EH72FI surging

[KMA]

Hoping someone might have advice regarding my engine issue. It happened the other day when I was in the middle of digging an underground electrical wire run to a detached garage. At first I thought it was bad gas, so I drained and replaced it with fresh stuff. That didn't work, so I took off the intake and cleaned it and the injectors. I found a small rubber plug under the air filter that appeared to have been chewed or worn away. It may have allowed dirty air to enter through a small orifice. I replaced it with something else and put things back, but it still had the issue. I made a video showing the governor moving and the engine surging. It actually got a bit worse after I stopped recording. I think it is running lean since the exhaust was getting hotter than usual (pipes were red).

http://m.youtube.com/watch?v=98yiu6NqHLw

What do you guys think?

Thanks!

 

[MossRoad]

Go to this manual and see if you see the rubber thing you found under your air cleaner. I suspect it is something to do with the governer or speed control. Something to do with friction, perhaps, that keeps the thing from surging. Anyhow, just a guess.

http://www.subarupower.com/media/manuals/129248184237409238.pdf

 

[MossRoad]

Also, a picture of the part you found might be helpful.

 

[KMA]

Thanks Moss.

I have that manual, but the part isn't labeled. I've attached a diagram with the rubber cover/plug circled.

 

[ponytug]

With a fuel injected engine, I tend to think of air/vacuum leaks when an engine is surging. If it were me, I would be looking for other vacuum lines or plugs that might be leaking air. If you didn't have an exact fit replacement for your plug, I would tend to suspect the plug as being the primary issue and the replacement as leaking air.

Free advice...

Good luck.

All the best,

Peter

 

[KentT]

One way I've successfully found leaks around intake gaskets and such is to use a spray bottle of water while the engine is running. Carefully spray it around the intake gaskets, on vacuum lines, etc. while the engine is running and stumbling -- if it momentarily smooths out, you've found a leak. The water will tend to seal the leak for a tiny fraction of second before it is sucked into the combustion chamber and the leak resumes....

Small amounts of water being injected won't hurt the engine.

 

[MossRoad]

Thanks Moss.

I have that manual, but the part isn't labeled. I've attached a diagram with the rubber cover/plug circled.

Is that the same thing as shown on page 9, second picture down?
And on page 10 looking down at the cleaner adapter?
Wonder what its for?

Also, what's the 'pulsation damper' do?

Just throwing out questions. Don't know any answers. :laughing:

 

[KMA]

The "plug" appears to close off a port into the throttle body. Maybe it could be used for testing, or in a different configuration... not sure. I'm assuming the pulsation damper is intended to smooth the flow coming from the fuel pump, but that's just a guess.

I went ahead an ordered a new universal fuel pump that should replace the one there. Unfortunately, Robin does not list a part number for it anywhere, but I found the expected output pressure referenced in one of the diagrams and used that to located a different one. Hopefully I'll be able to swap it out this weekend. Thanks.

 

[Gravy]

Looking at the rest of the manual, it is clear that the plug goes into the air cleaner adapter, which is before the throttle body. Small leaks there may let in some unfiltered air, but should not cause surging. My first suspicion would be fuel starvation. Have you replaced the fuel filter?

 

[MossRoad]

On an old lawnmower we had with a carb, it started surging like in that video one day. I found a small foam ring that was under the linkage to the pin on the butterfly that the governor attached to was just hanging there. It apparently was a damper of some sort that suppressed the surge of the governor. That's why I suggested looking at the governor when he said he found a rubber part. Anyhow, could be fuel related, too. Gotta start somewhere! :laughing:

 

[KMA]

Looking at the rest of the manual, it is clear that the plug goes into the air cleaner adapter, which is before the throttle body. Small leaks there may let in some unfiltered air, but should not cause surging. My first suspicion would be fuel starvation. Have you replaced the fuel filter?

Yes, I forgot to put in the first post that I replaced the fuel filter (and air filter) early on, right after draining what I thought was the "bad" gas. The reason I ordered a new fuel pump is that it really seems fuel related, and I tried cleaning everything already. Plus, I recall that the pump would "tick tick tick" once the key was put into the ACC position. It still does that, but sounds like it gets quieter after a few seconds, and then eventually stops. I believe there isn't any "smarts" to control whether the fuel pump should turn on/off... It's just always on with the key position since there isn't a fuel pressure "sensor" or similar back to the ECU, etc.

