MS - Pin 37, Controlling 2 Relays

[CBDZ]

I am wiring my buggy from scratch, and I have run into something unexpected. I have some type of feed-back that is related to the fuel pump ground, pin 37, which I have grounding 2 different relays.

My circuit contains:
1. Main power relay (#1) which is controlled by the key ('ON' Position).
2. Sub-relay (#2) which is fed by relay (#1), and activated by the fuel pump ground circuit
3. Fuel pump relay (#3) which is red by a different fuse circuit, and activated by the fuel pump ground circuit.

Upon attaching the battery terminals, both relays #2 & #3 will flicker at a fast rate. This is confusing to me because there shouldn't even be power available to these two relays until I turn on the ignition switch. Once I activate the trigger for relay #1 (turn key to 'ON') the CPU will cycle the pump for 3 seconds, and then stop, killing all the power to the injector circuits, wide band controller, coil, and idle control. After this 3 second cycle, the relays don't flicker any more, but, if I turn off the ignition switch again, and turn it back on, nothing happens.

If I remove either relay #2 or #3, the circuit functions as intended, but by doing so I either don't have power to my fuel pump or none to the injectors, wide band, coil or idle valve.

So, the goal is to have the ECU controlled by the keyed switch. I want the injector 12V, coil 12V, wide-band 12V, and idle 12V to also shut down if the ECU senses that the engine is stalled.

Please help me troubleshoot this.

Click for Larger Image




EDIT----------PROBLEM SOLVED-----------EDIT

So, I don't really understand the reason behind the fix, but I went back out to the garage, and studied what I have a little more, and solved the problem. Here is the fix. The corrected connection has been "clouded".

Click for Larger Image

[Dale M.]

Hmmm.... Dont see where there was problem with first diagram, it should have worked...

Suggest there was a different issue (short) and you inadvertently corrected it while making wiring change to supply +12v to relay #2....

Dale

[trbugman]

You need to have switched power to the relays. If the relays have power while the MS if off it'll do weird things.

[Dale M.]

Most times relays don't care where the control switching comes from (+12 volts or ground)...

In this case there could have been some sort of weird feed back from one of the "controlled" circuits (switched power side) that was supplying some sort of power to relays causing them to chatter..

Dale

[trbugman]

Agreed the relay doesn't care where it gets power from, in this case it is the MS that cares. When the MS isn't powered the outputs can be floating or grounded, anything being controlled by the MS needs to have its power turned no/off with the MS or you can have unexpected behavior.

[CBDZ]

I am pretty sure that I have all the components that provide a signal or which are directly controlled by MS on circuits that are turned on and off by MS.

1. Megasquirt - Main power source is controlled by a relay. Power comes directly off the + terminal on the starter. Trigger is controlled by the ignition switch. (Relay #1 on the above diagram)

2. Fuel Pump - Controlled by a relay. Power source is a dedicated circuit directly off the main distribution fuse block. Triggered by Pin 37 of MS (Shown as Relay #3 on above diagram)

3. Injectors, Ignition Coil, Wide Band Controller, Idle Control Valve. These are all controlled by the same relay. The relay branched off to fused circuits for each device. This relay is controlled by Pin 37 of MS.

Everything else are just temperature sensors that get signal directly from MS, or the TPS.

So, basically, Megasquirt will be turned on by the key. All components will be on during the priming cycle. They will turn off after the 3 second priming cycle. Upon cranking, they will all turn back on. In the event of an engine stall, all will again turn off.

I don't see any issues with this, but this is my first MS install. If this is a bad practice, then please let me know.

[trbugman]

Is the 12v switched to the relay? If it isn't it needs to be, the relay cannot have power on the signal side while the MS is powered down.

[jhoefer]

As mentioned, when the MS has no power, the state of Pin 37 is undefined which means your fuel pump could run at any time whether the key was on or not. You need to change Relay3's terminal #86 so it connects to switched power, not constant power. That is, Relay3 #86 should connect to the ignition switch output (same as Relay1 #86), not to the fusebox.

If you do that, you should be able to change Relay2's wiring back to the original layout.

[CBDZ]

So, you are saying that I should change it to this?

Click Here for Larger Image

[trbugman]

That will work.

[Dale M.]

That should work....But for me I would think everything should be controlled by relay #1 so relay #3 power should be connected to output of #1...

FUELPUMPCIRCUIT-1.jpg

The is how MS does it on their relay board (sort of).......

http://www.bgsoflex.com/mspower/mspower_ShemV1.2.pdf

Dale

[jhoefer]

That'll work too.

[CBDZ]

Thanks for all the input.

The reason that I have relay #3 getting main power supply is that it is physically placed far away from the other portions. I have the main fuse box which provides power to all the lights, horn, gauges, etc. mounted on the front fire wall. The fuel pump is also at the front of the car, underneath the fuel tank.
Relay #1 & #2 are mounted at the rear of the car where the rear parcel tray is. I don't want to run another power line from the rear to the front for the fuel pump.

I think that I have this figured out. Again. Thank for your help and advice.

[Dale M.]

Its not about the main power for the fuel pump through #3 relay, it is the control circuit and power for operate path of #3 relay..... It does not matter where relay is, its how its control....

If it requires another wire run you gotta do it, short cuts will only bring you grief later....

Dale