Presure relief valve??

cougar20th

Registered User
is there a boost pressure relief valve on the supercoupe. and where would it be located. i had something stick today and it seemed and sounded like the air was bypassing the motor somewhere. then it fixed itself. so my guess is that something stuck open and then released.
 
There is no pressure relief valve. But there is a bypass valve that reroutes boost through the SC when the engine is under vacuum. This reduces the load of the SC on the engine when boost isn't called for. It's located directly behind the SC and should open and close if you snap open the throttle from under the hood.
 
IAT - Intake Air Temperture (tells the EEC the temp of the intake charge after running through the intercooler. Used to figure out fuel delivery)
IAC - Idle Air Control (Used by the EEC to control idle speed on the engine by allowing some air to bypass the throttle plates. Also used by the EEC to soften release of the throttle)

Both can go bad but both play different roles
 
Mike8675309 said:
IAC - Idle Air Control (Used by the EEC to control idle speed on the engine by allowing some air to bypass the throttle plates. Also used by the EEC to soften release of the throttle)

Mike, I am assuming by "Soften" you mean a SLOW drop in RPM's after relaesing the throttle.
Are there any ways to modify the IAC to allow engine RPM to drop faster? Like when the MAFS is unplugged, the motor revs very quickly and drops equally as fast.
 
BobGPz said:
Mike, I am assuming by "Soften" you mean a SLOW drop in RPM's after relaesing the throttle.
Are there any ways to modify the IAC to allow engine RPM to drop faster? Like when the MAFS is unplugged, the motor revs very quickly and drops equally as fast.

No Bob dont do that. I know guy's that insist on having the engine RPM to drop instantly after releasing throttle and all that does is create more problems.

Whats wrong? Why do you want to do that?
What are you trying to do?
 
ok. if theres not a "releif valve" does anyone know what would create the motor to register boost on the guage but not feel like it had any boost. at the same time making a wooshing sound of air bypassing or being released.

whatever the problem was it corrected itself a few hours later. the night before the problem the car hit the highest boost it has ever reached. i still feel something stuck open. ideas on stuff to check?
 
MIKE 38sc said:
No Bob dont do that. I know guy's that insist on having the engine RPM to drop instantly after releasing throttle and all that does is create more problems. Whats wrong? Why do you want to do that? What are you trying to do?

I just liked the way it was so quick and responsive, keep in mind I ride street bike and when I let off the throttle, I am used to the quickness of the response. I guess I can see that that would be pretty hard on a larger engine (ie: rods, bearings, wrist pins). It sure didn't idle for crud, and was not very crisp in the upper rpm's.
 
Bob its not so much that its hard on the engine parts but car engines are sealed up somewhat in the engine bay unlike your bike engine. There in a warmer enviroment.
Its done to keep the engine from stalling out after coming down from speed. If you will notice as long as your car is rolling the idle is alittle high because the speedo is telling the ECU that the car is rolling. But once you stop the idle comes on down.
The problem guy's that have made there idle drop like that are now having is the engine stalls on them when stopping after a highway run.
Its funny you can tell them whats wrong they will put it back stock and everything works fine but then turn right around and change it back and the stalling starts happening again. Yet they say there little mod does not cause the stalling, funny you remove there mod and it doesnt stall anymore. I just quit trying to talk to them.

Many carbs in the pre FI era had solenoids mounted on them to do the same thing.
 
cougar20th said:
ok. if theres not a "releif valve" does anyone know what would create the motor to register boost on the guage but not feel like it had any boost. at the same time making a wooshing sound of air bypassing or being released.

My first thought to a complaint like that is exhaust blockage. If the bypass valve is stuck generating boost, then it really is generating boost, you should feel it. So I'm not thinking a stuck bypass valve would be causing that. But something blocking exhaust would allow boost to be high, yet low power produced. Things would get hot enough you should be able to smell the exhaust pipes getting very hot from something like that.
 
If the bypass is stuck open there will be very little boost (less than 2 psi) So I would rule that out as your problem.

Sounds like a cat is broken up. This will cause the sound you mentioned plus the extra boost you mentioned. Check it out with a rubber mallet.

Jeff
 
Youre right! Could be a cat!
I fixed a turbo car that did that and it was the cat stopped up.
Man I foregot that car.

Good call Jeff.
 
that sounds like the answer. something bouncing around in the exhaust and blocking it. i get a clanking from something in the exhaust occassonly. and come to think of it there was a odd smell the other night. although i didnt drive far it could have gotten hot enough. looks like ill be pulling it apart this week.

thanks everybody.
 
Keep in mind that if the converter is coming apart and blocking at the converter, chunks may have made their way through the exhaust system and become trapped in the resonator or either of the mufflers as well.

I mention that simply so you'll be aware of any noises you might still hear, or odd performance events you might notice even after fixing the converter itself.
 
Unless your cat was physically damaged (i.e. it hangs too low and caught a bump or something) you should figure out why it failed before replacing it. Otherwise chances are the new one will just fail too. One of the common causes of failure is a misfiring cylinder dumping unburned fuel in the exhaust, then this fuel burns in the cat.
 
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