86 Johnson 150 Sudden Loss of RPM

[Devchad1]

I've got a 86 Glastron with a 150 Johnson VRO V6 motor.
The problem I'm having is that while cruising at WOT it will suddenly all but die until I back the throttle off to idle. It will idle fine but as soon as I try to apply any throttle it tries to die again. Sometimes if I put it in neutral and free rev it it will rev up fine but as soon as I drop into drive it falls on its face again. Most of the time if I just let it idle in drive and just putt around it will eventually start working again, about 10-20 minutes. The compression is good, 100-105 across the board, new plugs, new fuel filter, fresh 92 octane fuel, etc.

Anyone have experience with this or any ideas what ay be the problem.

I don't get the VRO alarm when this happens but a few things I've seen on the web talk about the VRO possibly causing issues similar. I'm not opposed to disabling the VRO and premixing but if that's not the problem years of riding 2 stroke bikes and premixing makes the oil injection seem pretty nice.

Any suggestions would be greatly appreciated.

 

[Joe Reeves]

Re: 86 Johnson 150 Sudden Loss of RPM

The warning horn should beep just once when you turn the key to the ON position. Does it?

Test the horn by having the key in the ON position (engine not running), then ground out one of the TAN wires (heat sensor) you see protruding from the cylinder heads. The horn should beep constantly. Does it?

How long does the engine run normally after the initial starting procedure... (priming the fuel primer bulb up hard, cracking the throttle slightly, cranking the engine while pushing the key in, etc)?

Have someone constantly pumping the fuel primer bulb, acting as a manual fuel pump when this problem exists. Does this pumping action cause the problem to cease? If so, rebuild or replace the VRO pump.

 

[Devchad1]

Re: 86 Johnson 150 Sudden Loss of RPM

Joe,

The answer to your first two questions is no, no beep or constant buzz.

To your third question, I assume you mean once it starts will it continue to idle fine, if so yes, when I first start it I usually let it idle for 5 minutes or so to warm up before I leave he dock. Other wise the problem is very irratic, sometimes it will run all day with no problems other times I barely get off the dock before it falls flat. It usually happens whet I'm WOT but has occasionally happened at partial throttle.

I have tried pumping the fuel primer ball as well as the oil primer ball but have not seen any change or improvement. I have replaced the fuel primer ball and fuel lines.
The fuel primer ball does not collapse or seem unusually soft when the problem occurs.

 

[Joe Reeves]

Re: 86 Johnson 150 Sudden Loss of RPM

With the engine NOT running but with the key turned to the ON position, ground out one of the TAN wires (heat sensor) that you see protruding from the cylinder heads. Thhat should make the horn sound constantly.

Are you using the common white OMC control box that would have the warning horn secured inside OR do you have some console type control whereas the horn would be hanging off the wiring harness under the console?

 

[Devchad1]

Re: 86 Johnson 150 Sudden Loss of RPM

Followed your instructions exactly, tried both wires but no sound.

I believe it is the standard white OMC box. I am the second owner of the boat and the original owner did know mods that I am aware of.

 

[Devchad1]

Re: 86 Johnson 150 Sudden Loss of RPM

If it means anything the tach has been acting irratically for a whil also. I'm not sure if it's related or not.

 

[Joe Reeves]

Re: 86 Johnson 150 Sudden Loss of RPM

Followed your instructions exactly, tried both wires but no sound. I believe it is the standard white OMC box. I am the second owner of the boat and the original owner did know mods that I am aware of.

The warning horn would have anything to do with the engine falling on its face (unless it's overheating) BUT you do need to have it functional. Perhaps the previous owner eliminated it for some reason (bad move).

Find out why that warning horn isn't working as it is the only warning you'll receive (3 different warnings) if the engine overheats, has a fuel restriction, the oil level goes low, loses oil feed at the VRO.

 

[Devchad1]

Re: 86 Johnson 150 Sudden Loss of RPM

I'll look into that this weekend. Would any of the symptoms that trigger the alarm also trigger what's happening?

