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This is an article about how I bypassed a failed ELECTRONIC FUEL MANAGEMENT (EFM) module (p/n 796352 or 796352s) on a Briggs and Stratton 28hp Extended Life Series w/XRD V-twin motor (don't know how these engines run with plain ol' RD, but mine has the eXtraRD and runs really well).




Given that there are all levels of expertise out there on this forum, I will write part of this as a tutorial that may bore those with higher skill levels, but can be used by those just learning, since, after all, we enthusiasts have shown an interest in My Tractor Forum, and you may want to learn and do more on your own. Remember that this is what worked for ME, these are MY opinions, and you should take responsibility for your own actions and/or repairs to your equipment. Follow all rules and regulations applicable in your jurisdiction. Recognize all engineering and design changes, etc.

I would also like to add that you can buy all the parts to do the manual choke conversion from the dealer. The primary pieces are 1) the choke cable and 2) the bellcrank and its mounting bracket that attaches the choke cable to the choke link.

The details of the failure are as follows:

The tractor is a Craftsman PGT9000 (917-28974 / 289740), vintage 2008-2009 hydrostatic, made by AYP / Husqvarna, with the battery behind the engine under the hood, and the gas tank under the seat. The tractor had 37 hrs on it when it failed. My wife and I cut almost an acre of frontage out by the main road, and somehow, SHE always gets to ride the tractor, while I chase snakes in the ditch with the string trimmer. She got down the driveway, engaged the electric clutch for the deck, and it quit. Dead. No crank, nothing.

I looked for the usual suspects and eventually found the very well hidden 20A ATC fuse tucked way back under the battery tray, as if nobody expected the unit would ever blow a fuse. The rule for blown fuses is, if you replace the fuse and everything works again for a long time, it probably was fuse fatigue (a rare failure these days). If it blows again right away, you have a problem. So, I replaced the fuse and almost immediately, I knew I had a problem.

From my experience, I knew without a detailed wiring diagram (I did have one that I printed from the Sears Parts web site, but the EFM wiring was not there, probably since it came as a unit with the engine), that I could go through a number of fuses, plugging and unplugging connectors trying to find the source of the failure. (BTW, a sincere Thank you to Sears for providing that copy on the Parts website.) I ended up buying an ATC compatible 20A circuit breaker, one that would stay tripped until the power to it was dropped, whereupon it would reset itself. Perfect. Let the diagnosis begin.

Thinking that the 20A breaker would protect the circuits, I turned the key one notch. I saw the ammeter peg itself in the negative direction, which is at least 20A. Since I suspected the electric deck clutch, I was surprised to see smoke emanating from the EFM module (similar to the sports cars of my youth). I don't know that my pricey circuit breaker ever tripped before I could shut off the key. In any case, I figured the EFM was now trashed, if it wasn't before. There are 16 wires in 3 connectors on the back of the EFM module, so I unplugged them, and turned the ignition back on. Nothing bad, which is good. This EFM module is a small circuit board encased in a type of weatherproofing plastic inside a black plastic housing. I could see evidence of a power transistor trying to burn its way out of the protective coating. A quick parts search and a delivered price of between $80-$90 made me wonder how we used to get by without this (although it does work very well).

Sometimes when things like this go bad, it's the module itself. Sometimes it's a sensor or other outside device CAUSING the module to overload and destroy itself. I suspected that since what burned up was a power transistor, it was probably the circuit board itself. I couldn't find enough information on the EFM module to know if it also controlled ignition, which in today's world of "making your life better using too much technology" was a distinct possibility. A quick test for ignition is to spray a little starting fluid in the air cleaner, and hit the starter (not recommended for diesels with run problems, BTW). Did that, bang! Got a few revs out of the engine. Houston, we have ignition, but it didn't stay running, so we probably didn't have fuel.

It turns out that this is one of those engines that uses a fuel shutoff solenoid on the bottom of the carburetor bowl. I don't know if that's ALL it does, but after fixing the tractor (more on that later), it does not appear to interfere with normal running once it starts, i.e. it doesn't appear to control the mixture. I made the basic assumption that without any visible electronics, other than the EFM (which was now off the tractor), that everything would run on 12VDC (vs 5V which appears to be design engineer's 2nd favorite). I felt that nothing would burn up, so I jumped the fuel solenoid on the carburetor to my headlight wiring, and turned the ignition on, headlight switch on, and the solenoid clicked with no smoke.

