M50 coils, main relay or fuel pump relay?

[Jon K]

When do the coils get their +12v? Is it when the fuel pump relay clicks over or the main relay clicks over? I am wanting to make sure that they come on when the fuel pump relay clicks over because I don't want to have my coils loading if the car isn't running else pop pop pop

[Javier]

But I don't see your point!

Javier

[winfred]

they power up off the main, they still don't do anything till the computer triggers them

[joshua43214]

The coils remain ungrounded until its time for them to start making spark. They won't "load up" until they are grounded by the ECU, and that won't happen until it sees an RPM signal.

[Javier]

12+ is received from ignition key, not the main relay, nor the pump relay. Main relay feeds, besides ECU, injectors, pump relay, oxygen sensor relay, evaporative purge valve, ICV, EGS, and MAF.

I do agree that having 12 Vdc at one pin of the primary coil does nothing until you get the other pin grounded (unless you have coil issues), that won't happen until ECU decides to do so. Not sure about your special retrofitted ECU, but guess it won't either fire the coils until you get a sync. signal from CPS.

When the cars were build with distributors and contacts, yes you could be in trouble keeping ignition key turned on for long time if the contacts were closed (that happens in more than 50% of the distribution rotation). You may be too young to remember those times! (just kidding).

Javier

[Jon K]

I think he is seeking to understand where the potential difference across the primary comes from. He can not find the schematics to be enough...


Bite me - you have no idea what I am trying to do.


There are NUMEROUS conflicting wiring diagrams floating around - you think I haven't checked it out? Sigh. Stay out of my threads.


by the way:

Rustam has just replied to a thread you have subscribed to entitled - M50 coils, main relay or fuel pump relay? - in the 5 Series BMW forum of Bimmer.Info Forums.

This thread is located at:
http://www.bimmer.info/forum/showthread.php?t=22386&goto=newpost

Here is the message that has just been posted:
***************
How about looking at the wiring there Jon?

And he calls me "ridiculous"...
Pathetic.
***************


No - you're ridiculous, and pathetic.

[Jon K]

12+ is received from ignition key, not the main relay, nor the pump relay. Main relay feeds, besides ECU, injectors, pump relay, oxygen sensor relay, evaporative purge valve, ICV, EGS, and MAF.

I do agree that having 12 Vdc at one pin of the primary coil does nothing until you get the other pin grounded (unless you have coil issues), that won't happen until ECU decides to do so. Not sure about your special retrofitted ECU, but guess it won't either fire the coils until you get a sync. signal from CPS.

When the cars were build with distributors and contacts, yes you could be in trouble keeping ignition key turned on for long time if the contacts were closed (that happens in more than 50% of the distribution rotation). You may be too young to remember those times! (just kidding).

Javier

That's exactly what I needed to rule out Javier - I am reading MUCH literature and finding that the aftermarket ECUs insist to use the fuel pump relay as a +12v source for the "coil". However, I have multiple coils and a completely different circuit than distributed cars, and so I was given a warning by another MS user to isolate the coil +12v from the rest of the car by using fuel pump so as not to burn it up if ign key is left "ON". I thought to myself well, this doesn't happen with OE system so... and I wanted to make sure. I have about 3 diagrams saying the 12v comes from various sources... I'd rather ask the EXPERTS (thanks javier, no thanks Crustam) what their thoughts were on it.

[Javier]

I'm not sure it will be fine, I meant switching the 12V supply to the coils from the key to the pump relay. The pump relay gets a priming pulse when you turn key on, and then stops waiting for CPS/ECU to turn it back on. I don't know details on the criteria to turn it back on. If it requires a minimum rpm that is only achieved when firing gets in, you will end with a non starting engine.

Best solution is to check for this. The coil supply line is a green wire coming from the key switch, and going to all the coils together and the ECU pin 56. You need to keep the feeding to the ECU from the key, so can loose the green wire at splice X6831 (when all coil green wires mets together), and substitute for a wire from fuse F23 (Feed side, by the way coils are unfused). Test for proper starting. You can select to avoid permanent wiring damage testing the pump relay for kick in wile cranking the car without the coils connected. If cranking speed is enough for pump to be energized (sorry I doubt it), you will be fine making the mod. If not, this will confirm my suspicion that if the engine does not kick in, the pump is not energized. May be Bill R. can tell us about the criteria.

If there is a recommendation to control the 12V supply to the coils, may mean that aftermarket ECU is grounding the coils as a steady state condition wile the engine is not running (like old distribution cars). Bad indeed!

Javier

Edit: By the way, may be the aftermarket ECU criteria to turn the pump back on is different to DME, and do it as soon as it sees CPS pulses, them permitting the coils connected to the pump relay to fire up the engine.

