Well, as I said the Manta's been certified, and in fact it's been certified for over a year now. The car was with my friend Preston in Orange County for around four months until we were in a position to get it back. Since then it's been parked in the garage and pretty much untouched other than a couple of trips around the area where we live, I hurt my back while moving and I've not really been up to doing much.
Slowly getting it off the transporter without grounding
Back with the rest of the fleet
All that fuss for this sticker - California certification
Actually two labels, notice the white vacuum diagram on the right hand inner wing. The battery's new too - they must have left it connected while it was being stored prior to certification and destroyed it. Sigh.
First trip - all of half a mile down to the post office!
Present from Santa to keep it clean in the garage
One area of the car was still nagging me, though, and that's the centre console. The cassette holders are a nice period feature, but honestly they're totally useless nowadays. I actually have a few C90 cassettes still at home but not enough to fill all the slots, and besides, I don't have a tape player in the car! There had to be something I could do with it.
One idea was to get a cheap Android tablet and fit it into the area vacated by the cassette holders, then I could run Google Maps on it and have a built-in nav system, music player and other useful apps. The only problem with that was an Internet connection and I haven't yet installed a WiFi hot spot in the car... I suppose I could use my iPhone as a mobile hotspot, but at that point I might as well just put the iPhone in the instrument binnacle and use it to nav for me (which is what I do when I need a nav system these days).
The next idea was to use a Raspberry Pi - it's a reasonably powerful computer you can hold in the palm of your hand, it's cheap and it has loads of expansion possibilities. I actually went as far as making up a nav system with a nice big touch screen, GPS receiver, the Raspberry Pi, and a set of maps for the US on an SD card and it worked fairly well. The only problems were 1) I still didn't have a WiFi hotspot so I still couldn't do much with it and 2) it was very distracting looking down at the centre console all the time to consult the map. OK, scrap that one too.
My final idea was a trip computer, it's a useful toy, it'll fit down in the centre console and you don't have to stare at it all the time. The Monza has one and so do all cars these days, so why not the Manta? Can't be that difficult.
I had a BMW trip computer in my stash of parts and initially thought about using that, but BMW wiring and Opel wiring are different enough that it was going to be quite a mess to use, so scratch that.
The next idea was a RHD Monza trip computer. My Monzas are LHD and the trip computer's a big sucker, but the RHD ones are completely different for some reason and small enough to fit in the centre console. I'd bought one off Derek Thompson at GM6 in Penzance years ago so it was worth a go. With unusual foresight I had included most of the wiring for a trip computer when I was rewiring the car and so I just had to find all the connectors and run the wires over to the unit and give it a go.
Monza trip computer test fit
Well it worked, but there were problems.
- Firstly, the Monza is a 6-cylinder 3.0 litre car and the Manta's a 4-cylinder 2.4. That was easy enough to fix, the Monza workshop manual showed there was a setting you could make to tell the trip computer it was a 2.0 or 2.2 litre 4-cylinder car and that would work perfectly. Done.
- Secondly the speed didn't display correctly, and that was down to different gearing. I have a vehicle speed sensor in the car for the Becker stereo and it calibrates itself to whatever it sees for speed pulses, so all I'd need to do would be to find the right speed sensor to give me the correct number of pulses per revolution. Again, luck was on my side as the sensor I was using (Ascona C) had multiple flavours, and the 8 pulse one would be just what I needed. Quick order to OCP and it was on its way.
- Finally the fuel tank was a different size. The Monza is 70 litres and the Manta only 50, so I'd need to do some magic there to convince the trip computer to show the correct range. A twist to this one is that the trip computer really didn't like the Manta's old mechanical instrument voltage regulator. Because of the way the instruments are designed, Opel could get away with the cheap mechanical voltage regulator that switches between zero and battery voltage periodically, making an average of 10V. The trip computer needed to see a voltage referenced against a true constant 10V source, so I had to make a solid state voltage regulator to replace it. Not hard, just fiddly...
It was about that time that I stumbled across the Senator B trip computer in a magazine and it looked perfect. The Monza trip computer had a tiny display and buttons on the trip computer itself (quite a stretch from the driver's seat) but the Senator one was almost exactly the same size but had a bigger display and remote operating buttons, so I could place them where it would be easiest to reach.
A call to Derek at GM6 and a week later I had one in my hands.
Senator B trip computer, luckily similar connections to the Monza one
Now these trip computers can be "personalized" by little plug-in modules to work for 4-cylinder Carltons or 6-cylinder Carlton / Senators and unfortunately all Derek had in stock was one from a 6-cylinder car. Oh well, back to that problem again, but this time it was worse because you had to get the module reprogrammed in order to change the personality and I didn't have the means to do it.
