M30B35 Swap FAQ

[BDK]

Friggin Great write up!!!
Does auto vs 5 spd play into this at all?
Sorry, i suck at anything eletrical ....
I ask cuz I just picked up a late 88 e24 B35 out of an Auto car and I am going to slap this into my 89 e30 5 spd cab...
I am researching the swap now on the e30 forums but thought I would ask here while everyone was talking about it...
Thanks

[Brad D.]

No, the transmission doesn't matter. It has its own ECU and is totally independent from the engine's ECU. I am not 100% sure on this, but I think you are going to want to get a e34 b35 wiring harness for your e30 swap since it already has the correct C101 fuse box connector whereas the e24 b35 harness has a square fuse box plug like the e28.

[BDK]

Ok, B35 gurus,
I picked up my early B35 mit 115K today and it has the early 150 ECU, this is 1.1 Motronics same as the later M20's (like mine) have so this should be plug and play now pretty much correct.
I have kinda researched (R3V archives) that I should be able to just use my M20 harness mit extending some wires...
Is the 179 ECU mit 1.3 that much better?
Is my hp/tq the same as the typical B35? 208/225?
all I can find is the B35 info listing as such and this motor looks to be B35 all but the ECU...
Anyway, I like what I got for the price I paid so now we head forward....
Thanks for any and all wisdom...

[Bimmerguy2002]

if you have an 88+ and on wiring harness that has the quick release under the intake manifold. Cut that connector off and use a normal set of injector wiring from a 87 325i or super eta e28 harness, they have the quick clips that dont require a pick. Like a couple feet of wiring Anyway....

If you have an 87 325i, then you just need to extend. Both require extending regardless.

[lito]

will the oilpan of a m90 engine fit a m30b35 block?

[lito]

m30b35 is it wasted spark or full sequential?

[SamSpade]

Lito, we met at the track 2 weeks ago. The guy has some serious turbo power in his 30 yr old e24, 430rwhp at 1.2 bar iirc.

The m30b35 uses Motronic 1.3, which means it's still a single coil rotor-distributed spark, albeit timed by the ECU. Injectors are batch-fired 1/3/5 and 2/4/6.

Let's get together sometime before or after I finish the m30b35 transplant on my e23.

[lito]

ok..tnx mr sam...hope to hear from you soon

[jaydick]

Okay as I prepare to carry out a M30B35 swap on my 1986 BMW 635csi, I have some questions regarding the wiring harnesses. My M30B35 motor came from a 1989 635csi. I obtained the wiring harness with the unit and there is a plug 12-pin plug that resides near the DME that I am not sure what it connects to or what has to be connected to to it (see picture with large black plug figure 1.). On my 86 manual 635csi near the DME on wire harness is a green and white 4-pin plug that interfaces (see figure 2). Can someone that has done the engine swap tell me what needs to be hooked up from the green & white plug to make this swap work?

Need help.

Thanks

Jay

Figure 1.

Figure 2.

[Brad D.]

Since I'm not entirely sure what the first plug is it would really help to see where the plug is in reference to the rest of the harness. In the second pic you only need to be interested in the white connector, which is C103. With the e24 harness it should just plug into your e28's C103 connector.

[Kyle in NO]

Figure 1 should be the connector that plugs into your fuse box.

[jaydick]

Since I'm not entirely sure what the first plug is it would really help to see where the plug is in reference to the rest of the harness. In the second pic you only need to be interested in the white connector, which is C103. With the e24 harness it should just plug into your e28's C103 connector.

Brad I will take a few more shots of the 89 E24 wiring harnness to better exhibit where this plug comes from and post back here in the forum for additional analysis.

Thanks

Jay

[Brad D.]

Figure 1 should be the connector that plugs into your fuse box.

That's what I thought too at first but the fusebox plug (C101) is a 17 pin plug, not a 12 pin plug like that one.

[Jean]

No, the transmission doesn't matter. It has its own ECU and is totally independent from the engine's ECU. I am not 100% sure on this, but I think you are going to want to get a e34 b35 wiring harness for your e30 swap since it already has the correct C101 fuse box connector whereas the e24 b35 harness has a square fuse box plug like the e28.

Wrong info. E34 b35 harness has a 25 pin X20 connector, not the same connector as on the e30 with 20 pins.

[Brad D.]

I used an e34 harness and I could have sworn its C101 connector has 20 pins.

[Bimmerguy2002]

Hey Brad, did all you modify was the C101 and the other plug inside the car coming off the harness?

[Jean]

Here is my e34 5speed harness. 25 pin

[Brad D.]

I stand corrected. Thanks for the clarification.

[Jean]

I stand corrected. Thanks for the clarification.

I think we are both right on this one There must have been a cut off time when they switched from the 20 pin to the 25 pin. I just got back from a local yard where I pulled an m30b35 harness from another e34 (automatic) with a build date of 10/88 and it's got a 20 pin plug.

