Merc 115 fault code and surging
I've fitted a new Merc 115 EFI to my boat and, having sorted most of my last set of installation issues, got the fuel system in and decided to run it up on the muffs to make sure everything worked. The fuel system is a 70l tank in the console (brand new), mercury supplied filter/separator (also in the console) and about 5m of fuel line to the engine (no primer bulb, as per the instructions). The fuel tank vent is on a combined filler vent cap, which seems to always be open.
So I put about 15l in the tank, (which didn't register on the gauge so I guess my sender might be a bit short), turned the key and off she ran, no priming done what so ever. First off it ran a little rough, as I would expect, but ran, and kept running. I noticed that there was at one point some fuel flowing through separator. At the end of the test I couldn't tell if there was fuel in the separator bulb or not, fuel being clear and all.
Next time I ran it up, again on muffs, it fired fine but ran a little lumpy at tick over and was surging badly at 2-2500 rpm, not going above 2500 at all. I could put the rough idle down to it being about 4 degrees but there must be an issue causing the surging. I would not normally go above about 2000 on the muffs but slipped with the idle lever.
Assuming this was a fuel flow issue, and concious that I hadn't primed the fuel lines I disconnected the feed at the engine, purged the fuel line by pressurising the tank until the fuel ran bubble free, then re-connected. Syphoning had failed as there seemed to be too much air in the system and I was fed up of drinking petrol. I hasten to add I did not pressurise the tank with the engine connected. Sadly I ran out of time to run again that night.
Tonight, I've fired it up again and again, starts fine, runs a little lumpy, although it is pretty cold, but was surging again. Tried running for a few mins on tick over then up the revs slightly and again it surged until the smartcraft alarm sounded. I dropped the revs to tick over (about 550 rpm) and read the alarm. It was showing a system fault 66 - shift position sensor, non critical. At the same time the alarm went off, the surging stopped and it ran sweet as a nut. I turned the engine off, waited a few mins then re-started. No fault code but surging and rough tick over again, then the alarm sounds and the engine runs fine again.
Could these issues be linked? Could the surging be due to a shift sensor telling the engine I'm trying to shift gear and dropping the revs or something? Is it the engine trying to stop me revving too high out of gear? It seems too much of a coincidence that the fault appeared and the engine suddenly ran smoothly. Any help or suggestions greatly appreciated.