Help Updating a Non-EBL System to ESC

[TR One]

Hi everyone, 

I have a 73 that had been running a standard Howell system for some time.  It never really ran correctly,  and from reading here and on the GMC forums, I wanted to try out updating it to EBL with spark control to see if I could get it running better.

Following some instructions here and on the other GMC sites, I had my ECU updated to EBL by Dynamic EFI, and began to install it....  I set it up with a wideband using the ADL function on the ECU to help tuning, and used a modified Applied BIN shared in a previous post here.

However, I had a trip planned that was rapidly approaching, and I was only able to get it installed running the fuel injection, and not the spark control.  I left the standard HEI distributor in place and ran the coach like that for my trip.  Even with the partial install, it still ran much better than it did on the old Howell tune, so I considered it a win.   

However, I do want to get the spark control up and running, as that was one of the main reasons I went with the EBL.  I believe I have the parts needed. (knock sensor, pigtails, distributor, etc.) and I have the pinout diagram from the Dynamic EFI page.  

What I am missing is a pinout from the old Howell wiring harness.  Would anyone have any advice on where to find that information?  It may be that the Howell wiring harness follows the same layout as a factory GM configuration, but without knowing that for sure, I don't want to start swapping around wires on the harness.

Any help would be appreciated!

Mark

[BruceHislop]

Mark,

The wiring diagrams on the Dynamic EFI site are basically the same as Howell's, except for the distributor.  The 7747 ECM as used by Howell has ESC control built-in but Howell did not use ESC as a rule, just the HEI ignition. However the ECM needs a spark trigger to know the engine is running and at which RPM.  Howell used the TACH output of the HEI distributor, but that is a nasty looking 12 volt pulse and the 7747 ECM (and the EBL as well) needs a 5 volt pulse on pin B5 of the ECM.  So on the white TACH wire in the Howell wiring harness there is a little circuit board with a chip to reduce and clean up the TACH pulse.  This circuit board needs to be removed (along with the ground and 5 volt power wires to the board).

You also need a 3 more wires from the ECM to the ESC distributor.
B3 to pin A of the Ignition module
D5 to pin B (you should put a quick disconnect on this wire. It must be disconnected to set the timing)
D4 to pin E (this wire tells the distributor module when to 5 the coil)

The Dynamic EFI site tells you how to remove and install additional connections into the ECM connectors.

You also need a knock sensor and a knock filter module.  I purchased my filter module from Howell.

This should get you started.

Bruce Hislop

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[TR One]

Thanks very much, Bruce.  That's exactly the data I was looking for! 

[BruceHislop]

That little circuit board in the Howell wiring harness is enclosed in shrink tubing.  There are 4 wires going to it:
- Red 5 volt power wire (can be removed)
- black ground wire (can be removed)
- White wire going to the TACH connection of the HEI distributor
- White (I'm guessing) Wire going to pin D4 of of the ECM.

FYI, Some articles about this circuit board state that it is to trick the ECM into thinking there is a knock sensor.  This is incorrect. 

I added a 4 conductor cable from the ECM to the ESC distributor so I could easily distinguish the ESC wiring.

Bruce Hislop

To view this discussion on the web visit https://groups.google.com/d/msgid/gmcmh-efi/59f517a1-416e-490c-be12-e056ecf6b255n%40googlegroups.com.

[TR One]

Thanks Bruce.  That's a nice idea about the 4 conductor wire...  I'll incorporate that as well.

As for the knock control, I don't have a full enough understanding of this system to determine if this is related, but on my what's up display, the knock count grows to a massive number using the HEI distributor with no knock sensor.  My assumption was that something else must be hooked up to the one of the input pins for the knock sensor?  I plan on working on it this weekend, so will report back what I find.... 

[George Beckman]

EBL Spark is the way to go. But, check when those counts are being made. Some engines run up high counts when cranking.

On Feb 8, 2024, at 8:11 AM, TR One <mark.s...@gmail.com> wrote:

As for the knock control, I don't have a full enough understanding of this system to determine if this is related, but on my what's up display, the knock count grows to a massive number using the HEI distributor with no knock sensor.  My assumption was that something else must be hooked up to the one of the input pins for the knock sensor?  I plan on working on it this weekend, so will report back what I find.... 

---------

Best Wishes,

George
gbec...@graestone.org

[Bruce Hislop]

Look on dynamic's wiring diagram for the knock sensor and its filter.  The filter is specific to the engine size (mostly piston diameter).  I'd go for on from a 454. 

The knock sensor retarts the spark to eliminate knock when it occurs 

Bruce Hislop

To view this discussion on the web visit https://groups.google.com/d/msgid/gmcmh-efi/563f7e04-9eca-4daf-8703-e9ee6ff8c0d8n%40googlegroups.com.