Put me out of my misery - Cutting out on high Boost

[ChasR]

It seems that this is not the week for me and cars! My daily snapped a spring and to top it off it looks like it will need a cylinder head refurbished (low pressure on a couple of cylinders). To top it off the 951 is misbehaving.

Basically since it has been my daily for a short while I have been driving it rather carefully (it doesn't help when your daily does the equivalent of over 50MPG!). Anyway, as the red mist descended on me today and I came to put my foot down, the boost gauge swung towards 2 Bar, but with a difference; it hesitated and cut the power fairly hard, initially I was quite surprised and fear the worst. Thankfully the car drove but it did this again for another mile or so upon applying the power.

After that, the car was behaving absolutely fine, pulling very well indeed. What do you chaps believe is the issue? FWIW it's the car in my signature. To my knowledge it is stock bar a Bailey DV30 valve.

I would like to think the car was rebelling against being driven carefully but that may be wishful thinking!

 

[Lowtimer]

Most likely an air leak somewhere on the induction side. This is the usual behaviour in such circumstances.

 

[924nutter]

Did it cut with a bang. Mine does this in second when you hit the rev limiter (you can't hit the limiter in 3rd as you are doing over 100 mph I believe) so if it does then maybe the ecu is misreading the RPM incorrectly. Like the 924 the 944 must have overboost protection too, so maybe this protection device is cutting the power prematurely. My knowledge of ancillary systems on the 944 is limited and this is all I can suggest.

 

[simkin911]

ORIGINAL: Lowtimer

Most likely an air leak somewhere on the induction side. This is the usual behaviour in such circumstances.

I had exactly the same in my turbo s. I feared the worst thinking a) may be expensive and/or b) hard to find. Turned out was an air leak. Loose connection. Found in minutes and fixed in even less time.

 

[944 man]

Are people suggesting a vacuum leak, leading to fuel cut?

 

[u63af]

Yeah agree with others mine did this. Took ages to find, checked all vac hoses which were fine. Turned out to be one of the bigger hoses around the air flow meter. Had a crack underneath it.

Don't think it will be fuel cut as its doing it on boost so there won't be any negative vac pressure. From memory I think mine was one of the hoses that feeds back after the air flow meter so it might have been sucking in unmetered air.

 

[944 man]

Sucking in unmetered air will be the KLR cutting boost due to detonation, surely. A vacuum leak will prevent the wastegate from opening (as much as they ever close!) leading excessive boost which leads to fuel cut, I believe.

 

[Eric_Oz_S2]

The ECU cuts fuel when boost is over about 16psi (depending on RPM). Are you running the standard DME maps?

 

[Hairyarse]

I had similar, was split vacuum pipe as suggested - the one just under the top of the air filter box on turbo inlet had snapped under the cotton braiding so was difficult to see. It solved the issue for a while and has come back again, now traced down to suspected failed dump valve. Will have a spare fitted on Monday to prove the point

 

[944Turbo]

The overboost protection in standard chips will cut the power once triggered. For people with a boost enhancer it is classic to hit it in in cold damp weather due to the increased density of the air and when my car was otherwise standard had to loosen the boost enhancer a turn in the winter.
I would check the state of the rubber pipe down to the wastegate it goes hard near the end and cracks (wastegate gets hot!). It is supposed to take the boost signal from the KLR (under the rear of the inlet manifold) to open the wastegate and limit the boost. (the boost enhancer also holds back this signal)
Tony

 

[Diver944]

It really does sound like the standard factory overboost protection which jumps in if you hit over 0.8 bar boost (1.8 on the dash gauge).

You say your car is standard with a DV30 but it also has a large bore Wortec exhaust. In this cold weather when air is dense and with those mods your turbocharger can be spooling up quicker than the factory chips expect, hence the cutout.

You need to fit a boost controller so you can actually turn the boost DOWN in cold weather, or fit an aftermarket chipset which will give you safe fuel for the extra boost and remove the factory overboost cutout.

 

[MarkK]

Has it really got standard chips??That car was owned by someone who would never have left standard chips in it??

 

[ChasR]

A bit of a bump from the past!

The chips I do not know about. I guess I could always take a look at the ECU to clarify that. AFAIK the engine seems relatively standard (it still has the cycling valve etc.). What chips Mr. Sweetenaham left on this car is unknown for now.

Since that one off occurrence it has not done it again, but I may just investigate it to be safe. Considering how much it is boosting as Paul Smith has pointed out (the two mods on the car would aid that (Wortec and DV30)!), I may take a look.

After looking at the vacuum connections all of them seem to be OK, although it is good to know where they do fail (I may just double check them).

 

[Lowtimer]

It can be an induction leak anywhere. My last one turned out to be around the ISV.

 

[Eldavo]

My car did this to me Sunday whilst hooning about the Northumberland wilds.

Stuck behind cars, went to overtake, dropped into 3rd, accelerated hard, 4500rpm and it felt like I'd hit the rev limiter, changed up foot flat to the floor and it did it again once the revs built. Didn't do it again for the rest of the hour-long run though.

Have a look at the bottom of this page: http://www.clarks-garage.com/951faq.htm

I figured at the time that it was the overboost protection from how Simon had described it in the past. Just check the vacuum hoses first and foremost. I'm changing to a DPW with promax chips, etc soon so it'll get a once-over then.

 

[simon macturbo]

Who sells a hard vacum pipe kit to replace all these 20year knackerd pipes ????

 

[Frenchy]

Look on Bailey Motorsport website and buy it at a couple of quid a meter along with fittings (T Pieces)

 

[ChasR]

I may end up getting some silicon hoses as some of my T Pieces are not in the best of shape.

There is another development here though mind you. I came to start it yesterday and the boost gauge upon turning it went to 1 and then straight back down to the bottom of the scale accompanied by a clicking of the relays. It turned over but it refused to fire up.

I went over to the fuse box, tapped the DME relay a little (I am fairly sure that it clicked as well) and the gauge went back to 1. Sure enough it fired up straight away. I was only thinking about getting a spare DME relay the other week as well! Sure enough, another relay (a genuine 993 numbered part) has been ordered. Unsurprisingly the DME relay did not look all that old! To think that my last 944 as a daily driver never suffered with an iffy DME relay.

Whether it is related to the cutting out issue (which has since never occured again) is another matter. I haven't used it for around a month since last Sunday. It is scary to think that since March I have put on almost 1500 miles onto it as a second car over the months February and March!

 

[944Turbo]

Good question - Porsche probably, however the pipes are probably fine its the rubber couplings that go hard and leak. You can use silicon hose and metal t-pieces to join the hard lines. I have silicon hoses on the coupe but have wondered about returning to the hard lines as they will not expand under boost.
Best regards,
Tony

ORIGINAL: simon macturbo

Who sells a hard vacum pipe kit to replace all these 20year knackerd pipes ????

 

[944 man]

ORIGINAL: simon macturbo

Who sells a hard vacum pipe kit to replace all these 20year knackerd pipes ????

Jon Mitchell (JMG) have a ready to go kit IIRC, which uses the correct bore pipe.