New OMS (VRO) pump, odd mix ratio?

[d.boat]

Hi: this could be a very unusual problem as I posted the same question on another forum and nobody with any experience with this responded. So here goes...

The short version: Brand new OMS fuel pump, oil seems to be mixing at 80:1 rather than what I would expect (50-60:1). Have run about 20 gallons through it, and burned only 1 quart of oil. (I'm also pre-mixing at 50:1 until new pump operation is verified).

Long version:

This a 1990 low hours 200 HP V6. J200txesm

I just replaced the original VRO2 fuel pump with a brand new, current OMS pump and updated the oil tank and all lines, pick up filter and pulse limiter. The old pump was working fine, but I decided that since I use this engine in remote places, I'd just go ahead and update the fuel pump and oil system.

It really was not a difficult job, very straight forward, and I used an OEM shop manual, proper fasteners, torque wrench when called for, etc.

All oil system hose connections are with the correct ratchet type clamps, and they all appear to be air tight. I purged the air out of the oil line and collected about 1/2 pint in a jar before I connected it to the fuel pump.

I've tested the "no oil" and "low oil" alarms and both work properly, sounding when appropriate, stopping when appropriate.

I marked the oil tank in 1 pint increments as I was filling it for the first time (from quart containers) and have been monitoring on that basis.

The engine is running perfectly: starts easy, idles smoothly, accelerates well and runs around 5800 RPM at wide open. No alarms. It really is a nice running engine and I'm very happy with the way it runs.

The odd part is that the oil seems to be mixing at about 80:1 running at 3/4 to full throttle. My understanding is that the OMS pump is supposed to be close to 50 or 60:1 at all RPM's. Over the past week or so, I've run about 20 gallons of the pre-mix gasoline and it's burned at most about 1 quart of oil.

My measurements, while good, aren't perfect. I can measure fuel consumption to the nearest gallon or two, and the oil consumption within an ounce or two.

So the gas consumption could be 18-22 gallons, let's say, the oil 30-34 ounces. That would be high (worst case) ratio of 93:1, low (best case) ratio of 67:1.

But it's not 50 or 60:1 or even close to that.

What's going on? What should I check?

I've double checked the lines and everything seems good. Like I said, the engine runs like a complete champ.

Thanks.

 

[galamb]

The little bit of information I have from OMC states that the OMS system mixes at an "average" of about 60:1 - slightly leaner at idle and slightly richer a WOT.

They just don't define "slightly" - but 80:1 at 3/4+ throttle doesn't quite sound correct - the mix rate usually drops (like into the 50:1 range) at higher rpms for every other oiler out there.

Unlike the OMS data, my 1986 Johnson brochure, the year they introduced the VRO2 with the alarm system gives the mix rate range of between 50:1 and 150:1

You should be able to obtain flow rate data from BRP and then use a pre-measured oil charge in a clear plastic tube to feed the pump and then just time how long it takes to consume it at a given rpm to determine if it's "eating properly"...

 

[dcramer]

There is a procedure in the manual that details marking off a clear hose with a sharpie and measuring how much oil is used after a couple pulses of the pump. I like your method of measuring though. I too marked off my tank in 1 pt increments. The suggestion I would make is to try a portable 6 gallon fuel tank if you have access to one. That way, your fuel consumption can be detailed much more closely. If you can document the pump is out of spec, the dealer should be able to warranty the pump for you.

For what it's worth, I've never seen a pump consistantly run a leaner than normal mix. If you disconnect the oil line and run premix, the oil pump will fail from running dry. It tends to mix an inconsistant ratio in that case.

There isn't a fourstroke kicker sucking additional fuel from the tank or some other explanation of fuel loss is there? Not trying to insult-Just trying to cover all the possibilities no matter how remote.

 

[d.boat]

Re: SOLUTION!? New OMS (VRO) pump, odd mix ratio?

Thanks for your comments this afternoon guys.

Today I just did a very careful measurment of fuel and oil (boat perfectly level) and ran 14 gallons of gas through it. I burned 34- 35 ounces of oil (measured), therefore a mix rate of 50-55:1. CLOSE ENOUGH, especially what the spec of the pump, as mentioned above, is indeed: 60:1 average, leaner at idle, richer at wot.

By the way, after today, I'm very confident that my earlier measurements were reasonably accurate and the odd mixture rate I got was accurate, probably closer to 100:1 than 50:1.

Why you ask did it change from the much higher ratio (too little oil/gallon)?

Today I looked at the oil tank installation. I thought: there's a lot of curves in that line in a short distance, I wonder if the oil flow would be restricted enough to "starve" the oil side without actually causing an alarm?

The line was about 4-5 feet long. None of the curves was really sharp, but it did a 90 upwards to the transom (~5 inch radius), then a similar 90 to run along the transom, then a big sweep 180 (12+ inch radius) to reverse direction to join the fuel line up to the engine.

I changed the tank installation to the other (starboard) side and made the run of the oil line as straight and smooth as possible. Re-checked all connections, re-purged.

I took it out and ran it 3/4 to full throttle for a little over an hour and got the above excellent results! I plan to run one more tank of 50:1, but am confident that I'm good to go.

So I think the lesson for posterity is that it appears that it is possible to rig the oil line in a way that the OMS/VRO pump is starved for oil, but not enough to sound the alarm. Just a reason to keep rough track of the burn ratio w/ every fuel and oil fill up.

 

[galamb]

That's an interesting assumption - something I might play around with sometime when I'm bored (moving the oil tank around) to see if it makes a measurable difference

 

[d.boat]

That's an interesting assumption - something I might play around with sometime when I'm bored (moving the oil tank around) to see if it makes a measurable difference

Yea, I was surprised that what I did solved the problem. I really wish I'd taken a photo because I'd be interested in hearing from the experts if the way I had it set up was obviously a problem.

The oil line was not a ridiculous twisty thing. It was not kinked. In 4-5 feet it had two 90 degree turns within the first couple of feet with a reasonable (to me anyway) radius and then a 180 degree turn with an even more gradual radius, a real sweeping turn. Nothing that I would ever think twice about w/ a fuel line. And, in re-reading Bill Grannis' article and the OEM service manual, understanding that there should be no kinks, etc, I see no special warnings about being super careful to minimize turns in the oil line.

But I made the change and the oil consumption changed from 1/2 to 3/4 of what it should have been to right on. And, I'm confident that my earlier measurements were reasonably accurate with the above + and -.

Just an interesting story about the little things that can mess you up and can be very easy to fix.