Cut Out at 5-6k rpm

[will lyons]

Hi guys

Driving home today I pushed for full boost in third and cut out just over 5000 rpm now the question arrises

Thursday last week the car failed MOT on emissions I need to contact testing garage to see if any adjustment has been made to AFM symptoms seemed to be lack of fuel. I am as sure as I can be all was fine before this

I increased RPM without load and the engine red lined to 6k no problem everything else is fine and acceleration adequate for normal driving. I have good boost on the cars boost gauge running up to 2 and holding for a second or two before correctly settling at 1.8 Oil pressure is good throughout the range so as previously said only at the top end under load.

Wil

 

[Fen]

Could be the knock detector, but I doubt it. Most people say that they need to cycle the ignition to reset when it trips and while that wasn't the case with my car it did take 30 seconds or so before it went back to normal and within that time it wouldn't take much throttle at all.

I'm sure it isn't the same, but that's exactly what my car did before it went bang; once as a warning, the second time accompanied by shrapnel, steam and bits of con-rod on the top of the bellhousing. I assume it was sudden and quite severe fuel starvation in my car's case and by then it didn't have a knock detector at all.

I would expect the knock detector to halt play if it's fuel starvation as that should result in knock, but I did once have a problem which was traced to the fuel line becoming kinked during a filter change and it didn't trigger the KLR, but it did bring the speed down quite significantly.

Overall not much help then. Has it only done it once? If so are you avoiding full bore at 5,000 rpm to prevent it or is it sometimes OK? Was it a full ignition cut (suggesting maybe an electrical problem) or more of a severe misfire which could be that or fuel?

BTW your car should make 1.7 rather than 1.82 bar, but the gauge is hardly accurate.

Was it you who won the interior on eBay?

 

[will lyons]

Hi Fen

First yes I did win the Interior on ebay I have comfort seats with a slightly damaged bolster on the drivers seat in my turbo and was somewhat dissapointed to find the lack of sports seats when I bought the car.

back to the question of occurence .. yes it has only done it the once I will check the knock sensors for secure attachment and the wiring but as previous post it is only at the top end I have not been avoiding high RPM to eliminate the problem so maybe a good check all round is necessary I have booked on the Dyno later this month and rememeber only too well when yours gave up I dont think any of us would like to see a repeat of that.

Wil

 

[944 man]

Overboost leading to fuel cut? If its a brick wall then it sounds like it.....

 

[944 man]

Thats a generic suggestion, as opposed to a 951-specific one, btw.

 

[Fen]

The circumstances therefore are max boost and wide open throttle, but not repeatable. A sudden cut (like a hard rev-limiter) would suggest either an electrical glitch cutting ignition for a short period or a deliberate safety cut-out doing the same thing, a softer cut sounds more like a fuel glitch.

In a generic way I'd agree with the post above, but with the Turbo if it cuts due to over boost (or more correctly knock generated by excess boost creating a lean mixture) my experience (confirmed by others) is that it doesn't let you play again for some time; somewhere between 30 seconds and until you cycle the ignition swtich. I'm therefore thinking electrical gremlin cutting the spark. Distributor, king lead, coil, low tension wiring, engine earth, ECU, DME relay etc.

 

[homesea]

Wil is it the same as mine was doing when you lent me your AFM? Maybe it caught it from my car[8|].

Still havent got to the bottom of mine, so far:

New TPS
New AFM
New Leads
New Plugs
New Cap
New Rotor Arm
All vac and boost hoses off 100's of time to check for a leak.

Next on the list is fuel, I need to check my fuel reg, pump, lines etc.

When mine cuts in, if you press the accelerator it just splutters so you need to flick the ignition off and on again (interesting when your over-taking another car).

On another point I found out yesterday on my car it runs sweet as a nut when cold but when warm it holds back then the overboost thing kicks in. Dont floor it normaly when cold but had to yesterday. So also thinking a temp sensor??

 

[Fen]

Yours sounds like the knock protection, Tom.

 

[will lyons]

well

I tried to force it today and got full boost right up to 7k without cutout if its not confusing enough[]

so I am thinking a loose connection somewhere taking Fens advice initially and checking the Knock sensors and vaccum lines. I will give it full boost on same stretch of road tomorrow and Friday to see if I can duplicate the fault but it did seem to be cutout similar to redline protection rather than Fuel starvation .

Now theres a thought from your previous post Fen cut out due to a lean mixture I did add some Forte fuel system cleaner on Thursday before the test ?? a delayed response to octane changes possibly [8|] thoughts on this one

 

[944Turbo]

Overboost will trigger more readily in cold damp conditions, have you got a boost enhancer?

 

[will lyons]

Hi Tony

No boost enhancer the car is totally standard other than K&N panel air filter

wil

 

[Fen]

Fuel system sycleaner in the tank? It should have mixed through rather than all come through in a slug, but I guess it's a possible cause.

 

[944Turbo]

If the rubber signal pipe to the the wastegate is loose or perished you can achive a boost enhancer style effect. Didn't think 7k rpm was possible with standard chips but its a long time since I drove with them.