poor acceleration after manual trans swap in 325e/m20b27

[Andy.B]

IIRC, e30's DO do that. There is a wire connected to the shift selector that informs the DME when it is in neutral/park vs D/R. It was a while ago that I did a manual swap, but I should have some info here somewhere...

Edit: It looks like OP found their issue anyway. That's what I get for not reading to the bottom of a thread first.

I worked on figuring out the wiring differences between the auto and manual transmission, while also sorting out how to make sure cruise control still works. It was actually easier than I thought, but pretty much every auto -> 5speed swap guide I read was incorrect (at least for my car), or made it harder than it needs to be .

First off, although I never have any intention of converting this car back to an automatic transmission, I avoided cutting or hacking anything in a way that would prevent restoring it to its original condition. For the wiring, that meant cutting the harness off of the shift selector side of the connector instead of the car harness side.

Then I modified the shift selector side of the harness to make it a plug in adapter. To do this, cut the harness about 4 inches or so past the range selector connector to create a pigtail harness.

The harness now has 5 wires:
Brown (ground for indicator light)
Green/Black (Park/Neutral signal)
2x Green/Yellow (Hot on run or start)
Blue/White (Reverse light)

To modify:
Connect 1x Green/Yellow to Green Black
Connect 1x Green/Yellow to either one of the two reverse light harness wires
Connect Blue/White to the other reverse light harness wire
Cap off the Brown wire.


I used heat shrink tubing to make it nice and tidy.
This modified harness provides the signal for the manual transmission reverse light switch, and the Park/Neutral signal to the ignition relay to allow the car to start.

For bonus points, cut a car harness side C301 from a parts car to wire into the modified selector range pigtail to connect to the manual transmission reverse light harness, making it a truly plug and play job.

That's it at the shifter, but there are two wires that need to be tracked down and disconnected. The Black/Green wire that provides 12v when in Park/Neutral goes to the DME and Cruise Control module as well.

One of the Green/Black wires goes to the DME harness to a Blue/Red wire, and provides the DME with 12v when in Park or Neutral. This 12v signal tells the DME to correct the idle speed for the engine load imposed by the torque converter when the transmission is in gear and the car is stopped. If you disconnect this on an automatic car when in gear, the idle bogs down. Since we don't have a torque converter putting a constant load on the engine, we don't need this function anymore.

Simply unplug the Green/Black wire from the Blue/Red wire coming out of the DME harness, and tape them up out of the way.


The next wire to disconnect is the 'cruise enable' signal wire (connector C143) from the cruise control harness. The ETK wiring manual states 'For manual transmission C143 is taped to cruise control harness'. C143 is located under the ABS computer on the driver side. The Cruise Control harness side is Blue/Brown and on the car harness side, you will find another Green/Black wire that come from the auto transmission gear selector harness). All you have to do here is disconnect wires and tape them up.
My phone died before I could get pictures of this connector.

What you are left with is a single Green/Black wire in the car harness telling the starter relay that the automatic transmission range switch is in Park/Neutral so it can engage the starter, even though the the range selector is now gone. The DME does not need this signal, since it isn't an automatic car anymore, and the Cruise Control won't work when getting this signal.

The effect of the modified wiring pigtail is picture below... it's really much simpler than it's made out to be:


* I haven't verified the cruise control yet due to a faulty cruise control system, but considering the ETK tells you it should be taped out of the way on a manual car, that one is pretty obvious.

*According the the diagram, the Brown/Red wire coming out of the DME harness next to the Park/Neutral signal is unused. This is not true (at least on my car). It provides the speed signal to the instrument cluster through a Blue/Yellow wire that runs through the dashboard, and plugs into the green connector right next to the Cruise Control's speed signal wire at the cluster.

There you have it. Without cutting anything on the cars harness, you now have the car working as if it was equipped with a manual transmission from the factory. If anybody, for whatever crazy reason, decides they want to swap back at some point, then all they have to do is reconnect those other two Green/Black wires.

[Todd Black 88]

I only think I've found the problem. I won't know for sure until I pull the trans, reclock, and all that jazz. I'd be very interested in your experiences with your manual swap as it relates to the DME and Idle Control Unit (for a motronic v1.0 car, naturally).

I am bugged by the fact that maybe the DME but certainly the Idle Speed Control unit (which is separate in a motronic 1.0 unit such as this) needs to know when we're in park or neutral in an automatic application.

