MS controlling relay for power

czb83 · Post by **czb83** » Fri Aug 11, 2006 8:41 pm

I ran into a problem with my jeep, where the stock computer turns off power to everything via a relay if it doesnt recieve hall sensor input after 2 seconds. I'm using the hall sensors on the MS, so I had to jumper the relay to keep power on. I only did this for testing and have no intention of keeping it that way.

I don't want to leave it jumpered as that could be a safety issue possibly. I figure if i get in wreck the ign is ON, the fuel pump and ignition coil will still be energized if its jumpered, which could be dangerous.

So I need a way to trigger the relay another way. Its 12V to trigger it. Any ideas on best way to do this with MS? Ideally it would work in same way as stock computer. Don't know if anyone has dealt with this issue already.

jsmcortina · Post by **jsmcortina** » Sat Aug 12, 2006 3:08 am

The Megasquirt fuel pump relay is doing the same function - if the engine stalls the fuel pump cuts out. I would take a power wire from the fuel pump relay and run you coil and other items from it.
You might also want to install an inertia (mercury) switch if you don't have one already so that the fuel pump is directly cut in the event of an impact.

James

newtyres1 · Post by **newtyres1** » Sat Aug 12, 2006 3:35 am

Sorry, misread your post deleted mine.

Ian.

czb83 · Post by **czb83** » Sat Aug 12, 2006 6:03 pm

Cool, thanks. I guess I'll be using pin 37 to control the relay then.

czb83 · Post by **czb83** » Sat Aug 19, 2006 7:25 pm

I have a related question to the original. It turns out I also had to jumper the fuel pump to get it to work, as the same signal to turn on ASD relay was sent to FUEL relay. Well, Im going to use the pin 37, fuel pump relay signal to take the place of that signal, so that should be all good. Theres another signal sent though, theres a ballast resistor relay. It turns out the fuel pump only runs on full current for a couple seconds after IGN on, and perhaps during WOT. So there is another output from the stock computer to control this relay. Has anything like this been configured on MS before. I could use same signal to send to Ballast resistor relay, and have it always run at lowered current, or full current. I'm afraid that always running at full current will burn out the motor, and always having it on lowered current might not provide enough fuel on WOT.

Anybody had to deal with this before?

czb83 · Post by **czb83** » Sat Sep 02, 2006 11:11 pm

Well, I'm able to start the jeep

This was temporary though as I had the relays jumpered. I'm thinking the -best- solution is to leave the stock comptuer controlling the relays. This would also allow it to drive the tach.
I realize MS can do this, but I think its best for the stock to do this job.

I was wondering if anybody had any success using an opamp as a voltage follower(unity gain buffer) on hall sensor output. Right now I have 5V going to the hall line across a resistor. I guess the stock computer also puts voltage to this line. Is there anyway for me to hook up both devices. It works on MS with this 5V run to it, and it works on stock, but they dont work togther. Is it possible to configure a device, like an opamp, to isolate the two so that both devices work? My electronics background is pretty weak, so any help would be greatly appreciated.

Project7 · Post by **Project7** » Mon Sep 11, 2006 7:18 am

Just so you know the fuel pump is triggered via ground. It does not supply +12 to trigger relays. So you would have to rewire the relay to always get +12 and then trigger the relay with ground.

Project7 · Post by **Project7** » Mon Sep 11, 2006 7:18 am

Just so you know the fuel pump is triggered via ground. It does not supply +12 to trigger relays. So you would have to rewire the relay to always get +12 and then trigger the relay with ground.
Jeep - 94 4.0L HO V3.0 MS Fuel
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czb83 · Post by **czb83** » Thu Dec 28, 2006 8:15 pm

Well, I just got this taken care of. I ended up splitting the hall signals, so that both megasquirt and existing PCM can read signal. This means the stock PCM can continuing to power the existing relays and ballast resistors for controlling power to things. I think this is the best solution.

I ended up getting my unity gain buffer working after many hours and days spent. I kept trying different configurations and it ended up being the chip. I was using TL082CP, a JFET Op Amp. I kept following diagrams online and things never worked right. I finally tried a different chip, LM324, and it just worked! I don't know why, but i'm no EE.