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Megasquirt EFI conversion, part 1.

Discussion in 'Fuel System & Electrics' started by beep, Jul 5, 2008.

  1. beep

    beep Member

    Hi Everyone. I am on the way to a full electronic injection/ ignition conversion on my much loved 74 bus. The experience so far has been fantastic so I thought I'd write something detailed for anyone thinking of going this way (and I warn you this is likely be very long winded).

    I've been thinking of going injection for years now, and after deciding to take the plunge and spending some time collecting parts it all came together pretty quickly. My original plan was to get the EFI computer in the car, then use it to control a distributorless ignition system, then fuel injection. It didn't turn out that way though.

    I had to do some other work on the engine first, the heads were stuffed and the clutch was pretty bad too. So I fixed that and put the computer in the car with a wide band oxygen sensor to see what the engine did normally. Straight away I saw the the engine had some lean spots in normal driving so I decided not to worry about the ignition, to leave the 009 dizzy in and go straight for the injection. These lean places coincided with a bit of a flat spot and I was really worried about damaging my new heads. I thought it may have been the lack of vac advance but now that the EFI is working I'm totally sure it wasn't.

    I would drive along without much load then put the accelerator like half way down and I was seeing 16:1 on the laptop. If I really planted it the throttle pump would make it rich for about half a second then lean out again, so I found myself trying to get a better mixture by pumping on the throttle all the time.. not cool. It was marginal wide open but this three-quarters-load lean out really bothered me. I wonder how long this had been going on with the carbs.. maybe they never worked properly. And one of the side effects of the new heads (2L mexican ones I think) was that they were a bit wider which made the carb linkage even sloppier than usual. Bugger it. Time for injection.

    Previously I had scored a whole EFI intake from someone here on the forum (cheers Riley) and I started by taking the injectors to an EFI guy to check them out. The EFI guy said that they were DOA but was able to supply some other ones pretty cheap. They're out of a VL turbo dunnydore which I believe has a Nissan engine (hope this doesn't offend the bus..) but they were dirt cheap. (Original combi bosch ones cost a buttload.. if you can get them).

    So once it was all in the car and wired, the engine started up pretty quickly. It took a bit of cranking and adjusting the settings and stuff.. but in about 10 minutes it was idling. And not long after that it was driving. There's plenty of reading on the web for those interested in how the megasquirt works but the thing that really blows me away is that you tune by driving. You log some data, run a program, click ok.. and then your engine runs better than ever. Its unreal. And you wouldn't believe the difference its made to the engine. Its like a different car (a RACING car). It goes so fast now that I've ordered a rear swaybar and will get down to some work on the brakes tomorrow (No kidding this thing flies!)

    Now: nuts and bolts. For those thinking of changing your dual carb combi to EFI, there are a few things you're going to have to do. Its relatively easy for us though, because you can get a whole intake/etc from a bus that had EFI. Assuming you do that, there are still some things you have to do:

    Get the fuel back into the fuel tank
    Mount the electric fuel pump somewhere
    Get rid of your mechanical fuel pump
    Sort out your throttle cable
    Sort out some kind of air filter

    And that's it!

    Here's how I did it.


    The air filter is really cheesey cheap one that says DRIFT on it (!). There's supposed to be a temperature sensor in the intake, but I haven't got around to putting it anywhere yet. Its just kind of hanging around in the engine bay.

    Serious issues are: mounting the electric fuel pump and getting rid of the mechanical one. I just bolted the new pump under the car kind of near the starter and made a plate to block off the hole made by removing the old pump by cutting out a bit of steel and drilling two holes in it.


    Also, you have to re-route the throttle cable. I had to drill a 10mm hole in the apron tin, and also part of the thing that the gearbox is bolted to. And you need a slightly longer cable outer (couple of inches). The carby setup has a kind of small tube in the tin to hold the cable outer which I duplicated by drilling two holes in a bolt. A 4mm one all the way through and a 9mm a bit into the bolt head to hold the cable outer.


