Before I start, I just want everyone to know that this is just what happened from MY experiences... I'm sure I will get many "My LT4 Knock Module works fine" replies, and that's ok. I'm just explaining the situation that happened with me...

I first got the LT4 knock module back in the fall. Didn't notice any problems with it, however after I put the Hot Cam in, I had some misfiring. I was relieved that it went away after a new opti and street tuned programming, however my car still lacked a lot of power after the tuning (see times in sig)

So I Decided to get PCMforless tuning after all the great Hot Cam stories I had read on the board. I have a big track event Thursday, and thankfully the PCM arrived today after an initial delay. I told Bryan that in my programming, I planned to continue using my LT4 KM. When I got the PCM, I found a LT1 KM in the PCM, which i switched out with my LT4 KM. When i started the car up, it sounded pretty good, but a little different. So i took it for a dry. At Low RPMs, I noticed a weird reaction. IT's hard to explain, but it felt like there was a seperate "lope" to my cam. I could feel a vibration at low RPMs, but it seemed to smooth out at higher RPMs. So i decided to give it WOT from a dead stop. This is where the horrifying events happened. The engine RPMs seemed to violently vibrate from 1100-3800 RPMs. During this the car accelerated very slowly. I have been in Carbed 350s that have dropped valve springs or were running on six cylinders, and this felt WORSE. I tunred the car on and off a few times to see if some Key cycles would help, no difference.

At this point, i thought to send the PCM back, but then for the hell of it, i decided to swap KMs. 100% different. This was the programming I was looking for. Smooth low RPM acceleration with aggressive high RPM power. The car felt like it had dropped a few tenths from the programming.

I'm not sure exactly what happened, but I don't plan on using an LT4 KM anytime soon. Anyone know a possible reason for this problem? Thanx for reading and I would appreciate any insights.

 

I find your post interesting because I too have the Hotcam and other mods similar to yours. I am also running the LT4 KM and swapped it in when I got my PCM from PCMforless.Although I haven't had any vibration, my best with this combo is 13.63 @ 103. The time in my sig is before the cam. I'll try the LT1 KM and let you know. In the meantime... anyone else have this problem?
Matt

 

dang, now i have even more things to take into consideration before i even get half way to the hotcam kit. do alot of people use lt4 km's over the lt1's after pcmforless tunning? why is this?

 

i think im gonna wait til i get programming because the LT1 knock module can be made less sensitive

 

he may have programmed the PCM using the stock KM, and when you put in the Lt4 KM, it was cancelling out the programming because of the redundancy.

 

When Ed Wright programmed my PCM, he desensitized the knock retard function for the LT1 knock module. I asked him what would happen if I installed the LT4 knock module. He said it wouldn't hurt anything.

 

Sounds like you may merely have a bad knock module.

 

It sounds to me like you have defective LT4 knock module. Or something else happened like the PCM wasn't plugged in quite right or something fluky like that. Also, your PCM takes some time to acclimate to your car. I just put headers on and it ran like total **** for the first hour, my friend in a mustang could *almost* hang with me, haha. After the first hour of driving 95% of the stumble was gone.

There are SOOO many people using them and this is the first time i've heard of one going berzerk. The two should be fully compatible, it's just that the LT4 has a better filters on it allowing narrower ranges of frequencys through.

edit* shoebox snuck in there and stole my idea!!! i'm with ^him

 

Another vote for a faulty KM. Do you know anyone else with a LT4KM? See if you can put thiers in your car to test it out. Also make sure you undo the battery or pull the PCM fuse when you are swapping.

 

Did the LT4 module get dropped, wet, or exposed to any type of electrical charge(static)? Sounds like a bad one regardless.

 

I'm still running my stock KM and stock engine, cam, heads, etc and was noticing the various 1/4 ET's on here. I'm excited my car is running 13.39 @ 104.67 with just a UD pulley, Moroso CAI, Jethot LTs, 3"y no cats, open Borla, free mods & Nitto DRs.

I can't wait to see what I'll get with 4:10 gears.

 

The knock module hasn't been damaged as far as i know. But maybe Shoebox and Bennyboy are right. How easily can a knock module be damaged?

Nothing was plugged in improperly. I double checked the connections after the first bad run. Everything was good. Simply swapping out the knock modules made the HUGE difference.

Another question/thought: I didn't think the PCM had to be programmed for the LT4 knock module, i thought it was almost a "bolt-on" which the computer adapts to? If Brian programmed to desensitize the LT1 knock module, would there be any point to me buying a new LT4 KM?

Thanx again everyone for the replies.

 

KMs can go bad. I found my old LT1 rolling around in my glove box a while back and for the hell of it just put it in my PCM to see if i got more knock retard with it over the LT4. what i found was that the LT1 must have been in there a little long b/c i got 12 degrees KR constantly that would sometimes just drop to 0 for a sec and jump right back up to 12 degrees. the KM didnt act like it was giving me false knock... it simply went bad.

 

you dont program a computer for the LT1/LT4 KM. you can "desensitize" the knock sensor with some resistors but the same cannot be done with knock modules. there are tables to change in the pcm related to KR like max retard vs RPM which would likely be THE ONLY table Bryan changes and it has no effect on sensativity or functionality of the KM.

 

So would it be a good idea to pick up a new LT4 Knock Module? Or should I just stick with the LT1 KM i have in there now? I'm starting to wonder if the reason for my ****ty times (see sig) were the result of a bad LT4 knock module that was retarding too much timing.