Ox66 stalls under load at idle

[slcarley]

1997 - port side engine stalls under load at idle - runs great otherwise - trying to limit the trial and error approach to figuring it out!!

 

[DennisG01]

I assume you mean when "idling in gear" it stalls? But it idles in neutral OK? Boy, this could be any number of things and more info would help. "How" does it stall - like someone flipped a switch? Gradually? Could be electrical, sensors, fuel. Do both engines pull from the same tank? What have you done/checked so far?

 

[slcarley]

I realized after posting I was light on details!!
- both engines draw from the same tank
- eventually the port side will stall in idle after the engine warms up and the rpms drop
- turns off like a switch under load, generally when I am trying to dock and bump in and out.
I haven't tried anything yet
- fuel filters are recently changes
- low pressure pump were changed out last year (or so I'm told)
I've heard
-could be ox sensors
-could be low pressure pumps
-could be vst filters
I'm hoping for a systematic approach to determine the issue. I've often overlooked the simplest answer - like replacing my starter rather than triple checking the electrical connection

Thanks for the quick response!

 

[seasick]

I realized after posting I was light on details!!
- both engines draw from the same tank
- eventually the port side will stall in idle after the engine warms up and the rpms drop
- turns off like a switch under load, generally when I am trying to dock and bump in and out.
I haven't tried anything yet
- fuel filters are recently changes
- low pressure pump were changed out last year (or so I'm told)
I've heard
-could be ox sensors
-could be low pressure pumps
-could be vst filters
I'm hoping for a systematic approach to determine the issue. I've often overlooked the simplest answer - like replacing my starter rather than triple checking the electrical connection

Thanks for the quick response!

 

[seasick]

I doubt O2 sensor
VST problems usually start at higher revs not low
You need to check fuel pressure at the high pressure side of the pump. The pressure regulator could be bad.

Does the motor 'sneeze' or just die?

 

[DennisG01]

It could be a number of things, but what comes to mind...

-- Fuel line. Does the on-engine filter stay about 2/3 full? Doubtfull it's the VST pump as I think you'd have issues at other RPM's. Don't think O2, either.
-- TPS or possibly throttle body is out of sync. The computer is looking for a certain value from the TPS, but I am not positive if it will, in fact, cause a stall.
-- Could be a flaky neutral position switch.

TPS and NPS can be swapped from one motor to the other. Can also swap fuel lines - but if engine filter stays full, the issue is not fuel to the engine.

Does it EVER idle at a normal RPM (700-ish, I think)?

You might want to get a service manual - they're relatively cheap and they have good info it it. Especially if you're planning on doing your own work.

 

[seasick]

It could be a number of things, but what comes to mind...

-- Fuel line. Does the on-engine filter stay about 2/3 full? Doubtfull it's the VST pump as I think you'd have issues at other RPM's. Don't think O2, either.
-- TPS or possibly throttle body is out of sync. The computer is looking for a certain value from the TPS, but I am not positive if it will, in fact, cause a stall.
-- Could be a flaky neutral position switch.

TPS and NPS can be swapped from one motor to the other. Can also swap fuel lines - but if engine filter stays full, the issue is not fuel to the engine.

Does it EVER idle at a normal RPM (700-ish, I think)?

You might want to get a service manual - they're relatively cheap and they have good info it it. Especially if you're planning on doing your own work.

I thought about the neutral switch but I believe that blocks the starter (solenoid) signal and not general ignition power.

I know first hand that a low idle setting will cause the motor to stall but the moor always shudders and/or sneezes before stalling.

 

[slcarley]

Thanks for all the tips - it idles at 800 no issues, once dropped into gear the idle drops to 600 and that's when it dies. On engine filter stays 3/4 full always - not sure if it sneezes or not...................

 

[DennisG01]

You'd know it if it sneezed - it's an obvious sound.

I wonder if the throttle plates are out of sync. I think it's referred to as a "sync and link"... or something like that. That might be a good place to start to make sure they're all opening at the right time. It takes less to idle - so once you put it in gear, there's more stress on everything.

