Hapy not Spittin Fuel

I managed to get Hapy, the 1972 TDI-powered microbus, over to Justin to get the injection pump re-sealed this weekend. Today's post covers that adventure as well as a quick trip thru a K'Lack (2004 VW Jetta Wagon) issue.

 

Getting There

head seal complete

It has been 2 years since Hapy really went much of anywhere. Most of that time, he sat waiting for attention either in an unknown, but unstartable state or in pieces. Once I had him re-assembled with a new flywheel/ring gear and had a test drive, the original reason for him to have starting problems re-appeared: Injection Pump losing prime. I was able to prime the pump with a MityVac and then crack the injectors to get him running. And, in that way I took him on a short test drive, found some issues with the lights, etc. There remained many other issues, but at least I could get him running, stopping and had my lights so I could drive him an hour and 20 minutes to Justin's shop.

 

The night before our start-of-day appointment, I got Hapy out of the back and filled with B-20 biodiesel ($6.40/gal. same as dinoDiesel. Thanks, Trump). That morning, I filled up with coffee and hit the road. Most of the drive from West Beaverton to Justin's shop is on back country roads with few other drivers on an early Saturday morning and even fewer traffic lights. It was in the 50's (F low-teens C) and clear, making the drive very pleasant. At some point after I fixed the rear speakers, the stereo lost access to 12V so I drove in silence, a familiar scene for Hapy. The road was so easy, the thermostat never opened. I had the cabin heat on, so I may have been pulling just enough heat off the engine to keep the thermostat closed. Based on the UltraGauge, the engine temp was hovering around 180*F so running "cold". When I pulled into town off the country roads, I had a few cases of not finding 2nd gear. I noted that for followup later. When I arrived, Justin and I hung out for a bit before getting started. He has so many interesting projects all going at once, you have to absorb it all. I mean, who puts a TDI in an Audi TT while also putting one into a Rabbit pickup? Love that! The way he scraps discards and re-uses them for the basis of tools is pretty awesome too. He's even teaching himself TIG welding. Small crush, maybe. Okay, fine. He does do some impressive stuff.

 

Injection Pump (IP) Reseal

hammer mod perfecting IQ

Justin had encouraged me to get the seal kit from Cascade German, since they are local-to-Oregon, when we first set the apointment. I had already purchased the deluxe kit from DieselGeek. I didn't understand the difference. These 2 kits definitely vary in their intended purpose, so they have some meaningful differences. The Cascade German version is actually less expensive, but it includes all of the little seals usually replaced when a legit shop does the re-seal. The DieselGeek kit has far fewer seals (just the 2 on top and the head-to-base seal) and it is designed for the home-mechanic to re-seal the pump in their garage without removing the pump from the vehicle. The DieselGeek deluxe kit is more expensive because it includes specialty bits a car owner probably does not have, but are needed for the job. This differentiation is important and your case may lead you to the larger kit even if you do not intend to replace much more than the 3 included in the DieselGeek deluxe.

 

Once Justin discovered the gap, we made-do with the smaller kit. Justin replaced the top 2 seals first and then moved onto the head-to-base seal. Rather than use the included "retraction limiting bolt" and try to fit the new head seal over the top of it, the head was removed, and I held the guts of the pump in-place while Justin cleaned all the surfaces and installed the new seal onto the head. Once installed, he hooked up the VagCom and hammer-mod'd (link to Hammer Mod thread on TDIClub) the injection quantity (IQ). Justin was aiming for 6.0 mg/stk because the engine was cold (54*C).

 

The engine bay was pretty dirty, so lots of time was spent getting the IP clean before we began as well as afterwards when the whole engine got a cleaning. After it dried off a bit, we let the engine idle and we looked for leaks. None found. Justin did ask about how the starter was mating to the flywheel. It does sound loud, like it may not be meshing quite right. I'll need to remove and reinstall the starter and the starter adapter to see if I can get things to sit right. The original adapter and starter that I put in just worked for years. I would expect the new-also-stock starter would fit the same. Since this is a new adapter, that is actually designed for the application, versus one I dremel'd to fit, I would think it would fit better. It's a puzzler, but one I will consider carefully as I remove/reinstall (R&R) the starter to get it to hit the ring gear more cleanly.

