poulsen11@yahoo.

i have twin 700s in my boat and the one side is lagging in rpm at same throttle position by about 3-400. Leak down test is all good. No codes or warnings being thrown. per vessel view that side is burning about 2-3 gallons less fuel per hour than the other side at 4k rpm. Props were just reconditioned about 5 hours ago and show no damage.

Any advise on how to diagnose what could be happening. Could it just be coils, spark plugs and wires?

Knot 4 Me

I'd say you are down a cylinder on that side. Check wires/plugs. Could also have an injector not firing.

poulsen11@yahoo.

i assume starting with just replacing wires/plugs and see if that fixes is best way to find out? Will injector not firing throw a code?

F-2 Speedy

iTrader: (6)

Have you hooked a scanner to it or just reading V-V

Edit: also check fuel pressure

poulsen11@yahoo.

All i know right now is it is it wont run at same rpms as other engine throughout the rpm range. Will scanner tell injector or ignition issues? I assumed V-V would tell me anything that a scanner would tell me.

fossil fuel

I had 700's and had the same issue. Although it was not readily apparent other that I noticed a slight change in the exhaust sound. The coils will not show on the computer as not firing. The computer shows a signal sent to fire but does not know if it did. Mine ended up a bad engine wiring harness after testing everything. We also swapped coils around. It took lots of time to troubleshoot that one......

poulsen11@yahoo.

Was it an igntion harness? Did you also see the rpm difference between the engines?

F-2 Speedy

iTrader: (6)

I think with a scanner you can invoke a cylinder miss fire test with the 555 controller to see if all is well or may point you to a particular cyld.......... have you tested the fuel pressure ?

Sydwayz

iTrader: (1)

Years ago, I had an issue with my pair of 496HOs where one engine was always lagging by 300-400 RPM. It turned out to be a bad Crankshaft Position Sensor. The CPS can start to go as such can start go bad as such before throwing out error codes.
That would be something I would replace just for good measure. They are fragile, so not sure I would try swapping them.

zz28zz

Blower belt slipping??