 

[Joe Reeves]

Re: 86 Johnson 150 Sudden Loss of RPM

I'll look into that this weekend. Would any of the symptoms that trigger the alarm also trigger what's happening?

Yes..... Overheating = Engine starts to seize..... Loss of oil at VRO = Seizing..... Fuel restriction = Not enough fuel for the rpms.

 

[Devchad1]

Re: 86 Johnson 150 Sudden Loss of RPM

Found the warning buzzer problem, the buzzer itself was melted down! I removed the buzzer and used my multimeter to check for voltage across the tan and purple wires that were connected to the buzzer. I got 12 volts when I shorted the temp sensor wires at the heads. Strangely the voltage didn't immediately drop when the short was removed. It instead slowly bled off.
Is there a capacitor in the warning system wiring that would cause this? Is this normal?

 

[Joe Reeves]

Re: 86 Johnson 150 Sudden Loss of RPM

Someone had a problem where the horn was sounding constantly and was ignored, and finally it simply got hot enough to melt down. I assume the problem still exists.

No capacitor that I'm aware of other within the electronic connected components.

When the short was removed? I assume you mean that the meter wires were still connected across the TAN (Sensor) and PURPLE (12v Source) and that you simply disconnected the TAN wire from its ground point at the powerhead?

If so, yes, that voltage would still be present momentarily in the wiring harness and the electrical and electronic components however they're attached. I've never checked the wiring in that fashion but I can understand it would have a bleed off factor. I wouldn't be concerned about it.

 

[Devchad1]

Re: 86 Johnson 150 Sudden Loss of RPM

Joe,

Ok, now that I know that at least the overheat warning should be working what would be the next trouble shooting step?
I did run a compression test and it was lower than I originally thought but it is still 90 across the board with less than 1 variance.

 

[Joe Reeves]

Re: 86 Johnson 150 Sudden Loss of RPM

If all of the head bolts are tight (18 to 20 foot pounds, tightened in the below sequence)... no water is entering the cylinders... the compression is as it should be... and with the spark plugs removed, the spark jumps a 7/16" gap with a strong blue lightning like flame, a real SNAP!... then due to the problem being intermitent, it's possible that the timer base (spark advance) under the flywheel is sticking in the retarded position occasionally.

Torquing head bolt sequence is:

13..14
9....10
5.....6
1.....2
4.....3
8.....7
12..11

Unlikely it is a carburetor problem as carburetors do not come and go.... they are either okay or they are not UNLESS something is floating around in the fuel lines and jamming the float needle valve from time to time OR being drawn into one of the high speed jets.

Is water present in the oil tank.... in the oil line at the VRO?

Hesitation when applying throttle is normally caused by:

Fouled carburetors, clogged high speed jets.
Throttle butterflies opening too soon (not synchronized).
Timer base sticking.

Should you decide to convert back to premix............

(VRO Changeover Judgement Call)
(J. Reeves)

The VROs first came out in 1984 and have been upgraded quite a few times. In my opinion, back around 1988, they had perfected them but I think that they were upgraded even more since then. As long as the warning system is operating as it should, I feel quite at ease with them.

Some boaters have voiced their thoughts such as "What if that overpriced plastic horn should fail while I'm under way for some reason, and the VRO decides to fail five minutes later?" Obviously that would result in a big problem which really brings their fears into view.

The word "ease" is the key word though. If one has the slightest feeling of being ill at ease with that setup, then they should take the route they feel more at ease with. A judgement call each individual would need to make on their own.

********************
(VRO Pump Conversion To Straight Fuel Pump)
(J. Reeves)

You can convert the VRO pump into a straight fuel pump, eliminating the oil tank and VRO pump warning system, but retain the overheat warning setup (and fuel restriction warning if so equipped) by doing the following:

1 - Cut and plug the oil line at the engine so that the oil side of the VRO pump will not draw air into its system. Trace the wires from the back of the VRO to its rubber plug (electrical plug) and disconnect it.

