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Hey Nick

It's looking very nice :-)

Did you get the info on the hose clamps?

https://www.wirecare.com/searches?utf8=✓&search[term]=gates )

I found this link while skimming through your post and think i might be able to find a few things i need on there :-)


I have managed to get the brakes sorted on mine, so its now the hydraulic clutch to sort and then i think im going to drop the engine and box and fit that clutch kit before i get her on the road :-)  So im starting to get going on it again. I might even get her running for the summer!!



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Hey Andy, thanks! Yes, I followed the links with the hose clamps, I'm going to give them a try on the Manta forward heater hose - that's the one that goes from the block to the heater radiator and has multiple connections on it in mine - there's the T for the throttle body heater hose and then there's the heater valve, so 6 clamps in all. I've used constant tension clamps on it at the moment as I'm worried about destroying the plastic heater valve with normal clamps (and they're black so they're not as obvious) but the heatshrink ones would look much better. I don't like the clamp removal tool, I'd be nervous about digging into the hose, but I guess I'll cross that bridge when I come to it as the hose isn't exactly hard to find if I do have a problem.

Vehicle Wiring Products are great - they've had everything I've needed for the new looms and very prompt (only a week from order to delivery here in the US). Andy Clears put me onto them years ago and I've never gone anywhere else.

You might try Car Builder Solutions for other non wiring stuff - that's where I found the heater valve and a bunch of other small parts. Their catalogue is massive and good reading. They have tech tips in there too - one I used was how to make up braided steel brake hoses, very useful. I think that was another Andy Clears recommendation.

Looking forward to seeing a pic of the clutch once you've got it sorted out. Hope the weather has warmed up and the garage isn't so icy. The garage here has decided to double as a fridge with all the cold and rain we've had. Still, an excuse for more frequent cups of tea...



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I think that it was Opels original intension that the whole recess area below the boot lid and around the rear lamps was to be mat black, a P reg Manta that passed through my hands ( picture below ) was painted like this and it was deffinately original genuine Opel paint, not something added by an owner at a later date, MK 1 Cavaliers where painted like this, wether they decided that it didn't look so good or the bean counters got involved i don't know but i've never seen another Manta painted like this.


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Hey Kev,

Yes, still around but not on the forum much at the moment. In April we started to look for a new house and we've just moved in, so that's been taking all my attention recently.

The Manta finally passed its California certification (they only needed to replace two hoses, apparently) but it's been stored down in Orange County with a friend of mine since it passed as I had nowhere to put it - the new house has an incredible garage, but we were holed up in a temporary apartment between houses for ages and that came with only one parking space. With some luck we should get the car back next week as I have a transporter lined up to bring it back home.

As I said, the garage in the new place is great, I'm currently building racks for parts and trying to find homes for everything so I can fit all the cars in... :)

I'll do an update on the car once I get it back. There's still more to do but it's going to be slow as setting up the garage is going to take ages.


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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

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Back with the rest of the fleet

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All that fuss for this sticker - California certification

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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.

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First trip - all of half a mile down to the post office!

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Present from Santa to keep it clean in the garage

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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

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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

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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

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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!

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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

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Centre console modified to take the control buttons

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The console back in place, if you look carefully you can see the USB in the centre under the shelf

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I really need to tidy this wiring up!

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300 miles to empty...

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0.4 gallons per hour at idle

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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.


Edited by CalCol
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Fascinating post Nick. I always enjoy reading about what you have been tinkering with and this latest project does not disappoint! Hope you get to enjoy driving the car a little now.

I feel your pain about moving as we have just done the same. I ended up having to take out a new unit to clear out my garage whilst we moved and low and behold, once bad back and 4 months later and all my stuff is still in storage. Slowly getting the garage to where I need it to be but lots still to do before the weather turns. I can Ill afford 2 storage units so time to get posterior into forward drive! 

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