Anyway, hopefully the new fuel pump is the fix. If so, the one good thing that would've come out of all this is finding the chewed plug. That would have done damage for sure over time. Unfortunately, my yard and walkway is torn up from digging the electrical run, and now it's been freezing and snowing, so I'll have to wait for a thaw to get back at it. I have ropes and markers everywhere so no one falls or trips. It's a mess, and my wife is annoyed. Whatayagunnado? :jaded:

To add some visuals... here's a pic of the trenches (electrical and drainage) just before the snow and freezing weather came. You can see the PT in the background where I was just about to swap out what I hoped was bad gas.

 

[MossRoad]

You got some rocky soil there.

 

[Gravy]

You got some rocky soil there.

Gee, and I was just envying Kevin's dirt-to rocks ratio. Just goes to show how much variation there is in local conditions.

 

[Gravy]

You got some rocky soil there.

Gee, and I was just envying Kevin's dirt-to rocks ratio. Just goes to show how much variation there is in local conditions.

 

[MossRoad]

Yeah! I have pretty much 8" of black dirt on top of 40' of sand at our house. On our property 9 miles away, I have sand dunes, sand, and a little bit of sand. A pocket of gravel 8' deep under 2' of sand, and some sandy muck.... on top of sand! We call any rocks we find dinosaur eggs. :laughing:

 

[KMA]

:laughing: Yeah, the only reason you see somewhat normal looking soil is because I trucked in tons and tons of it when putting in my lawn. In my area, you are lucky to have a foot or two of heavy, clay "soil" and rocks, with hard pan, solid clay just underneath it... and I'm talking the type of clay you can form into a shape and put in the oven to make pottery (I actually did this once for my daughter).

The good news is that my replacement fuel pump arrived. It isn't the OE (that was $90+), but it I think it should work okay. We'll see...:begging:

 

[Gravy]

:laughing: Yeah, the only reason you see somewhat normal looking soil is because I trucked in tons and tons of it when putting in my lawn. In my area, you are lucky to have a foot or two of heavy, clay "soil" and rocks, with hard pan, solid clay just underneath it... and I'm talking the type of clay you can form into a shape and put in the oven to make pottery (I actually did this once for my daughter).

The good news is that my replacement fuel pump arrived. It isn't the OE (that was $90+), but it I think it should work okay. We'll see...:begging:

I think you're on the right track. When the sound of a fuel pump changes, it's generally not a good sign.

 

[marrt]

KMA,

Did you ever get this sorted? If not, try this stuff: Chevron 65740 Techron. If you can add a little choke to stop the surging, there's a decent change the surging is due to deposits and other problems associated with bad gas and ethanol. I was VERY skeptical this stuff would do anything. However, it was highly recommended online and for a couple bucks what could it hurt. I've since used it to "fix" three different engines. It's not a miracle worker. However, if you have deposit problems, it seems to work good and sure beats a carb rebuild.

marrt

 

[KMA]

Hi Marrt,

No, unfortunately I'm still working on it. I'm exchanging emails with Subaru support. I tried an aftermarket pump and it acted the same. This engine is fuel injected, so no carb rebuild (or choke)... but I did take apart and clean the intake manifold and injectors, although they looked fine. I always use Ethanol treatment (either Star Tron or Lucas) in all my small engines, and added a fuel injector cleaner (Rislone) earlier on when replacing what I thought was bad fuel.

Thanks for the feedback.
Kevin

 

[ponytug]

I have a couple more ideas.

Did you check your MAP sensor? They can be cleaned, but you need special cleaners. I have had them go bad, and when they are flaky or bad, they generate lousy engine performance.
The other global item is the fuel regulator that sets the pressure for the ignition system. If it is sticky or worn, it will also be ugly.

Wiring issues? e.g.

• Bad RPM sensor
• Bad RPM sensor wiring
• Bad connector/wiring harness
• Bad coil (How were your plugs?)
• Bad spark plug wires (Was there a difference between the plugs?)

Did you check your pulsation damper to see if it is still functional?

Good luck...

All the best,

Peter