Well got this little software toy and here is what I found:

only while accelerating (not even hard), I will see retard come into play. The harder the acceleration, the more retard I get. It starts at idle up to 6000+ RPM. At 100% TPS, I will generally see max. timing retard under load.

However, if I am say like in 2nd gear and rev. slowly up past 6000 RPM, no knock will appear at all. It can run up there constantly without seeing retard - as long as I don't load the engine.

I put in 101 unleaded with no change. I wrapped the knock sensor in header wrap to try and eliminate possible header vibration interference (cheesy quick job just to cover it so I can test header theory). I have hooker shorties - and no leaks are apparent. No changes have been made to the PCM.

I do not want to desensitize the senor - although I only run 91 or a combo of 91 and 101. Will protecting it better work if it is the headers causing vibrations?

Thanks all for the help!

 

BTW, from my user name, I guess you would know I have a '95 LT1 with 52K miles, mild porting and 1.6 rockers. In addition I have a LT4 knock sensor installed.

Also, DataMaster is showing I am running rich based upon the LT BLM's. I am constantly below 110 both right and left cruising down the road in closed loop. This seems to coincide with my bad gas mileage also.

 

With that octane it should not be knocking with just those mods (unless you messed with your timing chain/gears).

Seems more like something is causing a rattle. Also just a little concerned all the passages on the heads are ok (I have never swapped it so I have no questions or advice there).

I know you said only under load but does it do it parked and reving? If so, does your engine twist a great deal when reving?

Hal

 

Hal,

What do you mean about my passages? As for the motor having extreme vibration, it does not. I will check in detail tomorrow for anything rattling.

If anyone has ANY kind of input, even if you have never had the problem, give me your thoughts please.

I know I am missing out on many horses because of this.

Ben

 

I don't think you are going to have much choice desesitizing it, you are already doing that by wrapping it up anyway. However, there are some things you could check. First thing is to do do it verify that you put in the LT4 knock sensor in correctly. There have been several case where it was on too tight or too loose. Just back it off, and tighten it EXACTLY to spec. Remember this is a very sensitive piece, so torquing is critical.

Second, you could have a touchy sensor, swap back in your LT1 knock module and sensor and see if it changes.

Third, just to verify that it's not something like a rocker coming loose, double check your rockers and retighten to spec. The last time I had knock everywhere it was a loose rocker. Knock throughout the band is pretty serious.

Fourth, fill it up with 104 or 110 unleaded only, just get as low in the tank as you can to get rid of your 91 and make a few passes. See if there are any changes.

Fifth, if you are POSITIVE that it's not anything else, desensitive it. Sometimes it 's the only way

-Ernest

 

Thanks Ernest,

I have my header collector off and tomorrow I am going to run it with it off to see if that is possibly the issue.

As for desensitizing it, I tried 10% and it made minimal difference. I have the resistors for a 20% and a 30% reduction in sensitivity.

As for tightening to spec's, Thank you for the reminder. Even if the collector off shows a difference (and thus the false knock), I am still going to take off the sensor, clean the threads and retighten to spec's.

Man, I was under that engine all day today and I found nothing that would be banging against the engine to give me false knock. However, I feel I am getting closer to a solution. I will post when I find it. Now once I do this, I can start programming my computer!


Ben

 

Well, thanks for all the help everyone. I have in addition to your responses read about every post regarding false knock on this whole board.

I went up to 30% desensitization with minimal change (max retard was reduced some that is it). I check the whole engine compartment for rattles with nothing found.

One big thing I see different from all the other posts on this subject is the fact that I only see timing retard when I load the engine - no other time. Not even when I have the engine at high RPM like in 2nd gear (thus not much load) do I see any retard. Could this be my Hooker shorties and the vibrations they set off that are bouncing off of the block? That is the only thing I can see that could be and issue because that is when the most vibration happens through the headers. If it was rockers or my 135 lb springs I use, wouldn't the knock be constantly present?

Thanks all.

 

Pull the timing or add 104 unleaded like I suggested, this will give us a better clue. We still need to make sure it's false. just pull out a ridiculous amount, like 10 degrees from 2000rpm to 6000rpm. Then drive it. If it's still retarding, it's most likely false. Then we can focus on what is causing the flase knock.

-Ernest

 

Ernest,

do you mean for me to specifically use 104 octane even though I have tried pure 101? Will the 3 octane ratings make that much of a difference.

As for pulling timing, I will do that as soon as I get TunerCat underway in the next few days. Will let you all know so others can learn from my problems.

 

no, I'm sorry, I must have missed that. If you have filled up your tank with 101 unleaded gas, that's still good enough, that's 8 extra octane points over regular supreme. If it still knocks, it's false (or your car is broken big time ). That's interesting that the 30% made little difference. Have you swapped with an LT4 or someone else's lt1 to make sure the knock module is not just loco? It's a fairly inexpensive piece to purchase if you have to (LT4 knock module is $25).

As for other locations for banging, it doesn't have to be up front, I once had a tranny crossmemeber that was loose and caused it to me. DO you have any datmaster scans we can look at to see if we can spot any other dicrepenancies? Or diacom, I think I can convert that.

-Ernest

 

If you had no change in knock after going to 101 oct I would say its false. I have the hooker shorties and roller rockers and get alot of false knock too. I just used Tunercat to change the max retard to 4* at wot .

 

It is my understanding that under hard accel timing will retard, then pick back up. Are you seeing knock from the sensor or just seeing timing being retarded? You might not have a problem at all. Under hard accel mine will retard to 33-35 degrees with no knock signal.

Larry

 

I am seeing both. If I blip the accelerator, my knock numbers go up (datamaster is couple hundred at a time) and it retards timing. However, as for putting a load on the engine like from 1000 RPM to 5000 RPM in WOT, the knock numbers do not move, but I get retard. However, this could just be that is sees a couple and retards timing and DataMaster is not registering it yet because it hasn't reached the 100-200 mark yet where it registers it.

 

If I can figure out how, I will try to put some numbers up tomorrow from the DataMaster...can someone tell me how to do it?

 

Yeah believe me, I will be making changes to my computer to reduce the effects of knock. However I think this is a problem not just I am having and it would be nice to find the solution.