 

Getting Home

If there is anything we have learned over the years about Hapy, its that he loves going places and really does not like going home. How many times have I left home and the road trip to 4 Peaks or some camping spot went great and the drive home was either very challenging or partially performed by a flatbed? Too many. This trip was no different. At first, Hapy ran great. The engine was responsive and stayed cool. Somewhere around McMinnville a charged air pipe popped off, leaving me running naturally aspirated the rest of the drive home. This served as yet another reminder to never leave home with Hapy without some tools. While the turbo is great for the overall power-band, its absence is really noticeable when trying to leave the line and get up to traffic speed. Now that it was about noon on an absolutely stunner of a day, the roads were busy where they had been empty a few hours before.

 

By the time I was approaching the Dundee Bypass, I was having increasing difficulty finding 1st and 2nd gear. Sometimes, one or the other would be right there. Other times, it was a "can't find it, grind it" experience. This persisted all the way home, forcing me to sometimes leave a stop line in 3rd. When you add in the no-turbo, I had some dissatisfied fellow travelers around me. I did get home, however, and I drove Hapy all the way into the shop so I can chase these issues.

K'Lack

After having something to eat, I switched over to K'Lack, the 2004 TDI Jetta Wagon with a BEW motor. It had been throwing a crank position sensor error, lighting up the check engine light (CEL), preventing it from passing smog. I had ordered a replacement from Cascade on Thursday, and it was in the morning mail on Saturday when I got home from Justin's. The removal/replacement of these is not complicated (remove bolt, unplug from harness, install is reverse), but getting to the sensor and the weird bolt head complicate things. The sensor sits right behind the oil filter on the front, when the engine installed transverse like normal. The bolt head is a 9mm 12-point. Half of my sockets are 6-point and the other half are 12's, designed, I think, for easier application onto hex bolts. In this weird case, that socket set perfectly onto the 12-point bolt head. With the right socket, short extension and ratchet the bolt comes out fairly easily. The plug end is fitted into a metal tang, but otherwise once unplugged, the whole thing can just get dropped through the gaps onto the ground.

 

To install, I plugged it in first and then covered the sensor with a rubber glove to lower it past the engine ick and then below the car. Could I have cleaned the engine bay before starting? Yes. But then I would have been lying in mud since the car was on my front lawn, not back in the shop and I didn't want to lay in a puddle. At this point, I found having another person to be your eyes is very helpful. I got under the car, un-gloved and suspended sensor in hand and had Boo tell me east-west, up down until I was able to send the sensor into the hole. By doing it in this order, the sensor wanted to be oriented such that the bolt holes lined up naturally. I sent the bolt thru, tightened with the socket/ratchet combo and I was done. Since I cleared the code we need to run a few cycles until it is ready to smog.

 

For the legal-minded, Oregon cops are interested in registration violations after years of looking the other way post-CoViD. K'Lack got a registration-violation ticket while legally parked in downtown Portland. Drivers beware.

 

Hapy Wrenching

Feeling confident, I switched back to Hapy, and re-connected the charged air hose. As I suspected, it was one of the rubber-to-metal bits. I cleaned both the outside of the metal pipe and the inside of the rubber with brake cleaner so they were more apt to stay together and then tightened the clamp down.

 

I next wanted to chase why the lower gears were sporadically missing. I checked the front of the transaxle to see if it was out of position at all. Nope. Right before Boo and I bought this house, I bought a Gene Berg shifter. The new-at-that-time seats were higher than stock, moving the approximately-stock-length Scat gear shift further away. The Gene Berg shifter is a few inches longer, so I figured there would be less leaning. I had not gotten to installing it before the house was bought and life took a turn. Anyway, at this point I looked at the Scat shifter I had installed, probably over 15 years ago and slid the vinyl boot up the shifter. The plastic bits on either side of the shifter appeared to be allowing more play than I remembered. Hmm. Then, I looked at the rest of that mechanism. It was very rusty, especially the foot that rests on the floor. I shot the bolts with Kroil and after waiting a couple of minutes, removed them with a 13mm spanner/socket combination.

