View Full Version : Starter Solenoid with on-board computer


68 Broncoholic
01/24/10, 10:42 PM
I've had issues with the starter not starting after the truck is up to temp.
I replaced the starter to find it did it again. I'm onto the starter solenoid but the new soleniod instructions say "Do not use this solenoid for vehicles fitted with an on-board computer. Use of this soleniod for such vehicles will result in perminant damage to the EEC processor. The damage processor can cause a rough running engine or a no start condition. Vehicles with a computer require a solenoid with suppression diodes".

I run the Holley ProJection system with a ECU computer but I couldn't imagine a starter solenoid causing a spike to the computer but maybe so. I'll probably contact Holley and see what they say before I replace it.
Do you think I need a solenoid with suppression diodes?

http://www.hannay.com/pages/downloads/Diode%20Suppression%20Wiring.pdf

Viperwolf1
01/24/10, 11:01 PM
It's possible. When the solenoid coil current is turned off the magnetic field collapses and induces a negative voltage spike back toward the ignition switch or anything else attached to the "S" terminal.

broncnaz
01/25/10, 12:39 AM
While probably not a good idea to run that solenoid when you have a computer. I'd get the suppression wire just to be safe. You might also try late model solenoids off EFI ford trucks I would think they would be built for use with computers.

Steve83
01/25/10, 08:01 AM
...or just install a diode from the S terminal to the base plate (or any ground). It's not that big a deal. I ran my old non-supressed starter relay for years after converting the '83 to EFI, and it's still running fine.

byson1
01/25/10, 10:14 AM
First I've heard of this. I just installed/rewired a 93 Cougar 5.0 in my Bronco and used the original (68 model or something equivalnet) solenoid. I've only ran it for about 1-2 miles but it seems to be fine. Is this something I should be concerned about, and if so, where can I get a diode/suppresion wire?

Viperwolf1
01/25/10, 10:33 AM
First I've heard of this. I just installed/rewired a 93 Cougar 5.0 in my Bronco and used the original (68 model or something equivalnet) solenoid. I've only ran it for about 1-2 miles but it seems to be fine. Is this something I should be concerned about, and if so, where can I get a diode/suppresion wire?

Radio Shack for the diode. http://www.radioshack.com/product/index.jsp?productId=2036268&filterName=Category

Here's how it's wired.

68 Broncoholic
01/25/10, 09:02 PM
It makes sence and I sure hope it clears up my no start condition after its warms up. She starts every time when cold.

The starter I run now is the Mini Tom's Bronco Parts sells that suposedly produces more torque. I also wrapped it with heat barier wrap. She seems to start better than the stock starter but died the same way once I was warmed up. Actually when I got home it started right up but then 10 min later it wouldn't start. I don't think i've hurt the computer becuase I can pop the clutch down hill and she starts just fine...

78Scronco
01/25/10, 10:00 PM
Dang, this is the first I've heard of Not using the solenoid. I've not started my efi yet, but what is the answer here? remove and replace or what?

68 Broncoholic
01/25/10, 10:09 PM
It sounds like anyone with a computer should use a diode to supress any spikes that might back draw into the ingnition and then to the computer. It seems like the correct path. We do it with my work on electronic door hardware where we get voltage spikes within a building and it basically protects the surge. Here we are dealing with it on automotive now...

68 Broncoholic
01/30/10, 12:22 PM
I got the diode (in stock at radio shack) but does it matter which direction it goes? It has an arrow showing the direction of voltage flow. Does it point to ground to supress a spike?

Viperwolf1
01/30/10, 12:50 PM
I got the diode (in stock at radio shack) but does it matter which direction it goes? It has an arrow showing the direction of voltage flow. Does it point to ground to supress a spike?

Yes it matters. Reference my diagram above.

68 Broncoholic
01/30/10, 01:20 PM
I know it connects to the S terminal and to ground but which direction does the diode face? It seems to be directional. All the directions say is put it in the direction of power which I assume is off the S terminal and to be able to supress into the diode and to ground.

Viperwolf1
01/30/10, 01:55 PM
The end of the diode with the silver bar needs to go toward the "S" terminal. This diagram might help.

68 Broncoholic
01/30/10, 03:18 PM
Cool thanks! I'm going to give it a whirl but I'll need to extend the end of the diode as it can't reach ground. Its only 3" long...

ransil
01/31/10, 06:25 AM
simple solution is to get a late model solenoid..

68 Broncoholic
02/01/10, 04:39 PM
simple solution is to get a late model solenoid..

Thats what I wanted but I was dealing with Shmucks and they didn't agree... %)

After installing the new solenoid/diode it seems to be starting without issue now. Since it was late and I had several drinks in me I decided to do some night wheeling on my property. I must have brushed up against something...


http://img148.imageshack.us/img148/7857/img00441z.th.jpg (http://img148.imageshack.us/i/img00441z.jpg/)

Viperwolf1
02/01/10, 05:14 PM
simple solution is to get a late model solenoid..

I don't think you can get a solenoid for $.99.

68 Broncoholic
02/02/10, 01:56 PM
I agree and thanks for the help Viperwolf1!

Steve83
10/01/10, 11:26 AM
I just found out why the diode is in there. It's not for the EEC; it's for the ignition module.NOTE: Disconnecting the start wire at the starter relay with the key on will cause the TFI-IV ICM to revert to start mode timing after the vehicle is started. Reconnecting the start wire after the vehicle is running will not correct the timing. Use the ignition key only to start the vehicle for adjusting base timing.So without the diode, any transients as the solenoid releases could throw the ICM into start mode for the whole drive.