cryscromolina
New member
Hi! As the post title suggests, I have an Optimax outboard that isn't running as it should. It’s a 90 hp engine from 2007. It behaves roughly like this: it starts quite easily and idles relatively smoothly. However, when you try to accelerate, the RPMs climb toward 3,000–3,500, but within a second, the engine begins to sputter and run very poorly. If you then back off the throttle and the RPMs drop below 2,000, it runs quite well again, with no signs of rough running. I have checked the fuel tank, replaced the fuel with fresh gasoline, and inspected the fuel chamber (where the pumps are located) for any contaminants. I’ve also checked all the pumps, and they appear to be functioning normally. I measured both the air and fuel pressures; the air pressure is around 100–110, while the fuel pressure is 60–70—which is too low. On the pump side, the fuel pressure measures approximately 2 bar. The compression is consistent across all three cylinders, at 10–11 bar. I also checked for spark on all the spark plugs—which are new—and everything seems fine there. However, spark plug number 3 becomes completely fouled with soot after only a short period of operation (5–10 minutes). The other plugs (numbers 1 and 2, counting from the top of the engine) show no significant discoloration—it almost seems as if they might be running too lean. Plug number 3, meanwhile, appears to be receiving far too much fuel, given how heavily it soots up. I tried replacing the injector on that cylinder, reasoning that since there was so much soot and the fuel pressure was quite low, perhaps a faulty injector was to blame—possibly injecting far too much fuel into the bottom cylinder, which in turn caused the fuel pressure to drop. However, replacing the injector didn't help. The engine is behaving exactly as previously described, and I’m not really sure what the next step in the troubleshooting process should be. Does anyone here have any thoughts on this issue? Best regards, Ola A. Skogstad