Cajun

Hey Guys,

My car has a 1 bar boost spring, but I have yet to see more than .9. That is NOT the problem though.

Lately, my car refuses to see more than .8 on my aftermarket boost gauge (fitted where the clock used to be...)

I have noticed that while accelerating at anything less than full throttle past 3k rpm, the boost will come up to around .5 and the car will begin to stumble and hesitate. The boost will become "jerky" and the car will not "catch" and smooth out until I floor it and hold it for a couple of seconds.

Do you guys have any ideas what might be causing this or where I should begin my trouble shooting?

Thanks in advance!

-Cajun

911rudy

Cajun,
I had a similar problem caused by water in the gas tank. Hav you recently filled up?

Cajun

Yes...two or three times since this problem has arisen.

Due to time constrants, I maybe put 100 miles on the car a month...

Miles965uk

Check the outlet hose and o-ring to the TB to see if they are loose. I had similar prob and the outlet hose wasnt on good enough

Cajun

First let me say that I like your name!!! (My name is the same as yours, but with a "y")

Can you give a an idea of where this hose is located?

Thanks in advance...

Miles965uk

Haha cheers.
Its the big one going to your intercooler. Right at the back of the engine.

Cajun

Thanks for the road map. I will check it tonight after work...I will let you know what I find.

ferraripete

myles, i don't know that you will see more than .9 bar w/ a 1.0 bar spring. especially w/ the andial type clock replaced guage. i think .9 is about what you should expect. now the o-ring that miles is suggesting you change may not be a bad idea anyway.

Cajun

Thanks Pete.

I will be making an appointment for the car with my mechanic today. It is time for the 60K service anyway.

Mark Houghton

Another thing to be aware of is that if any of the orange O-rings fail and allow boost air to leak, it will affect your AFR somewhat at idle. If the leak is bad enough, it will cause a stumbling idle, because your vehicle will be running richer than it should (that leaking air is supposed to make it into the combustion chamber). Remember, with CIS the fuel addition rate has already been determined by the volume of air moving across and deflecting the plennum. And if all that air doesn't make it to the combustion chamber (i.e, it leaks out somewhere via a bad o-ring), things will be too rich. You should know right away via poor idle. This happened to me once when I was setting up my boost control and went just a wee bit too high, causing the overboost protection circuit to shut everything down. If you haven't experienced this, it's rather violent as the fuel shuts off...then starts right back up after the boost is bled off. It caused one of my o-rings to dislodge, and the car ran like crap and would barely idle.

mark '87 930

Mark, I may be totally wrong here, but I'll ask anyhow.

At idle, your car operates on vacuum and not boost. So wouldn't the leak between the turbo and Throttle body be more of a 'sucking air in' action, hence giving you a lean condition?

Just my logic... not actual fact (that's why I am asking).

nathanUK '81 930 G50

I thought that too. It would be nice to know for sure.

WERK-I

I would check out your control pressures out of the WUR. Sounds like an over rich condition. Check your manifold pressure hose coming of the throttle body to the base WUR. Also, check your atmospheric vent on the top of the WUR.

Mark Houghton

And, to be honest , I may be totally whacko!!! (I'm just a shade-tree mechanic with a vivid imagination). At idle, I could be convinced that the system is working in a vacuum mode. Although the turbo is spinning and producing a minimal boost, the boost diversion valve (that opens when off-throttle during shifting) would normally be open during idle, thus preventing any degree of boost from building. So, I guess you've convinced me that at idle, we're talking vacuum and any poor running due to bad o'rings would be due to a reduced vacuum affecting timing. I'm on the fence, though, regarding whether is would cause a lean condition. Only if the reduced vacuum causes the fuel distributor plennum to deflect less, which I guess is possible.

However, at anything over idle with the throttle plate opening up, the turbo will begin to generate some boost (once the boost pressure becomes greater than the vacuum generated by the engine) and my guess is that the intake system would be at some degree of positive pressure even at minimal throttle position. And under those condtions, a leak in the system would cause an overly rich in mixture (see my earlier logic - faulted though it may be).

Since there just aren't enough true experts to go around, I guess that's what this forum is all about. We all learn by sharing our thoughts and experiences, and if we didn't challenge eachother, then nobody would learn anything. All I know is that my machine ran like crap at idle and at boost when one of my orange o'rings dislodged. Probalby due to ignition timing changes because of reduced vacuum at idle, and ignition timing + AFR changes because of reduced boost beyond idle.

Thanks for reading, and thanks for your push-back!

nathanUK '81 930 G50

I agree that the turbo is always spinning, but I don't agree about there not being a vacuum. You need to get some gas flow to get the turbo to charge. A supercharger would be different. I reckon you (we) will be lean at idle and cruise, rich just before the boost gauge starts to move. Just a theory.