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M20B25 to M20B25 swap

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Just a quick query,

Swapping the original engine and manual box out of my PFL 325i (Motronic 1.1) to replace it with a FL 325i (Motronic 1.3) engine and manual box. Swapping the whole thing with the entire engine loom, ecu etc has the same radiator etc already, am I right in saying it is just a swap in, swap out job? Will have to use my PFL drive shaft but other than that I can't imagine any issues.

Will I need to pull the pins on the c101 connector and match them up and that's it?

Any help is appreciated, planning on making the most of the long weekend.

Cheers, Nathan

Edited by Brams

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Just a quick query,

Swapping the original engine and manual box out of my PFL 325i (Motronic 1.1) to replace it with a FL 325i (Motronic 1.3) engine and manual box. Swapping the whole thing with the entire engine loom, ecu etc has the same radiator etc already, am I right in saying it is just a swap in, swap out job? Will have to use my PFL drive shaft but other than that I can't imagine any issues.

Will I need to pull the pins on the c101 connector and match them up and that's it?

Any help is appreciated, planning on making the most of the long weekend.

Cheers, Nathan

Just done the exact same thing (sort of... put 1.3 on to a Pre-FL motor so I could run a facelift gearbox)

If you want to keep using motronic 1.1, you'll have to use the original box and flywheel (as it has sensors in the bellhousing) and take the oil level sensor, oil pressure sensor (different plugs between 1.1 and 1.3) off the old motor. Might need to swap the water pumps + hoses from the Pre-FL to put on the FL motor to allow you to keep using the old radiator.

If you want to use Motronic 1.3 you'll need a FL loom, the computer and that will allow you to use a FL gearbox (without sensors), toothed cam wheel + crank angle sensor, the spark lead pulse generator (optional but not necessary) and you'll also need to enlarge the firewall hole to put the computer through (easy with an iron bar...)

- also, putting the toothed wheel on requires removing the water pump pulley, which requires removing the fan, which requires a thin 32mm tool to remove it (clockwise, reverse threaded) - I had the luxury of having a mechanic let me borrow their BMW tool to do it + very large vice grips to hold the pulley, you'll see what I mean when you get to it!

The 'spark pulse generator' plugs in below the diagnostic port on Motronic 1.3 in a plug that is identical to the plug from the crank angle sensor. If you get no-spark/fuel, try swapping these over. It's an easy mistake to make.

I got lucky with the C101 - However it does pay to check against wiring diagrams first, PM me your e-mail address and I'll send you some through. Your tach most likely will not work - get the source wire for this from the engine side of the C101 (top) - it's a thin black wire, this then is pulled back right to the computer, you cut a heap off it, and run it into a three pin connector below the instrument cluster.. It goes into the black pin. The other two are not used.

Edited by Surge

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^ Thanks for the help.

If my first post wasn't clear enough,

Taking the engine + manual gearbox +engine loom out of a PFL (so completely removing Motronic 1.1) and in it's place putting a different engine + different manual gearbox and engine loom out of a motronic 1.3 car, that all works correctly before I pulled it out of the car.

So basically the only thing I might need to change is the signal wire to make my tacho work?

Will send you a PM now for the wiring diagram, thanks for the help.

Any other input is appreciated.

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Are the radiators not different? On PFL top hose is on right hand side, on FL top hose is left hand side. So you would need FL radiator to go with it, or swap the PFL cooling system to the new engine.

Could be wrong here, been a long time.

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Ok sweet. I've sent you the wiring diagram which I've found accurate when I did the swap on my car - it's a good one as it has the pre-fl body plug, and the fl engine plug diagram. Just pull back the boots on the C101 to check the colours - generally it doesn't matter if there is more pins used on the engine side than there is on the car side - as long as they don't mate up wrong.. (ie 12v coming off the engine side going to something that needs 1v on the other side..) - check your car against the diagram.

You'll be dropping it all it as it stands, so you'll definately need to make the hole in the firewall bigger to fit the plug through and should not have to swap anything electrical on the engine side.

The only issue would be the radiator one - they are different between the Pre-FL one and the FL. If you've got a FL rad (and hoses + expansion tank) use that then you won't have to pull the water pump off (I think the FL pump has an additional outlet or something..) - regardless, the coolant plumbing is very different.

And yeah, signal wire for the tacho - done. Make sure you earth the motor too - one from the sump to the body is easy to forget about.

If the FL loom has a plug below the intake manifold (from the injectors + coolant sensor) to the rest of the engine loom - un-plug it and check it for rust, they can cause all sorts of problems if they are bad. Do it while it's out of the car to save the swearing!

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Are the radiators not different? On PFL top hose is on right hand side, on FL top hose is left hand side. So you would need FL radiator to go with it, or swap the PFL cooling system to the new engine.

Could be wrong here, been a long time.

PFL top hose goes to top of radiator drivers side. Other hose runs BEHIND/NEXT to the alternator to the passenger side lowest outlet of the radiator. I managed to successfuly route my lower hose into the alternator cooling blades, which diced it up rather well.... :P

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Have both PFL and FL radiators here if one or the other doesn't work.

