Perplexing Check Engine Light

[bubbatrucklover]

When I first got my truck(not quite a year ago) the check engine light was on. The p.o. said it was ________(all his "possibilities" were b.s.) I had it scanned and it was the knock sensors.

I had a GM mechaninc replace both knocks the harness etc. THE F'N LIGHT CAME ON AGAIN!!

Now when it was scanned the Discount Auto person said knocks ,but a secondary thing was pre cat O2s

SOOOOOO I replaced both pre cat O 2s..... AGAIN the damn light came on.

BANK ONE AND BANK TWO knocks. WTF?????

All the times I disconnected the battery and after the scan had them erase the codes.

Any thoughts as to TWO faulty knocks and/or harness? Or something causing the knocks to register and it NOT being the actual knocks?

Thanks.

 

[Bigredmariner]

The knock sensors have a bad habit of pooling water around the connections. When they are replaced it is advised to run a bead of silicone around them sealing them up, if the previous mechanic didn't do this then that may explain another failure so quickly.

 

[CJ Hungus]

The knock sensors have a bad habit of pooling water around the connections. When they are replaced it is advised to run a bead of silicone around them sealing them up, if the previous mechanic didn't do this then that may explain another failure so quickly.

Especially if he likes to play in the ocean like his sig.

 

[DV2000NJ]

When they replaced the knock sensors, did they replace the little sub-harness that runs from the sensors to the main engine harness as well?

 

[Bigredmariner]

When they replaced the knock sensors, did they replace the little sub-harness that runs from the sensors to the main engine harness as well?

The way I read his OP yes. I may look for some of the how to's I've seen about replacing the knock sensors, some that show the silicone beading deal. You did it didn't you Dan?

 

[DV2000NJ]

When they replaced the knock sensors, did they replace the little sub-harness that runs from the sensors to the main engine harness as well?

The way I read his OP yes. I may look for some of the how to's I've seen about replacing the knock sensors, some that show the silicone beading deal. You did it didn't you Dan?

Yeah I did. I'm actually going to write it up tonight once my roommates go out. (Of course I get a f*cking stomach virus on Halloweekend ).

EDIT: Also, if the knock sensors aren't torqued to EXACTLY 15 ft-lbs, they will register false knock.

 

[Texas Jim]

When they replaced the knock sensors, did they replace the little sub-harness that runs from the sensors to the main engine harness as well?

The way I read his OP yes. I may look for some of the how to's I've seen about replacing the knock sensors, some that show the silicone beading deal. You did it didn't you Dan?

Yeah I did. I'm actually going to write it up tonight once my roommates go out. (Of course I get a f*cking stomach virus on Halloweekend ).

EDIT: Also, if the knock sensors aren't torqued to EXACTLY 15 ft-lbs, they will register false knock.

I didn't know that...THANKS...

 

[bubbatrucklover]

The knock sensors have a bad habit of pooling water around the connections. When they are replaced it is advised to run a bead of silicone around them sealing them up, if the previous mechanic didn't do this then that may explain another failure so quickly.

Yes sir he has replaced many before and when I mentioned silicone he already had planned on it.

like his sig.

I haven't been back since. I have been close to where the pic is from a few times. Maybe for my trucks one year anniversary.........

When they replaced the knock sensors, did they replace the little sub-harness that runs from the sensors to the main engine harness as well?

Yes sir the mechanic had suggested it and I planned on everything done at once. Even had him put dielectric grease in the conector.

Yeah I did. I'm actually going to write it up tonight once my roommates go out. (Of course I get a f*cking stomach virus on Halloweekend ).

EDIT: Also, if the knock sensors aren't torqued to EXACTLY 15 ft-lbs, they will register false knock.

He didn't use a torque wrench as he's done this precedure many times before,but

I didn't know that...THANKS...

Yah me neither(OBVIOUSLY). Go figure an exact torque would be needed on something I would need to tear apart, re torque it, clear the codes and see.

 

[bubbatrucklover]

So does anyone know aproximately how much the knocks are affecting the performance of the engine thus affecting mpg's?

Could it be as much as 1-3 mpg's that would warrant tearing it apart to see.Or would I be doing it (more or less) so I don't have to look at
the F'n idiot light?

 

[Texas Jim]

So does anyone know aproximately how much the knocks are affecting the performance of the engine thus affecting mpg's?

Could it be as much as 1-3 mpg's that would warrant tearing it apart to see.Or would I be doing it (more or less) so I don't have to look at
the F'n idiot light?

The knock sensors will retard the timing which will effect the fuel mileage.
How "MUCH" it will effect mileage...depends on how much timing the knock sensors are pulling.
It "COULD" be up to 3mpg...easy...
Plus it could cause a noticeable loss of power when it pulls timing...