Overboost!

[e170drvr]

Ok, I have an 87 with the usual mods in place. tial 46 w .9 bar spring. My car is never tracked. with quick bursts up to 1 bar, not sustained. Frankly, I usually run out of gear, real estate, or balls. usually in that order, before I get it into sustained boost. So I had the car out this morning, wonderful crisp cold air, and she is just running like a scalded cat. Get out in a nice wide-open clear stretch and decide to let her run a bit. 1st and 2nd gear are gone in a nano-second get it into third, and we are really digging! Right after I went plaid, I got into the boost kill switch. Now i'm wondering how much I have been running boost in excess of 1 bar! Car seems fine but I need to take care of this problem. I guess I need a boost controller of some sort. Do you guys have one that you recommend? With simplicity and cost being a concern. I know there is plenty on this on the board written about this, but would you guys have a suggestion considering the car is street only? I was running the .9 spring with my stock headers but since I installed my GSF headers the boost goes higher. I would like to run at .9 bar.

Thanks Eric

[rsrmike]

You might have a leak in the wastegate "signal" hose?

Overboost switch usually turns off the fuel pumps around 1.35 bar...

Are you only using the factory boost gauge in the tach? If so, get another one, even a simple one, plumbed in for testing purposes.

A boost controller will only raise boost above whatever spring is in the wastegate, you either have the wrong spring, or have a problem with your wastegate, unless your overboost circuit is malfunctioning. I'd say, get a good mechanical boost gauge and have a friend ride w/ you to confirm you are, in fact, overboosting

[rsrmike]

You can buy a 944 brake booster check valve, w/ nipple, and replace your existing one w/ it to have an easy way to plumb a mechanical boost gauge...

It's in the trunk on the back of the brake boost, not more than 2 feet from where the clock mounts

[911boost]

Before getting too worried about it, make sure the electrical connection to the overboost switch is nice and tight. I was having intermittent overboost issues, so I unhooked the electrical connector, squeezed it a little with a pair of pinch nose pliers, then reconnected it. It was much tighter, and I haven't had any problems since.

Bill

[e170drvr]

Hmm, will check the hose. I have the clock style boost guage. not sure where it is plumbed. will check it out.

Thanks

[e170drvr]

Bill that could be the problem, I know that connector is not too tight. I don't know how I could have hit 1.34 bar. The thing that bugs me is it kicked in when boosting hard on a cold day.

Thanks
Eric

[Miguel Antonett]

Just curious, how do you know it was the overboost kill switch?

[jimmcc]

How early into your drive were you when you went for boost and believe you the overboost switch kicked in?

Jim

1980 930
1995 993

[A930Rocket]

Has it always pegged at .9 bar? I know when I went to GHL headers, I had to use a .8 bar spring to get 1 bar or it would overboost and cut out. A set with bigger wastegate pipe fixed it.

It might be this or the cold air.

[e170drvr]

Thank you guys for the ideas, I think it was in fact the overboost switch connector being loose, I tightened it up with pliers. I just got back from a drive ran it real hard, could not duplicate the problem. That connection was very loose, I don't know why I didn't tighten it last time I had the IC out.
Miguel, I don't know that it is the boost kill switch, but I can't think of anything else that would cause that behaviour, other than a rev limiter, which I don't have. It hit the cutout then ran like nothing had happened.
Jim, the car was completely warmed up, and had been driving probably close to an hour.
Rocket, the car would stay at .9 with the stock headers. With the GSF it is slightly higher and will creep up to 1 bar but won't go any higher.

Eric

[911boost]

Glad to hear it Eric.

[cl8ton]

Eric, great post as I battled over boost for a while now!
My engine is out for maint and will apply 800 grit SP/Jewel file to all connections

[Miguel Antonett]

If you don't have a rev limiter, then there is nothing else with those symtoms. Keep us informed.

[mark houghton]

Originally Posted by A930Rocket

Has it always pegged at .9 bar? I know when I went to GHL headers, I had to use a .8 bar spring to get 1 bar or it would overboost and cut out. A set with bigger wastegate pipe fixed it.

It might be this or the cold air.

I think 930Rocket and RSRMike hit the real salient points. You go with a free-flowing aftermarket header, and your boost characteristics change. Add cold dense air, and suddenly you're overboostiing beyond what you normally experienced. Without an accurate boost gauge, you don't really know if the overboost kill switch activated because of out-of-control 1.3+ boost, or just because the connections were loose. Either way, it's conforting to know that your overboost fuel cutout circuit works as intended!
You may want to drop down to a .8 bar spring and add a boost controller to get the .9 or 1.0 that you desire.

[Miguel Antonett]

I agree with temp comment from A930Rocket above.

FYI. My tach gauge indicates .5~6 during the summer and .8 during cold weather.

[Schwarzeritter]

I'll have to agree with Mark,
often we have seen engines with similar issues and not just porsche applications.
It wont be super easy to replicate the exhact condition in which your vehicle was run.
Because Altitiude, Ambiant tempreture, moisture in the air, in addition any such modifications.
For a N.A. car ( depending ofcourse ) it's typically just going to create a rich or lean condition
and the car might not preform correctly. However in most turbocharged applications things
can go lean and tend too ( depending on how advanced management is ) but surely the 930
has its own limits control wise. Even though you might feel comfertable that the connector
was lose, I would certantly consider a proper gauge. Typically when so called cold air intakes
are added and turbomanifolds or exhaust systems are added depending on how extensive
and the turbochargers capabilitys things tend to go leaner because there is a increase is flow
vs restriction. Each engine will differ slightly for whatever and there for no 930 will react the sameway exhactly. Could be as simple as your heads flow a little better or a little worser etc
Thats my only 2cents.

Good luck ^_^

[Miguel Antonett]

Who is this tian149? it is in every thread out there... Wayne time to act.