m42 wiring clarification (fuel pump)

[captain awesome]

So I think I've got my head wrapped around all this from reading other posts regarding the swap. Here's what I have planned, so if you see anything suspect please let me know. The only thing I would prefer to know clarification on is whether Grn/Blk (3) or Grn/Viol (6) is the fuel pump connect at the c20h plug. I've seen it mentioned both ways, and just want to make sure it's right. I'm fairly certain the connection from 6 to 6 is unnecessary and can be ignored. The car is an 83 if that helps any and I see the Grn/Blk runs all the way to the fuel pump which kinda answers my previously mention clarification. I would like to connect the green/black wire within the fuse box to where my old rear defroster fuse was and use a 7.5a fuse or similar size.

In other words the wiring for the fuel pump circuit would be c101 pin 13 ----> c20h pin 3 ----> fuse 3 ----> fuel pump

c20h ----- c101

1 ----- 5
3 ----- 13
8 ----- 7
10 ----- 18
13 ----- 4
15 ----- 9

EDIT: I previously wired the pump to fuse 10, but it really needed to be on fuse 3 so it's on the proper bus bar located in the fuse box.

[Somjuan]

Would the M50 diagram help? I had concerns with how the fuse was used in the m42/m50 harness vs. the m10 harness where I'm pretty sure that the m10 fuel pump fuse becomes useless. Me personally, I'd just rewire the fuel pump in the car to the relay itself the way it's done on the m42 and make sure the positive wire power wire is carrying the right size fuse specced out for the m42.

[captain awesome]

Would the M50 diagram help? I had concerns with how the fuse was used in the m42/m50 harness vs. the m10 harness where I'm pretty sure that the m10 fuel pump fuse becomes useless. Me personally, I'd just rewire the fuel pump in the car to the relay itself the way it's done on the m42 and make sure the positive wire power wire is carrying the right size fuse specced out for the m42.

Essentially that's what I posted above, but I forgot to put the relay and battery hookup. Sounds like I got it correct though. Did you connect to the blk/grn or blk/violet with your fuel pump wiring?

It should end up being this:

battery ----> relay ----> c101 pin 13 ----> c20h pin 3 ----> fuse 3 ----> fuel pump


EDIT: I previously wired the pump to fuse 10, but it really needed to be on fuse 3 so it's on the proper bus bar located in the fuse box.

[Tom D]

i forget off hand, just make sure it's fuse protected, which it's not if you just tie it into the c101.

- - - Updated - - -

..... I'd just rewire the fuel pump in the car to the relay itself the way it's done on the m42 .....

while this is sounds straight forward, it not a very good way to wire the pump. the hot wire coming out of the relay going to the pump is far to small of a gauge.

[captain awesome]

The info I listed above will put a 7.5 amp or similar size in between like the stock m42 harness runs. I'll be running a Deatschwerks DW200 fuel pump in the tank like I run with my 318is as well so it won't be running the high pressures that the m10 ones do. The stock m10 fuel pump and filter stuff will all be removed. I'll add back in a standard m42 filter due to cost and simplicity of the setup.

[Somjuan]

Looks perfect to me

[captain awesome]

Looks perfect to me

Did you hook up the o2 wires between the c101 and c20h? From what I have read, it isn't necessary as the engine harness provides the o2 circuit.

[Tom D]

From what I have read, ...... the engine harness provides the o2 circuit.

this is correct. the O2 and its relay are all part of the M42's engine harness.

[captain awesome]

Thanks Tom. I'm excited to compare the e21 m42 vs my e30 m42. It won't be a fair comparison, especially with the e21 being 5-600 lbs. less in overall weight, but a fun one.

[Tom D]

^ also if you have the engine as back as i place them then there is also far less mass in front of the front axle then in the E30.

you said you have an 83, you know that you can run the 83's G240 behind the M42 and keep your mechanical speedo.

[captain awesome]

^ also if you have the engine as back as i place them then there is also far less mass in front of the front axle then in the E30.

you said you have an 83, you know that you can run the 83's G240 behind the M42 and keep your mechanical speedo.

I don't know if mine was just a late 82 build or not, but it had a G245 in it. I expected the G240, so I don't know if it was swapped in at a later date by someone else? If they did that would require the driveshaft swapped as well, so I don't know. Either way I'm going to run the trans from the 318is since it has the dual trans mounts. Since it's basically a "race" car I'm not too worried about the speedo working right now. The GPS speedos are getting cheaper by the day so I'll probably just run one of those at a later date.

[Tom D]

i was running a speed app on my iPhone, it was cool at night because i could prop it on the console and read the display on the windshield, just like a heads up setup.

i too chose the E30 trans for it's double mount and I-beam shifter support, far better format then the E21's.

for my son's car we sourced an E21 G240 and it is really, really nice to see the speedometer spinning.

[jaredmac11]

In other words the wiring for the fuel pump circuit would be c101 pin 13 ----> c20h pin 3 ----> fuse 10 ----> fuel pump

c20h ----- c101

1 ----- 5
3 ----- 13
8 ----- 7
10 ----- 18
13 ----- 4
15 ----- 9

Youre correct. I added a fuse as well. Youre close!

[captain awesome]

Youre correct. I added a fuse as well. Youre close!

So close. I'm trying to take the time to get it all right so when I turn the key the first time that things just work correctly. End of February if all goes to plan I'll be doing some test hits through the neighborhood.

[jaredmac11]

It's worth it! If you continue doing your homework and go through the wiring diagram it's not bad! I had 2 issues with starting: Coil on plugs were installed in wrong order and one of my relays was bad. Otherwise she fired right up.

[captain awesome]

Okay, bringing this back from the dead to see if you guys have had the same issue or could possibly point to what I may have done wrong.

When I turn the key to IGNITION the pump doesn't just prime, it runs, and keeps running. I don't think that's normal.

What's possibly different between your setups and mine is the key switch I have installed. It's a 4 pole switch used for Jeeps and is wired as such:

RED -- BATTERY
PURPLE -- ACC
GREEN -- IGNITION
BLACK -- STARTER

There's a couple smaller wires related to dash cluster stuff I'll need to attach to accessory circuit, but I'm pretty sure they are cluster light stuff.

s-l1600 by hatchethairy, on Flickr

[captain awesome]

Oh, I guess should also mention the stock fuel pump and filter assembly is gone with the accumulator. Could that be part of it? I've wired up an in tank pump looped through a fuel filter, but no lift pump anymore.

[captain awesome]

Okay, I figured out the issue. The fuse 10 spot I used is connected to the wrong bus bar in the fuse panel to work on the circuit like I needed it. I noticed spot 3 on the panel goes to the correct bus bar and oddly enough is listed as the fuel pump on the fuse box cover. I removed the green/violet wire from the inside of the fuse box and connected the green/black wires to both sides instead. Since the Lambda wires aren't used with the m42 swap it's no big deal, but at least this way I have a fuse inline for the fuel pump. It now primes the pump as needed and runs when started without fail.