1991 Riv engine/trans into 1990 Reatta

[fjr48]

I would like to ask about replacing the LN3 / 4T60 in my 1990 Reatta with the L27 / 4T60E from a 1991 Riviera. The Riv is wrecked, but the engine and transmission are fine and in much better condition that my Reatta engine and transmission.

I have both complete cars so I think ( I hope ) I would have all the necessary components.

Would I have to change the ecm harness as well as using the 91 ecm ? Would the ecm still be able to communicate with the bcm ? I know that I will have to install at least part of the Riv harness to get the transmission wiring for the 4T60E.

I would appreciate any input on just what would need to be done. I have read were some of you have put the L67 in and I assume you ran into the same issues I will encounter. Thank you for any help

[Barney Eaton]

I will start and others with more experience will jump in..........

Yes it can be done, you must use the 1991 ECM but I don't know if it will communicate with the 1990 BCM. I do know that the 1991 BCM is different, it has different plugs so if you are forced to use the '91 you may need to change the cable harness.

[KDirk]

I am not positive, but I am pretty sure this would require re-harnessing the engine bay and the dash with the complete harness from the 91. Another issue is the different ABS systems. This may factor into wiring differences as well, and may partly explain the change in the BCM.

Also, the 91 omits the CPS (central power supply) used in the previous three model years entirely, so that is another change in the harness and probably in the way the BCM is programmed and wired. Since the 91 BCM doesn't expect to see a CPS, I don't think it could be left in circuit, and removing it would require the 1991 harness or you would have dangling connectors and incomplete circuits where they pass in/out of the CPS. Really, changing everything out would be cleanest anyway since a hybrid of two model years would be a nightmare to service down the road since you couldn't rely on any one version of the service data completely.

Simplest way to go if you want to do this is to graft in the complete engine, transmission, exhaust (is larger diameter than the 88-90 setup) and electrical (including major modules) from the donor car. If you are tearing it down that far, and the Rivi has ABS (was optional on that model AFAIK) then you could swap out the ABS/brake system as well. This is a whole lot of work, but it can be done. If your 90 is in really nice condition it may well be worth the effort and expense.

KDirk

KDirk

[D-a-n-i-e-l]

Way off!!!!

Get ECM with engine and trans. Wire in ECM to run trans only. Spen 90 bucks with sinister performance and reprogram original ECM. This way all functions of diagnostic ect. keep working.

You will also have to grab the passenger side axle and modify the passenger side tranny mount. I would jus get a Series one SC engine and tranny out of a 94-95 car and go from there. More power/torque and the same issues.

[fjr48]

Thank you all for your reply. You have really helped me, giving me a lot of things to consider. I was not aware of all the differences, (elimination of CPS,different BCM etc.) as I have never done anything on a 1991 model. I have a lot more thinking to do.

Thanks again, this is sure a great place to get help !

[padgett]

If you can get the Riv BCM as well, do so, that would talk to the ECM correctly andboth use the same dash. If the Riv does not have ABS then some dddling with the Teves would be needed