Check out these wiring schematics...
Automatic:


Same but for manual (notice how it sends nothing to the ICU regarding neutral):


...page 122, the idle speed control unit showing either autos or manuals:


So it seems to me that the ICU gets a hot/not-hot signal from an automatic equipped car when the key is in run/start depending on if we're in park and neutral or not. It further seems to me that a manual trans equipped car gets an always-hot signal as long as the key position is in run or start on this same ICU pin (pin 7 just south of C131). This suggests a push by the engineers for manual cars that says "meh, we don't really care if a manual is in gear or not, just give this line some juice because the ____________ function isn't important for manuals." Now fill in the blank :)

Can someone with a factory manual transmission E30/325e from 1984 or 1985 tell me if they've got a neutral safety function? I cannot find that such a thing existed in these earlier cars. The pedal box I got did not have a provision for a switch on the clutch pedal, only the switch for the brake pedal for the brake lights. My car starts in gear the way I wired it and I'm starting to believe the factory manual cars did too (which seems weird, but the mid-80s were a different era, I suppose).

Meanwhile, I'm currently corralling my friends for assistance with the upcoming trans pull.

Manual cars will start in gear. No neutral safety, or clutch safety.

[Leftlane]

Manual cars will start in gear. No neutral safety, or clutch safety.

Thanks! This is great news from my perspective. I was sweating the fact that my car was starting in gear and this was different from as-designed. I guess it's totally factory now ;)

One of the Green/Black wires goes to the DME harness to a Blue/Red wire, and provides the DME with 12v when in Park or Neutral. This 12v signal tells the DME to correct the idle speed for the engine load imposed by the torque converter when the transmission is in gear and the car is stopped. If you disconnect this on an automatic car when in gear, the idle bogs down. Since we don't have a torque converter putting a constant load on the engine, we don't need this function anymore.

Aha! This is good stuff. Great post, thanks for digging it up. Makes sense that the torque converter would tax the engine differently and that would have to be taken into account at low RPMs.

What's slightly confusing to me is that it seemed - looking at the schematic I posted for the manual car - that the manuals in 1985 (or Motronic 1.0 if you like) were getting +voltage on this line at all times (well, while the key was in start or run), so the computer (ICU or DME) would be doing the same thing it was doing for an auto in park and neutral. That confusion stems from the assumption that the ICU is the same for an auto or manual. Thinking about it, they're probably different and the manual ICU just ignores whatever is coming in on this line.** Just spitballin' here, no semblance to fact expressed or implied.

I'm willing to bet your diagrams are from a motronic 1.1 or 1.3 just because I see the "2.5i" in the picture. They were clearly doing something _slightly_ different, but the effect may yet still be the same.

**EDIT: wait, if this guess is true, then keeping my automatic ICU will be problematic because the computer would in theory be trying to apply this load-of-the-torque-converter function against a car which now no longer has such an animal. Idle would then be probably not where it needs to be. Which I think is why you're suggesting to disconnect this at what is the "injection electronis" in your diagram. It does seem that I may have two things incorrect - the flywheel and the fact that I'm sending voltage to the ICU based on how I did the wire splice at the shifter to avoid the neutral safety function of the automatic. Okay this makes my head hurt. I'll stop thinking too much about this and just focus on one thing at a time - flywheel.

Thanks again, all. I'll keep the thread posted as details emerge on the flywheel re-clocking.

[vicecaptainred]

There should be a line on the crank pulley that matches up to a little line on the block itself to line up cyl#1 to tdc but hell straws and sharpies will get it done too!! Yes my flywheel pin was at like 4oclock and it needed to be at 7oclock (if youre looking at the back of your engine with flywheel on) an i was about 1/4 behind tdc so it was a 90° or two bolt holes late sending the signal. Is it an aftermarket flywheel?

[Leftlane]

Solved!

I wanted to come back to this thread to close it out. I believe the problem is solved.

It indeed was the flywheel being mis-clocked. I disassembled everything after marking the block where the CPS mounting boss on the bellhousing was. Then I put the flywheel back on with the engine at #1 TDC with the metal tab on the perimeter pointing at my mark. Actually, I oriented the flywheel in the closest of the two positions around my mark - it wasn't exactly lined up, just as close as I could align with my particular method (recall you only get 45° adjustment out of the 8 bolt holes).

I then made this video:


Thanks to everybody for your input. I've got to finish getting everything all buttoned up and then it'll be time for a test drive when I'll know for sure I nailed it.