During the summer of 2006 I really started to make some progress with my Megasquirt ECU. I had suffered a number of problems, mainly fuel pressure and mapping related.
After I got some of these problems sorted out I really started to make some progress with the mapping. With the introduction of an 'AutoTune' function that actively adjusts the map against a target AFR map according to the wideband sensor input things really seemed to start to come together.
At the time of my MOT test the mapping up to around 5000 rpm was pretty much finished, and as I drove home again I did have to wonder why I was about to rip the Meqasquirt out. However, the route home didn't involve any extended revs and that is where the problem existed.
As the mapping had started to progress, so I had been able to extend the rev range that I was using and venture to higher rpm on a more frequent basis. I started to notice that I was suffering from what felt like a misfire at about 4500 rpm. When accelerating it wasn't really noticeable, only occasionally did I feel it. The problem was mainly apparent when I held consistent revs in the problem 'zone' at which point I would see all my shift lights flash and feel a slight loss of power/hesitation.
When I checked back through some datalogs form the ECU I could see no sign of a problem so I concluded that the problem must be elsewhere. I tried a new crank sensor, and new spark plugs. No change. I borrowed another coil pack and EDIS unit (thanks Steve!) but again, no change. I then ran the engine in the garage with the lights off and I could make out some slight tracking along the HT leads. I bought a new set from a local motorfactor and after an jubilant test drive where the problem seemed to have gone, I gave the engine some beans and was dismayed when I saw the shifts flicker again. Another garage test and the leads still seemed to be giving some tracking issues, so I arranged for some high quality leads to be made to my measurements (slightly different due to a Raceline coil mounting plate). Again, the engine seemed to run better but the problem remained.
Whilst driving to work I had one of those bolt of lightning moments and thought 'I wonder if it is a rev limiter in the ECU'. When I got home I had a look and sure enough I had a limiter set for just over 7k. I effectively disabled this by increasing the rev limit to above 10k and the problem was gone. The shift lights would still flash, but the misfire had gone. From this I deduced that the problem was the ECU was getting a false trigger for the engine speed and this was triggering the shift lights, and previously the rev limiter.
I next called on help from Kevin (Megasquirt guru with Zetec Westie) and we arranged for me to pop down to him so he could have a look. Kevin hooked up an oscilloscope and checked various points on my loom and found some noise during the closing of the injectors. To try to get rid of this I changed a large part of the loom to move the ground all back to a single point. Unfortunately it didn't make any difference.
It was at the point that I pretty much decided that I had had enough of trying to find the problem. I didn't want to give up the ECU as I had invested a lot of time and effort into it and had enjoyed both the build and the learning involved. However, I had to call an end to the seemingly endless problems and throw in the towel. I don't have the electronic knowledge and I didn't want to be reliant on others to try and help me not just in the short term, but obviously long term as well.
So, when I got back from the MOT, I ripped out the Megasquirt and set about fitting an Emerald M3DK ECU. I changed the location for the ECU from under the dash where space was too tight to into the engine bay. I also took the opportunity to fit a relay and fuse box as I was removing the relay Board. As all the old wiring went into the dash area, everything was long enough to reach the new location, so it was simply a case of working out the pin numbers and plugging the cables into the appropriate positions. I got a starting base map from Brent, whose Zetec was a similar spec when he fitted an Emerald.
Once completed, the engine started first time and ran much more smoothly, so I can only assume that the ignition problem was effecting the engine across the entire rev range. For the remainder of the year I worked on tuning the map using Chris Good script and got a reasonable amount done. The only problem is I am struggling to map the higher rev ranges because a) everything is happening to quickly and b)you simply don't get an awful lot of opportunities to use the high revs on the roads. A rolling road day may be the order of the day.
At the end of the day I have to say that I enjoyed the Megasquirt experience and would have liked to have kept the ECU on the car as I do like the idea of open source and some of the developments being made were really quite cool. However, I had to admit defeat and I have to say that the Emerald experience was, and still is a very good one. I have had excellent service from Emerald and as mentioned above, everything worked first time. The Megasquirt is living on though, as Tony has taken on the project for his K-Series car which he is planning on upgrading with TB's and I believe he is currently staging the upgrade so the Megasquirt will control the injection and the standard Mems controlling the ignition.