Mi16 - XU9J4 - engine rebuild to go into a 309

[SRDT 228]

It looks like you could just drill the rivets heads on a 16v coil and bolt the bracket on a 8v coil.

[hoodygoodwood 78 3 Cars]

Thanks , i just wanted to be sure . When i bought the couple of Mi's last year they came with the usual assortment of dodgy looking old bits , 2 of the coils had the riveted on bracket but one was held on by 4 very long bolts , i took the bracket off ( which was in 2 pieces ) and got it replated along with all the other bits recently . I managed to find a new in box Bosch coil which takes the brackets nicely and is fitted in the photo although it looks like a more recently manufactured 'made in China' item . I thought i would shorten the bolts while i was at it as 2 inches long looked ridiculous . I have been looking into throttle cable brackets and possible cable routes and there are a number of options , the little bracket and rubber bush that came with this engine i have refitted for now but i will be experimenting to see what works best once the engine and box are in .

[hoodygoodwood 78 3 Cars]

The 405 that donated this engine had a fuel pressure damper in the fuel line which i have seen in other 405 engine bay pics , i cannot remember seeing this fitted to a 309GTI16 , does it ever cause problems deleting the damper ?

[SRDT 228]

There is some kind of damper on the 309 fuel pump itself.

[Tom Fenton 1,621]

7 hours ago, hoodygoodwood said:

The 405 that donated this engine had a fuel pressure damper in the fuel line which i have seen in other 405 engine bay pics , i cannot remember seeing this fitted to a 309GTI16 , does it ever cause problems deleting the damper ?

I have run a number of 205 Mi over the years and never had one of those fitted. No issue.

[Duroc 2 1 Cars]

We've deleted it in all 205 1.9 mi16 conversions, so doesn't seem to be a problem

[hoodygoodwood 78 3 Cars]

Progress has been slow on the Mi swap but have removed the 1.9 GTI engine and box , its an opportunity to smarten up the engine bay and get some of the other parts ready so i have fitted a new Febi bush to the lower mount . I might be fitting the finished short engine and the original gearbox back in soon and use a bare head for now so i can start trying to mock up some sort of exhaust and get the 405 Mi16 loom trial fitted , will be asking a few questions about the loom now i have got it stripped back to the bare essentials .

[hoodygoodwood 78 3 Cars]

I have been working on the 405 Mi16 engine bay loom that came with this engine and box for a while now , all the wiring for lights and ancillaries was removed and i have it stripped  back to the engine related loom from ecu to all the sensors/relays/fuses etc . Its surprising how self contained it is , there are 3 wires on one plug for the live feed from the shunt box , one earth connection , one wire to the fuel pump , 5 diagnostic related wires which i have moved to one position inside the car ( near the ECU )  , a shielded green wire which goes to the rev counter and a blue wire that i believe goes to the ignition lock . I am hoping to mount the ecu under the dash near the steering column and have the wiring come through the bulkhead near the expansion tank , i am opening up the existing hole they drilled for the Omex loom and i will make the original  grommet on the mi loom fit so it looks right .

The car was a 1988 309 XL so a carb fed 1300 cc , i fitted a GTI fuel tank/pump/piping , GTI instrument binnacle  then a 1.9 GTI engine running on Omex management  , this XU9JA has now been removed and the Mi16 will be installed this autumn  . The original loom is doing all the other connections in the engine bay , alternator , starter , reversing light , oil pressure , water temps etc so this loom just has to run the engine but it seems too simple to me , it has a permanent + positive feed on 3 wires which go to , 1 fuel pump relay , 2 injector supply relay , 3 ECU , i assume the thick blue wire ( No 2 ) to the ignition switches the 2 relays on when the key is moved to the first position , i would appreciate some advice on this as i was expecting there to be more to connect .

 

[hoodygoodwood 78 3 Cars]

[hoodygoodwood 78 3 Cars]

I wanted to use the original oval grommet that came on the Mi loom so i measured the size required and increased the size of the round hole that was cut in the bulkhead for the Omex loom to pass through , hacksaw and then some filing did the trick and the grommet fits perfectly . I am making up a bracket to hold the ECU under the dash near the steering column .

[hoodygoodwood 78 3 Cars]

This thick green wire comes from the coil plug and runs i believe to the rev counter , it has another wire within it - shielding ? - and a thin earth wire running alongside it ( which goes to the ignition amp plug at one end and an earth block at the other ) . Its all at the wrong end of the loom and will be too short to reach the dash binnacle once its all been fitted so i will need to replace or extend it , What sort of wire should i use to retain the same qualities of the original and to get the rev counter working ?

[hoodygoodwood 78 3 Cars]

Short engine and gearbox are back into the 309 . Will be fitting a dummy head plus manifolds so i can see how it all fits and begin to mod the engine loom to suit . Have made a bracket to hold the Bosch ECU to the bulkhead above the throttle pedal and will route the loom above the pedalbox then under the heater box and through above the fuseboard .

[hoodygoodwood 78 3 Cars]

My Mi16 ECU has some non standard looking writing and sealant on what i assume are 4 screws on the underside of the body ,  is this is evidence that its been opened up in the past , the entire engine , gearbox , loom and ECU came out of a 1989 405 MI16 recently and i have seen no other modifications . Why would someone have opened it up , to fit a modified chip or do something to the printed circuit board would seem likely , what do you think ? I am looking for a standard one to compare with and have as a spare but there does not seem to be many about at the moment .

[welshpug 1,712]

These do have a chip that can be changed unlike The jetronic ecu, the other thing it could have been was a repair after water ingress, it was far from uncommon for them to become waterlogged on the 405 due to their location in the scuttle tray.

[petert 630]

It doesn’t appear to have been opened, by looking at the folded tabs. Open it up and have a look at the chip. You will soon know if it’s oem. I have chips for these if needed.

 

https://taylor-eng.com/ecu/case_opening2.html

Edited November 20, 2025 by petert

[SRDT 228]

If the EPROM is original you will see a BOSCH sticker with the software revision printed on it. I don't have the original file for your 125 ECU but I should have the one from a 119 ECU if needed.

Do note that the 139 and 140 ECU are for newer XU9J4 with a #4 inlet cam pulley instead of #2. Those ECU have another Peugeot part number so the engine won't run as well as it should if you mix and match.

The newer ECU should be compatible with the older software so if you find a cheap 139 or 140 ECU you can try to convert it.

[petert 630]

My Mi16x4 has a 139 and #2 inlet, so I wouldn't treat that as gospel. In any case, my upgraded chip works in either 125 or 139, if you'd like one.

[SRDT 228]

The 139 ECU is the correct one for a x4, it's the #2 pulley that is more of a mystery on a x4 but after all spare parts catalogs don't tell the full story, they just here to help you order new parts.