Bosch Gen 3 injector swap 750il ('98-01 M73N)

[cooptroop123]

Feel free to skip to the good bits down below, but here is the back-story that led to this swap, im sure many of you can relate... I had a fuel trim code (bank 1 lean) and although it was running great still, I figured it was vacuum leak and did smoke test. Yep, ended up being a broken fuel injector in cyl 1, the hose fitting on the injector cracked off. the injectors and distribution hoses are original, 174k miles. The hoses were really brittle, felt like hard plastic and cracked under force, I knew I needed to replace all of them while I had it apart but the injectors were so brittle and weak that all 12 of them broke when getting the hoses off. I was careful for the first few but trust me, they were not coming off even with trying to cut them. Besides, the injector body itself was weak and brittle so even with new hoses, another would have cracked just like the first one so I would rather replace them now than waste time fixing a bunch of vacuum leaks in the future. many of you know, replacements are expensive, and there is little info on anyone swapping injectors on the M73N since they have the air-shrouded injector setup, but I decided to try it to save money and upgrade to newer injector technology (and get rid of these silly air-shrouded injectors)

Now for the actual info on the swap, note that this is only relevant to the M73N engine, any M70 or M73 before '98 and any 15 lb/hr EV1 or EV6 long injector will work.

First, flowrate:
15 lb/hr is good, pretty much the exact same as '97 and earlier M73 engines and fuel pressure for both applications is 3.5 bar so I just matched that. the problem is that these are not common, all the mustang injectors are the right physical size but start @ 19 lb/hr which is only good if you re-tune as you need room for the fuel trims to work properly(I asked DUDMD about injector scaling, very common in the tuning world but it seems he hasn't figured that out on the 5.2.1 DME that these 750's use)

second, physical size -
the OEM injector is unique, there is nothing else with the same size and same flow rate that I could find, and I looked for hours. there are a few other air-shrouded injectors used by BMW and others but none had the right flow, which is fairly important since I don't have the ability to simply scale the injectors in the tune. I knew I wanted a standard size, readily available, and the new style the 4 hole type injectors. the Jetronic type connector is a must because I do not want wiring adapters or to modify the harness.

I ended up settling on using a Bosch gen 3 EV6 long style injector (60mm length). The 0280155885 is perfect and five 0 Motorsports advertises it for use in the M73 for '95-'97, the only issue for M73N is the size difference compared to the OEM M73N injectors, we will get to that... there is also a good EV1 style injector (fits exactly the same just bigger diameter body) that would work too and is cheaper than the gen 3 Bosch, you can use injectors from a GM 2.8L 3.1L 3.3L. very common and cheap, they have the right flow rate, and those can be found both in gen 1 (single pintle) and gen 2 (4 hole) like from here . I wanted

IN SUMMARY, USE ONE OF THESE:
budget option ---- EV1 style---- google "GM 2.8 2.1 3.3 injector" and you will find a lot, most you see on google will be the single pintle but here is an example of a nice refurb gen 2 unit with the updated 4 hole style https://southbayfuelinjectors.com/15...s-gm-1985-1992
performance option --------- Bosch 0280155885

both of these have the right type of connector and they can accommodate the OEM retainer clips. There are others out there advertised for older ford 3.0 and 4.9 engines but those are basically the same as those GM injectors and most will be gen 1 single pintle. the only Bosch gen 3 with 15 lb/hr flow is the one I listed above

Now to make the standard size injectors work, it ended up being very simple, see the attached drawing comparing the M73N OEM to the Bosch EV6 long (which is interchangeable for EV1). The only differences are the height of the injector (EV1/EV6 long is longer than M73N) and the lower o-ring size (EV1/EV6 has smaller lower o-ring). the top o-ring that goes to the fuel rail is exactly the same for all of them.

So, all you need to do is use spacers under the fuel rail where it bolts to the intake, and get different sized lower o-rings. measurements show that the fuel rail needs to come up 6.35mm (.25") and I just used realOEM to find that the ORM lower injector o-ring is 9.93x2.62, so OD is 15.17......as luck has it, this is pretty much exactly the same as swapping a GM LS1/LS6 injector into an LS2/LS3/etc.. intake manifold. there are kits for this that are pretty cheap and common, here are are options:

https://www.amazon.com/Michigan-Moto...el+rail+spacer
https://www.lingenfelter.com/product/L750025305.html

there are many other sources, and lots of info on the google about putting LS1 injectors on other LS manifolds so that should be easy.

as for the vacuum ports, they serve no purpose. I am just detaching the air line that feeds the rail that the distribution hoses attach to and capping it, so the rail which feeds the distribution hoses is completely open from all sides, no hoses connected anywhere on it. you could also just cap all the ports where the distribution hoses connect to and leave the main feed for that rail intact, doesn't matter as long as you close the vacuum system that was going to the injectors before.


TAKEAWAY: buy a standard 15 lb/hr injector and buy a kit to use LS1 injectors with an LS3 intake manifold and you are good to go!



injectors.jpg

[Hemidog]

Awesome research Thanks alot!

[Hemidog]

FYI: https://www.bimmerfest.com/forums/sh....php?t=1329929

[tominizer]

Have you completed and tested out this little project ? Any final thoughts if you have ??

[Hemidog]

So far so good. I have driven around 350km since the replacement, and the engine seems fine, no fuel leaks.
I think(and hope) that the new 4 hole pintle vs the old 2 hole pintle makes up the atomization of the fuel that the old air-shrouding system made.
The ilde when the engine is warm is a bit on the low side, around 500-600 rpm (is that normal?)
As far as power, I cannot feel any difference. The vacuum leaks around the old injectors would not be as prominent on higher rpms I would think.
The wiring loom box above the fuel rails still fit fine after the spacing, but I did space out the acoustic cover front bracket, because it felt a little tight on the box, but the cover still looks good.

I will report back if there are changes.

[tominizer]

Looking forward to hearing how this plays out. Nice work. Any pictures of the whole adventure ??

[Hemidog]

Check the bimmerfest link, I have posted pictures there, I don't see any option to post pictures on this forum.