Engine Performance Mystery

[howardc64]

Had been noticing excellent engine performance improvements each time I disconnect the battery (always disconnecting it for some period of time) Then once I get a "Performance Reduced" message, all of the performance gains are gone. As soon as the engine is turned off, the message is gone. The improvement performance never comes back until I disconnect the battery again. I've done ETM cleaning and eliminated that as the cause of the problem.

I can blame the ETM but I have no definitive proof. So I got myself an Auterra dyno scan OBD II reader/tool. Very nice tool. Here is what I observed

When I have the lower performance, I had no error codes. But the vehical monitor test screen's none continuous tests was all incomplete. As soon as I did the battery disconnect, performance came back as well as these tests all completing.

So I have no codes stored or pending in either case but clearly the car computer behaves differently with the OBD II reader in each case. Any clues?

by the way, these car repair forums are peer to peer message boards. It would be really cool if these computer based OBD II tool have a live peer to peer connection infrastructure like the chat programs. We can debug each other's car remotely!

[Johann]

The moment the ECU goes reduced mode it will use substitute values for a lot of functions. I think this is the reason why you can't see anything.

For you reduced power mode problem can be many things. First check the IAT and see if it gives representative values. If it goes way below freezing the sensor is shot. Then there is the MAF which could be out of bandwidth because it's dirty. The ECU will pick a substitute value for it but the only way for it to be sure it will operate within safe range is to take over the ETB and only use as much throttle as needed for the substitute and unmeasured value.

Another thing is the turbo solenoid and the vacuum hoses but normally that would give you an overboost DTC.

If the solenoid isn't functioning the throttle plate needs to adjust for it making it run out of line with the paramters expected. ME 7 is load based. It calculates boost based on load using the MAF as a measuring point, the ETB and the solenoid as a regulator and MAP as a verification. The throttle pedal only tells the ECU how much load the driver is asking from the engine.

By resetting the ECU you will reset all the adaptive parameters. If you want to blow up the engine please proceed with this procedure...