GM ESC modules and matched knock sensors.

[dfarr67]

I know it's up to me to see whats best for my system but I wanted to know what experience is out there with false knock or overly sensitive system. 383 TPI (EBL) in 89 K1500. Was using BLH ESC module with correct knock sensor for vehicle (mismatch), I am going to try going back to the correct ESC module and log, has the matched knock sensor for the BLH module proved to be best, just want to be sure before purchasing ACD 213325, have ACD 213324 installed with 45deg elbow. Robert R says they will work together, my reading suggests match components.

[NomakeWan]

The unfortunate truth is that once you start changing components around, you lose the "precision" of the knock module intended for the original application. The module is a filter that rejects certain frequencies and allows others, converting this into a simple on/off for the ECM/PCM to read as knock. The only "right" way to get a knock module to work with a particular custom setup is to use a scope on the knock sensors to monitor knock and then induce some on purpose on a dyno, note the frequency range, and then create your own knock module accordingly. Which...yanno, kind of out of reach of just about everyone since at the moment, the knock modules are something of a black box, not to mention the skill required.

I do wish you the best of luck though. Maybe you'll get lucky and there'll just happen to be an existing module that works decently for you.

[dfarr67]

I have 3 or 4 EC modules I can try and log, easy swap.

http://www.gearhead-efi.com/Fuel-Inj...ESC-and-swaps!
http://www.gearhead-efi.com/Fuel-Inj...-(My-91-C1500)

[1project2many]

Which...yanno, kind of out of reach of just about everyone since at the moment, the knock modules are something of a black box, not to mention the skill required.

There are interesting discussions about how to do this reasonably well with budget tools. I believe there was a great thread on thirdgen.org. When you consider the aftermarket uses the same sensor for several different engines it seems like it would be easy to make an improvement.

Technology has changed so much over the years. Are there any aftermarket systems that monitor spark energy and pattern to determine knock? I could often see it on an analog oscilloscope.

[dfarr67]

I bought a stand alone system out of Iceland for the Toyota- which at the time didn't offer knock, for an extra $200 now you purchase an option which includes WB and knock- have to force knock on a dyno to tune. This is off my topic tho, I tested the oem ESC module on the Chev and it was the same if not a little more sensitive, not sure I want to purchase the matching knock sensor- both applications are 350cid one is a 85 Corvette TPI (BLH) and one is 89 K1500 TBI.

[NomakeWan]

Just remember that the sensor and the module are two totally different things. I'm not suggesting you need to do anything with the sensor. But if you want the existing EFI to do knock retard like factory, then the knock module is what you have to adjust, and all it does is pull a line low to tell the ECM/PCM when it thinks knock is occurring. Sounds simple in theory, but when we don't know the pinouts for the module and have to account for how much knock to report and when, things get tricky.

There are absolutely other ways of doing it. It's ultimately only if you want to use factory hardware that you end up in the situation where you would need to create your own custom knock module.

[dfarr67]

There are absolutely other ways of doing it. It's ultimately only if you want to use factory hardware that you end up in the situation where you would need to create your own custom knock module.

And there is the rub- the engine is far from factory- and relatively noisy, so the knock system is not that useful.

As an aside, engine was intended to be 9.5:1 modeled after vortec with AFR head/FIRST TPI, have been trying to tune to 87 octane- I have a few avenues left to try but have audible ping in certain areas. Where do you give up and move up in octane?

[1project2many]

I have a few avenues left to try but have audible ping in certain areas. Where do you give up and move up in octane?

After failing to reduce knock by adding 1oz MEK per gallon to your 87 octane fuel. :-)

[dfarr67]

This is an EBL setup, and the ping has been an issue for some time. I dabble in tuning so don't really know it well. I was thinking last night that the learns is doing its thing, I've cut PE/SA to 0, I've taken 5 deg out universally and although it clears up most of the knock table it will still ping in a certain area even with 0 timing. I've filled up it up with better octane and the same thing. So I'm thinking it's going lean under heavy throttle and options are PE, AE, or VE adjustments. This is a 383 sbc with modern alum heads and a version of tpi- so I'm also thinking the tuned ram is really doing something.

[1project2many]

In order to stop kock the KS system will reduce spark advance when knock is detected then advance spark back to the ECM desired timing while knock is not occurring. If knock occurrs at any time then spark advance will again be reduced. In order to ensure effectiveness I would look at the kock and spark advance during knock to ensure the minimum allowed advance is not too high. If spark advance cannot be reduced enough then knocking will not stop. I would then look at the initial retard when knock occurrs and the rate at which the system returns advance.

And I wouldn't be afraid to add MEK. :)

[dfarr67]

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[Tom H]

I have been looking at the knock module from various LT1 and V6 applications in the late '90s. The circuit is housed in a plastic carrier with eight contacts. Inside there is a hybrid circuit (I believe it is thin film). On the circuit are a number of capacitors (one looks to be a larger polarized tantalum cap), LASER trimmed resistors and two ICs. One of the integrated circuits is a soic 8 pin manufactured by philips (marked NE532D dual op-amp [edit]) the other has a higher pin count (perhaps 16 pin) and is not packaged. The second chip has no markings because it is not packaged. I believe the part is made with solder bumps and is mounted directly on the substrate.

I find it interesting that when manufactured, the hybrid is mounted in the top of the plastic housing with some very low density elastomer. This material is very soft and I believe is used as a sound deadener to prevent flexing of the substrate from becoming microphonic. That is to say that the module could under some circumstance pick up vibrations and turn them into unwanted signal.

I plan to look at this module in the future & try to find it's operation, but for now this is all I have found.

One question for the group... knock is when the compression cycle heats the mixture to the point where it ignites before the spark (pre-ignition). How does retarding the spark seek to cure this? I can see how making the mixture richer might cool things. Overall retarding the timing would cool things when knock isn't present. Perhaps someone could explain?

-Tom

[brian617]

One question for the group... knock is when the compression cycle heats the mixture to the point where it ignites before the spark (pre-ignition). How does retarding the spark seek to cure this? I can see how making the mixture richer might cool things. Overall retarding the timing would cool things when knock isn't present. Perhaps someone could explain?

-Tom

Pre-ignition (ignition before spark) and "Knock" Detonation (after ignition) are two different events.

[dfarr67]

I think the trick is to prevent rather than recover. I did order the sensor, I just found it odd that the same style and engine displacement demanded a different part number.

[Tom H]

Pre-ignition (ignition before spark) and "Knock" Detonation (after ignition) are two different events.

I understand a little more now... with knock the plug ignites the mixture and a flame front starts from it's tip. Normal ignition the front continues, pressure builds and all is good. With Knock what happens next. Could someone point to a good link that describes all this??

-Tom