Van

You may have seen in another thread that my car isn't running quite right.

It builds boost, then keeps building until the computer goes into over-boost protection mode (limits the boost pressure to 0.3 bar over absoloute by cutting fuel and spark).

Shutting off the ignition and restarting the car will reset the computer.

Basically, there is some failure to divert exhaust gas away from the turbo charger.

It's a real pain at the track, because I can't use full throttle - I have to keep a sharp eye on the boost gauge and only use about 3/4 throttle to prevent it from over-boosting.

theedge

Could be one of a bunch of things on that list... Ill go with a split hose somewhere to start. Check the one that has the banjo bolt that goes to the intercooler pipe, and the hose that leads down to the wastegate itself, and the connections at the cycling valve.

You could pressurize your intake to test this easily. Get a 3" PCV pipe end, a 3" pipe cap, and a Shreader valve. Drill hole in cap, thread valve into it, add some epoxy to seal it, crank cap into pipe end. Put the tester in the J-Boot in place of the AFM and pump it up with air from a bike pump. Thatll pressurize most of the hoses and let you find leaks.

Van

I actually have an old fuel filter that I cut in half and put an air-hose fitting on. It fits in the place of the air flow sensor nicely.

zoltan944

because your car wants to go faster!

HD911

Have you recently installed a new wastegate by chance?

Van

Actually, yes. I found that the diaphragm on the old wastegate was torn/cracked... which I thought was the issue. I installed the Lindsey club-gate, but it didn't fix the problem (so don't vote for that in the poll!)

HansB

If you use the car on the track, why would you want to keep the cycling valve?

This is a rhetorical question: There is no reason at all.

With a MBC you will get a very simple circuit, and this problem will surely be gone.

reno808

From my understanding he cant because in the class that he races limits the use of MBC. I am not sure i am sure he is going to answer that.

HansB

Ah, class rules. You have got to love them!

Van

Yup, I'm running the car in SP3 class (that's a NASA & PCA class) - and have to keep the engine stock.

333pg333

Do you have a boost gauge to see what it's hitting at WOT?

Van

Just the stock one in the dash - I know they tend to be inaccurate, but overall mine seems to be pretty close.

Anyway, at WOT, it goes up to 2 bar and stays there. After about 2 seconds, it goes into overboost protection.

It used to go up to 2 bar just momentarily, then come back down to 1.6 to 1.75 bar.

Van

Update: it's looking like the knock sensor - I started measuring things with my multi meter... The TPS measures within spec, the cycling valve seems OK, but the knock sensor shows no resistance (measures open).

I'll order a new one and see if that solves the problem!

LUCKY DAVE

Mine does the same thing....but only once in a while. Shtting off the car and restarting (rebooting the computer) fixes it. No vacuum leaks, boost gage on dash (original) shows 2 bar at full boost, I don't get it. Brain tumor in dme maybe?

chrly924s

Bad cycling valve will cause that. Happened to me about two years ago.