The local Vauxhall dealer in Reading was a bust - I asked them if they could reprogram them (Vauxhall's workshop manual "TIS" said they could) but they looked at me as though I was from Mars and said they had no idea what I was talking about. Oh well. A bit of Googling landed me a chap who a couple of years ago had built a programmer for them and offered a reprogramming service if you could tell him what personality number you needed. I knew just what I needed so I contacted him.
After a bit of to-ing and fro-ing we agreed we had different number lists. I had a list on TIS that said I needed number 31, he said his numbers started at 50, so he offered to reprogram it to the closest number he could find - 55. A while later I had a reprogrammed module in my hand, I connected it up and found that 55 was a later number for a C30NE Senator B. Sigh. I had changed it from being an early 6-cylinder to a later one. I had to do something different.
The good thing is that I used to do electronics as a hobby (and even as a job before I switched to software) so I had some options. My first try was to build a divide by 1.5 circuit on the basis that the injection signal was pulsing at 1.5x the number I needed (6 cylinders instead of 4, right) but the problem was that it didn't preserve the widths of the injection pulses, and it was those that were important.
If you think about it, the amount of fuel being used is determined by two things - the pressure of the fuel in the rail and the amount of time the injector is open. Since the pressure is constant, it's the amount of time the injector is open that we're measuring in the trip computer, so I actually needed to divide the number of pulses by 1.5 but keep the actual width of the pulses the same so that it divided the amount of fuel measured by 1.5.
Trust me, there's no simple electronic circuit to do that!
There's a popular little computer you can buy for a few pounds at Amazon (and other places) called an Arduino. It's a lot less powerful than the Raspberry Pi, but it's a great little thing for connecting to motors and switches to make something computer controlled. It's also great for what I needed. I just happened to have the smallest one (the Arduino Nano) in a drawer at home so I started prototyping what I'd need. To make a long story short, a little external circuitry and only 75 lines of C++ code later and I had exactly what I needed. It converted the signal from the ECU from 12V down to 5V, fed that into the Arduino where it did it's divide by 1.5 (preserving the pulse widths and relative frequency) and then converted the output signal back to 12V for the trip computer.
The Arduino being tested. The little board closest to the camera generates the test signal that mimics the Motronic ECU
Well, that was my fuel signal sorted and I had the different speed sensor swapped in, the only thing left was the fuel level. My first (and badly thought out) attempt was to try to level shift the signal from the fuel tank to make the tank seem more empty than it was, but I got that one so badly wrong I blew up the solid state instrument voltage stabilizer, something I've never been able to do before! Out with the instruments and more soldering...
Notice the diagonal crack in the casing? Takes real skill to do this!
Back to the drawing board, and I realized I had the ideal solution just staring me in the face - the Arduino; it claimed it could read analog signals (i.e. voltages) and output them too. It really wasn't taxing itself much with the divide by 1.5 routine, so I set to and added the fuel level adjustment into it - that worked out well because it needed a little fudging to match the fuel tank sender to what the book says it should have been producing and that sort of thing is simple in code, just a single line in fact. So another 30 lines of C++ later and I had my fuel level adjustment sorted. The only twist in the tale was that it really couldn't output voltages, instead it output pulses that could be (fairly easily) converted into voltages. I was never good with analog electronics, but the Internet makes everyone a genius, and a couple of integrated circuits later I had exactly what I needed.
Back in the car and a short trip round the block and things were looking good, it was time to get the whole lot to fit.
I bought some sheet ABS and made up a replacement for the cassette trays. The trip computer fills the entire space, top to bottom, and is set over on the driver's side. The remainder I decided to split with a horizontal shelf, making a cubby for things like glasses (I'm getting old, I have multiple sets) and a space below that was the original tray. I wanted to hide the USB power connector and aux connector out of the way so I put them at the back of the lower shelf. It's fiddly to find, but beautifully hidden out of the way.
The trip computer and shelf
Centre console modified to take the control buttons
The console back in place, if you look carefully you can see the USB in the centre under the shelf
I really need to tidy this wiring up!
300 miles to empty...
0.4 gallons per hour at idle
I'm lighting everything up inside the car (it's a bit like a disco in there to tell the truth) so the shelves have short strips of LEDs to provide the lighting and I chose a suitable resistor to dim them down. With the shelf being coated in black speaker carpet (both to hide the shiny black ABS plastic and also help hold things in place) the effect is that the light isn't visible except when something is placed in the shelf, just what I wanted.
So that's where I am now, car's pretty much sorted. There are still some things to do, like swap the fuel tank (microscopic hole somewhere) and fit a centre arm rest (saw someone else's project on here and want to do the same thing) but now it's down to driving it.