BX25 loses power after engine warms up

[timpursell]

Thanks to all for the great ideas. It's going to take me a few days to get some additional tools and try a few more things. I'll keep everyone posted on my progress. I know it is frustrating to see a thread like this that has no closure and just keeps everyone hanging...

Well - I finally had a chance to adjust the valves earlier this evening. Most of them were in excess of .008", but the intake on cylinder 1 was real tight (less then .005, which is the smallest blade on my feeler gauge). I adjusted them all to .006" and was hopeful I had actually solved something.

It worked a -little- better, as I got nearly 30 minutes out of it until the problem reappeared.

Perhaps I should have adjusted them towards the upper end of the range (~.007)?

I paid a little more attention to the engine speed at both ends of the throttle limit this time. With no load -> When it is cold, it idles at 1200 rpm, and WOT is about 3500. When it gets warm and the power loss issue manifests itself, it idles at 900 rpm (almost stalling), and WOT is ~3300. I'm not sure if this additional information helps with the diagnosis or not.

I still don't have a compression tester, so haven't pursued that angle that yet. I assume it would be best to test through the glow plugs? I really don't want to take out the injectors again, as I had troubles getting them sealed back up after removing them the last time.

The saga continues...

 

[PNWBXer]

What is WOT?

 

[timpursell]

Sorry - Wide Open Throttle

 

[PNWBXer]

Sorry - Wide Open Throttle

You mentioned 2500 RPM max.....but I'm assuming under a load. So 3300 I would assume is no load max RPM?

 

[Whatscooking]

Have you replaced the fuel line. I have chased brake problems and finally found the inside of the rubber hose that made a check valve out of itself.

 

[timpursell]

You mentioned 2500 RPM max.....but I'm assuming under a load. So 3300 I would assume is no load max RPM?

Yes - it will drop as low as 2500 rpm under the slightest load when hot. The entire rpm range at NO load drops from 3500/1200 to 3300/900 as the engine warms up.

 

[timpursell]

Have you replaced the fuel line. I have chased brake problems and finally found the inside of the rubber hose that made a check valve out of itself.

Well, I repeated my "bypass the fuel tank" experiment last night and still have the same problem. That would ostensibly rule out the portion of the fuel line that feeds the pump, but I have never done anything with the line from the lift pump to the engine That might be worth checking out as you suggest.

[BTW - note that fuel overflow goes back to the tank, so after about 1/2 hour of operation, several gallons of fuel can make its way back to the tank. My little experiment emptied my external container and overfilled the actual tank...]

I'll try rerouting that portion of the fuel delivery via a new hose and report on what I find.

Thanks.

 

[timpursell]

My new compression tester kit arrived today, and I excitedly headed to the garage to give it a try. I guess I should have done a little research before I bought something, as the glow plugs on this tractor are TINY (M8, I believe). My kit didn't have that size, but upon further inspection it doesn't seem that many other ones do, either.

Does anyone have a product recommendation for a kit that worked for you? Or maybe an adapter that works with a specific kit (they seem to have different connectors for the gauges) ?

 

[oldguy]

bogs down when mowing ; just a shot in the dark, but place the power take off in neutral and see it the mower blades rotate easily by hand with the engine off. Maybe the mower gear box or spindle bearing is heating up and trying to sieze which would drag on the engine.

 

[timpursell]

bogs down when mowing ; just a shot in the dark, but place the power take off in neutral and see it the mower blades rotate easily by hand with the engine off. Maybe the mower gear box or spindle bearing is heating up and trying to sieze which would drag on the engine.

That's a great thought. I suspected that at some point as well. But the blades turn just fine by hand even when hot. Also, just trying to drive the mower up a small incline when warm (with all PTOs disengaged) will bog down the engine.

I'm waiting for my special 8mm adapter to arrive and then I'll give the compression test a whirl. I certainly hope I get this figured out soon!

 

[timpursell]

Well... I FINALLY got all the right parts to actually do a compression test. I was able to to check all three cylinders code before the cheap brass glow plug adapter broke and the internal schrader valve started leaking.

Anyway, here's what I got:

• First cylinder tested ~ 450 psi on the first few turns and eventually made it to 600
• Other two cylinders tested ~150 on the first few turns and eventually made it to 200

When I returned to the first cylinder to repeat the tests (just to make sure), the tester wouldn't maintain pressure anymore.

