OX66 stals at high RPM!!!

[scjmc]

My 97 OX66 250 is stalling at speed. It seems to stall when fuel consumption is high. It will go from a cruise 4000+rpm to stall in about 3 seconds.....but sometimes the rpm jumps around and gradually falls. The engine mounted fuel filter stays about 80% full while running. The engine still stalls even when pumping the ball. The stall interval is inconsistent, and sometimes it will just bog down and not die. I recently had a high rpm fuel problem and I cleaned the VST filter. That solved the problem about 120 gallons of gas ago, but it was not stalling. Any thoughts? Racor is clean and no water in the seperator. The engine will start right after stalling too...

 

[scjmc]

Re: OX66 stals at high RPM!!!

I took the VST filter out again and it is dirty. After only about 10 hours of use!! I found a bad electrical splice on the yellow/white wire that comes out of the bottom of the power pack and loops back up. Anyone know what this wire is? I also found a bad splice on a black wire coming from a black plastic box tapped to the starbord side of the harness.

 

[rodbolt]

Re: OX66 stals at high RPM!!!

the yellow wire is a manual emergency bypass, splice wasnt bad and should have had a bullet connector.may have been going bad, unplug it and fuel is fixed rich and timing is fixed at 7*BTDC, high idle and no power.

black lead I would need a picture of.

 

[scjmc]

Re: OX66 stals at high RPM!!!

After running it today after cleaning the VST the problem is the same. It dies suddenly or gradually at high RPM. I had a friend pump the ball constantly and that didn't seem to have any effect. Any other thoughts? I took the fuel rail off and did not see any screens for the injectors. Rodbolt thanks for replying to my thread I hoped you would... I will try to provide a pic of the second bad connector tomorow. The yellow white looked super corroded and came apart easilly when I tried to disconnect it. It did have bullet connectors, but I spliced it back with a butt connector. Like I said cleaning the dirty VSP filter and fixing those two connections did not improve my situation.

 

[scjmc]

Re: OX66 stals at high RPM!!!

Wel... I removed the check valve between the engine mounted filter and the first LP pump. I also ran it off of a pony tank. No better... Any other help?? Totally out of ideas at this point.

 

[cousinabe]

Re: OX66 stals at high RPM!!!

when you say it dies, do you mean it suddenly turns off like the ignition is cut or does it slowly drop rpm's(then does it stall?)
do your gauges flicker? is your motor going into reduction mode?
sounds like an electrical issue... bad ground?

post a pic of the wiring rodbolt is looking for.

 

[aquanutfl]

Re: OX66 stals at high RPM!!!

I am having the same problem. So far, I have replaced the LP pumps, cleaned the VST and injector filters, replaced f/w separator, took out the O2 sensor and soaked in Sea Foam overnight and replaced the gasket, and re-did the tank hose connect. I plan to do more troubleshooting but any input would be helpful. Mine is a 2001 OX 66 225.

 

[scjmc]

Re: OX66 stals at high RPM!!!

I dont think it is electrical because sometimes the RPMS fall off then it dies. When it dies suddenly it happens over the course of 2-3 seconds. The gauges do not flicker and they do indicate the RPM falloff. I cant get my digital camera to work, so I am having trouble taking a pic of the splice rodbolt wanted to see. I renewed all of my battery connections, and inspected the engine harness again. All looks OK. I tested the spark plug boots and 3 were bad. I could only get one locally, so I put it in. I have a trip to the dry tortugas next thursday that I have been planning for a year, so I am taking it to the mechanic. I will let everyone know what it was.

 

[scjmc]

Re: OX66 stals at high RPM!!!

Cousinabe--sorry to hear about your motor. I wonder if the oil transfer pump went bad (happened to me before) and the oil tank float was stuck.

 

[scjmc]

Re: OX66 stals at high RPM!!!

Well, the mechanic couldnt find anything wrong (figures). It worked perfectly the whole time he had it. We took our trip, but only went to the marquesas because of paranioa of the engine problem. We got out there (70ish miles) without incedent. The next day and the entire trip afterwards it would run fine, expept if pushed. If I gave it WOT it would start losing RPM and eventually stall. This is really annoying, but by staying conservative I was able to keep it running for the 4 days and 200 miles we were out there. I am still open to suggestions...

 

[rodbolt]

Re: OX66 stals at high RPM!!!

and I am still telling you to fix your fuel system BEFORE it runs lean and smokes a piston.
you either have a restriction, bad lift pumps or a clogged VST screen or possibly a bad fuel pressure regulator.
its simply running out of fuel, when it does the shutdown can be quite violent, almost like the key was switched off.
you will have to run it at the problem RPM with a fuel vacum guage tied in at the lower lift pump intake and the test guage connected to the fuel rail.
if it hasnt been done unscrew and gut the check valve between the engine filter and lower lift pump.

 

[ARCHSEA BUNKER]

Re: OX66 stals at high RPM!!!

check your fuel tank vent

 

[scjmc]

Re: OX66 stals at high RPM!!!

I will buy the proper test equipment and check vacuum and rail pressure when the problem occurs. It seems to be random. I removed the guts from the check valve as Rodbolt suggested in another post. The fuel tank vent is clear. I can easily blow into the fill and get air out of the vent.

 

[scjmc]

Re: OX66 stals at high RPM!!!

I finally resolved this issue. The O2 sensor was the culprit. It was intermitently sending false information to the ECU. It was telling it that the mixture was extremily lean even though it was not. The ECU would dump fuel into the motor at varying levels. Sometimes my fuel consumption would double. When the engine was running very rich it would vary RPMs, bog, and do other wierd stuff. This was very hard to track down because the O2 sensor always passed dock side tests because the problem only occured at higher RPM. Testing the sensor when the trouble was occuring was the only way to figure it out.