Motronic 1.3 conversion

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Lock
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Motronic 1.3 conversion

Post by Lock » Fri Aug 30, 2019 11:31 pm

This thread will be following my project removing the L-Jet and installing Motronic 1.3 (179 ECU) onto the original M30B28 motor.

Why? Background - I bought an e34 535i with a blown head gasket intending on fixing it and putting it into my e12 but the block was cracked because when the head gasket was changed last, they did not clean out the head bolt holes and either when torquing it, or under heat, that oil cracked into the water jacket. Coolant seeped into the head and oil over time damaging the internals and also requiring constant top-ups. PO decided to pour radiator stop-leak into the coolant, that didn't work and caused more overheating and oil damage, eventually got behind on the coolant level and the gasket blew. Ironically the head wasn't cracked but the engine overall is toast. Separately from that, my e12 decided to stall under load and despite weeks of troubleshooting and parts it's no better, so the only solution was to start with a new EFI system. Plus the log manifold has vacuum leaks and requires total disassembly to seal it properly.

I realize the ECU is tuned for a different motor, but I've reprogrammed Nissan ECUs in the past and Motronics are similar so if it runs badly I'll adjust the fuel and ignition maps. Also, this is phase 0.5 of installing a B35, so on the upside if I find a good condition B35, the wiring will be plug and play.

The biggest decision I had was whether to keep the log manifold, or use the B35 manifold, I even drew up a pros and cons list and it was about 50/50 either way. The B35 manifold does fit and looks good but it's a very big piece. I was not happy with how tight it was, it was tough to get in and even harder to get out again and access underneath is totally blocked off. It would have caused coolant reservoir plumbing issues and I don't know what the longer tubes would have done to the engine characteristics, additionally I didn't want to deal with the throttle linkage to cable adapter so I decided to retrofit the Motronic into the log manifold.

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The throttle switch screwed straight onto the old throttle and worked correctly, almost as if it was made for it.

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The injectors have the same shape and will accept the L-Jet style mounts. Dirty Motronic on left, L-Jet on right (I bought reconditioned injectors only year ago).

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Just needed to buy and fit some Bosch pintle caps to make them fit the OEM seals.

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Shot of the intake, looks surprisingly clean.

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Next I'm going to install the injectors and mount the injector assembly back onto the engine with all new gaskets.

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1979 528i 5-speed conversion G260/6

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Re: Motronic 1.3 conversion

Post by Lock » Tue Sep 03, 2019 11:22 pm

Someone used both gaskets and gasket sealant on the manifold - possibly why it was so leaky. Took a long time to get all surfaces clean. You can also see how low-quality the AMC head casting is, the middle intake port in this photo is missing a section of metal on the lower right.

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While the manifold was out I swapped the starter for the newer smaller model. It won't have the same classic start sound, but will be much easier to replace.

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A picture to show how simple the L-Jetronic and engine wiring harnesses are, linked by the combo relay. That explains why the L-Jet wiring is all white and looks different to the rest of the car wiring, it was probably an 'off the shelf' item from Bosch.

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I also cleaned all the parts while they were out. A test fit of the Motronic injector in the log manifold. The injectors are on a slight angle - waiting on some hardware and will test fit the hard fuel rail if it will seal with the injectors tilted like that.

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The e34 harness is designed with the ECU to live in the engine bay, it won't reach the the glove compartment and the engine connector is integrated with other e34 body wiring making it annoying to adapt to the e12. To simplify, I have ordered a 1988 528e Motronic 1.3 wiring harness which, as it's essentially the same chassis will allow the ECU to be in the glove compartment, most components in the same spot, and also the engine connector becomes e12-e28 connectivity which due to this website is easy.
1979 528i 5-speed conversion G260/6

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tschultz
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Re: Motronic 1.3 conversion

Post by tschultz » Wed Sep 04, 2019 9:58 am

I did the conversion as well on an '81 Motronic 635CSi.

