Cat 3116 Engine Missing above 1500 RPM

I was out on a friends boat th

I was out on a friends boat this weekend and we had problems with the starboard engine periodically dropping several hundred RPm after we went over 1500 rpm it would get a progrsiively higher drop the higher the RPM went. You could see a increase in the exhaust smoke at the samne time so I'm assuming it was going rich. The Racor bowl was clean and filter are clean. The fuel tanks are only two years old.

I'm not very knowledgable on the mechanical rack type injection so we'r looking on a little help. Ubfortunately he's had it worked on several time with parts like the fuel solenoid etc being change which obvously was not the problem as the engine runs fine but just goes into a symptom like a dropped cylinged. There isn't any sound from the injectors or engine like you would hear if one was hanging or air in them like you would get possibly after draining a filter and having to get the air out of the lines. It's just seems to be the equivalent of a the engine going rich on all cylinders at the same time.

"put a fuel line sight glass &

"put a fuel line sight glass ( plastic tube)made for fuel, in the return line from engine and see if there is lots of air coming out when you get to 1500 rpm. have seen engines when they get boost up higher un-set the injector fromthe copper sleeve in head, and then you get lots of air in the return line and the engine runs like forget it. if this is what is happening then you have to have the injector or injectors re-setted and the coppers reemed for trueness. they make a special tool to seat the injector into the coppers. use it, it makes a big difference in seating the injectors."

The engine seems to run fine b

The engine seems to run fine but as I said it appears to be over fueling and drops varying amounts of RPM as you get over 1500 but only does it for about 5 to 10 seconds and goes back to running fine.

I also noticed when we came back in the the whole back of the transom had a pretty good coat of diesel soot on both sides which seemed to me to be a little abnormal. I wonder if the engine is set a little rich as we weren't running high RPM most of the trip (120mi) there's about 1100 hours on the engines.

How do you set fuel rate on these engines? I did a little research on the internet last night and it looked like you need to use a dial indicator to set it with a dial indicator on the rack???? I'm more familiar with non rack type systems. I don't intend to fool with it but was just wondering.

I'll talk to Jeff about putting a sight line in the return to check it. I had wondered about a return problem but didn't think about a air problem in the return.

"could be and air fuel ratio v

"could be and air fuel ratio valve is bad! at the point your getting boost it is hasitating, could be a hole in the diaphram. have to change the hole air fuel valve. it would also expalin the smoke being on and off. if working correctly not a lot of smoke sould be seen."