It does have some extra connectors near the ecu area, a 4 pin single row white plug, a black single row 4 pin, a 3 row 11 pin plug and a dual pin plug connected to what looks like a temp sensor INSIDE the area where ECU and relays are... I have no idea what that is....

[jaydick]

Figure 1 should be the connector that plugs into your fuse box.

That's what I thought too at first but the fusebox plug (C101) is a 17 pin plug, not a 12 pin plug like that one.

Okay I am really confused. I thought that I would have to match up the leads from the 20 pin connector of the wire harness into the 17 pin interface from the fusebox? Isn't this what the wiring diagram at the beginning of the tech article points out? I removed the 20 pin male portion of the connector from a 1989 635csi so that I could interface the M30B35 engine wiring harness with the M30B34 fusebox.

Please let me know if I am interpreting this incorrectly.

Regards,

Jay

[jaydick]

I stand corrected. Thanks for the clarification.

Brad is your 635 and automatic or manual? for your 535 that you did the swap on is it manual or automatic transmission? The reason I ask is that my 20-pin harness for my swap came from a 89 635csi automatic while my 85 csi that is receiving the 89's engine is a manual trans.

Regards,

Jay

[Jean]

Regarding the C101 pins 9 and 14. Which one feeds the speedo ?

Also, what are these plugs for, they are part of the 89 535i automatic harness. Can they be ignored, or does anything need to be 'jumpered' in order for an automatic harness to work as 5 speed?

[LA]

Thanks to all - I have learned a lot here. I have been a proponent of the b35 swap for years, although I have always done an in frame rebuild and used b35 rods, pistons, head and used Metric Mechanic ported exhaust manifolds and their single pipe system.You avoid the oil pan & engine mount issues (as someone previously said) by staying with the block from your orig b34. It can be honed in place if you wrap the crank with newspaper and tape it sealed to keep metal particles off the bearing journals. I think it's important to use cast iron rings with the b35 pistins for good seating if you go with the in frame hone.

There was a VERY noticable improvement. I just chipped the old motronic , but it looks like I missed the boat there. Based on consensus here, I'll be swapping to 1.3 DME, again, thanks to all!


Regards

[lito]

will the oilpan and oilpump of a m90 block fit an m30b35 block?

[itsbrokeagain]

i have been reading this thread over and over just to make sure I don't have an issue when I do my swap.

I recently acquired a later 735 M30B35 from a friend for 250 with all the accessories on it, but with a cut harness, so I have to go digging around for an E34 one.

Are they usually hard to find? I looked it up on real OEM and a brand new harness from an E34 manual is 600 something bucks, which to me is not really that expensive. Id almost rather have a brand new harness to eliminate 20 year old wiring (I just recently did a headgasket on an E34 535 and I was worried I might break the connectors or the wiring because it was so hard and brittle)

Other than that, a top end rebuild is the only thing I have planned, in addition to new belts and seals and what not. The motor only has 150k on it, but since it will be up on an engine stand for a few months, Im going to take the time out to do the timing chain and new guides, so this thing will run another 300k. I have 236k on the E28 I just bought, original everything, and doesnt even consume a drop of oil (pan gasket is starting to get wet tho, need to drop it and clean it up for the time being)

I really am surprised about cheap this swap really is to do, and the potential of easy power...

[Bimmerguy2002]

the harnesses arent that hard to find, you can use an automatic or manual harness. i can have a harness shipped to ya for 125 if interested.
You are correct though, it is a great swap, it has tons of torque and you hardly ever have to downshift going up hills and it was a motor meant for the chassis since its a direct bolt in.

Throw in an oil pan gasket and rear main seal which you are doing the rest of the stuff, get new hoses, and vacuum lines in addition

[draztik]

the harnesses arent that hard to find, you can use an automatic or manual harness. i can have a harness shipped to ya for 125 if interested.
You are correct though, it is a great swap, it has tons of torque and you hardly ever have to downshift going up hills and it was a motor meant for the chassis since its a direct bolt in.

Throw in an oil pan gasket and rear main seal which you are doing the rest of the stuff, get new hoses, and vacuum lines in addition

I bought my Super ETA harness for my m30b35 swap from Matt, it made life a lot easier. The Super ETA harness is virtually plug n play for this swap.

[Brad D.]

I still prefer the look and cleanliness of an e34 harness to the super-e harness. While it take a bit more work at C101, the end result is really clean looking.

[draztik]

I still prefer the look and cleanliness of an e34 harness to the super-e harness. While it take a bit more work at C101, the end result is really clean looking.

I agree it looks much cleaner. I ended up creating a hybrid Super ETA/e34 harness as my end result. I wasn't happy with the look of the Super ETA harness either.

[Brad D.]

That does look very nice!