LT4 Knock Module Less Sensitive - Urban Myth??
 

Everywhere I go I read that the LT4 KM is less sensitive than the LT1. I'm wondering if this is true or just a popular belief. Does anyone have definitive proof the LT4 KM is less sensitive?

I installed GMPP 1.6RR (with LT4 springs / new lifters) on my LT1. At various RPMs with hot oil I hear them ticking, and when they tick I can watch the knock counts rolling. This is sitting in neutral in my garage using the LT1 KM.

I figured a LT4 KM would help the problem. So I bought a LT4 KM off Ebay and tried it. Well with the LT4 module the knock counts are totally out of control. The slightest noise at all causes it to count. So I'm wondering, is it a bad module or is it just that the LT4 module is tuned differently and it doesn't agree with my noisy LT1?

Opinions? I thinking about ordering another new module from GM, but figure I'm wasting my money...

:cheers:

you are running 93 octane fuel and a reprogrammed ECM correct?

I still have my LT1 Knock Module installed, false knock due my valve train was taken care by the tuner.



Mike

The LT4 knock module was designed to work with the GMPP RR's. Are you sure the rockers are adjusted properly? How much spark retard are you experiencing?

Are you using Datamaster? If so, send me a data log. I'd like to see what's going on.

Also, I'm using the LT4 KM in my 94 LT1 with success.

Yep. It's definitely not true knock.

I don't see how you can tune false knock out in the PCM. You can disable the spark retard which is a result of the false knock, but not the false knock itself which is a function of the KM. I don't want to mess with the knock retard parameters because I want the safety. All I want is to make the KM a little less sensitive to the rocker rattle. That's why I'm asking about the LT4 KM which in my tests seems to be much more sensitive. Unless I have a bad LT4 KM.

Looking for someone else who has "tested" the LT4 module and therefore can confirm my module is bad.

Yes, the RR are adjusted properly. My tests are sitting in neutral in the garage watching the knock counts when I hear the rockers clicking. When driving I get huge retard using the LT4 KM, not too bad with my LT1 module. Yes, I use TTS, I'll send you the logs from my neutral tests from both KMs - you'll see the LT4 module going nuts with the counts.

I suppose I can answer a portion of your questions. Yes, the LT4 module is less sensitive than the LT1. (I was the ESC calibration engineer for the LT1. I retired just prior to the LT4 introduction, so my only knowledge of it is the ESC data sheet for assorted calibrations.) Roughly speaking, the low end sensitivity of the LT4 module is about 20% less, and the high end is about 5% less than the LT1 calibration.
Getting rid of false knock while recognizing real knock is difficult. (Trust me on this one.) Due to the fact that this is a vibration based system (knock pressure waves excite the cylinder walls, making the pinging sound) other noise sources such as piston slap caused by aftermarket pistons will also make the cylinder walls ring, causing false knock. And, as you and GM Powertrain found out, broadband noise sources (in this case, roller rockers) of sufficient magnitude can sometimes swamp out the filtering in the ESC module and be read as knock. Unless the (factory) calibration is made less sensitive (at the risk of it being deaf to real knock), or have the software only read the knock signal at distinct crankshaft angles where knock is expected (requiring more complex software), you're left with limited options with a vibration based system.

:thumbs: :thumbs:

I believe the actual LT4 knock sensor is a different part number than the LT1 version. And I'm not talking about the knock MODULE. That is definitely different.

But, as a generality you can "desensitize" a knock sensor by wrapping a few rounds of teflon tape about it and torquing it to spec.

Also... these knock sensors are sensitive to torque specs. If you crank 'em down then they will be more likely to pick up "knock". Put 'em in like the book says (15 lb/ft) and they'll be good.

Thanks! This is what I was looking for. So it seems that the LT4 KM I have must be defective. It is extremely sensitive compared to my LT1 module. Here are the TTS Datamaster files. Watch the knock counts as I try to hold the RPM around 1000.

http://www3.ns.sympatico.ca/krichar/temp/LT1-KM.uni

http://www3.ns.sympatico.ca/krichar/temp/LT4-KM.uni

I'm not sure what GMPP 1.6RR are.

But, if they are the Crane units, unless they have changed, I'm not impressed with them.

Years ago, I tried the Crane Gold Narrow-Body Self-Aligning roller rockers.
Not only did they make noise, I had one of the roller trunnion bearings fall apart and put needle bearings throughout my motor at about 5K miles.

After that, I went to Crower stainless steel self-aligning and I have been very happy with them for the last 45K miles.
They make less noise, I never get knock retard from them.


Tom Piper

I checked out the data logs and everything looked pretty good except fpr the knock counts? Compared the logs to one of mine, my car is running 4* more spark advance at idle and doesn't reach much over 2000 knock counts in a 20 minute run.

Someone with more tuning knowledge than myself will have to fiqure this one out. :willy:

It is very cool to hear from someone with actual technical knowledge on this subject.


I have a question you might know the answer to - since the OBD2 and OBD1 LT1 computers require different knock sensors, should the knock sensor be matched with the knock module? Or does the signal first go through some other circuitry in the PCM which handles the impedance difference, so that the OBD1 and OBD2 KM are expecting identical input signals?


Come to think of it, I have another question - there are 5 different LT1 KM part numbers, being different for OBD1 vs. OBD2 and Y vs F vs B bodies (if I recall correctly there was one module shared, thus 5 variants.) Do you have any information on the differences among these different KMs?

I just spent an hour typing up a somewhat detailed reply to a previous post, but when I hit the submit button the stinkin' computer told me it couldn't find the forum web address. I'm so PO'd at the moment I can't see straight, and I'm just not in the mood to type it all again. I will try to answer these questions at a later date. (This was an hour of my life I'll never get back!)

Exactly! If you are the least bit concerned you don't have the actual sensor installed right, remove it, throw it out, get another, install and torque correctly.

That really sucks, I feel your frustration. If I know a reply is going to be very long, I'll type it in Notepad first. :lol:

:willy: been there before... if i`m making a long post, i try to copy it, before i click post, in case something goes wrong...
that has saved me a few times...

Maybe I've got them too tight. I did have them both out recently when I flushed the coolant. I suppose it wouldn't hurt to loosen them and re-torque. This is such a small little tick at 1000rpm I'm surprised it's picking it up.

Anyone know for sure that the LT4 knock sensors are the same as the LT1 Corvette sensors?

:cheers:

I searched the AC Delco website for LTx knock sensors. Here's what it shows.

1996 LT1 and LT4 engines use AC Delco part number 213-325

1994 and 1995 LT1 engines use AC Delco part number 213-96

So it appears that the OBDII engines use a different part from the OBDI engines.

Thanks Klaus. Now I wonder if I should be using the 213-325 knock sensors with the LT4 knock module? Maybe they are matched?

69427, can you comment? You're the guy when it comes to this ESC stuff. Could this be what is causing my knock counts to go nuts when I install my LT4 module? Or do I just have a bad LT4 module?