JB
Honorary Moderator Emeritus
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The following article was published as a reprint from a Bass & Walleye Boats<br />magazine article in Jan. 2000, and Trailer Boats magazine in Feb. 2000.<br /><br />The Association of Marine Technicians (AMTECH) reprinted it in a newsletter <br />a couple of years ago<br />with permission from the magazines and the author Bill Grannis, an AMTECH<br />member:<br /><br /><br />Whenever there is a gathering of boaters, the conversation usually turns to<br />engines, then gravitates to stories about problems. One of the bones OMC<br />owners like to pick concerns the oiling system. A typical conversation that<br />we've all heard at one time or another might go something like this:<br /><br />"Yeah, my boat smokes like the ****ens at low speeds and fouls the plugs,"<br />bemoans one boater. "Must be that worthless VRO pump acting up."<br /><br />"Uh huh, my neighbor had a blown engine," quips another. " Took out 2<br />cylinders on his V6. the mechanic told him the VRO went bad. He didn't get<br />an alarm or anything."<br /><br />"Come to think of it," the third member of the group chimes in, " my<br />brother- in-law's offshore rig with twin outboards must have a flaky VRO;<br />one motor always uses more oil than the other."<br /><br />"My engine is hard starting at times," says a fourth angler, "the VRO pump<br />must be getting weak and the warning horn blows constantly whenever I run at<br />full throttle on my 150."<br /><br />The truth of these stories is that none of the symptoms described is the<br />fault of the VRO, yet the poor VRO pump gets the blame. Each rig has a<br />different problem that is blamed on the oil pump because of misunderstanding<br />and misinformation. Even many "experienced" mechanics do not have the<br />knowledge of how the system operates and are quick to blame something that<br />is unfamiliar to them.<br />For instance, the first boat owner's problem is an air leak somewhere in the<br />boat's fuel system causing "foamy" fuel instead of a solid column of liquid.<br />This aerated gasoline has less volume and less resistance causing the fuel<br />pump diaphragm to cycle faster. Each cycle pulses oil into the foamy mix,<br />increasing the oil:fuel ratio to the carbs creating a smoky exhaust. The<br />mechanic of the second guy's neighbor did not understand that the VRO mixes<br />the fuel and oil internally then delivers the mixture through the fuel lines<br />to each of the carbs. Since each carb receives the same oil to gas ratio,<br />the VRO cannot cause only two cylinders to fail. Since the VRO did not<br />malfunction, there was no alarm to sound. On the other hand, the<br />brother-in-law's motors have two different year's pumps on them. The later<br />model VROs pump more oil at low speeds than the original ones do. The last<br />guy blames the VRO because he once had a car with a weak fuel pump and a<br />replacement cured its hard starting problem. Actually, he only needs a<br />refresher in the correct starting procedure. As for the constant sounding<br />horn at high speed that stops when slowing down, that's a fuel restriction<br />warning, not a VRO malfunction. A lack of oil flow is a pulsing on and off<br />horn every second or so. A decal is available (# 335707) for the dashboard<br />that illustrates the different warning signals and what they mean.<br /><br />A LITTLE HISTORY: OMC introduced the VRO on the V-4 and V-6 engines in 1984.<br />The pump consisted of a combination oil pump and fuel pump actuated by<br />crankcase pulses through an air motor. Gasoline reformulation in those early<br />years contained alcohols and solvents that softened the internal rubber<br />components and caused pump failures and damaged engines. Back then, no<br />company had alarm systems for a pump failure or loss of oil flow. OMC took<br />care of the blown powerheads and improved the pumps considerably.