[valiant67]

You are going to have to find people parting the cars out for the bumper fillers. No body pieces or trim is reproduced for the Imperial, not the 1980s ones either.
There are lots of areas of concern on these cars, so keep an eye on these things:
1) Transmission
2) Anti-lock brakes
3) Rear or 4 wheel air suspension
4) Fuel rail leaks

 

[valiant67]

Any car build after March of 1990 (which means all 1991 models) has the Bendix 10 system.
You can tell if they just repaired or replaced by looking at the master cylinder. If it looks like the setup in this video, they fixed what was there:

bendix 10 abs - Google Search

.
If it's got a traditional master cylinder and booster then they did the conversion to regular brakes.

 

[valiant67]

Since the ABS is taken care of the next thing I'd worry about is the transmission.
Look at the transmission computer. If it is a plain box, it should be upgraded. If it's got fins on the edge, it has already been updated. If you need to upgrade look for part number 4792122. Donor can be any 1990-1991 3.3 or 3.8 equipped car (Imperial, New Yorker, Dynasty) or minivan. it's plug and play.

 

[valiant67]

The failure to start will have nothing to do with the battery - if it's cranking over the battery is good.
That means either spark or fuel isn't present. Most likely it is fuel pressure bleeding off. You can experiment by forcing the car to build fuel pressure. Cycle the key from off to run (but not start) 2 or 3 times before trying to start. If this eliminates the problem then you know fuel pressure is bleeding off while it sits and that's why it's hard to start.
Hopefully it is the check valve in the pump and not the fuel leaking out of the fuel rail as new fuel rails for these cars do not exist.

 

[valiant67]

Where is the transmission computer at?

Passenger side inner fender. Here is what the updated one looks like (just an eBay example, not a recommendation to buy this particular one). If yours is missing those fins I'd recommend upgrading.

TRANSMISSION COMPUTER Caravan Voyager Dynasty 1990 90 04796122 1080536 | eBay

Find many great new & used options and get the best deals for TRANSMISSION COMPUTER Caravan Voyager Dynasty 1990 90 04796122 1080536 at the best online prices at eBay! Free shipping for many products!

www.ebay.com

 

[valiant67]

The biggest issue with shift quality is going to be when the car is really hot in stop and go traffic. The fluid gets warm and you get "bump shift" and rough down shifts. These often happen due to lower fluid pressure. Besides fresh ATF+4 fluid and a new filter, the updated TCM helps with shift quality in those situations.

 

[valiant67]

Especially that A604 transmission. If it works now, DON'T TOUCH IT, period. As long as the fluid is bright purple (it may still have the ATF3, you can safely top off with ATF4 if it needs any, it shouldn't unless there's a leak), leave it alone.

ATF+4 will help the transmission. It deals better with heat than ATF+4. I had a low mile 1992 New Yorker with rough shifts in stop and go traffic in the summer. Out with the still clean ATF+3 and in went ATF+4. Gone was the rough shifts.

 

[valiant67]

Years back I had a 1990 Imperial and my friend had a 1990 Buick Park Avenue.
Comparing the two, what the Imperial lacked was width. They never expanded beyond the base K car width and a few more inched wide would have made Imperial even more comfortable. The only K based vehicles that were widened was the minivans. The Imperial was a great car, though.