M20 noob observations-love/hate relationship

[Nohawkscott]

So I had my new to ‘85 325e running pretty well and handling really well with all new bushings, H&R sports and Koni’s. It was slow as hell with the eta engine but that’s what I knew to expect.

I had no real plans to build a hot rod but some new developments are pushing me in that direction.

I did all the expected things that usually need to be done to get these things back on the road…

Complete fuel system rebuild: Both pumps, filter, all hoses replaced, new FPR, all injectors removed and cleaned and tested. O2 sensor replaced with Bosch replacement.

Ignition: Cap and rotor;I did cheap out on these, bought Wells Automotive brand that looked pretty good but the cap fitment was awful. New plugs; Initially NGKs but then Bosch, twice. More on that later. New coil, New crank position sensors, also cheap ones, can’t remember the brand but they are still testing within Bentley specs.

Cylinder head: This was replaced by the previous owner along with the timing belt and water pump in 2023 and the car was never driven because they missed diagnosing a bad CPS.

I also replaced the clutch master cylinder and slave along with a braided hose and all the bushings in the pedal assembly.

The car ran well for about 300 miles and all was well, even with the obnoxious straight pipe exhaust. I was actually on my way to the muffler shop to get a muffler when things went south.

Basiclly this thing has developed a misfire and exhaust backfire at all rpm’s between idle and WOT. It idles a little rough, not too bad and it’ll rev to redline clean but anything in between is awful. Loud backfires and completely un-drivable. This issue is what led me to replace all the ignition components mentioned above. When I briefly had it running, I had only replaced the plugs. Now I’ve replaced the plugs twice more due to gas fouling.

I’ve tested everything at the DME pin-outs as instructed in the manual an all seems good. The only exception is the AFM. The testing results with anything other than an oscilloscope seems pointless.

I have done a compression test as well but I don’t have the numbers with me right now. I think they were all around 140 cold.

Smoke test? Yes I have a smoke tester that works pretty well. The shaft in the throttle body is leaking a bit but no leaks anywhere else after installing all new silicone hoses. I have cleaned, adjusted and tested the TPS..

So what am I going to do. I’ve got a line on a m20b25 with a Getrag 260 bolted to it out of a ‘90 325i and a 3.73 lsd out of a ‘89 325i. I don’t need the transmission and I’m thinking about just using the 885 head, the Motronic 1.3 stuff and the 325i intake, TB and AFM, all on the stock eta bottom end. I know this low compression set-up isn’t ideal but how bad would it be with the 3.73 diff while I educate myself on turbo’s and stand alone ecu’s?

I see this thing snowballing but all I really want is a powertrain I can trust on a road trip. Well, I’m not gonna lie, 250hp sounds pretty good too but I still want reliability.

This forum has already helped me a bunch and I hoping you guys can point me in the right direction with this thing that I’ve really grown to like. I’ve actually been pressured by some friends to engine swap it, one friend owns a classic truck shop that does LS swaps all the time and my neighbor has a shop full of 500-800hp Hondas and he’s in my ear about K swaps but I really dig these M20’s now.

Look forward to some guidance from the pros here…

[Nohawkscott]

Just found the thread from Aveman that clears things up for me. Great stuff. I’m going to do the head swap along with the motronic upgrade and diff. It sounds like a decent combo to use while I figure out the boost options.

[82eye]

I see this thing snowballing but all I really want is a powertrain I can trust on a road trip. Well, I’m not gonna lie, 250hp sounds pretty good too but I still want reliability.

if you can't chase down and fix a misfire how are you expecting to tune a turbo set up? i'd try get the car running correct first. there's a pile more learning curve getting the turbo tuned than there is in fixing a misfire. you'll need standalone engine mgmt, dynos and access to a good tuner, as well as developing tuning skills yourself.

reliable, fun, fast - you generally get to pick 2. no one's gonna tell you not to turbo, but there are plenty of great ways to get to reliable and fun in an e30 with only basic mods using the engine options you have available.

first job is always understanding the car you have and ensuring you know how to have it running correct in the first place. planning a power build to fix a misfire does not sound intuitive.

[Nohawkscott]

That’s fair. I do realize it seems irrational but I’ve owned a few water cooled VWs with aftermarket turbo and ecu configurations. A turbo car can be reliable, fast and fun but I know it takes some dyno time to get it there. I currently have a mk7 golf r that’s chipped, tuned, big turbo, down pipe, injectors blah, blah and I trust that car to go cross country.

I guess the thing with this ‘85 eta that I feel the least positive about is the ancient motronic management system. I think I have figured out how to troubleshoot this system for the most part but it seems that sensor failures are always right around the corner, which lead to excessively bad A/F mixtures, fouled plugs, ruined O2’s and tow trucks.

