Re: Black Scorpion Timing?
I read manual #31 ignition section. Thanks for the info. I have a Seloc repair manual that is similar. Mercruiser serial number on my engine is
0W390691
The issue started last year. We got a wakesurfboard in June and took it to the lake. The boat ran great for half the day. Then at slow speed under load the boat started making noises you could hear out the back. It sounded a little like a harley davidson. I took it immediately to a local non mercruiser shop. They said the distributor was very corroded. They replaced the cap, rotor and plugs. They said the computer didn't pick up and issues. I was worried about the noise. The compression tested all 8 cylindars at 165 psi. The boat came back and the noise level was reduced, but you could still hear the problem. I called them and told them I thought the timing might be off. They said their computer said everything was fine.
This year, I got it summerized and on the lake, the noise started getting louder again. I called a mechanic that could come to the lake (different than first mechanic). He said my intake manifold pressure was reading weird. Something around 12 and that he thought my TPS and MAP sensors were causing a problem. I repalced both. MAP pressure read 18 last time he was out and he said it was working fine. TPS at an RPM around 1500-2000 was reading 2.5 volts, so he thought that was good. While we were testing the boat, he said "wow, it's popping a little like you have water in your fuel". This continued. I replaced the fuel filter, and emptied the fuel water seperator about 5 times. I poured the fuel from the FW seperator into a glass and have never seen any water. This mechanic went in for some surgery and I had to take it to another mechanic.
Finally I found a mercruiser certified mechanic. He ran his computer - no problems. He checked the plugs that were put in last summer and said some looked a little lean. The plugs were not recommended by mercrusier, so we replaced them with approved plugs. He was worried about possible valve issues and possible injector issues. He cleaned the injectors, and at the request of mercury did a drop down test. This drop down test was to check the valves. If a valve was a problem, he said he could pull a plug wire and look for RPM drop and if the drop was less on one cylindar, it could be a tuliped valve. I think he started at 2000 rpm, and all cylindars were between 1530 and 1570 rpms on drop. Mercruiser said it's probably not a valve.
I took the boat back to the lake after all this and still had the same problem. I asked the mechanic to come to the lake and I invited a friend who is a boat and auto mechanic. They both said it sounded like a misfire. The mercruiser certified technician called mercruiser again and the final diagnosis was that I need to send my ECM in for recalibration. I asked him if I should run it and send the ECM in over the winter. He said that's what he would do if it was his boat.
I decided to check resistance in the spark plug wires since they hadn't been replaced. With my ohmeter set at 200K, it read between 13 and 18 resistance on each wire. The longer wires had 18 and the shorter wires around 13. I assume this is such small resistance that it is negligable. The cap on my motor is different than the one in manual #31.
I've become pretty educated over the past several months on EFI systems and general engine mechanics. Not sure where to go from here. The boat sounds good if the throttle remains on. Translated from wakeboarding, load it up and it is always on which sounds better. When the throttle is reducing, it has a rumble like a harley that you can hear. The fuel system has been looked at by me and by the mercruiser guy. The mercruiser guy says no water or bad gas problems. The problem is intermittant. At specific RPM's it is not always present. I don't know if that has to do with weight, air temperature, or what.
Any help anyone can give me would be appreciated. I feel like I've hit a dead end. Not sure if the mercruiser people are blowing me off with this ECM recalibration idea or if that might actually fix something.
Thanks for the help.