I can't seem to shake these Fiats! Because of my success with the Spider and my mental hangups with the inefficiencies of carburetors I decided to inject the sedan. I was pleased to discover the Megasquirt project had been evolving the whole time. The current support system in addition to complete and well written documentation has made a conversion much easier. http://megasquirt.info/ The Sedan is now purring away nicely using the MS v2.2 and MS relay board. As usual I took pictures of the process:
I ordered up the latest revision of the MS board and all the appropriate parts from DigiKey, lots of stuff. Assembly of the MS board takes some simple soldering. I went out and bought chip sockets for all the ICs on the MS board. A set of metal clips can also be used to as a heat sink when soldering in transistors. I still do not trust my soldering skills enough to not fry them.
As I mentioned earlier I also purchased the new MS relay board. When installing the older system in the Spider I had to wire up a number of relays for the main MS Power and the Fuel pump. This added a number of extra wires under the dash in addition to numerous crimped connections, more points of failure. The relay board takes care of all of this and fuses important links so in my opinion totally worth it.
Having way to many spare Fiat parts around I used yet another wiring harness from an injected 124 Spider. I took all of the unnecessary wires out of the harness to reduce weight and clutter. The wires I pulled out were great for making the patch cable to connect the MS board to the relay board.
To test the assembled MS unit I pieced together a circuit to simulate a pulsing ignition, a little RC circuit. I put an LED into one of the injector plugs to simulate an injector. When I powered everything up the LED had a nice regular pulse. I used some resistors to test the other sensor inputs, no problems there. Done with the electrical hardware! Now it was time to go out to the car. its amazing the amount of free time school affords you. With work during the week so many activities are pushed to the weekend it took over about a year for me to get around to actually installing the system in the car. The whole install took about two days, and I had the car up and running in three. I found my previous experience helped, mainly in knowing what materials I would require.
Part of this project involved minimizing the amount of time the car was off the road. To facilitate this I installed the MS system in a specific order.
On the spider the F.I. wiring harness goes through the firewall on the passenger side. I decided to do this on the sedan as well. I used a hole saw to create a circular hole to pass the wires through. The exhaust manifold is on this side so I tried to drill as high up as possible. There is plenty of space under the dash on the passengers side and the MS box tucked nicely under the glove-box. This way I have easy access to the serial port and I can check out the lights if I need to. I secured the relay board to the back of the glove-box using two screws.
This time I did not even bother trying to trigger the MS unit off the coil and opted to install a second ignition module. I attempted to make a nice mount for the 2nd module. Its basically just a scrap piece of sheet metal. I spliced into the magnetic pickup lead coming from the distributor and added a pigtail for the second module. This second module does not have to drive any low impedance coil so it should not heat up too much.
I have a number of the GM 4 lead ignition modules laying around so I just grabbed the first one I saw. Unfortunately with everything wired up the engine would start only briefly then stall with a high pitched squealing noise coming from the module connected to the coil. I am not sure why this happened but installing a different MS triggering module fixed it.
At this point I parked the car. The FI fuel pump would very quickly flood a carburetor so from here on out it was a race. You could wire up and place the F.I. pump before installing the fuel lines but I had alternate transportation at this point so I did not bother. The 124 Sedan series was never equipped with fuel injection so I had to use the gas tank designed for a carburetor. The fuel lines leaving the tank are considerably smaller than the input line on the F.I. fuel pump. F.I. fuel pumps rely on a high fuel flow for cooling and lubrication so the difference in line size has me concerned that I might burn up the pump. Although as of this writing everything is working fine. In the future I would like to fab up a larger tube leaving the tank just for piece of mind. I placed the pump on the floor of the trunk which puts it below most of the gas tank. This should help create a siphon effect to aid the pump in pulling in fuel. Being over 30 years old this gas tank has some slight rust issues. With the carburetor setup I had a clear fuel filter and could see the filter element turning red over time. I placed a high flow filter before the pump, hopefully it will catch any rust particles before they jam up the pump.
This seems like the largest task but really isn\u2019t bad. You have to drain the engine coolant and detach all hoses and cables prior to removing any bolts. Its a total of 8 bolts and the manifold comes right off. If yours has been on there awhile you might need to give it a little jerk to pop it off, make sure you have all the bolts out!! The rest of this process will depend on the type of intake manifold you are using. Some of the older cars had lots of linkage for the accelerator, now is the time to simplify this if you can. I used an accelerator cable from a F.I. spider. Using a stock Fiat manifold here makes the job much easier but is limiting for all out performance. The choice is yours.
Once again I used a GM water temp sensor. It looks like the newer version of MS has made it much easier to use other types of sensors but to me re-threading a sensor bung was easier. Using a large bolt and some washers I plugged one side of the coolant T and placed a chevy style thermostat under the water-neck. With this setup I only need two radiator hoses. If you do this you need two rubber rings to seal the thermostat under the water neck or coolant will leak by. Keep in mind this may not be the best setup as the thermostat will block coolant flow from the sensor when it is closed. However I believe once the engine is around normal operating temp the small fluctuation should be taken care of with the O2 sensor.
The pesky air temperature sensor. In reality this should be placed as far away from the engine as possible to avoid latent heat from giving a false reading. However, until I setup the fast idle solenoid I elected to plug its outlet on the intake tube using the air temp sensor.
Always an issue when starting out! After a few days of setting up the VE table I decided to floor it.... big mistake. The flyback transistor popped and smoked leaving me stranded, thankfully close to home. I replaced the transistor and started tuning the car again but after ~100 miles the car would no longer idle. I could remedy this by boosting up the PWM however this would only last a short time. Searching the MSEFI forum turned up a post attributing this behavior to a slow failure of the flyback circuit, and most likely the use of low impedance injectors. The stock Fiat injectors are low impedance, to reliably use them with the MS unit I would need a flyback board or a resistor pack to make them look like high impedance injectors to MS. Thankfully I had a set of four Ford SVO injectors from summit racing. (PN# FMS-M-9593-B302 ) These injectors are high impedance so no more worries about resistor packs or PWM or flyback boards. I had to cut plastic from the pintle caps and from the rail mount to make them fit the Fiat manifold, they have been working fine now for over 1000 miles.