I feel my current misfire is due to a bad AFM or the DME itself, or both. The AFM seems hard to test properly without specialized equipment and I hate just replacing parts. Plus there isn’t anyone around here that’s into these old BMW’s so swapping parts isn’t an option. The signal from the DME to coil is a bit concerning too. I don’t see my test light flickering like I think it’s supposed to when grounded to the primary side of the coil

So am I right in thinking that this early version of Motronic sucks?

It seems I have 4 options:

1: Keep replacing the parts needed on the eta

2: Add the i parts to the eta bottom end and maybe go the turbo route in the future, maybe just enjoy ~140hp

3: Go through the M20B25 engine I’m going to buy for 1200 bucks and install it.

4: Tear down both the eta and the i bottom ends and use the i pistons for a proper NA stroker build
This scope of work is something I have less experience at and I’d rather avoid.

Thanks for you feedback 82eye! Keep it coming, I’m fine with taking criticism on topics I’m not a pro on

[82eye]

That’s fair. I do realize it seems irrational but I’ve owned a few water cooled VWs with aftermarket turbo and ecu configurations. A turbo car can be reliable, fast and fun but I know it takes some dyno time to get it there. I currently have a mk7 golf r that’s chipped, tuned, big turbo, down pipe, injectors blah, blah and I trust that car to go cross country.

i came from vw as well.
what do you need another platform doing the same thing as the vw for? just asking. the goals here seem awfully undefined. if you don't know what you want you're not likely to get it.

I guess the thing with this ‘85 eta that I feel the least positive about is the ancient motronic management system. I think I have figured out how to troubleshoot this system for the most part but it seems that sensor failures are always right around the corner, which lead to excessively bad A/F mixtures, fouled plugs, ruined O2’s and tow trucks.

e30 motronics are the dirt simplest of engine mgmt systems. they use a total of 3 sensors. 4 in the e car but one is redundant. even if you turbo that will be the entire number of inputs.

I feel my current misfire is due to a bad AFM or the DME itself, or both. The AFM seems hard to test properly without specialized equipment and I hate just replacing parts. Plus there isn’t anyone around here that’s into these old BMW’s so swapping parts isn’t an option. The signal from the DME to coil is a bit concerning too. I don’t see my test light flickering like I think it’s supposed to when grounded to the primary side of the coil

i'm not sure what i'm missing here ... not sure adding complexity and a pile of work and cash to fix something simple is the best path. i would fix the e first so you have a reliable car while you plan the next move.

So am I right in thinking that this early version of Motronic sucks?

it is entirely of it's time. remember the majority of cars were still carbed when these were new.

It seems I have 4 options:

1: Keep replacing the parts needed on the eta

2: Add the i parts to the eta bottom end and maybe go the turbo route in the future, maybe just enjoy ~140hp

3: Go through the M20B25 engine I’m going to buy for 1200 bucks and install it.

4: Tear down both the eta and the i bottom ends and use the i pistons for a proper NA stroker build
This scope of work is something I have less experience at and I’d rather avoid.

Thanks for you feedback 82eye! Keep it coming, I’m fine with taking criticism on topics I’m not a pro on

you have all the options open with the engines available. turbo is only one path. the reliable aspect is what you are ultimately playing russian roulette with. that's simply standard when delving into turbos.

i'm running normally aspirated and lightly modded. my original plan was engine swap or turbo, i'm really grateful i did neither. i'll never find another e30 here and am happy i didn't ruin it chasing power.

[88Sedan]

I would personally prep the b25 to swap in WITH the getrag 260 and get your eta running right... I have read the 260 is a better transmission than the ones eta's came with (240 I think?). Then you'd have a fresh, running engine and all the time in the world to build it for a turbo if you are in fact ready/equipped to do that.

Check that your throttle switch is working correctly too and that your plug wires are in spec. On a different car I once had a plug wire intermittency that caused booming backfires when the ignition lit after skipping a cycle or two.

[It's Soda Not Pop]

I would personally prep the b25 to swap in WITH the getrag 260 and get your eta running right... I have read the 260 is a better transmission than the ones eta's came with (240 I think?). Then you'd have a fresh, running engine and all the time in the world to build it for a turbo if you are in fact ready/equipped to do that.

Check that your throttle switch is working correctly too and that your plug wires are in spec. On a different car I once had a plug wire intermittency that caused booming backfires when the ignition lit after skipping a cycle or two.

https://www.e30zone.net/e30wiki/index.php/Drivetrain

[McGyver]

Why did you swap out all the ignition components? Were the old ones bad? I've seen cheap parts wreak havoc (like using a cheap coolant temp sensor).

I've had a set of plug wires fail on one or two plugs and cause big problems. I've also had crazy issues caused by a bad coolant temp sensor (only buy Bosch).

