Timspu

Guys a couple of months ago i had my 930 BHP checked and the boost wound up to 1 bar. Tuner advised car is running really rich 10 AFR prior and on boost.
I have now changed the standard exhaust to a Rarly 8 muffler. I have also installed an Lm-1 wide band data logger. During a run up today the data logger is showing 17 Afr off throttle and 12 Afr on boost. As the boost is up and the car reaches 4500 rpm the engine cuts out as if the over boost has cut in.
I don't believe the data logger is accurate as it appears to be 2 afr too high.
A question is is there anything that can suddenly cause this, could the data logger be correct.? The car is standard other than silencer and manual boost controller at 1 bar.
My next check is to return back to standard boost to see if the car still cuts out.

Global Auto Sports

Quite the predicament here...returning back to standard boost and checking is definitely a good idea.

Timspu

I am hoping its just overboosting due to the colder temps in the UK.
But am concerned that my data logger is reading lean , hoping its out and the car has not leaned off . If it has what would cause this.
Due to the tuner saying the car was running at 10 AFR i now have a brian leask adjustable WUR which is not yet fitted as i wanted a base line reading with the standard unit fitted. Would the straight through exhaust cause the over boost in combination with cold weather as the car was set to 1 bar in the summer and standard exhaust.

Cheers
TIM
930 Targa Turbo

Mark Houghton

Could indeed be momentarily boosting beyond 1.0 bar, and if your overboost sensor switch has aged to where it's tripping prematurely (when new, I think they're supposed to trip at something like 1.3-1.4 bar...but can trip lower due to age).

Are you able to watch your boost gauge when this happens to confirm overboosting? And, are you sure it's acting like a complete overboost-situation shutdown (you can't miss the real thing as it quite violently throws you against the steering wheel when the pumps shut down).

Another potential possibility is that one of your IC O'rings is becoming partially dislodged when you build boost, letting boost air escape and causing a super rich condition and flat response/loss of power, but not as sudden as would be felt with the overboost circuits kicking in. Just some thoughts....

Timspu

Hi Mark,
It does appear as if the fuel is cutting out. With steady throttle the car performs fine, its just when WOT is used the engine cuts out.
If the data logger is correct then the fuel is generally lean.

Looks like i will disconnect the manual boost control and return to standard boost to see if it make a difference.

Mark Houghton

Well, on way to find out is to pull the wire on your overboost sensor switch (white wire with a brown stripe if I recall). Then, if you over boost, you'll just keep boosting to the moon 'till she blows!!! But as they say, "don't try this at home" unless you can watch your boost gauge and get off the throttle before your boost goes too high.

Timspu

Put back to standard boost with MBC removed. Car now works okay. Quite a bit slower.Have put the mbc back on and backed it off slightly, know more cut out so suspect over boost valve cutting in too early as the tuner set the boost to 1 bar.
I still have an issue of idle at 17 AFR, and off throttle around 19AFR. When full throttle in second AFR goes to 11.4 so on boost is fine. Looks like i will just fit the adjustable WUR and go from there.
What are the chances of the Wide band sensor for the LM-1 failing. It calibrates ok in air at 20.9%.
Will having the air pump connected cause a lean reading through out the rev range or just at idle? Suspect air pump is causing the lean setting whilst driving. Woul dthis be true.

Cheers

TIM

Mark Houghton

Do you have a deacceleration - or overrun - or whatever it's called valve in place? You know, the gold saucer shaped thing that should open up when off-throttle and allow some air to enter the intake manifold post-throttle body? Perhaps that thing is stuck open and sucking in too much air.
Or it could very well just be your WUR. As for the air pump, I don't have one so can't give any hints on that system.

Timspu

Apart from the muffler and MBC its standard. The performance is fine with no over run issues. Just wondering if the LM-1 is okay. I think i will fit th enew WUR and see what happens.
Will advise .

Cheers

TIM

gsxrken

Sure it could throw it off. Injecting extra air into your exhaust ports after the combustion process will not allow you to measure what AFR you have inside the chamber. Whether it's by 2 points who can tell. Can you remove the belt and let us know if that was it?

Timspu

Removing the belt looks like a real pain, i will have to review as i want to keep the air pump running. I will disconnect the air pipe to see what affect it has on idle AFR and go from there.

Cheers

Timspu

Idle AFR when hot is 17.9 AFR indicated on my LM-1 data logger.
I disconnected the air pipe off the air pump and the AFR dropped to 13.4 AFR. Which i think is in the ball park.
1. Does anyone know if the air pump delivers more air dependent on RPM or it delivers the same amount at high rpm as it does at Idle? I don't have anyone to push the throttle while i gauge how much air comes out.
2. Can i run the car at full rpm with the pipe disconnected from the air pump so it just pumps into the engine bay?

Does anyone have an AFR reader in their car with an air pump connected?

Based on these figures if they are linear then my car could well be running very rich on boost as it currently measures 11.4 AFR with the pump connected.


Cheers

TIM

Mark Houghton

Someone out there probably has the answer to your questions. Personally, I would leave the pipe disconnected and plugged so as not to draw any air in, and test run the car up to full boost. That air pump's purpose in life is to clean up emissions by adding oxygen and burning up any residual fuel in the exhaust, and I guess it would stand to reason that your AFR's read high at idle (because that's where the air pump is supposed to have it's affect).
But I would submit that when on full boost, the exhaust gas volume far exceeds the output of the air pump - so it's not as linear a relationship as you fear. I would bet that your boost AFR doesn't change at all with the pump connected or disconnected. 11.4 is good.

That's just my brain digesting this....no first-hand experience, but I can always talk myself into my own logic.

Timspu

Thanks Mark, I will give it a go and report back, my only concern was adiabatic heating of that air so need to ensure i don't get hot air blasting in the engine bay.
After thinking about it i tend to agree that at max chat the air pump won't have much effect on the AFR so 11.4 would be correct.

Will advise.

Cheers

TIM

Timspu

Completed run with pipe disconnected from smogg pump.

Warm idle 13.4
14.8 AFR part thottle
15.2 AFR Off throttle
11.1 AFR On boost

Just fitted adjustable WUR
Warm idle 14.9 AFR
Part throttle 15.1 AFR
Next check will be boost.

Cheers
TIM