HEI spark control

[lowrider]

Well, I finally took the plunge to control spark. I decided on using an 8-pin GM HEI and a welded up 280zx dizzy. I followed the wiring diagrams that are covered in the HEI section of the mega-manual and the tutorial here: http://www.diyautotune.com/tech_articles/megasquirt-carb-to-efi-part2-nova.htm . I’m using a MegaSquirt-II v3.57 ECU and the HEI mod kit available from diy autotune. I installed the mod kit per the instructions on the above tutorial.

 

The Four pin connector wired as such

G--TPSret

B--Vref

R--Tach

E--S5

 

VR input wired as such

P--green VR wire

N--red VR wire

 

The Two pin connector wired as such

+--Positive post on the coil

C--Negative post on the coil

 

I successfully have the car running with the Vref disconnected from the module. Tach signal is good, strong spark the problem comes when I connect Vref to the HEI.

When I go to connect the Vref as such to give the HEI module 5 volts and the megasquirt to control timing it fails to give spark and a tach signal. It just decides that it no longer wants to cooperate.

 

I changed the ignition settings in tunerstudio to the following as instructed in the tutorial.

•Ignition Input Capture: Falling Edge

•Cranking Trigger: Trigger Rise

•Coil Charging Scheme: Standard Coil Charge

•Spark Output: Going High (Inverted)

 

I have tried 3 different modules to no avail. I’m sorry for such a long winded post; I'm just pulling my hair out with frustration! Any help would be greatly appreciated!!

[Matt Cramer]

First, set your trigger angle to 10 degrees if it is not somewhere near there already. If it's more like 90 degrees (which would be normal for a stock L28ET '82-'83 distributor), it won't start.

 

Some brands of modules apparently don't like having the VREF connected until the engine is running. Try connecting the VREF after the engine is started and see what happens.

[mobythevan]

I have used the 7/8 pin HEI with megasquirt to run TPI chevy engines. I had the megasquirt controlling the Vref. That way the engine cranks/starts on HEI fixed timing, then transitions to megasquirt controlled timing.

 

Check this link to see how I had the 7/8 pin HEI wired, notice I used two output from megasquirt where you are trying to only use one.

 

http://forums.hybridz.org/index.php?showtopic=36691

[NewZed]

I have been studying this same setup recently for future reference. I don't have Megasquirt now but am interested in your problem.

 

If I could ask a couple of questions, for my own purposes and maybe to add a little clarity -

 

1. Have you measured voltage at B to be sure it's actually at ~ 5 volts? Maybe you're overpowering the B pin with 12 volts and that's why you're losing the R pin signal. Just a WAG but I wonder why you're losing your tach reading, it comes from the R pin on the module. I assume that what you mean is that you connect B before starting, hit the key and no more tach reading in Megatune.

 

2. Does your trigger offset in MegaTune match what you read with the timing light, with B disconnected? Your static distributor timing must be close already if it runs without the B pin. It sounds like mechanically everything is right but either Megasquirt is not getting its information from the R pin or it's sending out the wrong information to the E pin.

 

 

You must be connecting B before starting, as Matt Cramer suggests, since you don't mention the car dying, just not starting. To Matt Cramer's point about connecting B while running, the diagram on this page shows the use of a relay to disconnect B while cranking, and connect it only while running. http://www.megamanual.com/ms2/GM_7pinHEI.htm About halfway down the page.

 

 

Hope I'm not muddying things up...

 

Edit - came back to change your to you're...

Edited December 28, 2010 by NewZed

[lowrider]

Thanks for all of the replies! I just went back out to the garage to test all of the sugestions.

The car runs at 10 degrees btdc with the Vref disconnected. I checked the voltage of Vref at the connector with a reading of 4.94 volts. I adjusted the trigger offset to 10 degrees as Matt suggested.

I started the car with Vref disconnected let the car warm up a bit, then connected the Vref lead. The car died instantly.

 

Im going bald!

[lowrider]

Well, I started the car with the Vref disconnected and had tunerstudio open. I noticed my tps going crazy with varing values from 1% to 16% very sparadicly. Maybe this is related to my wiring. When I T-ed off of the Vref going to the tps, along with T-ing off of the ground TPSret for the ground to the module. Was I correct in doing this? Or does the HEI need seperate wires ran to it? Maybe someone can chime in?

[Matt Cramer]

What firmware are you running?

[lowrider]

Im running the BG 2.890 firmware.

My MS2 originally came with the BG 2.1.0d firmware but It corrupted and the 2.890 was the newest of the firmware in the megasquirt downloader file... so I reflashed the ecu with it instead since I was in a hurry.

[lowrider]

Matt, I have a quick question. What signal does the ecu send to the HEI module to tell it to advance the timing? Im not sure if my ecu is sending the signal and I would like to verify my hunch that it isnt recieving it.

Thanks everyone!

[Matt Cramer]

Matt, I have a quick question. What signal does the ecu send to the HEI module to tell it to advance the timing? Im not sure if my ecu is sending the signal and I would like to verify my hunch that it isnt recieving it.

Thanks everyone!

 

It's a 0 to 5 volt square wave.