Volvo 8.1 Missing/Surging

[tjh408]

New problem with this boat. After running and feeling good about the temp on the port motor, I noticed a surging or missing on the tach for the starboard motor. Initially at about 3200, so I pulled back to 2000. Seemed to run smooth at 2000, when I attempted to run it up again it began to surge. Fuel starved maybe? Not sure, not familiar with the MPI motors. When I got back to the dock and they cooled down I changed the fuel filter, hoping to find some crud in that, nothing. Ran it again, idled smooth up to about 3K than surged (this was a short no load at the dock test) again seems to run smooth below that RPM?

Thoughts

[Viper]

I assume the engine is actually surging and not just the tach? If so, it could be a number of things. I would start with ensuring the anti-siphon valve at the tank is operating properly, and check fuel pressure as there may be a failing pump or bad regulator. Also ensure there is no obstruction in the tank vent. You can confirm if that's the problem by running her with the fill cap off to vent through there instead. You can also do a cylinder drop test to see if all cylinders are firing. Another possibility is that one or more injectors need cleaning or replacing.

Don't rule out a poor electrical connection too.

BTW don't rev the engine up that high in neutral, you can do serious damage. It won't tell you much anyway as a lot of issues only present themselves under load.

[tjh408]

Thanks,

It was a very short time that the motor was run up that high w/o a load. at soon as it crossed 3K the issue began as when we were out with it. I am familiar with the check valve issue. I had that problem on a previous boat that would pick up metal shavings. This one will require some engine room yoga after this storm passes. Not sure where the vent is for the starboard tank, will have to trace that.
It certainly could be any of the electrical connections even the pump. What is odd is how smooth it is up to that point.

[bud37]

Do you have someone that can connect to the ecu and have a look at the data while under load ?

[Cliffm]

The GM big blocks can easily hide a "missfire" idling, put its more apparent at higher RPM. Verify all plug wires are firmly seated. if it persists, you may want to remove each plug and inspect looking for that elusive "odd" and maybe "wet" one.

Could even go as far as ohm'ing out the plug wires.

[bud37]

That is a good point about plug wires etc.......since this is a relatively new boat to you, it may be a good idea to have a good look at simple stuff like that, I know I have found some plug wires pinched up against ground lugs and exhaust manifolds.

[pepmyster]

When we bought our 360, the PO said that the tune up was done. Being a tech, I decided to do it again anyway. Low and behold, original plugs from the factory!!!!! Did all the plugs and oils, replaced 1 idle solenoid, clean the throttle bodies, running great ever since. Start fresh......

[tjh408]

Thanks for the suggestions! I will be at the boat on Friday and will take on the things I am comfortable with, such as the check valve or anti-siphon valve, and spark plugs. Then I guess I have to turn it over to the yard for help. Unless I hear the whine or screeching from the pump I have read about. I will up you all.

Thanks again

[mjk1040]

Are you sure you have only 1 fuel filter? Maybe a pancake style primary filter inline. Orburg Filter?

[tjh408]

I will look when performing my engine room yoga Friday, I didn't see one when I looked last week.