Kirk

<center><img src="http://www3.sympatico.ca/kirkgj/images/maf_data.gif"></center><p>... At 5200 rpms, my MAF readings start to fall and then by 5300 rpms, my actual boost is low enough to throw the car into limp mode by 5400 rpms. You can see the N75 go into limp mode at 5400.

Now for the MAF. It can only read 150 g/s or so... it never gets above 151. I'm not sure what it should be doing but I suspect as long as the turbo is bringing air and the RPMs are going up, the MAF data should continue to rise... It should never plateau.

Now if this MAF is not working properly, can it explain a "charge pressure: negative deviation" fault code? The way I see it, this fualt code could mean that I have a leak in the intake or the air being metered in the intake is not correct.

Further, is it possible that the GIAC requested boost is too high at 5400 RPMs?

Any input is greatly appreciated.
Thanks,
Kirk

Brent V

What kind of bypass valve do you have again?

Kirk

... I'm running the 710N (TT) by-pass valve. I dont think the valve itself is leaking... BUT... now I think the by-pass valve control solinoid is not working.

I'm going to hook up the by-pass valve to the intake manifold directly. This will eliminate the by-pass valve and the vacuum resevoir from the picture. (Damn, and I did such a nice job using the oetiker clamps and new vac lines).

Anyhow, I think its the by-pass valve leaking for one reason or another causing the turbo to recycle air and hence the MAF not needing to bring in as much air. Just a theory at this point.

Also, I might try and pick up a hyperboost by-pass valve and install that... but that will take a week or so. The 710N bpv was just replaced so I don't think its the bpv... but when I looked at the 710N that I took off, it was in poor shape.

Thanks Brent for all your comments.
Kirk

Brent V

With N75 duty cycle maxxed out like that your little turbo is trying with all its might to make the requested boost, that's why you see the gradual decrease in boost pressure. Higher the RPM the more demand on the turbo to meet the requirements.

You would probably be hearing some kind of air leak, can you? If not it might be something wrong with boost pressure control.

To rule out your N75 as the problem try disconnecting the vac line from the wastegate actuator diaphram and going for a *VERY* cautious drive. Ease into the throttle and keep a close eye on boost, if you can make 1 bar of boost at 5400 then you know something is wrong with the boost pressure regulation. Check the line from your N75 to the intake pipe and make sure it isn't kinked. If it's not then it might be the N75 that's broke. I can't remember if you've replaced that yet or not.