It seems to be much more reliable and I already had the correct intake manifold. I do suspect the log manifold was better breathing at high RPM, however.
Not especially difficult as my car already had the correct cam drive for later parts-- do you have a cam already?
http://drive4corners.com
1980 635CSi
1985 535i

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Re: Motronic 1.3 conversion

Post by Lock » Wed Sep 04, 2019 12:25 pm

Good to know. I see the stock log manifold has relatively short runners, good for higher RPM but the engine has plenty of pull down low.
The only cam I have is the B35 which has significantly higher lift and duration. The duration is okay but I don't know whether the lift is too high.
Initially I'm going to use the original distributor, not for timing, just for spark distribution. Not ideal but if I'm removing the head to swap the cam, for that amount of effort I may as well just get a whole B35 in there (if I can find a good one).
1979 528i 5-speed conversion G260/6

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Re: Motronic 1.3 conversion

Post by Lock » Fri Sep 06, 2019 12:31 am

New injectors in place

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The e34 fuel regulator will not fit under the banana, also the tilted injector angle means the fuel rail is unusable. Other BMW engines are 91mm cylinder and so injector spacing (not the m30's 100mm) so while there are some others with offset FPRs, they're too narrow.
I will get some Bosch injector top hat adapters to hose adapters and use the e12 fuel rail, and plumb in the e34 FPR.

https://www.efihardware.com/products/23 ... pter-Steel

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While I'm waiting for parts I'll take the front apart and get the Motronic harmonic balancer (and e34 alternator) installed. Pinhole leak in the radiator so debating fixing that, or e28 radiator.

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1979 528i 5-speed conversion G260/6

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maybeillbuyit
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Re: Motronic 1.3 conversion

Post by maybeillbuyit » Mon Sep 09, 2019 2:46 pm

Lock, Hey this is great to see you doing. I think staying with the old style log intake is the way to go for sure. Those injector top hat things are interesting. Going with the e12 fuel rail will simplify the fuel rail issue. Nice work. I see this conversion in my future someday after a bunch of other stuff. Keep the posts coming.
1977 530i another project
1979 635csi Euro "project"
1987 635csi

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Re: Motronic 1.3 conversion

Post by Lock » Tue Sep 17, 2019 12:27 am

Thanks. The log manifold is classic and I didn't really want to ditch it. Adds a bit more complexity but not as much as I thought and keeps it looking classic.
It also keeps the rod throttle linkage which I really like the feel of.
1979 528i 5-speed conversion G260/6

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Re: Motronic 1.3 conversion

Post by Lock » Tue Sep 17, 2019 1:09 am

Mounting the Motronic engine speed/position sensor took some planning as the AC compressor blocks it. Turns out the Motronic harmonic balancer fits with the original bracket which left me with a choice. I could either cut the oem AC bracket, or vacuum the lines, remove the compressor and (after fixing everything AC-related) install and regas the e34 compressor and bracket. But I am really trying to avoid scope creep and just get the car running again before it gets too cold, plus my AC works right now.

The original diagnostics sensor bracket is similar but alignment is wrong. (I also recently discovered putting gloves on makes cleaning my hands much easier plus I feel like I'm doing something important).

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I decided to cut the original AC bracket - if I break it, then I'll just commit to replacing the whole AC system next summer. Took several hours carefully cutting out the required shape, but eventually got there all OK.

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After adjusting the sensor clearance (I can't access its adjuster bolt installed), reassembling the belts and fan, breaking a bolt off in the crank hub, removing that and reinstalling a few times again, I found the AC tensioner that is held by one of the bolts that hold the new sensor wouldn't bend down far enough as it wasn't designed for that position. Also the original alternator was too loose as the Motronic pulley is smaller. After thinking and eyeballing it, I guessed that the curved, thinner alternator tensioner would fit here well, and the longer AC tensioner would give the tension I needed. The alternator bolt is covered by the harmonic balancer, so I took it all apart for probably the 6th time that day, swapped the brackets, reassembled, and by some miracle they both worked perfectly.

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I was too stubborn to remove the hood but it paid off. I consider that the least fun part out of the way so I'm happy the front is buttoned up again.
1979 528i 5-speed conversion G260/6

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