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Using the ESC box to make a knock gauge

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by Blue85, Jul 26, 2002.

  1. Blue85

    Blue85 Troll Premium Member

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    I have been working on getting my timing dialed and have come up with a good idea. What I want to do is look at the output of the ESC box that goes to the ignition module to see when spark knock (detonation) is detected. If anybody knows which wire(s) to look at and what the voltages mean, please let me know. Otherwise, I'll post back if I come up with anything cool.

    My thought was that then I can look at a voltmeter or rig up a gauge that shows me knock retard all the time I am driving (if it works, I can leave it in full-time). Then as I set my initial, centrifigal and vacuum advances, I can see with at a glance when I am getting close to detonation. I don't really like trying to listen for the beginnings of knock over my exhaust.

    I may have to temporarily bypass the ESC box so that the spark knock is indicated for long enough for me to see it before timing is retarded and the condition corrected. Hopefully not, though, because if the timing is advanced too far, the ESC should give retard for as long as the load on the engine remains the same.

    From what I understand the ESC output is not "on/off", but gives some variation in the amount of knock detected.

    Any more info anybody has on this system would be appreciated.
     
  2. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    Sounds like a cool idea...my kid uses my old ESC box as 'home plate'./forums/images/icons/grin.gif

    Rene
     
  3. dyeager535

    dyeager535 1 ton status Premium Member

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    Dealing with the CCC system and TBI, I've watched the knock counts, (scanner)and the knock count numbers are actually tallied up, like you said, its not on/off, so I'd have to assume that it retards/advances (if it doesn't just go "back" to normal when no knock occurs) the timing based on how much knock it is detecting. Never bothered to look at what was happening to timing though.

    There is only one wire from (or to) the knock sensor, so you've got to be able to measure that somehow....is there a spare plug somewhere indicated in the wiring manual that is a "diagnostic terminal" similar to the later ALDL's? I'd expect GM to have some type of tool, even back then, to watch that system in operation, because if they didn't, there would have to be a testing procedure in the manual.
     
  4. Blue85

    Blue85 Troll Premium Member

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    This is not a CCC system. The only electronic controls are the ignition module and the ESC box. Therefore there is no ALDL. There are 4 wires from the module to the spark box, one of which is switched ignition. One is an "out" and the other an "in" to allow the box to be in the timing control loop. One of these wires should be the one to monitor. I don't know what the other wire does. The ESC box is also tied with two wires to a vacuum ("tip in") switch.

    Monitoring the knock sensor itself doesn't seem that inviting. The sensor is a piezo device that will give very short, high frequency bursts. To turn this into something that you could monitor by eye would require something similar to the ESC box. So using the output of the ESC box seems like the logical place to monitor.

    I was thinking that I could use the "tap on the block" method while a timing light is hooked up to see how much retard corresponds to what voltage on the wires between the ignition module and ESC. Then I would just create a scale for a little 2" round voltmeter that I already have (fits nicely in a standard gauge spot). My hope is to have something that reads spark knock in degrees.
     
  5. dyeager535

    dyeager535 1 ton status Premium Member

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    </font><blockquote><font class="small">In reply to:</font><hr />
    This is not a CCC system. The only electronic controls are the ignition module and the ESC box. Therefore there is no ALDL. There are 4 wires from the module to the spark box, one of which is switched ignition.

    [/ QUOTE ]

    This I know. What I'm saying is that GM used diagnostic terminals in various places when it could be done, with or without an ALDL or ECM. Like the dwell terminal on CCC...its not in the ALDL, its seperate. But it was an electrical system, and GM needed to be able to check this, so they had a "test terminal".

    My whole thinking on that was that there MIGHT be a diagnostic lead in the ESC harness itself. I know the knock block with hammer/check for retard "test", and maybe thats the only test GM had, but I'd think they would have liked to see the knock count or further diagnose the ESC system than just hit the block with a hammer, especially since all the cars could be read with a scanner at that time.
     
  6. Blazer_Boy

    Blazer_Boy 1/2 ton status

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    Well, I'm no rocket scientist here, but I think the secret would lie in the plug going to the distributor. If ne is ground, one is switched power, and the other two are where the action happens. Couldn't you just tap into those two wires for you signal that ESC is working. I guess it's easier for me because I put a pre-ESC distributor in my '83 and can just leave that plug off.
     
  7. Blue85

    Blue85 Troll Premium Member

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    I tried all 4 wires running between the ESC box and the Distributor. I can't make the voltage change on any of them by tapping on the block. Maybe the voltage changes too fast for me to see it or it won't give retard at idle. Maybe I'll advance the timing, unlpug the knock sensor and look at each of these wires while driving...
     
  8. dyeager535

    dyeager535 1 ton status Premium Member

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    Wish I had a vehicle here that I could hook my scanner up to and re-check, but last time I had my scanner hooked up to my friends Astro, watching knock counts as we revved it in park, it exceeded 200 in maybe 20 seconds or so. (wasn't timing it) Not sure if thats typical or not, but with that kind of count, a voltmeter probably won't see it. Tried that on a fuel injector, and it didn't work either : )

    Are you seeing 12volts on some or all of the wires? Injectors were that way, 12V constant. (it appeared)
     
  9. Blazer_Boy

    Blazer_Boy 1/2 ton status

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    Well, jeez, get that stinking TPI done and check out the knock count /forums/images/icons/smirk.gif . There's a gotta be some guru out there that could figure this out. I think this is a really good idea.
     
