MSefi.com read only forum (Jan.15,2018)

I decided to ditch the HEI 7 pin module since I was having so many problems getting the truck to start. Switched to VR sensor only (which is from GM HEI). Added the high current circuit and ran the VR sensor wires direct to the relay board to TPS return (green) and Tach (Yellow). The tach wire goes straight to S5, and the BAT terminal goes to 12V. The only thing I can question is the VR wires - they aren't shielded, but they are ran outside of the truck (temporarily) to eliminate noise problems. The coil power and ground are about a foot from them.

Problem - when you turn the key off, sometimes the fuel pump continues to run. Sometimes it runs briefly, then actually sounds like it's (the pump) kicking over backwards.To further complicate things, the injectors even pulse wildly sometimes- with the pump running. Obviously this is getting very frustrating, it's flooding instantly.

At first, I thought the center ground on the internal coil body was the culprit, as it wasn't there. I added it, and grounded it to the cylinder head, but didn't help any. I've switched the VR sensor wires, added/moved grounds.. all with no changes.

I've updated the firmware to V2.891
I'm using tuner studio V0.999.9
MSII / V3 main board

**This is on a 383cid chevy, 82# injectors, Aeromotive fuel pump

Make sure you don't have a fan or other electric motor driven device that can "Back EMF" and drive the injectors or pump.
Simply put, if a relay has a fan AND the injectors on the output (Pins 87 or 87A, sometimes 30, but it's not supposed too), when the relay is shut off, the fan becomes a generator! Producing 12 V. This will drive your injectors crazy. Sometimes dumping all the fuel they have. Flooding the engine.

Hope this helps.
Holl

drholl wrote:Make sure you don't have a fan or other electric motor driven device that can "Back EMF" and drive the injectors or pump.
Simply put, if a relay has a fan AND the injectors on the output (Pins 87 or 87A, sometimes 30, but it's not supposed too), when the relay is shut off, the fan becomes a generator! Producing 12 V. This will drive your injectors crazy. Sometimes dumping all the fuel they have. Flooding the engine.

Hope this helps.
Holl

If you really must do this, you can get relays with twin outputs. Similar to standard ones as regards fitting, but the two outputs are only common when the relay is made.

Wonderful Trakkies. I was unaware of these relays. So in this case the fellow would put the fan on one post and the injectors on the other. Solving the back EMF problem.

Thanks Trakkies
Even an old guy can learn new stuff!

Holl

drholl wrote:Make sure you don't have a fan or other electric motor driven device that can "Back EMF" and drive the injectors or pump.
Simply put, if a relay has a fan AND the injectors on the output (Pins 87 or 87A, sometimes 30, but it's not supposed too), when the relay is shut off, the fan becomes a generator! Producing 12 V. This will drive your injectors crazy. Sometimes dumping all the fuel they have. Flooding the engine.

Hope this helps.
Holl

Amen! Been there-done that!

Ken

btw... very nifty item, Dave!

They're used for both main and pump on the Lucas flapper EFI as fitted to the UK Rover SDI etc. But the Federal version (TR8 too) got a special combination relay.
Wish I had a penny for each time someone replaced one with a standard SPDT type.