[Ausmpower]

That's exactly what I needed to rule out Javier - I am reading MUCH literature and finding that the aftermarket ECUs insist to use the fuel pump relay as a +12v source for the "coil". However, I have multiple coils and a completely different circuit than distributed cars, and so I was given a warning by another MS user to isolate the coil +12v from the rest of the car by using fuel pump so as not to burn it up if ign key is left "ON". I thought to myself well, this doesn't happen with OE system so... and I wanted to make sure. I have about 3 diagrams saying the 12v comes from various sources... I'd rather ask the EXPERTS (thanks javier, no thanks Crustam) what their thoughts were on it.

Re aftermarket ecu's:

Jon I've done quite a few retrofits of some common programable 3D (fuel/ignition) ecu's such as Microtech, Wolf and Greddy. Most of my setups have consisted of retrofitting direct fire coils to cars that had used traditional distributors.

My take is the following:

All of them use thier main relay (usually fuel pump) for the +12v feed to the coils (they all switch the coils on or off by the transistors switching 'on' and grounding the -12v side of the coil). This is a safety feature that allows you to pull one relay to isolate all the engine electrics if needed.

All coils are earth (-) switched be it by points (kettering) or electronic (transistor) ignition system, this reduces the load (amps) handled by the switch.

In the days of points (kettering) systems if you left the ignition on with the engine off you could burnout the capacitor (used to stop the points from arcing, increasing their service interval) or burn out the primary winding in the coil. most cars had a resistor in line with the coil that dropped the voltage going into the coil to around 8 volts, this reduced the risk of coil frying but didn't stop it all together.

But fear not those days are well gone now!

In a computerised system things are very different, the coils aren't triggered (grounded) by the ecu unless the ecu receives a valid rpm input from the crank (or cam) angle sensor.

So basically even though there is power to the coils the circut is incomplete (not grounded by the switching transistors in the ecu). Once the engine is cranked over the C.A.S. signal tells the ecu to switch the ignition transistors 'on' (to ground) in the correct order at the correct time (using the ecu's ignition / rpm map).

If the engine is not rotating the ecu DOES NOT receive any crank trigger reference or rpm signal, therefore the ignition transistors will be 'off' (open circuit) and the coils will not be 'charged' by the ignition system.

Logic tell us that if a switch is 'off' no current flows.

HTH ;)

Ross

[joshua43214]

As a follow up to Javier's post, I am 99% sure it is only rpm signal that is used to keep the fuel pump active. I think the only other criteria for fuel shut down is airbag deployment.

Either way, since the coils are powered by the ignition, the real concern is whether the aftermarket ECU grounds the coils with no rpm reference or not. If the new ECU does not ground the coils with no RPM signal, then just leave coil power supply stock and ignore any instructions for powering the coils. If the ECU does ground the coils with no RPM signal, then maybe just wire in a separate relay that will come on in the manner you find most pleasing.

[bjl4776]

It really shouldn't matter as everyone else has said, they won't ground out unless the are grounded through the ECU. Think about why I burnt mine. I didnt have the spark inverted so they were always grounded until they recieved the signal and turned them off, cause thats how traditional points work. The plugs fire when the points disconnect. It really isnt too much of a concern. I know that our coils are not powered through the fuel pump relay because the fuel pump relay turns off if the car doesnt start within a couple of seconds and the coils will continue to fire, i did some tests before i tore the OBD-1 off. My entire problem was due to mis configuration of megatune, not to wiring problems.

[Ausmpower]

As a follow up to Javier's post, I am 99% sure it is only rpm signal that is used to keep the fuel pump active. I think the only other criteria for fuel shut down is airbag deployment.



Not trying to inflame but some models use the oil pressure switch signal to switch the fuel pump on after the starter is disengaged. In the event of a roll over or the lack of oil in the sump shuts the engine down (common on GM cars).

FYI : The new BM models use the oil level sensor and will go into 1 of 3 limp home modes if he oil level drops to a predetermined level.
In the event of an accident they have a pyrotechnic device that seperates the positive battery lead at the battery triggered after the front curtain airbags deploy.

[bjl4776]

Im pretty sure that is a domestic only thing. I think GM does that on the older F-Body and maybe Vette. Not positive, but im pretty sure BMW never did that.

[joshua43214]

Im pretty sure that is a domestic only thing. I think GM does that on the older F-Body and maybe Vette. Not positive, but im pretty sure BMW never did that.

yep, and fords had the stupid switch that would pop when you hit a speed bump and make your care die infront of your kids school in front of all his friends, proving once again that parants are fools.