  10. dyeager535

    dyeager535 1 ton status Premium Member

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    Yes, I've been tempted to hook 12V up to the ALDL leads (which IS bolted into the truck, so what if the wires all dead end lol) so I can plug my scanner into it to pretend I'm checking my awesome setup out : )

    I *did* pickup the stock ECM mount/bracket this weekend, a spare 465/205, and some inline fusible links and relays for the TPI setup, so I *am* working on it. Engine still in the shop. August makes 11 months they've had it for the basic flux/bore/hone/balance.

    Better idea is to go TBI/TPI in the first place and not have to worry about a seperate ESC /forums/images/icons/smile.gif
     
  11. Blue85

    Blue85 Troll Premium Member

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    I feel like we're still talking about two different things. There is no scanner for a pre-87 truck. The electronics that are in there do not use digital communication. It would also be interesting to use a scanner to look at knock on a TBI machine, but it is an entirely different method.

    I still haven't found a way to make this work. It would be sweet to keep advancing different parts of the timing until the gauge starts to move, then just back that part off. Then you could make changes quickly when changing elevation or grades of gas. It would also be cool to use a stand-alone ignition box with a distributor from an ECM car to always read the knock sensor and always keep the timing advanced as far as it can be. You would almost have to make your own, though, since the ones that are used in vehicles today work by interfacing with a crank position sensor and/or the ECM.
     
  12. dyeager535

    dyeager535 1 ton status Premium Member

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    </font><blockquote><font class="small">In reply to:</font><hr />
    I feel like we're still talking about two different things. There is no scanner for a pre-87 truck. The electronics that are in there do not use digital communication. It would also be interesting to use a scanner to look at knock on a TBI machine, but it is an entirely different method.


    [/ QUOTE ]

    Thats what I wasn't sure of..if the methods to moitor knock were the same or different. I had just ASSuMEd that since cars that same vintage had ESC (heck, they still do in some shape or form) except it was integral with the ECM, that the ESC truck system was based on that, only a standalone.

    Am I incorrect in thinking that the knock sensor is the same whether car or truck (based on engine size) or did they in fact have different part #'s?

    I'm not really sure I understand you though on "how they communicate". Isn't the knock sensor "feed" and the dist. control going to have to be achieved the same way?

    In reality, with all of this work, you *could* probably retrofit a CCC system from a car on the truck. Although you couldn't make changes (easily lol) you could at least watch it real time with a scanner, or more easily interpret the data stream.

    It *does* seem like it would be easier to just use the entire CCC system instead of JUST trying to use the ESC setup.

    BTW, any year truck that could get ESC can also mount an ECM bracket apparently /forums/images/icons/smile.gif Anyone that ever wondered what the two funky brackets on the underside of the dash, above the glovebox/heater box were for, thats your answer!
     
  13. Blue85

    Blue85 Troll Premium Member

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    The two are quite different. The only thing that is the same is the sensor itself. The fuel injected trucks give the ECM complete control over timing, the knock sensor being just one of the factors that it looks at. The ECM lets you look at any of the parameters that it monitors using the scan tool.

    The carb trucks have timing from the mechanical advance, the vacuum advance, the initial timing and the ESC input. The ESC box is basically just an amplifier/signal conditioner for a knock sensor. The signal from the ESC is fed to the ignition module inside the distributor. I have also assumed that it is an analog signal (voltage proportional to severity of knock). If I knew exactly how this was supposed to work, I would try applying my own voltage to the ignition module to see how much retard it brings.

    The sensor itself is a piezoelectric device, just like in all vehicles. Piezo's convert mechanical vibrations to electric signals and vice versa. They are generally made from metal and ceramic and are also used to make tweeters and propane grill ignitors. So the pinging creates a vibration in the engine that is different from normal operation. The sensor converts this to a signal that is recognizable by the ESC or ECM.
     
  14. dyeager535

    dyeager535 1 ton status Premium Member

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    True, if the ESC system is still using mech and vac advance, its totally different than the "ECM controlled" ESC setup.

    Any comments on going to CCC though? As long as the cam isn't too radical, and the engine WAY too big (I'm thinking trying to run a 502 on a 305 ECM would be difficult) it wouldn't be that difficult to swap it over from a car...
     
  15. Blue85

    Blue85 Troll Premium Member

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    No way, man. Not worth the swap. I'll swap TBI if I find the right price, but not CCC. Those things still have a bad reputation, offer almost no economy/performance gains, are hard to modify and have almost no aftermarket support. Truck TBI offers all of the benefits and more and is just as easy to come by.

    If all I wanted was to read engine parameters, I could get just the computer and the sensors. The ECM would never be in run mode, but it might still support service requests from a scan tool. But to even go that far, why not just fuel inject?

    I found a web site where a guy uses a GM ESC module with a Casper knock guage. It is not the same as a K5 ESC module, though. web page I don't think this gauge would interface with a GM truck ESC, but this is pretty much the same idea I had.
     
  16. dyeager535

    dyeager535 1 ton status Premium Member

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    Yeah you are right about an FI conversion. Some people just like carbs though...

    You could be wondering what pin A10 on a TPI ECM connector is for right now though instead of what the knock sensor is putting out. lol /forums/images/icons/smile.gif
     

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