I searched through my parts stash today in an effort to see if I had another engine management computer to fit my MY94 car.
I did find two late 15CU ECUs but they are for slightly earlier cars. My car has a part number of DBC12522 which is a 93 - 94 ECU.
The two other ECUs I have are DBC6332 (MY 90 - 92) and DBC9622 (MY 91 - 92).
I am wondering if I can plug the DBC9622 ECU into my MY94 car without causing some huge issue.

I have an electrical guide for a 1993 car but I don't have one for the earlier 1991 - 1992 cars to see if there are any major electrical harness differences for the earlier 91 - 92 cars from my 93 - 94 era cars when it comes to the engine management system.

Anyone know for sure?

Spare Lucas 15CU ECUs I have in stock, DBC6332 and DBC9622


MY94 ECU in my car (DBC12522)

 

OK, thanks to looking through old posts here and finding as usual that Don had previously shared links to different MY electrical guides, I now have a MY91 electrical guide to compare to my MY93 electrical guide

So far, I do not see HUGE differences so I am inclined to try it.

Anyone see a huge problem with this plan?

 

Hi Steve,

The only problem I can think of is that the '93-'94 fuel injectors are designed for peak/hold operation, where the ECM delivers a large current pulse to open the injectors, then holds them open with pulse-width-modulation. The earlier cars used injectors designed for saturated operation, where the injectors always have 12V power applied and the ECM just grounds them to turn them on for a given pulse width according to the fueling map. It is possible that operating your fuel injectors with the earlier ECM could lead to excessive current draw, which could overheat the injector coils. But then again, it may work fine. I studied all of this years ago but can't remember what the possible consequences are of running peak/hold injectors in a saturated system.

BTW, Gus has a lot of the electrical guides at jagrepair.com, but the XJ40 guides are misfiled under the XJ6 & XJ12 category.

Cheers,

Don

 

I might have a set of earlier injectors in my stash of parts.
I will check the resistance readings of the various injectors in the car and the ones I have lying about and see if some are indeed low impedance versus high impedance.

 

The '92MY MAF has an adjustable potentiometer for adjusting Idle Fuel Trim. This circuit would be missing in your '94MY harness. That would set Fuel Fail 11. Your instrument cluster may or may not be programmed to display it. I'm not sure... 1993MY+ vehicles have adaptive idle fuel metering instead.

There is a big difference in Fuel Injectors as Don as stated. I'm not sure how different flow rate would be with the two different injectors, but it's something to consider.

There are a couple other software differences including operation of the AIR injection system. (AIR system enabled for 30 seconds after each hot start for 93MY+ cars, only after cold start for pre-93MY cars)

Those are the differences I can remember off the top of my head.

-Nick