EH72FI surging

   / EH72FI surging
  • Thread Starter
#21  
Peter,

Thanks for the great suggestions. I did check the MAP sensor, it is actually built into the ECU which is part of the throttle body. There is a small pathway in the aluminum to the sensor, which I cleaned. The throttle body/ECU is all one unit and can't be separated. I also disassembled the fuel pressure regulator, and it was clean and appeared fine. There aren't a ton of wires and I've done a cursory inspection, but I guess I'll need to look further. I thought about the pulsation damper, but it seems to work (fuel comes out of return line into tank in a relatively steady stream) and I don't know how to test it otherwise.

On a side note, I exchanged emails with Subaru support and it didn't go as well as I hoped. The guy offered some general advice that I had already covered, and then just sent me the service manual instead of answering my questions. My guess is that he has some basic knowledge of small engines, but maybe the fuel injected versions are a little out of his league (or they just don't provide them with enough information to answer in depth questions). The service manual isn't much use for trouble shooting other than the high level diagrams. Funny thing was... early on he asked me what the engine was in, and I told him a Power-trac tractor. He immediately responded back saying the engine was not meant to be in such a confined space and will have heat issues... sounds like he's heard about PTs before. :)
 
   / EH72FI surging #22  
FWIW: As far as I know, the only way to test a MAP sensor is to buy a new one and swap it. The advice I got was that many of the defects only really manifest themselves when in actual operation, and most setups, e.g. yours, aren't really something that can be tapped into.

I have to say that vacuum (air) leaks have fixed 90% of my fuel injection issues, bad oxygen sensors (which you don't have) another 6%, bad wires 2% and bad pumps, regulators, and MAP sensors make up the rest. My point being that by the time you have gotten to considering MAP sensors, you are in the improbable. In close to 750,000 miles of driving, I have had one MAP sensor go bad. I have had the diesel equivalent go bad once (HUEI IAP sensor).

Have you gotten to checking valve operation?

All the best,

Peter
 
   / EH72FI surging
  • Thread Starter
#23  
Thanks again. Yeah, swapping out much of anything involving the throttle body, ECU and injectors is not really possible in this design. Subaru lists the whole unit as a single part number.

Now the good news: I've got it running again. :cheerful: I went through all the wiring, moved it around and re-zip tied it here and there in case something was loose or rubbing. I also checked hoses, etc. didn't see anything obvious. I re-verified that the original fuel pump was shot, and wired up the aftermarket replacement which allowed it to run normally again. The weird part is that I'm pretty sure this setup didn't work the other day, but now it does. I have a few theories on why, but nothing concrete.

Now that I know the universal pump works, I may pick up the OE part to put in, but it's $90+... so maybe not. The strange thing is the pump won't operate using the stock wiring. The ground is controlled by the ECU, and I get the right voltage, but it must not allow enough current. I didn't do a voltage drop test or anything else, instead I ran a short ground wire to the battery and used the original positive connection for power. This way, the pump still turns on/off with the key, but the ECU is out of the loop. The downside is that the ECU can't shut down the pump if the engine RPMs get way too high for some reason. I'm hoping whatever is causing the ECU to incorrectly control the pump's ground wire, won't bite me another time. If it is indeed on the fritz, it can only be replaced with a new throttle body ($500+).

Anyway, spent a couple hours this morning filling in all the trenches and repairing the sidewalk, so my wife is happy. :thumbsup:
 
   / EH72FI surging #25  
When my new EH72FI engine kept shutting down when it overheated (temp sensor wire from the crankcase feeds into ECU) the mechanism the ECU uses to kill the engine is to cut the power to the fuel pump. So in your rewiring adventure keep in mind that you are circumventing this protective measure. Hopefully this won't "bite me another time" by cooking the engine come Summer.
 
   / EH72FI surging
  • Thread Starter
#26  
Kent said:
When my new EH72FI engine kept shutting down when it overheated (temp sensor wire from the crankcase feeds into ECU) the mechanism the ECU uses to kill the engine is to cut the power to the fuel pump. So in your rewiring adventure keep in mind that you are circumventing this protective measure. Hopefully this won't "bite me another time" by cooking the engine come Summer.
Click to expand...
Yup, I alluded to this earlier but I don't have another option, short of spending $500 to replace the throttle body/ECU. Before spending that much, I might go in another direction altogether. Since this is the second Subaru in my PT, I'd probably cut my losses quit giving them my money. :( I don't have a lot confidence in their small engines and would have preferred to use an alternative. They seem decent for generators, etc., but in the extreme conditions that PT has forced them into, I'd feel more comfortable with a Kawasaki (or maybe a Kohler). Liquid cooled would be even better given the heat issues. I spent a significant amount of time looking at alternatives before pulling the trigger on the EH72FI, but I didn't find something that would fit without modifying the tub. Since the tub is pretty much the "frame" on the PT, I wanted to avoid it.

Instead of dropping $500 to buy another year or two before something else breaks, I would rather run this engine into the ground and spend $2k on a better one. Maybe something like this:

Kawasaki Engines FD750DFS0301 FD750D 25 HP Horizontal Engine

:licking:

Hopefully, it just keeps working and I won't have to worry about it for a long while. :worried:
 
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   / EH72FI surging #27  
   / EH72FI surging #29  
yeah, but that is the stripped down version without the radiator.

hmm, might require a 3" tub extension.... but it would be totally worth it.

And than there is the little issue of where to put the fuel tank, since the radiator probably steals that space.

But it might work.

But 0.7 gph at full load would be nice...
 
   / EH72FI surging #30  
tmarks11 said:
yeah, but that is the stripped down version without the radiator. hmm, might require a 3" tub extension.... but it would be totally worth it. And than there is the little issue of where to put the fuel tank, since the radiator probably steals that space. But it might work. But 0.7 gph at full load would be nice...
Click to expand...

What the heck. If your going to modify the tub, may as well through in a V8. Seen 8n's with 350's in them. 😊

Sent from my iPhone using TractorByNet
 
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