can a exh. that rattles REAL BAD tell the sensor to pull timeing???

 

where is it rattling at??

i doubt it though. if you replace it make sure not to over tightn' it becouse it will break the sensor. why do you think its pulling timing?

 

I have heard from more than one person that yes a rattling exhaust can & will be picked up by the knock sensor.

 

its rattleing at the Ypipe and the cat.

it takes off real good (smoking the tires) then it falls on it face, I've been reading the DIY prom, but I as of right now have no idea what is being said.
All sensors, computer and prom (AC) are new motor & trans. both new, so I am at a loss.
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I have got conflicting answers about this, so I wanted to ask the masses at TGO.

 

I have never encounterd it yet as a Tech, but in the past have been told by a couple it is possible. Really would just depend on how hard something is hitting against the engine block. I seriously doubt it's your problem though. Check for codes if the SES light is on, if the light is not on, make sure the bulb isn't blown by seeing if it illuminates when you turn the key to run.

 

Yes its possible and yes I have seen it happen.

Bad accessories can do it as well.

It simply comes down to, "Is the vibration of the same frequency as the sensor is tuned to detect in the block as knock"

Easy as that.

I have seen exhaust, accessories and valvetrain cause it, so it is possible, especially if you are saying loud rattles onto the engine itself or the frame rails.

later
Jeremy

 

Yes its possible and yes I have seen it happen.

Bad accessories can do it as well.

It simply comes down to, "Is the vibration of the same frequency as the sensor is tuned to detect in the block as knock"

Easy as that.

I have seen exhaust, accessories and valvetrain cause it, so it is possible, especially if you are saying loud rattles onto the engine itself or the frame rails.

later
Jeremy

 

Thanks to all that replyed.....I did get some codes, MAF burn off (I have been trying to find out why, relay is new & working, and the MAF is new too) and.....42 the thing is that both the module and knock sensor are new (TPIparts.net's sensor kit)

the car is an 86 IROC that I put a L98 in (RR arms, everything else is stock) and all the sensors that gos with it, other than the exh. rattleing its a$$ off, is there anything else that I should look into?

thanks,
joe

 

Yes it can cause false knock counts, which will reduce your timing. I've recorded it with a data logger with my car. When I put aftermarket heads on it with the Edelbrock headers,Y-pipe and Poly Urethane motor mounts, the clearance between the y-pipe and the undercarriage was paper thin in spots causing it to come in contact under certain driving conditions. I bent the pipe out a little and bye bye knock count.

 

So important, he posted it TWICE!

If the accepted method for testing a detonation sensor in the field is to tap the side of the block casting with a small hammer, and that level of impact is supposed to (by the book) induce adequate signal to cause spark retard sufficient to be observed with a timing light, then it stands to reason that anything impacting the casting can do the same thing.

Even if it doesn't cause retard, why run around with a loose exhaust and artificially lean O² sensor?

 

Vader...that is a good question, I will get the exh. fixed and report back, if this gos on I will have to get a data logger.

thanks to all who replyed

 

I've had my laptop hooked up when my car was idling cold in open loop. If I rev'ed it and got a little snap/crackle/pop because it was in open loop, the knock sensor would pick it up. No, I'm not stupid enough to rev the heck out of my car when it's cold, it was just a simple test.

 

When I built my 355 engine I used foraged pistons and they were for racing (bad idea) so they had .006" clearance when the engine was cold and the engine sounded like a diesel at cold start up. When the engine reached normal operating temp the slapping noise was of course gone. I think you can see where I am going with this story. When I first started this engine the rpm's would go to 1800 (carbed) and slowley run down to around 1300 rpm. Now I had the choke adjusted for 1800 rpm so as the rpm fell the engine required less fuel but the choke was adjusted for 1800 rpm so the engine would start to load up. I have to tell you that it took me awaile to figure this one out. I just could not seem to get that choke adjusted correctly. Well, the ESC system is awake all the time so it heard the pistons slapping at cold start up so as you know the ESC talkes to the EST and it would retard the timing up to 20*. This is what caused the loss of rpm along with the rich mixture. So I went to Fleet Farm and bought a coolent temp sensor that closed at 170* and opened at 146*. I screwed this into the stat housing and wired it in series into the wire that runs from the knock sensor to the ESC Module. Problem solved. Phew!!

Auggie