tanner

running 3500 RPM all day with no problem, bump up to 4000-4200 RPM and the one engine drops out to 3300 - 3500 RPM momentarely, pulls to the right and then goes back to 4200. This keeps happening. Feels like it is starving for fuel or something. Maybe injectors, clogged fuel filter? By the way the other motor is just fine.... any help would be great.

Todd

jtmiller02

First and easiest thing is to check simple fuel related stuff, start with the filters, if they're more than a few months old they should be replaced anyway, make sure when changing fuel system components you drain everything into clear containers to examine water/contamination, I've been amazed a few times at what has come from a fuel water seperator.

It could be any number of things, but fuel system contamination is usually easy to diagnose, I typically drain a racor filter atleast once a week when a boat is constantly in use, doing routine checks like this always helps prevent bigger problems from ever starting.

The other things you can check are simple, harness connections which may be lose, any wires which might be coming in contact with heat/salt/water causing them to degrade. Especially ground wires or ignition/computer related wiring. Misfires are fuel or ignition related so something as simple as a severely corroded ground could be causing an issue. A thurough visual inspection of these type things is simple and should also be routine from time to time.

Also remember that anytime you have misfiring you should examine all your spark plugs, even when caused by other issues often the plugs take a real beating from being run with improper mixture. Realistically the goal is to do every simple check you can before calling in someone who will bill you to do the same simple things.

Working as a captain I've learned the best thing to do is do a comprehensive check of all common-sense causes, and if you cannot locate a problem, you will be prepared when you do have to call someone who bills $70/hr. Its much easier for a mechanic to get the job done efficiently when you have a list of checks and results to give him when he arrives, all these simple/small checks add up to big bucks. Instead of spending two hours thrashing away at filters etc. he will be able to start with ECU checks, fuel pressure checks etc.

txriverrat2001

You'll need someone with a fuel pressure guage to monitor the pressure while running. Scan it for codes ... check the plug wires etc....

Is it surging? Or a quick on and off from 4200??? Like it dropped a cylinder from misfiring?

jtmiller02

correct, if you cannot find the problem with any simple checks the next check is a fuel pressure guage and ecu under load, usually people have a mechanic do this, if that check shows no problems then diagnosis will turn to the injectors, if an injector fails it will typically not be diagnosed until you reach this point. Typically if there is clogging, you will start to see signs in the filters, and then the pump will be either diagnosed or eliminated by the pressure check.

I would start with this process...
1. all filters/inspect connections
2. pressure/ecu check
3. inspection of injectors/plugs

I would not reccomend removing the fuel rail and checking the injectors if you have never done it before, you don't want to risk damage to any good injectors. The steps should help to either eliminate possible causes or lead you to the correct answer if done in the right order.

tanner

Thank you guys for your help, I will check all those things and hopefullyit is not an injector issue.

Thanks again