<br />The VRO2 was introduced in 1986 and included a "no oil flow" alarm. Changes<br />included an electronic circuit to compare the oil pulses with the engine's<br />rpm, a better oil pump piston, alcohol resistant seals, and a brown fuel<br />outlet for recognition. Unfortunately, the damage was done. Public<br />perception fed by uneducated mechanics put the blame for almost every engine<br />problem on the VRO. No matter what happened to a motor, someone would utter<br />".must be a bad VRO." Actually, the much-maligned pump is very simple and<br />reliable. It consists of four basic sections: the air motor, a fuel pump, an<br />oil pump, and a "no oil flow" alarm system. The air motor converts the<br />pressure and vacuum pulses from the crankcase to a linear motion. These<br />pulses are routed through a pair of check valves above the lower gray<br />fitting. One directs pressure cycles to one side of the air motor's piston<br />and an inverted check valve directs the vacuum cycles to the opposite side.<br />Each engine revolution moves the piston incrementally to one side of the air<br />motor chamber and compresses the large spring. When the piston nears the end<br />of its travel, a small spring unloads a poppet valve located in the middle<br />of the piston assembly. The pressure on one side of the piston rushes into<br />the vacuum side as the large spring quickly pushes the piston back to its<br />starting point. As the throttle is advanced, the pressure pulse gets<br />stronger because of the increased airflow through the crankcase. This back<br />and forth motion of the air motor's piston is what powers the fuel pump and<br />the oil pump. At idle and low throttle settings, the weaker crankcase pulses<br />cause shorter piston movements, which in turn, pump less oil with each<br />cycle. As the throttle opening increases, the stronger crankcase pulses<br />cause greater piston travel resulting in longer oil pump strokes. That<br />means, more oil is delivered increasing the amount of lubricant in the fuel<br />up to a 50:1 ratio. The fuel pump, which is located in the middle chamber of<br />the VRO, consists of a push-pull piston & diaphragm with a flapper valve and<br />an inlet check valve. A rod connects the fuel pump piston directly to the<br />air motor piston and the two chambers are sealed from each other by an<br />o-ring. As the back and forth motion is generated in the air motor, the<br />double-action fuel pump's piston & diaphragm is pushed and pulled by the rod<br />cycling fuel to the carburetors. Gasoline is drawn into the blue area of the<br />chamber, travels through the piston's flapper valve, and is pressurized in<br />the green section on the following stroke. The oil pump is directly<br />connected to the fuel pump piston and diaphragm so they work in tandem. As<br />with the fuel pump, oil is drawn in through the inlet fitting and a check<br />valve as the air motor starts its travel. On the return stroke, the oil<br />pressurizes, exits directly into the fuel chamber, and is blended while<br />enroute to the carbs.<br /><br />DISTINGUISHING VROs: Of all the traditional two stroke outboards produced<br />worldwide, OMC products have the only automatic lubrication systems with a<br />"no oil flow" alarm. The VRO's electronic circuitry compares the rpm of the<br />engine to the number of pressure pulses from the oil pump piston. As the oil<br />flows into the fuel area, the pressure moves a small piston that actuates a<br />steel pin in the alarm module. The pin's movement is detected electronically<br />and "counted." If the engine revolutions exceed the preprogrammed oil pulse<br />ratios, the warning horn is activated sounding a rapid on and off sequence.<br />Since 1993, the VRO is actually called an oil metering system (OMS). The<br />ratio averages about 60:1, slightly leaner at idle and slightly richer at<br />full throttle. The older pumps idled between 150:1 ( prior to 1990) and<br />100:1 ('90-'92 ) then richened up to 50:1 as the engine load increased. They<br />are recognized by the brown fuel outlet fitting and/or a wiring harness<br />attached to the alarm module. The original VRO from '84 and '85 had a black<br />fuel outlet fitting and no wiring. OMS pumps have a blue/gray outlet nipple<br />or a blue/gray pulse nipple, or a black fitting held in place by an oval<br />metal bracket and two Torx headed screws. To simplify things just remember<br />that the air motor converts the crankcase pulses to a back and forth motion.<br />Directly connected to the air motor is the fuel pump and the oil pump. The<br />travel of the air motor pumps the fuel and the oil together to the<br />carburetors and the alarm system monitors the oil pressure counts. Just like<br />manually premixing the oil and gas, the VRO (OMS) automatically does the<br />same thing and sends that fuel mixture to the carburetors.