    And even then I was finding that I didn't have full throttle. In fact I'm pretty sure that the bus never had full throttle on carbies either. So my solution was to extend the thing under the front of the car where the cable connects to the lever thing. If you're not sure you get full throttle, give this a try. Its pretty easy. Its just thin panel steel and I've kind of bent the edges for a bit of extra strength.


    Finally, you need to return fuel to the tank. This is pretty tricky without major work. The tank isn't accessible because you have to take out the engine to remove the firewall (I did try) so I went for putting a copper pipe through the paint tin lid thing on the right side of the engine bay into the fuel filler. I thought I would take the filler out and braze the pipe into it but it turned out to be too hard to get out and impossible to get back in with any pipes sticking out of it. So I used some epoxy putty kind of stuff thats for repairing leaking radiators(!) The fuel level won't often be that high anyway so I doubt it would cause a problem even if it leaked. Speaking of which, I haven't smelled petrol since running on EFI.

    And finally, I put the computer itself in the spare wheel well. This is no inconvenience for me because the bed takes up that space and I haven't had an actual spare wheel there .. ever I think.

    Part 2 will be to get rid of the dizzy and use the megasquirt to control an electronic ignition system off an american ford. This is called EDIS and was never fitted to oz cars but works by a sensor that watches a toothed wheel on the crank. The advance signal comes from the computer and the EDIS module tells the computer the engine speed and fires the plugs at the right time. There'll be a bit of fabrication involved, but some dudes have already done it on this engine.

    So I hope this helps someone out.
    Last edited: Jul 5, 2008
  2. Das_Dubber

    Das_Dubber Member

    Gold Coast
    Great info Chris, There is some good detailed info re. mounting the 36-1 wheel on the type IV engines (on shoptalkforums.com in type4rum section)...however a lot it relates to a conventional pulley when the type IV is converted to upright cooling for use in a beetle.

    I'm sure you'll put that "Drift" air filter to good use with your new found power...maybe the bus will be capable of the odd "drift" around corners....hehehe :)

    I haven't played with megasquirt before but have read a bit about it....did you have a fuel map to start with? Any other sensors you needed to run (EGT, MAP etc)?

  3. beep

    beep Member

    Hi Al,

    I've had a pretty good look at shoptalkforums and the info there is great. I think I've got a pretty solid plan for mounting the wheel and sensor. The main thing slowing progress is that you have to take a lot of stuff off the engine to get to the crank (including the heater boxes because of the way the fan shroud fits into them) and I'm having a bit too much fun driving the bus to have it off the road for long :D I will get around to it though.

    The megasquirt has a map in it to start with that is just a kind of estimation for most engines. The reason it works pretty well is that you tell the computer a kind of baseline amount of fuel to inject (called Required Fuel). You tell the software the engine size, number of cylinders and flow of the injectors and it calculates the Req Fuel which is the number of milliseconds of injector open to deliver the right amount of fuel for a complete cylinder fill. This is then scaled by load/rpm when driving. In short, a bit of tweaking got it idling and then you just drive and use the logs to tweak the maps. It just gets better all the time. And actually it ran surprisingly well straight off with no tuning.

    As far as sensors go, the main ones are map (built into the megasquirt, you just put a vac hose from the intake manifold to the computer) and rpm (1 wire to the ignition coil). It also uses intake air temp, I used the GM one recommended by the MS guys. Also, for warmup enrichment I used the Temp Sensor II from the original Bosch EFI, which screws straight into the head near the intake port and has one wire to the computer. Easy!

    My acceleration enrichment (like the carby throttle pump) is done by rate of change of the map signal. Some people have a throttle position sensor, which would be nice information to have but was too hard to mount on the old VW throttle body. You don't really need it anyway.

    The megasquirt can also do some pretty sophisticated idle speed control, I think mainly for auto transmissions. I'm just using the old bosh thing that lets in some extra air when the engine is cold to keep the idle a little faster.

    Take care

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