2 - Trace the two wires from the oil tank to the engine, disconnect those two wires, then remove them and the oil tank.

3 - Mix the 50/1 oil in the proper amount with whatever quantity fuel you have. Disconnect the fuel line at the engine. Pump the fuel primer bulb until fuel exits that hose with the tint of whatever oil you used. Reconnect the fuel hose.

That's it. If you want to test the heat warning system to ease your mind, have the key in the on position, then ground out the tan heat sensor wire that you'll find protruding from the cylinder head. The warning horn should sound off.

And here's the warning horn's various sounds................

(VRO Horn Warnings)
(J. Reeves)

NOTE: I retired around 1991/92. Possibly some of the later V4 engines and others may also incorporate a fuel vacuum switch that would enable a fuel restriction warning to sound as mentioned below, an unknown factor to myself.

1 - A steady constant beep = Overheating - The V/6 engines, possibly some others, have a fuel restriction warning which is also a steady constant beep.

2 - A beep every 20 or 40 seconds = oil level has dropped to 1/4 tank. (Late model engine = Every 40 seconds)

3 - A beep every other second = VRO failure, air leak in oil line, oil restriction, (anything that would result in a lack of oil being supplied to the engine).

NOTE - If the warning horn is the black plastic (overpriced) three wire type horn, the warning horn should beep once when the ignition key is turned to the ON position. If it does not, it is either faulty or someone has disconnected it (a stupid move!). At any rate, if it does not beep which indicates that the horn is non functional, find out why and do not run the engine until the problem is corrected.

 

[Devchad1]

Re: 86 Johnson 150 Sudden Loss of RPM

Joe,

A little more info/discovery this weekend.
I replaced all the fuel line from the bulkhead transition into the engine housing and the fuel filter (although the existing filter was very clean) and as I was replacing the lines I found that the 3/16 line routing from the 'T' in the fuel line between the filter and the pump to I believe the fuel pressure sensor?? was leaking moderately at the T fitting.

I could not find a replacement buzzer so for now I found a very bright red 12v dc led light and mounted it right in the dash where I could see it well and extended the wires from the buzzer location to the dash. This seems to work well and the light passes all the tests you had me do earlier to check the buzzer.

Took the boat out afterwards and found the problem still existed but not as bad as before. After I put in I let it idle for a couple minutes then eased away from the dock at light throttle. As I was going I gradually eased up to eventually WOT (about 5 minutes) and started a hot lap around the lake. At about 3-5 minutes at WOT it hesitated a couple times (2-3 second hesitations) then dropped to an idle with the same symptoms. After about 2 minutes and a little free revving of the motor I was able to get it going normal again just for it to do the same thing about a minute later. I followed the same procedure as the first time to get it going again but this time I only went to about 1/2 to 2/3 throttle just to see what it would do. This time I was able to make 3 laps around the lake with no problem at all the I increased to WOT for another 2 laps still with no problem. Stayed out for another 2 hours (stopped and motor off for about an hour and half) the idled out the no wake zone (about a 5 minute trip) then went to WOT for 2 more laps and experienced no problem again.

Does this sound to you like a timer base issue or just simply a fuel issue, I.e. dirty carbs or a choke possibly malfunctioning?

Thanks in advance for your help

 

[Joe Reeves]

Re: 86 Johnson 150 Sudden Loss of RPM

Weird intermitent problem like that will drive one nuts. Carbs must be okay of it would never run at full throttle to begin with. Primer solenoid (replaces choke) either works or it doesn't but check for leaks. If engine hits full rpms, the timer base is at full spark advance BUT check it for intermitent sticking anyway.

Check s/plugs for water deposits.... water in fuel or oil tank.... intermitent fuel restriction somewhere. At the moment, I can't think of anything I haven't already stated.

 

[clanton]

Re: 86 Johnson 150 Sudden Loss of RPM

Try this, boat in water 3/4 to full throttle, as boat comes up on plane and gets up to speed. Touch the trim up button for a few seconds, if engines misfires or surges the stator is bad. Use meter to verify stator is defective.