<br /><br />PREVENTIVE MAINTENANCE<br />There is no mechanical maintenance that has to be performed on the pump<br />itself, but the VRO system should be inspected occasionally for cracked<br />lines, leaks, and broken clamps. One of the most common causes of engine<br />failure is water in the remote oil tank. Condensation and spray can build up<br />over time and, like water in a fuel tank, it stays on the bottom to be<br />sucked up at the worst possible moment. Water pumps through the system as<br />easily as oil, so several time a year use a turkey baster to draw off some<br />fluid from the base of the tank and squirt it into a clean jar. Look for<br />sediment or water settling to the bottom of the container. If you see any<br />signs of contamination, the tank should be flushed clean, the filter<br />(#174377) changed, and the oil line purged. Be sure to read and understand<br />the service manual before doing any of these procedures. If an oil tank is<br />exposed to the elements such as in an open boat, installing the tank inside<br />a covered battery box will protect it from spray. You can also replace the<br />clear plastic cap with the later model's solid black filler cap (#176217)<br />that provides much better water intrusion resistance. The oil line should be<br />OMC's ¼-inch I.D. inner "rubber" hose (#333485) without any splices. Early<br />systems had a smooth vinyl oil line that hardened after a few years and<br />sometimes caused air leaks. (Some installations even had 5/16-inch fuel line<br />squeezed down over the smaller fittings.) These air leaks can also trigger<br />"no oil" alarms, commonly at startup, idle, and trolling speeds.<br />Another service tip is to avoid Ty-raps or worm gear hose clamps on this<br />system. The ratchet clamps ( #322654) give the best seal and full 360-degree<br />clamping action. Late-model OMCs use a double-wire wound spring clamp<br />(#339277) that also works well in keeping lines air tight. Air leaks and/or<br />fuel restrictions will affect the VRO and usually show up as excessive oil<br />consumption, smoking, and fouling plugs. If air gets into the fuel, it<br />causes a foamy solution, similar to a head of beer in a tall glass. ( A<br />vapor lock situation does the same thing ). The volume of liquid fuel is<br />less and the oil delivered is the same as for a full chamber of fuel. Now<br />you have richer gas oil mix with its resulting symptoms. A fuel restriction<br />such as from a bad anti-siphon valve, kinked line, or a partially plugged<br />filter does not allow a full charge of gas to be drawn into the fuel pump<br />cavity. Again, you get the full shot of oil mixing with less gas. This is<br />also the reason to /not/ disconnect the gas line and run the engine "dry".<br />As you run out of fuel, the oil still pumps, filling the lines and carbs<br />with your favorite TC-W3 lubricant. Since the VRO depends on crankcase<br />pulses to operate, it is susceptible to backfires from a lean running<br />cylinder or an out of tune engine. If your motor is older than a 1993, make<br />sure it has the blue colored pulse limiter to protect the air motor and the<br />check valves in the pump. Follow the pulse line from the VRO to the engine<br />block and look for a hex shaped fitting threaded into the crankcase. If it<br />has a black face on it, replace it with a blue style (part # 435009). The<br />crossflow V-6s have a pulse limiter with a fitting at each end and spliced<br />in line with the VRO to crankcase hose. The inline replacement is part #<br />435010.<br />Since 1986 (and on updated '84s & '85s), the pumps have an alarm system that<br />operates off the alternator or tachometer circuits. Occasional checks should<br />be performed to make sure the charging system, warning horn, and related<br />parts are operational. The quickest and easiest test is the grounding of the<br />tan overheat temp switch wire to the engine block. To do this, turn the key<br />on, motor not running, and use a jumper wire to ground the tan wire from the<br />motor harness and listen for the warning horn. It should be a loud steady<br />tone. On 1996 and later engines with a SystemCheck® gauge, only the "hot"<br />light will come on, but no horn unless the motor is running. With the<br />SystemCheck® equipped motors you will have to disconnect the OMS (VRO) four<br />wire connector and carefully ground the tan motor harness wire lead to<br />illuminate the "no oil" light. The warning horn tone sequence