1980s New Display Controller for 1982-85 HT4100 Swaps, Diesels, RWD 307's

[eldofever58]

We've had discussions here over the years about the best way to conceal aftermarket gauges and how to address defunct electronics on the early 80's HT4100 cars after an engine swap. During the pandemic I went on a deep-dive into the systems on the '82-'85  DEFI cars and came up with some "fixes" for the Climate Control, external temp sensor and CC system. I've been sharing that info on the various FB groups as well as my Engine Swap page. I've also been thinking about penning an article for the Self Starter if I can find some time.

But this did not solve the problem of the defunct Fuel Data / MPG Sentinel display. A pet project that got out of hand, I'm now producing a small batch of what I call the E/K Display Controller. Though don't be fooled, it will work with any V6/V8 engine (screw terminal inputs for sensors). And it plugs into the back of any of Cadillac's 3 different style '82-85 Fuel Data panels. Which means if you have a diesel, '79 Eldo, or RWD Brougham, you can substitute a junkyard or ebay Fuel Data display in place of your blanking plate. It uses the original switches and 7-segment displays to show Coolant Temp, Oil Pressure and system Voltage. A new acrylic faceplate replaces the original.

It solves a couple of other problems, too. This unit takes over driving the torque converter lockup and the Coolant Temp light that the ECM used to do. And it has some nifty features that I wanted for my '85 ETC that I'm getting on the road (Olds 350), such as an over-temp alert.

I shot a short video today showing how it works:

And put a page together with some pricing and options, as well as a link to the PDF manual for those who want to know how it hooks up and what all it can do.

I'm not looking to produce these commercially, and turn-key kits are limited by the number of display connectors I've clipped off junkyard cars the last couple of years. But I know there are others that appreciate a factory look, and would like to know just what their engine is up to.

[TJ Hopland]

Nice work.  Are you having to drive the individual segments or feeding some sort of digital or analog signal to the display?  Looks like there are enough wires that the switches must be discrete.   With that music you need a version to fit a 67 Barris custom, at least that is the car I think about when I hear that music, way cooler than the later cars.

Have you had to figure out blower control modules yet?  I was thinking if I could figure out what the head is sending for a signal a pico adrduino could read it and operate relays through old school resistors.  Seems like there would be a small market for such a thing kinda like you are doing here from just a programmed board and instructions to maybe a full kit with relays and resistors.     

[eldofever58]

Thanks TJ. The display hardware was clearly designed around the original functions; decimal point only with avg MPG, diode-logic on the buttons, etc. The segments are individually driven, but the multiplexing to work around those constraints (including the status LEDs) was...interesting. Also, since these displays defaulted to Instant MPG on startup, the right two digits saw more burn-in over the years than the leftmost, so that had to be considered. Buttons use diode-logic on board which was also "fun".

I've stockpiled enough blower modules over the years to cover my needs (and they do vary by year and drivetrain), but a "fix" for failed modules is something I might take on in the future. Actually, I seem to recall a guy that repairs these...chipping away the potting and replacing the failed transistor with a modern equivalent. No system mods required.

[TJ Hopland]

Sounds like it must have been real fun to figure all that out.  I assume you started out cursing the original engineers because things didn't make sense and seemed more complicated than they needed to be but once you figured it out had to give them some credit for coming up with some pretty slick designs to make things practical.  I know that is usually where I end up once I figure it out.  Its like I would have used 3 wires and relays but they figured out a way to do it with one and got 99% of the functionality of my circuit with less parts.

I have not had blower module issues recently myself but have some friends that were asking for help even after they paid the big bucks for NOS or rebuilt modules. I didn't dig deep to find out the sources of the parts or do a current draw measurement on the blowers but one guy is like $1000 in and still doesn't have a working system.  I was thinking something that uses Bosh style relays and some still commonly available resistor block would be more tolerant and easy to service if it did have issues. 

Something I did discover doing some research on the blower issues is at least in 84 and the DEFI the 'heater on' isn't its own switch like the older cars had, its getting the engine temp from the engine computer.  It didn't say what sort of signal that is like is it some variable signal or if its just an on/off like the stand alone switches were.  I don't have enough earlier manuals handy to know if that was a thing anytime there was a computer or came later. I would assume this was something you had to figure out and simulate when needed?

[bcroe]

Nice job, hope it gets well documented.  An article
should call attention to the possibilities with these
cars.  I have not forgotten seeing them lined up at
the yard after problems with no solutions.  Bruce Roe