SOLVED - car cut out randomly
 

So, I am driving and I go to pass an RX-8, he guns it, so I do too. I redline my car, pass him, shift up and and get pretty high rpm when it feels like my gas is cut. Suddenly no power until the rpm comes down, then its fine. The car then runs fine when in the turbo lag rpms (under 3k) but when i build boost it cuts the power again. I pull over, turn the car off, wait 30 sec, then turn it on and the car is perfect again. I try redlining it and beating it pretty hard to see if the problem will come back, but no. Any ideas as to what caused this?

its an 86 951. only mods are a mbc and an after market air filter that got rid of the box. The mbc is set at 10/11psi of boost and the car is on stock chips.

Had it happen again. I hit it hard coming off an off ramp. 3rd gear pretty high rpm, then power gets cut. I slow down to about 30 and then smoothly get on the gas and the car is fine. If I hit the gas, the car cuts off. I am now at a stop light. car is idling fine. I rev the engine and it almost dies. I smoothly rev the engine and the car is fine. I get on it smoothly when the light turns green and everything is normal. I hit the gas and redline it and everything is still normal.

Also, when the car was cuting out, it was consistently cutting out when the boost meter hit .2 bar...

I have no idea what this could be

is there a rev limiter on the 951? perhaps that's the problem?

You are hitting the factory overboost protection...
Check your system for pressure leaks.
If there are no leaks, then most likely your AFM spring is a little weak. And you will need to turn down the boost to keep from hitting the overboost protection.

afm spring? I will turn the boost down and see if it pops up again. Thanks! I'll do a little search on this afm spring thing too....

is it really hot in DC right now? My car used to do this when it was super hot out side and the intercooler would heat soak. Never did it on the street mostly on the track in the summer.

It is pretty hot. How did you fix it?

You could try a vented nose panel to improve airflow to the intercooler so it stays cooler?

I had a similar situation. Josh was one of the knowledgeable people that helped me get it fixed. In my case, the barn door in the AFM opened too easily as a mechanic had adjusted the spring tension which should never be done. It is virtually impossible to get the tension set back correctly unless the original position has been marked on the wheel that allows you to adjust things.

Overboost protection kicks in based on a formula of time, rpm's and air flow. It is more likely to kick in in higher gears as it spends more time at the higher rps is 3rd-5th gears than it does in 1st or 2nd. When it kicks in, it will not let you boost beyond the 1.2 bar for 60 seconds or until the key is cycled off and on.

If the problem is electronic, you will need to replace your AFM with a good one. If the problem is mechanical, you will need to fix that issue. First thing I would suggest is to pressurize or smoke test the intake to make sure your vacuum leaks are fixed. If that is good, I would replace the AFM with a known good one and see if that does the trick.

It is also possible, since I am on an MBC that I set the boost too high, right? My boost was set to 11psi, but I haven't checked it recently, and I think it was going over by a couple of pounds in the high gears...

i had a vented nosepan when mine was cutting out- the vents do nothing in the location they are in. I went with a vitesse MAF and chipboard which eliminates the boost cut i believe.

+1

Yes, if you are overboosting, then the overboost protection will kick in...

So I ran the car up and down a straight setting the MBC correctly. I did not realize how high I had it! I had it set properly, but then had my turbo refurbished, and I did not check my boost level. Boost was going up to 13/14psi......oops! I have it set right now, ran it really hard around town, and no issues. Finally an easy solution with the car!