tells if a<br />problem is occurring while operating the engine. A rapid on - off sound is a<br />"no oil flow" indication. One beep every 20 to 40 seconds is a low oil level<br />in the remote tank. Of course a steady tone at all speeds is an overheat<br />condition. On V-6s a constant horn at high speeds that disappears instantly<br />when the throttle is pulled back indicates a fuel restriction. Loose<br />connections can also cause erroneous "beeps" and the most common open<br />circuits are battery cables with finger tightened wing nuts instead of<br />stainless steel hex nuts and lock washers tightened with a wrench. Incorrect<br />spark plugs occasionally cause false warning signals, too. Use only the "Q"<br />style suppresser plugs recommended by OMC for your motor. Resistor plugs are<br />not the same thing and may be the source of problems. The factory does not<br />endorse spark plug manufacturer's conversion charts.<br /><br />SYSTEM UPGRADES: In 1996, the SystemCheck® warning gauges were introduced. A<br />tach with four warning lights or a dash-mounted gauge with the same lights<br />show the type of malfunction that is occurring by which LED is illuminated.<br />The horn sounds for 10 seconds when a fault occurs and the proper light<br />stays on until the problem is corrected. There are indicator LED's for<br />overheat, no oil, low oil, and check engine, which means a fuel restriction<br />in a V6 carbureted motor. By the way, the SystemCheck® can be adapted (with<br />accessory kit # 176709) to any engine with a four-wire VRO pump. Even<br />better, there's a new VRO (OMS) pump that can be used to upgrade all the<br />previous years and model outboards. The new pump (# 5004558) contains <br />various<br />fittings for different outboards, and each internal part is replaceable for<br />easier and less expensive servicing. Part number #5004559 updates all early<br />three-wire VROs except those found on the two-cylinders. For those<br />outboards, kit # 5004562 is used. OMC also makes a wiring harness adapter (#<br />174710) for the 1984 and 1985 engines that did not have any warning systems.<br />Each OMC (VRO) kit contains the parts needed including a new pulse limiter<br />to install the system correctly.<br />So, contrary to boat ramp banter, VRO is a simple and reliable oiling system<br />that has been standard equipment on most OMC outboards from 40 to 300<br />horsepower for the past 16 years. Most of the misinformation and "scare<br />tactics" about its reliability originate from those who do not understand<br />how the system works-or fail to keep it maintained.<br />SERVICING: Since 1991, the OMC factory service manuals include a<br />troubleshooting chart and a section on how to test, take apart, and service<br />the VRO pumps. Besides Torx screwdrivers, you will need a pressure and a<br />vacuum source to test the integrity of the check valves and diaphragms. CDI<br />Electronics' #551-34PV gearcase vacuum/pressure tester work well, as does a<br />SnapOn YA-4000 or the old Stevens pumps.<br />Even though they are not listed in the parts catalogs, most of the<br />diaphragms are interchangeable. The air motor diaphragm kit is part number<br />435921 and the fuel pump repair kit is 436095. For those who premix their<br />fuel and oil, these kits allow the repair of the fuel pump section, avoiding<br />the high cost of a new assembly or the replumbing and rigging of one or two<br />traditional style fuel pumps.<br />Do not interchange any of the springs with other pump assemblies. They are<br />calibrated for each model of pump. The latest<br />#5004558 pump is a universal fit<br />that can be used as a replacement for all VRO equipped motors and each part<br />is available for servicing.<br />When working on a customer's fuel system, check for any restrictions or air<br />leaks which would affect the engine. You can use a clear piece of fuel line<br />connected to the VRO inlet and "Tee'd" off to a vacuum gauge. Run the motor<br />at all speeds while inspecting for air bubbles in the line and for any<br />vacuum restrictions above 4" Hg. A system with 3/8" fuel lines, a clean<br />"spin on" filter, and a quality anti-siphon valve should show between 2.5"<br />to 3" of vacuum at full speed.<br />Doing a thorough job the first time avoids expensive and sometimes highly<br />emotional "comebacks", keeps the customer happy, and makes your reputation<br />the best advertising there is.