Megasquirt 2 and fuel pump

[hotsaucewizard]

Hi guys,


I recently finished building a MS2 DIY unit and for the most part everything is working but I don't yet have a successful fire. I verified spark today and started to look at fuel.


As I understand the M20 (on motronic) does not ask anything of the fuel pump until it has begun cranking and does not fire a prime. In trying to keep my cranking to a minimum as I have neighbors directly above my garage (the garage directly under my unit becomes available at the end of this month thankfully) I've been trying to get the pump to fire via the priming pulse from MS in an effort to rule out fuel as an issue and then assuming MS can successfully fire the pump if it can prime it. Side note - for some reason my starter sounds like one for a loud truck.. anyway..


I've verified with my multimeter that MS outputs a priming ground closing the circuit to ~12v on the MS fuel pump relay wire vs switched 12v for a couple of seconds upon turn of the key which rules out issues with the build of the megasquirt unit itself (my soldering isn't the best). I've verified that this signal makes it through the stock motronic harness out to the relay by testing 12v+ right off the battery vs the corresponding fuel pump relay pin out of the motronic harness (pin 85 I think? hard to say back at the desk but I know I had it right out in the garage).



I'm able to get the pump to fire by jumpering 30 and 87.



I've verified that the main relay does talk to the fuel pump relay with voltage timing corresponding with the prime timing (by testing between 85 and 86 upon key turn) - however my multimeter shows around .25 volts for this established priming period of time. Being admittedly short on knowledge with relays and google not providing much help as far as switching voltage this has me at a loss.


Is that enough to switch the fuel pump relay? If not does this point towards the main relay not letting enough voltage through? Or to the aging fuel pump relay requiring more voltage than normal to switch? I suppose I can just pony up and buy both new as I've only had the car for around 4 months and god knows what laundry list of problems it came with considering rats have eaten much of my plastic and destroyed my comfort seat... but I figured I'd consult the collective knowledge held here as maybe the issue lies somewhere I hadn't yet considered.



The signal makes it through, but at a fraction of the voltage that it did when testing 85 and 86 vs 85 and 12v+ ... Is it fair to assume that even though the M20 did not originally prime it's pump that the pump should fire when presented with a ground on the fuel pump relay no matter what the condition is?



The car ran perfectly fine with the harness plugged into the motronic ECU before I unplugged it and started stuffing bare wires into the connectors so I'm at a loss as to how a relay could suddenly stop working..



Once I have everything verified I'll be buying an old ecu to make a connector from but for now I don't see any problems with stuffing copper in sockets


Any ideas?

[hotsaucewizard]

Forgot to add: removing the fuel pump relay and applying 12v to the coil does activate it and ohms show between remaining contacts afterwards...

[citizen_insane]

How are you controlling the main relay? In my car, I had to modify the main relay to switch on with the key instead of being controlled by the ECU like on the Motronic.

Here's a diagram, see how he changed the wiring on the main relay to be supplied accessory & key-on power and grounded the other side.

http://e30performance.info/viewtopic.php?t=1288#p23587

Once this is done, you will no longer have a signal on Pin 36 of the stock harness, you just fully bypass that whole setup and just provide power after the main relay to the ECU. This way power to the whole electronics system is controlled by the ignition instead of by the ECU (which MS is not provisioned for).

[hotsaucewizard]

How are you controlling the main relay? In my car, I had to modify the main relay to switch on with the key instead of being controlled by the ECU like on the Motronic.

Here's a diagram, see how he changed the wiring on the main relay to be supplied accessory & key-on power and grounded the other side.

http://e30performance.info/viewtopic.php?t=1288#p23587

Once this is done, you will no longer have a signal on Pin 36 of the stock harness, you just fully bypass that whole setup and just provide power after the main relay to the ECU. This way power to the whole electronics system is controlled by the ignition instead of by the ECU (which MS is not provisioned for).

Hm I haven't even touched the relays but I do recall seeing something about this early in my megasquirt research. Thank you! I'll give this a shot tonight

[hotsaucewizard]

That was the fix!! I have a priming fuel pump! megasquirt talks to the fuel pump!! Thank you so much

I'm almost scared to try and start it now... what issue am I going to run into next??

[hotsaucewizard]

I am beside myself. I can't believe I didn't fuck up somewhere along the way building the megasquirt. The car runs!!! Runs like shit but it runs!

[Digitalwave]

Congrats. I was astonished when the car I build a Megasquirt for fired up first try. I was sure at least something would have been wrong.

[citizen_insane]

Awesome!! Glad that was the issue. I was so excited too when I got mine running last summer. The fun is just staring though, there’s so much you can do with it, really cool project. Go get some datalogs!


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[nando]

Rather than modify the relay, you can leave everything stock and build this to turn on the relay with the ignition like the stock DME:

http://www.megasquirt.325ix.com/MS_to_Motronic/Start_Circuit.html

That diagram from Matt is ancient. Like, 2003-ish ancient. He must have had the first turbo M20 running on Megasquirt 1 - he got Isaac into it, and then that got me into it..

[citizen_insane]

Rather than modify the relay, you can leave everything stock and build this to turn on the relay with the ignition like the stock DME:

http://www.megasquirt.325ix.com/MS_to_Motronic/Start_Circuit.html

That diagram from Matt is ancient. Like, 2003-ish ancient. He must have had the first turbo M20 running on Megasquirt 1 - he got Isaac into it, and then that got me into it..

Is there any reason not to do it the old way? Having to package another circuit and deal with its reliability seems non-ideal. (I suppose chopping up the stock harness is as well...)


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[nando]

It's a really simple circuit, basically a copy of what the stock DME does. And I don't like hacking up my wire harnesses, personally. :)

[johnny bravo]

hello,

sorry if i post in wrong thread but i dont wanted to open my own one for this simple question

i want to wire ms2 on e30 m50

and i dont understand why pin 26 is connected to pin 27 with diode?

pin 26 is +12v and pin 27 is negative terminal.

[nando]

because when you turn on the ignition, it triggers the relay to power up the DME. exactly like the stock DME did.

There are other more direct ways to switch the relay but they usually have side effects.

[johnny bravo]

because when you turn on the ignition, it triggers the relay to power up the DME. exactly like the stock DME did.

There are other more direct ways to switch the relay but they usually have side effects.

thanks for reply

im trying to make ms plug and play adapter and if you know i must add this circuit on ms board(proto area) or in custom adapter?