Note that the jumpers attach to the original wire, still attached to the round, silver fuel cutoff solenoid, which went up to the EFM.



I then held the choke closed manually, started the tractor, and it ran. I turned the headlight switch off, and after 10-15 seconds or so, the tractor quit. Since manufacturers use parts across a multitude of different models, I suspected that this solenoid might be on units without the EFM module. This was backed up by the following: The solenoid has round pins and the EFM has square ones. There was a gray / black pair of wires coming out of the engine, connected to an extension gray / black pair that went into the EFM and came right back out as a gray / black pair and went to the fuel solenoid. All with round pins except on the EFM, which were square.

The arrow points to the round pins of the pair that came out of the engine, which was just long enough by itself to reach the solenoid.



I tested the gray wire for 12V with a test light, and turning the ignition on lit the light. I tested the black (commonly a ground wire color, except on VWs) and it was a ground. So here I had a switchable 12V circuit with round pins. Hmmmm. I plugged it up to the solenoid, held the choke on manually, and started the tractor. It ran until I turned the ignition off. So, we now have ignition and fuel. We need to address cold starting, i.e. the choke.

The choke is actuated on this unit by what appears to be a small 12V stepper motor, which is attached via 5 wires to the EFM. They call it "automotive starting" which simply means the EFM uses sensors and activates the choke as needed, until the smoke leaks out. Since many garden tractors, for many years, as well as older cars which I have had the privilege of owning, use a manual choke, I decided that this was going to be my bypass (I know, finally).

For under $7, I bought a choke cable 46" long. (made by Oregon)



I could have just extended the existing choke link out the grill of the nose of the tractor and not used the cable, but having an actual choke button up next to the throttle was just too irresistible and way more convenient. Besides, they provided a nice round place just below the throttle, in the event that one might someday want to add, say, a manual choke cable or a button for an ooga horn. I built my own bracket and bellcrank only to find out later that these parts are available from the dealer, if you can provide an engine number (which I couldn't). The only major thing different from a stock manual choke is that I replaced the original choke link with a spring so that the choke would be "protected" from being pulled on too hard. The return spring on the OEM choke baffle is very light and easy to overcome and thus activate the choke.

The following picture, during fabrication, shows the bellcrank pulled to the FULL ON position where it contacts the bracket (yellow arrow) and the spring which I used to replace the OEM choke link falling just short of the hole so that it will exert a small amount of force to ensure the choke is fully closed (red arrow).



When the choke button is pushed completely in (and this button snaps closed), there should be the smallest gap between the installed choke link (in this case, the spring) and the bellcrank. This ensures the choke will be free to open itself completely and not be held partially closed even though the choke button is pushed all the way in. You adjust this gap by moving the choke cable sheath with the choke button in (off) all the way.

The gap is shown in this picture by the yellow arrow.



Here's what it looks like now. Note that just below the throttle lever, the choke button fits in perfectly.



This 28HP ELS Briggs starts so easily that I now can set the throttle at about 1/3 open, crank it, and momentarily pull the new choke button up for a second, and when it fires and runs, immediately push the button all the way in. In really cold weather, it may need to stay out a little longer, we'll see.

One other item, this is the first failure I've had on this unit. But, I did have a deck spindle get stiff, and so took out all three, and found a thimble of grease in each one. I would recommend pulling apart your deck spindles, whether new or old, and hand packing the bearings with grease because the zerk fittings don't put the grease where it is needed, in my honest opinion, not as well as you can grease them by hand. Also, when you screw the deck spindles back down, put anti-seize compound on the bolts, because at 20 hrs of use mine had already seized and needed to be drilled out and re-tapped.

Here is a picture of my finished product. Note the spring that I used to replace the solid choke link. This spring is moderately stiff, and easily pulls the choke closed when needed. It gives just a little, which protects the choke from being pulled too hard when the choke cable is pulled out all the way.



This is what an original bracket and bellcrank looks like. This is on a 22HP Briggs twin. I suspect this piece will be very similar across all the different Briggs models that have separate choke and throttle cables.



This picture was taken from an angle slightly below the bracket, and shows the tip of the solid link that goes back to the choke. This particular model did not have the EFM from the factory, but still has the round fuel cutoff solenoid on the bowl on the bottom of the carb.
 
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