Swapping out IDMs and back again …

So, in my previous post, I talked about the bus not starting when the engine was hot (coolant temperature around 180 degrees), and I think the blame lies with the IDM (Injector Driver Module).  As such, I ordered one from Shop Injectors and went to replace it.

Searching on the internet, I had the vaguest of ideas where the IDM was in the 1995 T444E engine compartment, so I remembered to take pictures while I undertook the replacement.

The IDM in its natural habitat.

The IDM is located on the firewall above the engine, almost right up by the hood.  It is covered with a metal plate where some relays and positive cables are installed. The positive cables connect here and they’re live(!) so be careful about them touching anything.

Air Intake Sensor on the back of the intake line.

The cover is only held on by one screw, underneath the cover, so the easiest thing to do is remove the air intake line from the filter.  There’s a sensor just to port of the IDM case cover, so remember to unplug it before trying to move the intake.

Air Intake Line removed/swung out of the way.

As my bus has air brakes, the feed line for the compressor also comes off this air intake line, so rather than fully removing it, I just swung it back off to the driver’s side and out of the way.

Lower intake covered for safety!

Remember to cover up the lower end of the air intake so you don’t end up feeding gunk or spare screws and bits into the  turbo!

When removing the single screw holding the casing on (#3 phillips), be careful to try and catch the clip that the screw threads into.  Mine ended up on the transmission, but it could end up finding a place to hide there that would make your day miserable.

Casing removed and clipped to the radiator supports.

Once the screw is out, the top just needs to be lifted slightly, and the angles on the back of the top of the casing will come right off the back plate.  The two angles on the outer ends fit behind the plate, while the middle one rests in front of it, making it fairly secure.  I didn’t need to remove/unplug any of the wiring from the casing, as I was able to swing it also toward the driver’s side and hook the angles over the radiator supports.

The IDM, mounted on the firewall behind the engine, with the cover off.

The next step was to remove the plug from the IDM.  This requires a 10mm wrench or ratchet.  Given the voltages that this unit puts out, they don’t trust it to just clips, and the bolt is fairly long.

The IDM Plug that makes it all happen.

Once the bolt is loose there is one clip that you have to undo, but then the plug just slides out.  When I looked at mine, I saw some corrosion on the plug and the prongs of the IDM.  They are fairly easy to clean up with a pipe cleaner (since none of my files fit into the holes).

The back plate without the IDM in place. The bottom two screws dont need to come out.

All that remains after that is to undo the screws that hold the IDM to the back plate.  The top two need to come all the way out, and again have those clips that the screws fasten into.  The bottom two only have to be loosened up, as the IDM has grooves that they fit into, making the process (and that of inserting the new module in place) really painless.

Putting the new module in is as simple as reversing the process, making sure to snug but not over-tighten the bolt that holds the plug onto the IDM.

Unfortunately, after all that, the new IDM that I installed didn’t do anything!  The engine just spun when I tried to start it.  Swapping the old (now cleaned of corrosion) IDM back in, then engine started just like it always did (at least when it was cold).  I went back and forth between the old and new IDMs, and the new one just didn’t work.

I’ll now have to road-test the old module and see if it was a corrosion issue, and send the new IDM back to the company to have it tested.  The guy who I’d been in contact with before about the delivery was very helpful, so I don’t expect a problem.  But at least I now know how to make the change if I still have problems.





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