Anyone know what application of these is gonna work best with Holley's Commander 950 engine management system? I no longer have a knock sensor to install with it and the knock module is from the 305 and don't really wanna use that. By the way, it's for a HSR 383. Were there differences between the TBI and TPI senors and modules? I'm not really sure and wanna try and get the right ones the first time. I'd call Holley but if anyone has tried to call them, they probably know that it's a bitch getting the right person on the phone over there, plus it's Saturday.

Tom

 

I am not sure of what the CMDR950 is looking for as to a knock signal. With that said I can give an overview of the GM knock systems.

The TPI SD systems ('90-'92) use a low impedence sensor and an ECM internal knock filter.

The TPI MAF ('86-'89) & TBI ('8?-'92) use a high impedence sensor and an external knock filter. The CC carb'd systems also use an external knock filter.

The knock sensor is a microphone that feeds to the knock filter. The filter is what decides when knock is occurring. The knock filter signals the ECM by pulling the knock input low. As long as this signal is low the ECM is registering knock and acting accordingly.

Although there are differences between sensors for the various engines, the biggest difference is in the knock filters.

Being that the SD TPI systems have the knock filter integrated onto the MEMCAL I'd say to go with an external knock filter module along with the sensor. If you have a sensor and filter then try them and see how it works out. It is an easy matter to try different ones as they just plug in.

RBob.

 

You can go to the chevytalk.org site, they have a EFI tech board moderated by Doug Flynn, an engineer for holley, he has been extremely helpful with my 950 setup, and he even runs one himself.

 

Holley sells a harness that uses the GM KS module & sensor. I got one from Summit for around $35. I later decided it was not necessary (with the proper tune) & sold it to another TGO member.

 

And Im the guy that bought it because my stock one was screwed up! Seriouselly, I went to napa bought a knock sensor for a 350 (year 89 for use with external filter) then used rick's filter, or knock module, to power it and send the signal to the commander 950. Very simple, dont over complicate it. You probably have a knock module already, its square and has 3-4 wires coming out of one side of it. er... and it connects to the knock sensor, 12V and Ground.

Works good too. yeah i tested it. in fact i get on the highway and advance my timing until i got knock then retarded it a bit for the best cruise timing. So far I can run up to 46* of timing before i get a little timing retard.... So now i run about 41* total on the highway (87 octane) and i get super super Fuel economy now. Im averaging (city / highway) over 25MPG with rough driving. the commander makes it really easy to dial in your A/F ratio.

 

I do have a knock module now but can't use it since it was for my 305 and putting in a 383 now. Thanks for the help guys.

Tom

 

to bring an old thread back from the dead (shows I used the search)
Does it matter what engine the original knock sensor and module come from?
I'm putting in accel gen 7 dfi and I had 85 TPI. I've got a zz4 engine.
can I use my original knock sensor and module or do I need to get one from a newer car. I don't want to pay accel $240.

 

Since GM never put a ZZ4 into a production vehicle there isn't going to be a stock setup for it. Try the sensor and module you now have and see how it works out.

You'll probably have decent luck with the '85 module. The older modules tend to work better then the newer 3rd gen ones.

RBob.

 

so stick with the 305 sensor also? If not what should I get?

 

Closest sensor would be from an '89 TPI Corvette. Same bore, stroke, and heads. Same for module.

But at the same time, are you sure this is going to interface to the Accel unit?

RBob.

 

I've heard it does but I've not been able to get details. What type of signal does the module send to the ecm? If it's just a ground it shouldn't matter but I don't know. Accel told me that they basically use GM parts but wouldn't tell me what.

 

I was just looking at the accel website. It looks liek the sell an adapter now to hook up the stock one to their harness. I'll probably just wire it myself. Thanks for the help. I'll try to find that sensor.

 

The knock sensor is a three-piece setup.
The first thing is the sensor itself: the little round 1-wire screw-in freeze-plug size sensor that screws into the block. This device is "tuned" to a certain frequency that the given motor it was installed on would see if the engine was to encounter pre-ignition. This is the device that you need to keep from motor to motor, 350 to 305 to 427 to 400 etc... Each motor is different and will generate a slightly different frequency of "knock" therefore the sensor has to be designed for that specific motor.
This doesnt mean it WONT work on another given motor, it just wasnt designed to, and the frequency of the onset of knock may be different motor to motor. The POINT of this thing is to pick up knock at that specific frequency before it becomes damaging and audible AT ALL. So technically, if your sensor isnt picking up knock before you even hear it, it isnt working right.
Now this sensor is only 1 wire, and doesnt ground anything. Knock in the frequency of the sensor's range will generate VOLTAGE because of the crystal inside. Thats right, Its one of the 2-3 sensors on the entire car that actually generate a voltage output with no input. The other sensor is the O2 sensor that does this.
So your knock sensor gives out a Voltage when it detects knock, and sends the signal to the....

The second part of the system is the MODULE. This is the device that accepts the signal from the knock sensor itself, RBob: "The module interface to the ECM has a pull up on it. The module then brings this signal to ground upon knock detection. This grounding is what the ECM (GM) reagrds as a knock signal."

The ECU accepts that signal and has a little MAP (like everything else in the ECU) of acceptable "noise" from the sensor, and if the sensor outputs more "noise" than is acceptable it triggers another map in the ECU (usually a knock-spark retard map) and you know the rest from there.

Edited to reflect "RBob" interjection.

 

The module interface to the ECM has a pull up on it. The module then brings this signal to ground upon knock detection. This grounding is what the ECM (GM) reagrds as a knock signal.

RBob.