acrosby

Hello, Just bought a 87 944 turbo, 117000 miles. Stock except for a boost regulator I put in to bypass a failed cycling valve. Worked fine for 2 weeks. but Now the car stumbles and falls completely flat periodically while under hard acceleration. Boost guage(stock) reading about 1.8 bar. Have I got the boost too high and the DME cutting spark or fuel off? Anyones comments greatly appreciated!

Andrew

V2Rocket

BOV/wastegate opening?

Rock

Youre hitting the overboost (knock protection)

Try turning the boost down a bit.

This probably happens in 3-5th gear doesnt it?

acrosby

Maby. I'll check, but when the car decides to stop accelerating it does so comlpetely. There isnt even any na type of push happening. It really does stop. Feels like somebody stomped on the brakes and forgot to tell me. Wouldn't the car keep accelerating but do so at a much slower rate if it was a BOV failure? I dont know? I live on northern Vancouver Island and have to quickly pass logging trucks on a twisty highway. This alone is often hair raising but now with unpredictable acceleration a bit more than just hair is rising!

acrosby

Yeah! Thanks ROCK, it must be a overboost protector. It's only happening in 3-5th now that you mention it. Anyway to turn theoverboost protector off? Engine is old and will be rebuilt soon anyway.

Darwantae951

Since you've already bypassed the Cycling Valve, try getting a set of chips from Russel Berry or John Vitesse.

-Darwin

Rock

Yeah. Ive been there done that. Unfortuneatly for you (but fortuneatly for your engine) the boost cut cant be turned off unless you change the chipset.

I burnt a valve overboosting it was no fun.

Id just see if you cant open the boost controller a turn. It may just be overboosting by a bit and 1PSI may fix it. Keep in mind the stock turbo is basically useless after 15psi anyway. Intake temps skyrocket and power gain is minimal at best after 15psi.

The reason its only happening in 3rd-5th is thats when the turbo can stay spooling for longer periods. 1st is too short to really get full boost and 2nd if it does get full boost its usually only for a second.

V2Rocket

does your boost gauge read 1.8 total BAR in the intake or 1.8BAR ontop of atmospheric pressure?

acrosby

Good sound advice. Thanks. I'll turn it down and live to pass again.

acrosby

1.8 bar on the stock guage, so that would be .8 bar absoulte, or about 11 to 13 psi thereabouts. But I'm aware that the stock guages are notoriously innaccurate. like my spelling.

Keithr726

I think I'm having a similar problem but I know I'm not hitting over boost protection as I've got custom chips.

It does it randomly and can get really annoying. I mean I can push the pedal to the floor and it doesn't do anything then a few seconds later it just kicks in. I have a feeling its spark related. I a jacobs coil and the wires and plugs are two years old. My cars been running pretty rich so they're probably bad.

https://rennlist.com/forums/944-turbo-and-turbo-s-forum/382738-what-are-the-signs-of-a-clutch-on-its-way-out.html

V2Rocket

So on a boost gauge it normally would read 1BAR, and then you step on it and it goes up to 1.8.

Does that mean you are running ~12PSI boost, for a total of ~27PSI in the intake?

Keithr726

anything under 1 is vacuum so yes about 12psi

Rock

You do realize that if you hit it once, it will cut the boost soon thereafter.

So if you hit it once at like 15 PSI, it will cut out at like 6-7 PSI next time.

It takes time to reset or the car needs to be turned off and on