jgeorger

Did you mean to say you had an LT4 knock module (as opposed to knock sensor)? If you do have an LT4 knock sensor, that may very well be your problem. 95 and older knock sensors use a different resistance than 96 and newer.

Joe

95Blackhawk

Sorry I meant LT4 Knock Module. Sorry for the confusion. Actually, could a new knock sensor help in any way?

jgeorger

It's possible. However, you might not want to torque the knock sensor quite to spec. I wrap mine in teflon tape and torque it to something less than spec. I have also heard that aftermarket spark plug wires can induce false knock - that is according to Ed Wright. I was getting plenty in mine car, I thought my exhaust might be hitting somewhere. I just zeroed out my knock tables. My car is NA, so I'm not too worried. I might have fixed the exhaust but I haven't reflashed the pcm yet.

95Blackhawk

Thanks so much jgeorger for that thought on the aftermarket wires. I have Taylor 8mm's in my car. If that is it, well then I am screwed to try and fix it. However, would that answer the fact that I only see retard when I load the engine?

Here are my next steps:

Put my LT1 knock MODULE back in and read the retard.

Check the tranny for any banging (only checked engine bay)

Find a way to insulate my Taylor wires better (suggestion on new wires anyone??)

Finally, if these do not work, just eliminate the retard from my programming (and pray I never get bad gas...in my car).

Thanks all! I hope this is helping more than just me on this issue. In fact I recommend that if you have made any kind of mods, to check out your PCM. Doing this has been the biggest eye opener.

Ben

ryaskovic

Check your motor mounts. I got rid of knock by replacing mine (originals were old).

Rob
95Z28

95Blackhawk

Rob,

How do you know if you have bad mounts? I have 52K miles on my 95 so the mounts are over 7 years old (car was built in July of 95)

ryaskovic

Take a look at the rubber part and see if they are cracked or dry-rot looking. Mine weren't cracked but I could see how they were old and smooshed.

95Blackhawk

Thanks Rob,

I will be looking for smooshing in the next few days.

Just a note that I have been reading up on piezoeletric knock sensors. I found that when the wire carrying the signal itself is vibrated too much that this can cause false signals. This could be the reason why you had false knock Rob...and me also.

This seems to hold true as I accidentally forgot to reinstall my wire to the sensor once and so it was hanging loose. Man, was I getting serious retard!

Ben

Injuneer

If you are saying you saw serious retard with the sensor wire disconnected, that has nothing to do with the wire vibrating.... when the PCM can't find the knock sensor (i.e. - disconnected), it defaults to an internal retard program, and will pull anywhere from a couple degrees to 15-deg of timing.

You also seem puzzled why you only get knock retard when the engine is under load. Again..... that's when you normally see knock...... when the engine is under load. That's when cylinder pressure start to climb, producing "end gasses" that auto-ignite. At part load, cylinder pressures are nowhere near what they are when the engine is under load.

Highlander

Try swapping PCMs it is very common here that when cars are pingin for no apparent reason and start heavy timing retard the pcm may be at fault and its sending a lot more advance than what she has on spec or display....

Try that.

BTW I had a car with a huge problem like that today and all it was was the PCM.

95Blackhawk

Thanks Highlander,

This is an interesting issue and if it is common, it should be something we should all be checking.

Again, what you are saying is this: what my DataMaster is showing as timing at any particular RPM and MAP, may be incorrect and in fact may be more. Even if this matches up with my timing map?

Thanks for the input!

Ben

Highlander

It could be more since it will have a max retard set at a specific table...

What I was saying is that the car may be assigning 42º of advance and its actually sending 50-55 as a mistaken or damaged pcm....

Dont know why but i had seen huge knocking!!! and huge retard and changing the PCM fixed all of it.