Unless you replace the failed component with the head swap, you'll still have the misfire issue after the swap. Why not focus on getting the car to run right?

I think newer scanners can do everything the old school ones do, but getting something like a Baum Tools CS2000 Data Scanner can really help with troubleshooting Motronic 1.3. They pop up on ebay often, just make sure you get the plug-in cartridge for our year BMW.

[Nohawkscott]

i came from vw as well.
what do you need another platform doing the same thing as the vw for? just asking. the goals here seem awfully undefined. if you don't know what you want you're not likely to get it.

This is a great point. I did not consider the redundancy of owning 2 turbo’d cars. And yes, most of my car goals are always awfully undefined which is what leads to the snowball effect.




e30 motronics are the dirt simplest of engine mgmt systems. they use a total of 3 sensors. 4 in the e car but one is redundant. even if you turbo that will be the entire number of inputs.

So in your opinion there is no benefit to using something like megasquirt or the classic daily system on anything other than a turbo setup? I’d really like to delete the AFM.




i'm not sure what i'm missing here ... not sure adding complexity and a pile of work and cash to fix something simple is the best path. i would fix the e first so you have a reliable car while you plan the next move.

Starting to agree with keeping it NA..


i'm running normally aspirated and lightly modded. my original plan was engine swap or turbo, i'm really grateful i did neither. i'll never find another e30 here and am happy i didn't ruin it chasing power.

This makes a lot sense. I’m fortunate to have found a one owner car with no rust and no previous accident damage. It makes sense not to do too much to it.

Thanks for the insight and rationale!

[Nohawkscott]

I would personally prep the b25 to swap in WITH the getrag 260 and get your eta running right... I have read the 260 is a better transmission than the ones eta's came with (240 I think?). Then you'd have a fresh, running engine and all the time in the world to build it for a turbo if you are in fact ready/equipped to do that.

Check that your throttle switch is working correctly too and that your plug wires are in spec. On a different car I once had a plug wire intermittency that caused booming backfires when the ignition lit after skipping a cycle or two.

Good plan with just using the m20b25 while maybe building the b27 up as a turbo at my leisure. But the eta has a 260 already, pretty sure of that.

New plug wires (NGK) and TPS was taken apart and cleaned. Then reinstalled, adjusted and it’s testing good.

[82eye]

Good plan with just using the m20b25 while maybe building the b27 up as a turbo at my leisure. But the eta has a 260 already, pretty sure of that.

you'll have to take apart both engines and mix and match to build the stroker or turbo. going that direction takes the car off the road and leaves it engineless until you complete the build.

you'll need the engine mgmt off the i car to run the stroker, and the i car trans is gonna be the better choice to use. the diff from i will be a better choice as well until you re-gear. the e car is pretty much the bottom end only.

So in your opinion there is no benefit to using something like megasquirt or the classic daily system on anything other than a turbo setup? I’d really like to delete the AFM.

for most things NA i'd stick with the motronic and a good chip. you'll have zero choice but to go to a standalone if you ditch the afm for maf. no one does a maf conversion for NA motronic any longer.

research well, a lot of the maf conversions are a mess even with a standalone. the good news is there is a lot of experience with standalones, turbos, and mafs around, so you should be able to draw on a ton of information.

[Nohawkscott]

I’ve decided to do the 885 head and harness swap on the eta block. I got the m20b25 engine and harness/dme but the seller didn’t have the AFM. Is the Miller MAF conversion not a good idea in yalls opinion for the NA 885 head/eta bottom end combo? I was about to buy the Miller PSIK…

[82eye]

I’ve decided to do the 885 head and harness swap on the eta block. I got the m20b25 engine and harness/dme but the seller didn’t have the AFM. Is the Miller MAF conversion not a good idea in yalls opinion for the NA 885 head/eta bottom end combo? I was about to buy the Miller PSIK…

miller maf has been dead for a few yrs now. you can't pay people to use them and they never work.

we were talking about this in another thread. there is an ms based plug and play that folk are going to if they want maf, or they are building and tuning an ms kit themselves. that's about it, maybe a couple other aftermarket options requiring dyno tuning etc for big money.

have a look here

https://www.r3vlimited.com/board/forum/general-forums/general-discussion/10145664-what-s-up-with-sssquid

[Nohawkscott]

Hmm, millers website looks like they are still willing to take my money??

So the classic daily stuff is working well?

[82eye]

Hmm, millers website looks like they are still willing to take my money??

that's a big part of the problem. what you get won't work and you'll be on your own to try and figure it out with zero support. any random google will bring up pages of angry e30 owners.

So the classic daily stuff is working well?

they have support among the board members. there are no large companies doing a maf conversion. keep that in mind. companies like sssquid disappear fast when the market changes. classic daily is no different.