Motronic 1.3 conversion

[Lock]

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.









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



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).



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



Shot of the intake, looks surprisingly clean.



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

[Lock]

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.



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.



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.



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.



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.

[tschultz]

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?

[Lock]

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).

[Lock]

New injectors in place



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





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.

[maybeillbuyit]

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.

[Lock]

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.

[Lock]

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).



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.





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.



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.

[Lock]

Quick update

Idle speed controller test fit, purge valve mounting. The original PCV hose was the perfect adapter size for the larger Motronic piping size so ordered a new one for this purpose.



Installing the injector top hats





And on the FPR



Top manifold cleaned and mounted, measuring the fuel rail alignment. Wasn't sure how to connect the FPR, eventually settled on plugging the original FPR line with a M14-to-1/4" NPT adapter for the pressure gauge I used before, and will use the former cold start injector barb for the FPR. I may need to bleed the air out of the rail initially with this setup. Also cleaned the manifold with just white vinegar and elbow grease (see how shiny it is compared the the dirty banana) and plugged the cold start injector hole.

[528i-1981]

Nice progress, Lock. I especially like the fuel pressure gauge mounted on the fuel rail - that worked out nicely.

[PatinaBeforePolish]

Lock,

Thanks for sharing this. It's time consuming enough just doing the work let alone stopping to take pics, then posting later.

Question - in an earlier post you mentioned ordering an 88 528e wiring harness in order to keep the ecu inside behind the glove box. Did you find the part new? Looks like it's NLA.

Thanks!

[Lock]

Thanks guys. I was considering a plug on the end of the rail, but I got used to the convenience of a fuel pressure gauge for diagnostics. I actually bought a pack of adapters because I didn't know what size it was (turns out it is M14 coarse thread).

And as for the 88 528e wiring harness - I didn't get it new, but I found several used on eBay. Not cheap but turns out this particular harness is very useful for B34/B35 conversions into e28/e12s/e30s as it's the only harness made for the e28 chassis with the Motronic 1.3 and is engine-wiring-only. The e34 harness is so different and integrated with the body harness it's not reasonable for this application, leaving aside the fact the ECU won't reach the glovebox.

I will need to do some cutting and splicing - some parts are in different areas (the AFM is on the drivers side in an 528e with the M20 for example), some plugs are different plus I will solder in my original engine connector and remove wires/plugs for things like the oil level sender which we don't have.

But if you find one of these harnesses, grab it as they probably won't be around forever.

[Lock]

It was a cold weekend in my unheated garage but made progress. Started by cleaning the bananas before removing all of the sealant that PO had used instead of gaskets. Major difference after some light scrubbing.



I had some 8mm hose from my earlier fuel line replacement, following the F5 FAQ but it was too big for the top hats. I spoke to the vendor and he said to use Mercedes type 7.5mm, so I ordered some, fit great and also fit snugly over the existing rail nubs. Here it is mounted after I measured and cut.



A closeup of the FPR mounting near the original spot and you can see the pressure gauge installed. Below the 2nd cyl manifold is the purge valve for the evap canister.



A shot of the idle speed controller. I can't think of a better way to mount it right now, but I might trim the piping. That's the original pipe and it happened to be shaped the right way. Any higher and it'll hit the hood though. I need to clean the valve cover now to match everything else.



I don't regret at all keeping the log manifold over the later style, and adapting Motronic to it. Cleaned up I think it looks really great.



I took apart the radiator tube and as I suspected, the ends are disintegrating into rust even though it didn't look so bad with hoses on. This is not going back on my car. That part lists for $250+ and I don't like it anyway. I've ordered the equivalent e28 parts (total ~$30) - I'll see how they turn out and what modifications I need to make them fit. I'll share what I find here.



I'm nearing the end of the project. Currently I'm working on adapting the e28 528e wiring harness, labeling all plugs and relocating them to suit my engine bay. I'll mount it to the car and wrap it up in the engine bay.

[528i-1981]

Looks great and I've learned a lot following this project - thanks Lock. That rad tube photo is instructive. I'll be sure to check mine next time I have stuff apart.

[Joe Boston]

That is impressive "Lock".. I had asked the question in this forum to add Motronic 1.3 to 2.8l engine, you might have seen the post.
Nice work in upgrading your engine..another simple upgrade would be to install E21 intake runners, what a difference more more response on the lower rpms..

I am in the process of installing a M90 engine 3.5l, debating to go Motronic or Megasquirt, I am leaning with Megasquirt MSPNP2. Its plug and play for a Motronic 1.3 ..you can add megasquirt at a later date...

I also have upgrade my cam to Schrick 284 to get more horsepower.
I have both wiring harness from 91 535i and 1987 528e, look like the 528e wiring hardness requires less work to the main plug to fusebox..

good luck with your install..