 

[seasick]

Just to eliminate one possibility, can you rotate the prop easily when the motor is in neutral (and not running of course)

Also, does it stall if shifted in reverse as well as forward?

That motor runs on 4 cyls at low revs. Make sure that you have spark to those 4. Use a spark tester, pretty cheap at Harbor freight. You may have an ignition issue I cant remember which cylinders turn off at low revs but if you test all 6, one by one. 2 should have no spark. If more than 2 have no spark or wear spark, that is the place to start looking for the cause.

 

[slcarley]

Thanks again for all the input

Prop turns freely in neutral, engine dies in both forward and reverse!!

I'll check spark this weekend

 

[DennisG01]

FYI, I think (please double check me) that at idle speeds it's the #2 cylinder that doesn't have spark. And then within a few hundred RPM's on either side of 1,500 it's both #2 and #5 that are deactivated.

 

[SkunkBoat]

You have the problem when shifting at idle speed but not if you "gun" it?

What happens if you just throttle up in neutral without shifting?

 

[slcarley]

Skunkboat

Only stalls under load when I bump it in and out in both reverse and neutral, throttles up no problem in neutral and underway.

 

[SkunkBoat]

I'm new to my Ox66s but I would probably try swapping the Throttle Sensor Assy from one motor to the other. Or spraying the crap out of it, if that's possible.

As guys have said, there is a weird thing where it purposely doesn't fire all cylinders when at idle and not in gear
Not sure what combination of sensors tell the cpu to fire all, and when....

I doubt its a fuel problem if you can rev it up & down in neutral no problem.

 

[seasick]

I have been thinking about this problem and am really interested in what it turns out to be.
I am leaning towards ignition or lack of. If it were fuel delivery, I would expect it to die slower and probably 'sneeze'

It seems that the motor has some sort of neutral switch that tells the ECU that the motor is in or out of gear and that info is used in the activation/deactivation of some cyls at idle and lower speeds.
If there is a switch, it should be on the snifter linkage side of the motor and would have a mechanical connection to the shift level and a wire connector.

 

[Andrew93]

I would still check the low pressure fuel pumps. Unbolt them from the block with the hoses still connected and hit the primer, if fuel is leaking the pump is bad. I have had an OX66 with a clogged O2 sensor tube but it was searching for rpms at higher speeds. From everything I have always read on the OX66's if you think its an electrical issue, check the fuel system again!

Curious to see what you find out

Andrew

 

[seasick]

I would still check the low pressure fuel pumps. Unbolt them from the block with the hoses still connected and hit the primer, if fuel is leaking the pump is bad. I have had an OX66 with a clogged O2 sensor tube but it was searching for rpms at higher speeds. From everything I have always read on the OX66's if you think its an electrical issue, check the fuel system again!

Curious to see what you find out

Andrew

I can't see how bad lp pumps would allow a normal idle but not a normal idle in gear.
If the O2 were clogged, the motor will run rich. Of course that could cause fouling of plugs but not the instant shut down that is happening.

 

[Andrew93]

I agree it does not sound like an O2 issue. Last year I had my LP pumps go and I had some weird symptoms. I was around 1200-1500 rpms I think and I accidentally hit the key switch off. Hard starting back up and over the next day or two I had a lot of trouble getting the motor into gear and above 1500rpms without stalling. I think the rapid shutdown did the already weak diaphragms in on the pumps, new pumps and problem went away.

Not saying this isn't electrical, but worth checking the pumps even though they are only 1 year old.

 

[seasick]

I agree it does not sound like an O2 issue. Last year I had my LP pumps go and I had some weird symptoms. I was around 1200-1500 rpms I think and I accidentally hit the key switch off. Hard starting back up and over the next day or two I had a lot of trouble getting the motor into gear and above 1500rpms without stalling. I think the rapid shutdown did the already weak diaphragms in on the pumps, new pumps and problem went away.

Not saying this isn't electrical, but worth checking the pumps even though they are only 1 year old.

Interesting..
Let's see what the fix ends up being.