250hp Ox66 Problem / Sluggish, HIGH Fuel Burn Rate

[John_Madison CT]

Hi Guys ! It's been a long time. I lost the password to my old account so I had to re-register. No big deal.

Well, it looks like I finally have a problem I need all your help to solve.

Engine: 2002 250hp Ox66.
Hours: Approx 300.

Up until yesterday, the engine always ran perfectly.


While cruising out of the harbor I noticed that my Navman fuel flow gauge was showing higher than normal fuel burn. For example, at 4500RPM's I normally do not burn more than 15gph, but today it was reading close to 20gph. Otherwise though, the engine seemed to run fine.

When coming home from fishing, it felt as though the boat was being held back by something. I needed to advance the throttle more to get cruising RPM's. Now I noticed that the Navman was showing ALOT of fuel burn. It would fluctuate and show at least 50% higher than normal.

I was confused as to whether the Navman was bad or something with the engine.

At one point the engine RPM's kind of "broke free" and ran much better. I panicked and throttled back to idle and the engine stalled. (again this engine has always run perfectly and never ever stalled)

I sat there for 10 seconds, restarted the engine and came home. Once again, I noticed that the fuel burn rate was higher than normal.

Back at the dock I checked all the spark plugs, all were normal (no metals filing thank GOD. I replaced with new anyway). I also took out the O2 sensor and checked that. The transfer tube was clear, some gooey carbon, but the hole was fine. The sensor may need a cleaning, which I'm going to do, but this was not an obvious problem.

So, what to do next? What would cause the engine to feel sluggish and cause excessive fuel consumption??? Could it be bad low pressure fuel pumps? Clogged VST?


Thanks guys.


John

 

[John_Madison CT]

Re: 250hp Ox66 Problem / Sluggish, HIGH Fuel Burn Rate

C'Mon guys, help a brutha out.....

 

[Ray Neudecker]

Re: 250hp Ox66 Problem / Sluggish, HIGH Fuel Burn Rate

John, I am not an expert on the Oxy 66, but the increased fuel consumption and loss of power would indicate a fuel restriction or stuck injector. What did the plugs look like when you removed them?
What service has been done on the engine in regards to the pumps, Vst tank filter,ect?

 

[John_Madison CT]

Re: 250hp Ox66 Problem / Sluggish, HIGH Fuel Burn Rate

Ray: The plugs looked fine. No excess oil, metal filings or anything unusual.

No doubt, the O2 sensor is overdue to be cleaned, the VST filter done and the Low Pressure pumps. I will do all of these, then report back if I still have a problem.

What do you know of the TPS sensor? It's been suggested that this could be it.


John

 

[Ray Neudecker]

Re: 250hp Ox66 Problem / Sluggish, HIGH Fuel Burn Rate

TPS is basically a variable resistor which can be checked with an ohm meter. Not too likely to be the cause. Check for a smooth change when moving the arm.

 

[John_Madison CT]

Re: 250hp Ox66 Problem / Sluggish, HIGH Fuel Burn Rate

Guys: I installed a new(used) 02 sensor. ( I bought one off a guy on www.thehulltruth.com a year ago or so) and it seems to have fixed the problem.

I will only fully trust it after a few trips as I don't know if this is an intermittant problem.

Nonetheless, I'm a happy camper right now.

John

 

[John_Madison CT]

Re: 250hp Ox66 Problem / Sluggish, HIGH Fuel Burn Rate

This is kind of ironic, but nearly a year to the day, 2008 vs. 2007, the same exact thing happened to me yesterday.

The engine was very sluggish, low idle, couldn't get her above 4500RPM's and I noticed on my Navman Fuel Flow meter that my fuel burn was very very high. (20GPH when it's normally 13gph @ 4200RPM's).

As you see in the post above, a new O2 sensor fixed my problem last year. For now, I'm going to pull it, take a look. (last year it wasn't clogged) I will also do a VST filter change and low pressure fuel pumps as they are both somewhat overdue.