Now what?

 

[Henro]

Well... I FINALLY got all the right parts to actually do a compression test. I was able to to check all three cylinders code before the cheap brass glow plug adapter broke and the internal schrader valve started leaking.

Anyway, here's what I got:

• First cylinder tested ~ 450 psi on the first few turns and eventually made it to 600
• Other two cylinders tested ~150 on the first few turns and eventually made it to 200

When I returned to the first cylinder to repeat the tests (just to make sure), the tester wouldn't maintain pressure anymore.

Now what?

I would get a better compression tester and do it again.

Doubt I would trust those results...

 

[timpursell]

I would get a better compression tester and do it again.

Doubt I would trust those results...

Yeah, I kinda figured that. That is exactly why I was trying to repeat the tests. I didn't trust what I was seeing the first time.

...and the saga continues.

 

[timpursell]

I would get a better compression tester and do it again.

Doubt I would trust those results...

OK...i finally got some better test gear and repeated the tests. There appears to be good compression on all three cylinders when the engine is cold. About 450-500 (assume the gauge isn't calibrated perfectly, but I was doing a relative test, not absolute.)

I ran the tractor until the problem appeared again, then removed the glow plugs as fast as i could and tested them all again while the engine was still hot. Each was just a few psi less, but well above anything that would cause worry.

So now what do i turn my attention to? Seems like I'm back to the fuel delivery system. Injectors? Injector pump?

As always, any ideas would be GREATLY appreciated!

 

[JerryMT]

OK...i finally got some better test gear and repeated the tests. There appears to be good compression on all three cylinders when the engine is cold. About 450-500 (assume the gauge isn't calibrated perfectly, but I was doing a relative test, not absolute.)

I ran the tractor until the problem appeared again, then removed the glow plugs as fast as i could and tested them all again while the engine was still hot. Each was just a few psi less, but well above anything that would cause worry.

So now what do i turn my attention to? Seems like I'm back to the fuel delivery system. Injectors? Injector pump?

As always, any ideas would be GREATLY appreciated!

To make power you need air, fuel, and compression. You definitely have compression so that is not the issue. If you had a restricted air induction system, your power would be down from the git go unless something was getting into your intake continuously after a half an hour of operation. Unlikely. So it is most likely to be fuel flow reduction.

I heard one of the pump guys on another forum say that a worn hydromechanical injection pump can cause this problem problem. Do you have a hydro mechanical injection system or a common rail electronically controlled fuel injection system? If it's the latter, it could be something like a temperature sensor that is sending the
wrong info to the control computer causing it to limit fuel flow. As the engine warms up the sensor error maybe is increasing causing the problem you are experiencing. it may not be a temperature sensor but something else. Not being familiar with the system I can't offer any more than this.

You seem to have checked out all the other possible sources of fuel delivery reduction and eliminated them and so it seems to me that something like this is all that is left.

P.S. I applaud the systematic approach to trying to solve this problem.

 

[JerryMT]

Another thought... what kind of transmission does this tractor have ; HST or gear? If HST , is there a possibility that something in the HST tranny is increasing the load and causing the engine to be pulled down in rpm?

 

[timpursell]

FINALLY! I got it fixed.

For those of you wondering if this ever got resolved, here's the final chapter of the story.

There was only one last thing for me to consider - the injection pump. With great trepidation, I took it apart and tried to see if there was anything that could be cleaned or fixed. I ended up finding some corrosion that kept one of the valves from sliding smoothly (which presumably got worse when it warmed up.) I tried cleaning it up, but to no avail. I ended up purchasing a rebuilt injection pump off eBay and sure enough, that was the problem. Everything is working ok now!

 

[RCW]

Super! Glad you came back with the fix.

 

[leveraddict]

Tim congrats on the fix! How old is your machine? Wondering the life of those fuel pumps! Seems to be a common problem.

 

[Henro]

Tim congrats on the fix! How old is your machine? Wondering the life of those fuel pumps! Seems to be a common problem.

It wasn't the fuel pump. It was the injector pump.

Injector pump failures do not seem to be common...at least no where as common as fuel pumps.