Have you ever been laughed at by your service manager for coming up with a "left field" diagnosis? If you've been doing this for a while, then you probably have. If your new to the field, then at some point in time you probably will. For a moment, it will crush your confidance. For a moment, you will question your skills. And for a moment, you WILL FEEL LIKE A CHUMP. But hey, one of the best and worst things about a "moment" is that its short lived. And the best thing about that moment is it makes being right so much more satisfying.

   With the exponentially accelerating progress in technological capability, and the lightening fast processing speeds of todays computers, technicians have some pretty amazing diagnostic tools at there disposal. We have bidirectional control, fiber optic bore scopes, and data loggers smaller than credit cards that hold 30+ hours of info. Even your basic 2 channel DSO is taking 25 mega samples per second. We now have PC based software that can take inputs from mutiple tools like an ignition scope and a 5 gas, and cross analize the data to give you the most probable cause of failures that you may not even notice existed. Yes, its a great time to be a tech. What used to be wheeled around the shop on a cart, we now pull out of our third drawer down on the left, hook in, and drive down the road with it. Goodbye cathode ray tube, hello 16 bit resolution. But with all this high tech stuff at your finger tips, it becomes all to easy to overlook the most powerful tool of all... Good old fashioned logic.

   My story starts on a slow Monday morning. A '97 Ford F150 comes in with an inspection for "squeeky belt". I popped the hood to find that the crank pulley had a very visible wobble to it. I make my recommendations and move on to the next car. The ticket sells, I install the new belt and harmonic balancer and ship the truck. All goes smooth... for two days. Thursday morning I come walking in at 8 A.M. to find a work order for the same truck hanging on my hook waiting for me. Its making noise again. But this time its not a belt noise. This time its what the customer describes as a "spark noise". Of course the first thing I think is: ok, what was he in there doing because I didn't even touch the spark plug wires. But I kept that to myself and pulled the truck into my bay. Upon popping the hood I immediately heard the "spark noise" but it was too slow in tempo to be an ignition wire. It was happening about every 25-30 RPMs and coming from the front of the engine. As I crawled under the front of the truck I catch it out of the corner of my eye; a bright blue spark jumping from the timing cover to the outer rim of the crank pulley. I lay there for probably a full minute in dumfounded awe as it picked random spots all the way around to pulley to arch across the gap. My first thought was that the only electrical device in that area is the crank sensor, that has to be it. But that would surely cause a runability problem or at least a code and this thing runs tip top with no codes. I checked it anyway. Turns out the customer had to get going, he just wanted us to make sure it was drivable so he could go to work. I told him I couldn't see anything wrong other than the spark, and it didn't seem to effect anything while it was happening. We decided to order a factory harmonic balancer and I would do some research in the mean time.

   I decided to start by inspecting the old part. I noticed that like alot of harmonic balancers, this one had a layer of rubber between the outer "pulley" portion and the inner "hub" portion of the balancer. Now I've seen these two halves come appart before so I know that the rubber is the only thing holding them together. This raised an important point: Knowing what we do about the behavior of electricity, why would a stray current looking for a ground path jump a 2-3mm gap over to a pulley that is isolated from all other conductors by a layer of rubber? I wouldn't. That could only mean that the electrical charge was somehow originating in the pulley and jumping to the timing cover in search of a ground.

The next night I posted this on the iATN website as well as here on AutoPro:

    "I replaced the harmonic balancer because it was bent and the belt was making noise. Everything went smooth. The customer came back a few days later complaining of a "spark" noise under the hood. After inspection I found that there was a spark arching across from the timing cover to the outer edge of the balancer. I pulled codes... nothing. Checked PIDs and everything is normal with no anomalies when spark occurs. Not only is the crank signal good but it seems like it would take alot more voltage than that to jump that gap. I also noticed on the old balancer that the outter pulley portion of the unit is mounted with a rubber ring between it and the hub portion. So it would seem to me that if a stray current was looking for a ground it wouldn't jump a gap to a pulley thats suspended and isolated by rubber. So is it building up in the pulley and jumping to the block like static??? It seems semirythmic ocurring about every 25-30 rpms. I checked Identafix with no matches, and nobody I know has ever come across it. Anybody out there seen this before?"

   The customer was coming in the next day so I only received a few responses before taking a crack at fixing it. I was hoping that someone out there would tell me that they've seen it before and what the problem was. But all I got was encouragement. As it turns out though, thats all I needed. I went in the next day determined not to just throw parts at this thing and fix it by chance, I wanted to know what was going on. I decided the best way to test my static theory was to take one of the 59,874,592 coat hangers we have piling up in the changing room, unbend it, and buff the coating off both ends. I then crawled under the truck and "drug" one end of the hanger on the moving pulley and touched the other end to the frame wanting to see the current take the the path of least resistance through the hanger. I was rewarded with a high voltage shock to the finger tips... Victory. At that point I felt that the belt was the most likely culprit and alot easyer the change than the pulley. And of course my service manager had a field day with my static nonsence, but in the end he ordered the "gatorback" style belt that I asked him for and the problem was gone.

   I think the moral of the story is this: I could have gone a completely different direction with this. I could have spent hours looking at waveform patterns trying to find the source of this mystery electrical current. God knows I've spent alot of money on high quality tools and fancy equiptment for solving such problems. But when all the dust settled, I solved one of the most puzzling automotive problems of my career with three tools: logic, encouragement, and a coat hanger. And I didn't spent a dime on any of them.