boost weirdness

[wfoote]

Here is one I haven't been able to figure out.

When I first start up the car cold or hot, I consistently get one overboost to 20PSI with fuel cutoff if I don't back off. (It is a fun ride though) Here is the weirdness, after that first overboost it will consistently regulate boost at 5PSI no matter what I am doing. It also doesn't matter how long the duration from startup to the first overboost is. e.g. it takes me 15 minutes from my house before I can get on the car or if I start up running errands and get on it in a couple of minutes it behaves the same.

I should say the car is relatively new to me, but I have replaced a broken piston, done a valve job and any number of other things trying to chase down a rough idle. Including replacing a lot of vacuum, PCV and intake lines and components. I do get 18inhg at idle and 24inhg when decelerating and usually a rock solid 5PSI and a very smooth idle now.

I haven't checked for a restrictor in the line to the boost controller, but I would expect consistent problems with boost if it were missing.

93 SS auto Bone stock with a boost gauge.

[jefferson]

Sounds to me like your wastegate is sticking closed. I would check it for smooth operation and make sure there are no catches in it.

Jeff

[Arctic Assassian]

You beat on your car when it's cold? I never make boost till the thing has warmed up. 5psi sounds like ecu safe mode. and a stuck wastegate would cause you to overboost constantly, unless it was stuck OPEN.

[wfoote]

I will check the wastegate operation.

I was trying to keep the running commentary minimal. I live 7.5 miles from the highway. 3.5 miles on dirt and a one lane paved road for four miles. The car is plenty warm by the time I get to where I can open it up. In town, I was implying while running errands the car stays warm and the behavior was the same. I was trying to describe the behavior seems electrical, not time related.

For kicks and grins tonight I got the car warmed up and got initial overboost then 5psi limit. I turned the car off and on and was able to overboost again then back to the 5psi limit. I think you are right, the ecu seems to be in limp mode. Of course there isn't any ECU light...

thanks for the pointers guys.

[g20sleeperjdm]

You beat on your car when it's cold? I never make boost till the thing has warmed up. 5psi sounds like ecu safe mode. and a stuck wastegate would cause you to overboost constantly, unless it was stuck OPEN.

yup.. stock wastegate i'd assume? sand the inside of it and replace the spring while your in there.. should fix the problem.. mine got stuck closed one time.. hitting 20lbs is fun but you'll lean out quick and destroy your engine.. so fix it. lol

[wfoote]

Your honors, your client is a moron. That would be me.

I had the lines crossed between the wastegate actuator and supply.

Now, the boost is limited to about 10PSI yay!

The bad news, this only lasted about three runs and now it is back to 5PSI...

My thinking is the wastegate and actuator are functioning properly but the ECU is limiting the boost for some reason. The only stored code was for an improper air flow sensor. I recently ran the battery down and tried to start the car, I suspect it got an unexpected low voltage. I then hooked up the green connectors and verified the boost controller was clicking. I then hooked up the black connectors and went for a drive. I got a code 51 which is a neutral safety switch but nothing else with the low boost. I stopped and put the car in park then finished the drive home. By the time I got back the CEL was flashing indicating it had cleared all codes.