Knock sensor question

[JayRolla]

This is kind of stupid, but my car has been having power loss when I boost. I thought it was a boost leak because thats what it feels like, but I dont seem to have any leaks. Im at work and decided to check my knock sensor. Its brand new so I thought it wouldnt be that. The sensor was all loose and about to fall out. Would this cause me to retard timing so bad that my car feels like it has a boost leak. Im working so I cant go test it now but would this be the culprit?

 

[oldman]

I thought it was a boost leak because thats what it feels like, but I dont seem to have any leaks.

How did you come to this conclusion?

 

[olmytsi]

A loose knock sensor will indeed cause it to pick up knock when the motor is not knocking.

 

[JayRolla]

After I went to my mechanics and did a boost leak test. I had a small rip in the vaccuum line from the j-pipe to the actuator, so indeed I thought this was the reason I was losing power. Fixed it and still have the same problem. I waited till my car was cool today and checked the knock sensor. It was pretty lose. So my conclusion is that it was vibrating causing knock because my logger says its knocking 43 counts under WOT and I never had any real PK problems. I didnt know the ECU could pull timing that much. When I floor it, the turbo boosts but the car hesitates real bad feels like a N/A. So the ECU can pull the timing really hard right?



Also off subject. I just rebuilt my motor. Before it was rebuilt I was runnign 9psi, using the stock actuator and no MBC. After the build, all I changed was to 8.5:1 pistons, the turbo boosts 11psi. Would the higher compression cause me to run more boost? Or is it something else all together. Its just wierd to me.

 

[Newlogics]

After I went to my mechanics and did a boost leak test. I had a small rip in the vaccuum line from the j-pipe to the actuator, so indeed I thought this was the reason I was losing power. Fixed it and still have the same problem. I waited till my car was cool today and checked the knock sensor. It was pretty lose. So my conclusion is that it was vibrating causing knock because my logger says its knocking 43 counts under WOT and I never had any real PK problems. I didnt know the ECU could pull timing that much. When I floor it, the turbo boosts but the car hesitates real bad feels like a N/A. So the ECU can pull the timing really hard right?

Yes, ECU can pull a LOT of timing. Back in the day, when I had phantom knock problems on my 1G, I've seen timing get into negaives (~2* after TDC!) The car would actually decelerate every time I'd give it throttle.
In your case, it seems like loose knock sensor is causing that. It it wobbles and vibrates, it'll send a false knock signal. Tighten it back up (just a bit more then hand-tight though).



Also off subject. I just rebuilt my motor. Before it was rebuilt I was runnign 9psi, using the stock actuator and no MBC. After the build, all I changed was to 8.5:1 pistons, the turbo boosts 11psi. Would the higher compression cause me to run more boost? Or is it something else all together. Its just wierd to me.[/QUOTE]

 

[JayRolla]

Yea i tighted it but it is a pain to get a tool in there and tighen it. I think I got it tight enough this time, if it pops out again thin a little thread tape would be ok. I tightened it with the motor out of the car when I did the rebuild so I thought I tightened enough. Any ideas about my second question on the boost after the rebuild going up?

 

[olmytsi]

Just tighten the knock sensor to spec and go for a test drive.

 

[Newlogics]

Yea i tighted it but it is a pain to get a tool in there and tighen it. I think I got it tight enough this time, if it pops out again thin a little thread tape would be ok. I tightened it with the motor out of the car when I did the rebuild so I thought I tightened enough. Any ideas about my second question on the boost after the rebuild going up?

Could be several causes.

A bit more restrictive (smaller) vacuum lines
Imperfection is sealing somewhere in vacum line (bleeding air a little)
Sligtly bent actuator arm, providing more resistance.

 

[JayRolla]

All the vacuum lines are the same, and the actuator wasnt hit at all. I did the rebuild so im pretty sure they should be ok. Also did a boost leak, wouldnt that eliminate leaking vacuum lines. Thanks for all the info on the knock sensor, im getting off in about an hour so I hope it fixed my problem.