250 OX-66 problems

[Mikviy58]

2001 OX-66. Driving me crazy with a surging problem. this has been an on going problem for several months. Open the throttle and motor starts surging and sounds like it's only running on 4 cylinders. Replaced O2 sensor, changed/cleaned all filters, fuel pressure is fine. New ignition switches, harness and module.

Tach (new) is all over the pace with it's readings. When both motors are running the fuel management gauge either switches off, or blinks. Running on just the other motor it works fine. new gauge, sensors and harness. Sometimes, motor comes back to al 6 cylinders and the Tach and fuel gauge work fine.

After shutting the motor down today, it refused to start. This is a first, and I'm hoping it will show the problem.

Mechanic coming tomorrow and with blinky lights and gauges. will be held captive until everything is fixed!!

Any suggestions as where to look first?

[ausnoelm]

I suggest you do a search on this motor and posts by rodbolt, he has covered similar problems a thousand times (well it seems like a thousand) throwing parts at motors on a possibility will eventually fix the problem (maybe) but trouble shooting will be cheaper and faster.

[rodbolt17]

when I am sober and you can actually post model numbers and a clear description of the issue.
then we can get us down to brass tacks.

[Mikviy58]

SX250TURZ. Rodbolt, don't sober up on my account Done all the searches on this forum and many others and keep hearing the same.: Fuel pressure, O2 sensor, VST and other filters. Been there done that. Motor still wants to run on only 4 cylinders most of the time. Used to be intermittent after about 15 minutes of running. Now it's all the time. Sometimes all cylinders kick in and it runs like a raped ape. This is the 1st time it refused to start. Hopefully should know tomorrow after the second on-water diagnostics. last time couldn't get the motor to show a fault and it ran perfectly. I just think it hates me. I'll post results of water diagnostics tomorrow.

[rodbolt17]

still not sober.
still not enough information.

however I have enough to ask, fuel pressure at the failure rpm and load??

now the big one.
what is the CDI output port to stbd bank at the failure RPM and load??

this motor does not use high and low speed charge coils.
its bank to bank.

don't overlook the easy and obivious things.

[Mikviy58]

Rodbolt. Thanks for the suggestion. Will have the voltages checked today. Hopefully will be able to report the fix later. Just documenting this to try and help others. Fixing it is beyond me as I'm disabled and will pay a mechanic to fix it. Curious minds just want to know More knowledge always helps keep the mechanic honest

[rodbolt17]

when you said it would not start, would it crank over or not?

while the OX66 motors require NO battery power for ign they do require battery power for the fuel system.

[Mikviy58]

All fixed. The surging was caused by a loose ground wire on the block. Making the motor go into 4cyl limp mode. Wouldn't start because the power realay for the fuel pump went out. Was also a bad ignition wire near the engine (the yellow one). Took boat out and jumped waves trying to make it fail, but everything worked great. All the BS electrical problems with the gauges went away once the ground was taken care of.