Converting from Megasquirt back to Motronic?

[ImysE30]

I want to bin the Megasquirt/shit conversion and return it back to OEM.

What parts will I need to convert back? The car is a pre-facelift so has the high comp 2.5 M20 engine.

I'm going to need an ECU, engine wiring loom..... What else?

TIA

[Brianmoooore]

Wouldn't advise going back to what it left the factory with. Get yourself a M20 facelift loom and ECU, preferably 173, and a crank pulley toothed wheel with crank position sensor.
All the bits, except for the 'chip' in the ECU can come from a post facelift M20B20.

[ImysE30]

Is it a big/difficult job to do?

Do I keep the coilpack that's fitted?

[Brianmoooore]

M20 ECUs only have a single spark driver, so you'll have to go back to a simple coil, leads and distributor. Basically, replace anything that's been removed and replaced with something different for the Megasquirt.

[ImysE30]

Okay thanks.

I'll get on the hunt for the parts

[Grrrmachine]

A good idea may be to run through this page and check of the Parts Required with what you still have. As Brian states, this will include the coil, distributor cap and rotor.

http://www.e30zone.net/e30zonewiki/inde ... tronic_1.3

[Demlotcrew]

Wasn't long before we would see threads like this. Good luck with the conversion back, it should be pretty straight forward assuming your C101 connector has t been butchered.

[gromgsxr]

will need afm as well

[ImysE30]

Thanks guys. The car is up for sale but I'm thinking if I can covert it back, I might just keep it for another project.

Its fine apart from the Megasquirt causing the high idle

[b12rlw]

Thanks guys. The car is up for sale but I'm thinking if I can covert it back, I might just keep it for another project.

Its fine apart from the Megasquirt causing the high idle

might it not be simpler/cheaper/less hassle to have the squirt set up? email phil @ extra efi if you suspect it's a problem with the software.

philip.ringwood@ntlworld.com

he's at bit of a megasquirt wizard as he coded alot of the program.

[bss325i]

Being an '88 car it will not have a high comp engine or early motronic despite being a metal bumper car.

It will have been motronic 1.3 that all sept '87 onward cars used and will have had a 6k 25 engine with 8.8:1 compression ratio.

Also, i note that you have listed in your for sale ad that the car has an LSD and Bilsteins.

An LSD was not standard on Motorsport convertibles and in '88 the M technic suspension was Boge, not Bilstein.
Have you confirmed either are actually on the car?

[ImysE30]

Thanks for the info Barry, didn't know that. I thought all pre-facelift had the high comp engine

It's got none of that left now. Instead megasquirt

It's had Bilstein shocks fitted to replace the old Boge one's I assume.

Will check the LSD too, will try and check the spec sheet as well.

[Speedtouch]

Some high compression 25 6E engines were fitted in the 1988 model year - I had one, in a 1988 F-reg 325iSE, which also had the Motronic 1.3 '173' ECU.

The low compression 25 6K engine came in later on that year.

It's easy to check which yours has - 25 6E or 25 6K will be stamped into a machined flat on the engine block, to the right of the inlet side engine mount, just above the block:sump interface - but you may need to wire-brush/Jenolite the area first and use a torch to see it.

[bss325i]

The sept '87 - sept '88 engines were medium comp ratio not high.

Sept 85 to sept 87 is 9.7:1

Sept 87 to sept 88 is 9.4:1

Sept 88 onward or sept 87 with a cat is 8.8:1.

[Speedtouch]

True, but both high and 'medium' compression M20B25s have the same 25 6E engine code.

[bss325i]

True, but both high and 'medium' compression M20B25s have the same 25 6E engine code.

'fraid not me old mukka.

Right, it transpires that,

256E1 compression ratio of 9.7:1 (early motronic)

256E2 Compression ratio of 9.4:1 (late motronic)

256K1 Compression ratio of 8.8:1 (late motronic, cat prepped or with a cat)

For UK cars,

256E1 sept '85 to sept '87

256E2 sept '87 to june '88

256K1 june '88 to end of production.

From this thread,

http://www.e30zone.net/modules.php?name ... sc&start=0

[Speedtouch]

Aye, but the '25 6E' bit nevertheless remains the same. I doubt if most owners would be able to notice the effect of 0.3 difference in the CR. In fact, it begs the question of why BMW dropped it by that small amount, prior to dropping it to 8.8:1.

[duracel79]

I was thinking about this 9.7 to 9.4 to 8.8 difference.

Could the 9.4 engines just be a 9.7 with the 0.3mm thicker head gasket? My calcs say it would be about right?

Ben

[toby]

I know you sound set to switch back to standard management but there may be a simple fix. Sometimes people with Megasquirt wind out the throttle screw to raise the idle as it runs rough from cold due to the mapping limitations at colder engine temperatures of most DIY installs. If that is the case you could just wind back the throttle screw but you'd have to live with potential poor warm-up characteristics. An M20 warms up quickly though.

I like a well set up MS system but it has its niggles.

[Andyboy]

Aye, but the '25 6E' bit nevertheless remains the same. I doubt if most owners would be able to notice the effect of 0.3 difference in the CR. In fact, it begs the question of why BMW dropped it by that small amount, prior to dropping it to 8.8:1.

But it's not the same. 6E1 and 6E2 are different.
Converting back to Motronic is a sound plan, a good reliable system rather than flaky Megashit with 3 bhp more at the spare wheel and a crap idle.

[pacerpete]

Two batteries FTW !