M42 in 325e woes

[lolcantturn]

Dropped a m42 in a 325e. Didn't mess with the wiring just plugged it to the c101 directly. Car starts but it doesn't start well or run too well. It came out of a perfectly working car so it's nothing motor related for sure. For starters, the car backfires very heavily sometimes, REALLY heavily. This could be if I gave it sudden acceleration, or even when it's initially starting up. The starter when starting it up sometimes quits intermittenly, juttering the engine. It's like the starter is giving out at some points, but it still starts. The idle is ok, but the car definitely feels down on power, as if it's running on 3 cylinders when I give it gas. Additionally, the wiring harness fried a little bit causing it not to start and I pin pointed it to a wire that burnt out coming off the main relay. Any ideas? Something is definitely wrong with simply connecting the c101 to the 325e

[roguetoaster]

Insufficient fuel pressure, or did you use an M42 fuel pump?

[bmwman91]

Are you using an M42 starter? The ring teeth are different on the M42 and M20B27 flywheels.

Are you using the stock 325e fuel pump? The 325e is a 2.5BAR system and the M42 is a 3BAR system. The stock 325e pump may not be able to meet the fuel pressure needs.

When you say "no wiring" I assume that you at least swapped in the M42 engine harness? What did you do for ignition coils since there is no bracket for them in the 325 chassis? Are you using the 325e O2 sensor, and if so is it a 4-wire type?

[Dj Buttchug]

assuming you are running everything from the m42 car in the e chassis you need to change fuel pumps asap.

Check all your grounds as well. Early cars have slight differences in C101 connections compared to late cars. Paging Irish with the m42 swapped 318i early car...

[irish44j]

Fuel pump should be fine. The M10 pump and ETA dual-pump setups are interchangeable (my HP pump is from an ETA car), and I'm using the M10 lifter pump, an ETA HP pump, and all the stock M42 stuff and they all work great together. I'm pretty dubious about the two pumps putting out different pressure, after doing some reading on other forums where people have actually tested the fuel pressure (pre-regulator) with a gauge and got basically the same readings between the two setups. Odd, DJ I thought

The connector, I"m not sure about the ETA to M42 differences, but I am sure of one thing: YOU CAN'T CONNECT THEM DIRECTLY. The real key was just to MAKE SURE not to hook up the M42 harness ABS wire to the wire on the old C101, because that's a ground wire and it'll fry the ECU and a bunch of wires if you do that. I didn't, but I know someone who did, lol.. IIRC it's a yellow and black wire, but you should double-check that. It sounds like you did that, and you may have fried other parts of the wiring harness when the ABS wire was hooked up to the ground wire and grounded out. I've heard about people messing up their ECU doing that as well, so that's a possibility.

Since I had an M10 it had the old square C101, so I couldn't hook them up directly anyhow. I had to make a bridge piece using another square C101 and an ETA C101. I have a diagram and links to some wiring colors and stuff in my build thread. Probably from sometime last winter, not sure exactly when I did that.

Other thing it sounds like: your plug/coil wires are not correct. I had 2 of mine out of order when I first hooked up the engine. It would run, but would misfire, idle like crap, and have no power.

Since BMW wasn't nice enough to actually LABEL the wire numbers coming from the ECU to the coil, the only way to really check it is using a multimeter to the pin-out on the ECU plug and check resistance. Again, I think I have a little how-to of this in my thread someplace.

I'd love to link you to those parts of my thread, but honestly I have no better idea where in the thread this stuff is than anyone else, lol. It's someplace after I put the M42 in, so basically last winter at some point.

[irish44j]

Also the FPR could be bad.

And....where did you get the injectors? I'm not gonna name any names, but the injectors that me and a few others got from a forum member (various types) had some of them bad, which screwed up everything. So if you aren't using the injectors the engine came with, that could be your problem.