Thanks for the email and the help.

Stab in the dark here, but the FL engine, box and loom came out of a FL car that was converted from auto to manual, am I going to run into any issues throwing it into a car that was manual from factory, abeit a PFL?

Edited by Brams

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Have both PFL and FL radiators here if one or the other doesn't work.

Thanks for the email and the help.

Stab in the dark here, but the FL engine, box and loom came out of a FL car that was converted from auto to manual, am I going to run into any issues throwing it into a car that was manual from factory, abeit a PFL?

Engine looms are the same between auto and manual I believe, so you should have no issues.

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Nathan, have done this swap on both my cars and I still use the pre facelift radiators on both, plumbing becomes a mix and match (I use the facelift header tank but prefl water pump) - works fine. But I have a FL radiator if you need it. You welcome to come have a look.

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Stab in the dark here, but the FL engine, box and loom came out of a FL car that was converted from auto to manual, am I going to run into any issues throwing it into a car that was manual from factory, abeit a PFL?

Highly doubt it, but there is a possibility seeing as you are going fro fl to pfl. If ti was straight fl to fl it would be a no for sure

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Shouldn't be any issues. In terms of electronics I don't even think there is any automatic specific electronics on the engine loom at all - unless there was something on the fancy auto box with sport shift?...

When you are doing the radiator - be careful removing the hoses, the plastic barbs have a tendency to snap off (20 years old and all..)

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Cheers to everyone for the help and offers, it seems relatively straightforward as I thought. Will keep this updated if I come across any issues over the next few days.

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Shouldn't be any issues. In terms of electronics I don't even think there is any automatic specific electronics on the engine loom at all - unless there was something on the fancy auto box with sport shift?...

When you are doing the radiator - be careful removing the hoses, the plastic barbs have a tendency to snap off (20 years old and all..)

Yes the fancy one with the sport shift has a different engine loom, uses a different TPS.

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Shouldn't be any issues. In terms of electronics I don't even think there is any automatic specific electronics on the engine loom at all - unless there was something on the fancy auto box with sport shift?...

When you are doing the radiator - be careful removing the hoses, the plastic barbs have a tendency to snap off (20 years old and all..)

Also there is the immobilisor ( cant think of the right word sorry) that stops the enging starting in drive and reverse. Need to short that when doing a manual conversion, but iirc is usually shorted at the ecu in a factory manual.

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Also there is the immobilisor ( cant think of the right word sorry) that stops the enging starting in drive and reverse. Need to short that when doing a manual conversion, but iirc is usually shorted at the ecu in a factory manual.

Inhibitor switch. Its not part of the ECU or engine loom, but is part of the body loom, so in a factory manual car it will not be a problem.

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Inhibitor switch. Its not part of the ECU or engine loom, but is part of the body loom, so in a factory manual car it will not be a problem.

Learnt something! Sorru for going a bit o/t nathan!

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Anyone know if you are able to move a cert plate around in the engine bay or do you need approval? If I want to use the FL coolant reservoir I need to move it to the opposite wheel well. Ta

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sorry about this, little off topic.

is there any difference in the c101 plug between the normal and sport shift (auto) variants. might be putting a m50 in a 325 with it and dont want any proplems to be met. also when i quickly saw the car there appeared to be a 2nd computer in/above the glovebox. was longer and thinner but had a similar plug. will this be something to controll the gearbox

again sorry for the interuption, just thought some of you may know as your already talking about it

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^ Sorry I couldn't tell you for sure, but under the glovebox is also the ABS computer (that looks like another ECU) if the car has ABS? Sport auto's have a separate computer in the boot lining on the LHS

Managed to get this running with the new engine this morning. Not a bad effort I thought after starting on Thursday afternoon with two cars with engines and gearboxes attached, taking both out and putting one of them in my car. Car runs nice and smooth, massive thanks to Surge for his help with the diagrams, was a piece of cake. Cheers for all the help.

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Great news nathan! What was wrong with the old engine?

sorry about this, little off topic.

is there any difference in the c101 plug between the normal and sport shift (auto) variants. might be putting a m50 in a 325 with it and dont want any proplems to be met. also when i quickly saw the car there appeared to be a 2nd computer in/above the glovebox. was longer and thinner but had a similar plug. will this be something to controll the gearbox

again sorry for the interuption, just thought some of you may know as your already talking about it

Did the m20 have cruise control? Thats also under the dash

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320,000k old, using about 3-4 litres of oil every 1500-2000km

Sounds like my m50 ha

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^ Sorry I couldn't tell you for sure, but under the glovebox is also the ABS computer (that looks like another ECU) if the car has ABS? Sport auto's have a separate computer in the boot lining on the LHS

thanks for that, yea it has abs, not sure about cruze control as it was only a quick look at the car.

and good work with your swap, 2 and a half ish days, thats fast for at home in a garage (thats assuming you did do it at home)

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Anyone know if replacing gearbox oil would cause it to whine/should it quieten down? Brought from a manual conversion, so hasn't been used previously by me and came with no oil when purchased. Ta

The oil used was 75W-80, is this too thin?

Edited by Brams

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