 bar on the gauge), so you need to readjust the LBE for lower boost.

gmsracing

It sounds like your car was running properly for some time with the boost enhancer. If so, I would think it is something else that is causing your problem. You also mentioned cutting out at lower rpms. I had a very similar problem in my 951 where it ran perfectly off of boost. As soon as I was under load to about 1.2 bar the power would just shut down violently. After looking at the fuel pump & fuel pump check valve it turned out to be the fuel pressure regulator. It's the one on the back part of the fuel rail. Once I replaced it boosted properly and ran perfectly again. When I had the problem it just felt like it wasn't getting enough fuel!
Rob

tommye

Hosrom,
regarding the cleaning of the intercooler I thought that maybe it was partly filled with oil and thereby limiting flow and max boost at top rpm. Any experience here ?
I have seen the occasional 951 with black exhaust tip, this is also listed in the spare parts catalog as no longer available - I just wondered which 951 models might have been originally equipped with it ?

Special tool and Jake,
I'm already running the LBE unscrewed by 3 complete turns since I'm running with stock boost. Is the stock KLR set to cut out at exactly 1.9 bar? Of course, the dashboard meter is probably not that precise.

gmsracing,
I did indeed run with the LBE without problems, but since the problem appears so rarely, it's difficult to tell. On the occasion when it ran badly on low rpm:s, it really felt like I was out of fuel. It idled fine, but stumbled when trying to get going. This problem dissapeared after a few seconds.
Problem could well be related to fuel pressure/flow. Is there any way that the KLR or DME can detect a fuel-flow related problem and shut things down ??

Thanks guys,
Tommy

Jake951

I believe the stock overboost cutout point is only a couple psi above the factory maximum boost level and it could be around 1.9 bar on the gauge. All the aftermarket chips raise the cutout point to allow you to run more boost.

Russ Murphy

>>>However, twice now, I've had a new problem:<<<

Was the ambient air temp somewhat cooler (providing a tad more boost) than previously when you had no problems with the fuel cut?

I'm with special tool. Classic overboost fuel cut. Especially given that the problem goes away (briefly) after rebooting the DME.

tommye

Ambient temp was maybe a bit lower, at least on the 2:nd time around.
I think I'll ditch the LBE for the moment to see if it helps.
I'm just bothered about the occasion when pickup from idle was bad...
Tommy

alexands

Slightly off topic Question:

Jake951 posted that a gauge reading of 2.0 bar is equal to 15 psi of boost. I thought that bar is atmospheric pressure (~14.7lbs). So, I've always thought that if the boost gauge read 2.0, we're talking about 29.4 psi of boost (!!!). Can someone please explain how the factory boost gauge measures to boost psi?

Thanks.

tommye

Dash boost meter shows absolute pressure. Atmospheric pressure = 1 bar.
Turbo increases pressure from 1 to 2 bars meaning 1 bar of boost.
Dash meter measures both vacuum and boost (as well as atmospheric pressure when engine is stopped).
Tommy

alexands

Tommye,

Thanks for the info.

Does that mean that when the gauge reads 1 bar the turbo has just reached atmospheric pressure and really isn't boosting? Seems sorta confusing. I've always assumed (probably wrongly) that a NA car always operated at atmospheric pressure and a turbos job was to increase that pressure. Meaning, that if the turbo was spinning, it was generating pressure on top of the standard 14.7. If what you are saying is true, does it mean that NA cars do not operate at least 1 bar and there is a possibility that the manifold pressure can be less than atmospheric pressure?

I'm truely in the dark on this one, so I'm not trying to refute what you are saying. Just trying to clarify it so my thick skull can absorb it.

Thanks.

hosrom_951

Tommy: The intercooler (after all these years) will become a sort of restriction if you have a lot of oil blowby. When i cleaned out mine, it tpook me 2 hours of cleaning to make sure it was literaly spotless and oil free before i installed it back into the car (i even found some bird feathers in there ).

Even after cleaning it like 'brand new', give it some mileage and oil film will build up again, that is the nature of the car. I think that it would cause a boost drop at high revs IF it was really (and i do mean really) filled up with oil and gunk.

But as mentioned, boost dropping at upper rpms is NORMAL on a stock car due to the turbocharger and wastegate. I know a few people running a Tial wastegate and a stock turbocharger and holding boost to redline, but that is due to a healthy turbocharger.

So, basically cleaning the intercooler will improve the airflow/cooling/pressure dropping etc but wouldn't be related (unless stated above) to boost dropping.

Russ Murphy

>>>Does that mean that when the gauge reads 1 bar the turbo has just reached atmospheric pressure and really isn't boosting? Seems sorta confusing. I've always assumed (probably wrongly) that a NA car always operated at atmospheric pressure and a turbos job was to increase that pressure. Meaning, that if the turbo was spinning, it was generating pressure on top of the standard 14.7. If what you are saying is true, does it mean that NA cars do not operate at least 1 bar and there is a possibility that the manifold pressure can be less than atmospheric pressure?<<<

Most NA engines approach atmospheric pressure at full throttle, but usually a bit below it- maybe -2 in/hg or so. Some NA motors either through Helmholtz resonance (induction tuning) or ram air actually run at slightly greater than one bar.