Monday, August 1, 2016

Pedal on the Right

Today's posting is a continuation of the last (Another Tow). In that post, I described the initial cause and my reported first reaction. I actually forgot a part, so I'll start there.

$5 Multi-meter
TPS wiring diagram
When I first got into cars, I had already dabbled in computers and wiring stuff. I'd fixed wiring in houses, strung cables for networks, etc. Still, even with that history, I didn't recognize the extreme value in a multi-meter. The fact that you can get one for $5 at Harbor Freight will lead many folks to the same conclusion: if its a cheap tool, it probably isn't worth much. Wrong. I first started using my multi-meter to set the static timing on the original pancake engine. Muir, the interweb and the Bentley talk about a timing light. Sure, you could fabricate a timing light with a dashlight bulb and some wire, Or, you could buy a timing light at your local car parts place. They cost more than $5, by the way. The cheapest, and in my opinion smartest solution is to use your multi-meter set on the 10's of volts setting. Rotate that dizzy until the voltage jumps (this is when the light would have turned on in the Muir model), and you're golden.

The multi-meter has been sitting on the top of my toolbox from day one. In retrospect, it is probably the most used tool I have. My 13mm ratcheting wrench is probably second. Anyway, on to its use with the wiring troubles...

Continuity Testing
old TPS plug
My first thought about the issues with the 1200 RPM symptom was that they were caused by one of the wires coming from the accelerator pedal melting against something and shorting out. To verify this, I grabbed a long stretch of wire and ran it along the ground from the pedal wiring to the back of the bus where the ECU sits. One wire at a time, I verified the continuity by splicing my on-the-ground wire into the test subject wire. Then, at the ECU, I would verify a closed circuit existed. All of the wires in the bundle were good. It was at this point, I decided to clean up the wires as I described in my last post (Another Tow).

Potentiometer Potential
If the wiring was good, and the bad grounds weren't part of the problem, then the issue must be at the potentiometer (that big variable resistor the wires go to that sends the how-fast-to-go signal in the drive-by-wire set up). This is often referred to as the "Throttle Position Sensor" or TPS. I unplugged the TPS from the wire bundle and disconnected it from the under-floor of the bus. At first, I thought the TPS got wet from the trip to Bend and it would work after it dried out. I read some threads about that happening for folks. On closer inspection, I could see that as the wires left the TPS, the insulation had stripped away. I could see copper. Since the TPS was pressed against the metal underside of the bus, the signals were shorting out right there.

bad TPS wiring
Had I discovered this in the middle of nowhere, broken down on the side of the road, I would have solved this in classic hack-style: put a small bit of rubber between the TPS and the underside of the bus to get back on the road. Since we were in the driveway and I'd already gone back on my promise, this was a fix it right moment.

New Pedal
The 1998 New Beetle donor from which I got the engine and related components had an accelerator pedal / TPS that was unique. By 1999, the components had changed, and the wire plug had as well. Gone was the old 2x3 (2 rows of 3 pins) round-ish plug. In its place is a 1x6 flat plug. Neat. The old TPS could still be found on the interweb, but NOS and even used on eBay were going for upwards of $400. Snort-giggle. Yeah, like I'm paying that. The new pedal assembly is available online for just over $100 or almost $200 for a genuine VW part. Considering the failed promise, I got the genuine VW part. The new pedal has the TPS integrated into it. You can't just remove the TPS and use it like I had before. This meant that the first real change to the cabin was necessary: the old pedal would go away and a new model pedal would have to be retrofitted. *pausing for the purists' gasps of shock*

Wire Plug Wire Plug
wiring extension
First, I needed to get the existing bundle of wires mapped to the new flat plug. Oh, and I needed a plug. I got a plug from the pick-n-pull, cutting as much donor wire from the bundle as I could. I cut the wires off the old TPS too, and wired up a cable extension from the old TPS location up through an existing hole in the floor, and up into the back of the dashboard before heading back down to a location near the heat directional control (picture about mid-shin on your right leg behind the kick panel).

Suspend a Pedal
With the wiring in place, I plugged in the new TPS / pedal assembly and
pedal support
started the engine. The 1200 RPM Symptom was gone, and the engine revved with pedal presses in my hands. Sweet! After killing the engine, I messed around with placement options. I don't want to have to hold my leg in the air to get to the pedal, but I also don't want the floor to interrupt the pedal movement before maximum throttle. I found a Hapy medium, and grabbed some 1" angle aluminum. I chose aluminum because its light, strong and looks good. With the right angle, it won't flex under the pressure of my foot on the pedal. I cut a notch out of the top so it would fit tightly against the emergency brake support and cut a notch out of the bottom so I could bolt the bottom to the floor. After test fitting the support, I marked the spots for the holes to hold the pedal assembly. A quick run with the drill and a few bolts later, I had a pedal installed. The final steps were cleaning up the carpet so the new support had a notch to fit into, and completely removing the old pedal.

Test Driving
install complete
Of course, as soon as I had it together, I wanted to take a spin. My kids were at their other parents' houses and my wife was working, so it was just me, Hapy fired right up like he always does. I put him in reverse and feathered the throttle. He leaped backwards. Whoa. I backed out of the driveway without my foot on the pedal and turned so the nose was pointing down-street. I put him in first and stepped on the pedal. The front tires almost left the ground as we jumped into motion. I was thrown back into my seat. Holy crap. Still feeling for how hard to press the pedal I zoomed down the sides treet to the main street intersection. Just to see how quick I could go, when the light turned, I jumped on it and turned onto the main road. The RPM's flew up and I shifted and then again and again in the span of about 5 seconds I had gone from dead stop to 40+mph. This was possible the fastest car I had ever driven, and its a 1972 VW camper.

I think, as I look back on this build, I'll remember this moment. I did so many little things to make it better, faster. In the end, the second generation pedal and assembly allowed me to tap into the horsepower and torque I originally envisioned when I started this project. I can't wait for our next festival. Now that I've fulfilled my promise to Hapy, I don't think he can wait either.

That's it for today. As always, thanks for following along.