Periodically in the life of a vintage iron enthusiast, you will face trials and tribulations. Vexing and perplexing situations that defy logic and leave you in an exhausted state on the edge of putting the thing on Craigslist for a few hundred bucks. This is one of those sagas. For another, see To Spark or Not to Spark from the main blog.
This machine was not running. It cranked, but would not fire. The previous owner (PO) had tried various things and had been generally mucking about with the Throttle Position Sensor (TPS). The evidence is that he gave me 2 others in the box of assorted parts. Hhhmmmm. The first suspect is the HES. There are many stories on the forums about the strange results that can be produced by the deterioration of the HES wiring. Just like in the crime drama wher the bank heist takes place, and a just-released-from-prison serial bank robber is living nearby, it is natural to suspect the HES. It is a serial interrupter of spark. I decided to bring the HES in for questioning, but first I always check the basics. You never know, you may get lucky.
The sidestand cutoff switch was ok, the Motronic fuse was good, the engine cutoff switch was good. I swapped the horn relay and the fuel pump relay. Suddenly the fuel pump energized with the key. AHA ! Could it really be that simple ? It now cranked and cranked, but would not start. It did produce a deceptively encouraging sputter once in a while, but that was it. I checked the injectors, and both produced pulsing sprays when it cranked. So we have fuel. I checked the plugs. Both produced a spark. At this point, I ran out of time and ordered an HES from Euromotoelectric. Great folks and they sent it out overnight for very reasonable money.
Early the next morning, I checked the valves while the bike was cold. I found two intake and one exhaust loose, but not enough that it would not run. I changes the oil while I was at it as well just because I always do on a new-to-me machine. I did notice that there was crumbling protective sheathing over a few of the wiring bundles. I would have suspected fire/heat damage if all the sheathing was similar, but it was not. I thought it was strange that other bundles right beside them were fine. This of course was the reason cited for the HES failures, not the sensor, but the harness attached to it failing due to heat, water, etc. I replaced a few sections with some of my universal flex sheathing. This should have been a BMW recall.
I dismantled everything, and removed the old HES. I did have to improvise a flywheel TDC lock by bending a piece of roundbar I had laying around, but other than that no worries. The old unit had sketchy looking wiring at the senor end, and even some very small slivers of copper wiring exposed. It was dry and brittle as well. The sheathing was crumbling just like the rest that I had seen. This made sense, as it was the end getting all of the engine heat. Under the glare of interrogation lights, I asked the HES some probing questions. Where were you when the engine was turning over and attempting to fire? Have you ever failed to fire at top dead center? How do you account for this crumbling sheathing and wiring that is attached to you? The HES refused to answer. Online forums had suggested cutting the rest of the sheathing where you would be sure to find more problems, but I saw no point as the replacement was arriving. I sentenced the old one to the parts bin, as it was not yet fully convicted.
Fedex arrived and I eagerly put the shiny new HES in place. I also replaced the crank-pulley/alternator belt, even though the old one looked fine. With everything replaced, I reconnected the battery and paused before turning the key to offer a prayer to the appropriate deity for restarting an engine after repairs. There was an immediate stutter, then cranks but no firing. The next attempt was even more sputtering, and then about the sixth try, the engine actually fired and settled into a lumpy idle. I did the DAD (Deity Appreciation Dance) which looks a lot like an older guy mangling a dance that went out of style in the nineties, but I digress. And then it died. I did the NSF (Not So Fast), which looks a lot like the shuffling droopy walk of the crestfallen. Then it started immediately, and I was back to the DAD. However, it would not rev beyond about 2K, and would usually die just off idle.
OK, this was progress. I eyed the collection of TPS units suspiciously. I took the unit on the bike in for questioning. Can you attest to the fact that your potentiometers are functioning properly? Are you actually a new OEM unit? The TPS refused to answer. I grabbed my lie detector (some call it a multimeter) and it seemed to suggest the TPS might be innocent, even if not new. Hhhmmmm. I had air, fuel, and fire. What could it be? When in doubt, go back to the basics. The airbox was open, so I had plenty of air. Both plugs now had a healthy spark. In fact, I managed to give myself a nice little jolt to clear my thinking. Both injectors pulsed fuel. Hhhhmmmmm. I decided that the only thing I could not guarantee was that enough fuel was making it to the cylinders under load. I pulled the tank and took out the pump and filter. Now for another digression. Why in the world did anyone decide that it was a good idea to put an electrical pump and a filter inside a fuel tank? They had been external forever with o particular issues that modern engineering could not solve! Logically, it does not sound sensible to cool an electrical pump by immersing it in combustible fuel. It also adds a ton of time to the simple act of changing a pump or a filter. And why require everything to get doused in gasoline to get the job done? This is a dealer's dream and a home mechanic's nightmare where he drops a spanner and blows up his home. End rant.
I tested the pump and it was in good working order. The hoses looked good as well. I inspected everything, changed the filter, and put everything back together. Instant start, revs to 3K, DAD, but then has a huge flat spot, NSF. I replace the plugs more out of a change of focus than process of elimination. No change. I run out of time, and decide that the next day I will take it into the one place that I trust to work on my machines. I hate this step because it is either know when to say when, or admitting defeat. I also hate it because I will pay going labor rates for more diagnostics. However, they have the diagnostic tool, and a really good technician that I have known for decades.
The next day I drop off the bike and they say they hope to get to it the next week. I go home and cleanup the garage in order to shift attention to the R26 which coincidentally has a fuel issue. Leaky petcock. What the heck, I might as well continue to bathe in fuel. Suddenly the phone rings and it is the service manager. These are never good calls. He tells me the bike is done. Done, I ask? Yes, work is complete and you can pick it up. What? Yes, it was a fuel hose. They went on to explain that the diagnostic tool said fuel pressure, and once they put the pump and filter under pressure, the hose connecting them sprayed fuel everywhere due to a leak. The hoses looked good, but were far from it. ethanol and the machine sitting for some time were probably culprits. They replaced both hoses in the assembly, put things back together, and problem solved.
There was a definite mixture of emotions. Elation at a problem solved, gratitude that they jumped on it so soon, and disappointment that I was so close to the complete solution but missed it. In hindsight of course, it all makes sense. The HES being a big part of the issue, but the hose combining with it to create a more complex mystery. I can't help but go back to my rant on placing this whole aparatus inside the fuel tank. A faulty hose between pump and filter would have been diagnosed in 5 seconds. However, I did re-learn somethings. First, don't assume that you are looking for a single problem that matches all of the symptoms. You may have more than one issue. Second, don't assume a good looking component is good. Test it. Third, there is no substitute for the right tools. You can burn a lot of time and effort without them.