 

rust under shifter

The floor under the shifter had meaningful rust to match the rust on the shifter foot. I don't know how much play was created by the plastic bits, nor how much may have been introduced by the rust. I do recall, however, that the Scat shifter instructions did not account for adjusting the placement of the shifter front/back nor left/right. When looking at the foot profile, it looks very much like it is designed to sit squarely in the oval without any adjustment at all. I don't know if this was a terribly good design, but I will be installing the Gene Berg shifter which does allow for adjusting. I cleaned up the rust dust, shot the floor and the shift-rod end with brake cleaner and got everything as clean as I could. Then, I painted the area with Eastwood's Rust Encapsulater (the new stuff is even better than the original) and called it a day. I still need to treat from below. I shot the picture on the right here as I was almost done applying the paint.

 

Wrap

Well, that's where we stand right now. I have been in and out of the shop a few times since Saturday and there is not a single drop of fuel on the floor under Hapy. So, we can close the book on the IP leak. I intend to complete the shifter swap and then R&R the starter next. I hope that will be the end of both issues, but I suspect there will be more to do than that. Then, of course, there are all the other things like a fuel level gauge, the radio, and the diesel heater just off the top of my head. There are many incomplete items on Hapy. Now that I have a mostly-inside (one doorway remains), concrete floor'd space to work, my desire to work on these cars has really kicked into a new level.

 

Thanks, as always, for following along and more next time-

Oh, Nemo

Today's post covers my challenges with Nemo's electrical and computer system simply trying to get him to start, or maybe a signal on the OBD-2 port. The car-work hours that I did not want to spend sanding on Zed, I spent doing this... until this took over. Yeah, I know. I could use another hobby.

No Start

Like so many issues with these old cars, our challenges with Nemo started with him not starting. His battery had been sitting on a trickle charger all winter, but I had left his hood cracked to make room for the alligator clips, so this ultimately was self-inflicted. Love those. But, the path we took to get there was interesting. Nemo is sitting under the fabric carport blocking a garage door. Behind that garage door sits Oliver, the 1978 MGB convertible, that I would very much like to be road testing and otherwise driving around. So, enter my motivation for moving Nemo. Insert key, turn ignition to "RUN". I see some familiar idiot lights, including the battery, oil and check-engine. Turn to "START" and he rev'd but would not start. I went around to the tailpipe and could not smell gas, so I start with the assumption that it is fuel delivery.

Before I did anything else, I considered what I experienced when I turned the key to "RUN". I did not hear the fuel pump cycle. I did not hear the radiator fans kick on. So, something is not getting the "RUN" signal. So, I pull out the UltraGauge and plug it into the OBD-2 port. I get a never-ending "scanning..." message. Well, that's not good. I double-checked the UltraGauge in Hapy, and the computer linked within a few seconds. Okay, we have trouble with Nemo's diagnostic system which could prevent a start or we have multiple things going on. With this car, the latter is probably true. First, I tried to isolate the OBD-2 issue, and kill many many hours doing so.

OBD-2 Issue Diagnosis: General

The early B5 versions of the A4 had some interesting 1 or 2 year only issues. One of the oddities around 1997, when Nemo was sold, was the engineers choice to integrate the stock stereo with the "K-line": the signal processing wiring between the computer, many components and the OBD-2 plug. In these late 90's cars, it is the K-line you are subscribing to, not the more modern "CAN BUS". Okay, cool. There are many modules plugged into the K-line, but they are all in parallel. the diagnosis theory goes that when you get no signal on the K-line it is because one of the modules is faulting out, grounding the K-line. Once you can identify and remove the faulty module, you will get a signal on the K-line. You will probably get a failure code for that module, but you will at least get a signal. So, away we go, trying to figure out what modules are even on the K-line, and then isolating them.

OBD-2 Issue Diagnosis: Radio

The stock radio wiring was unceremoniously cut to pieces by the idiots at Car Toys when they installed an aftermarket stereo. Based on the wiring diagrams I have found and the commentary on the interwebs, I am not sure this car actually had that K-line-in-the-stereo thing. I did check the wires for the right color combinations, and for wires that were the correct colors for the K-line. I was unable to find them. There are, however, many wires sticking out of the hole where the radio used to be... before it was ripped off in Eugene. I intend to re-integrate an original plug before I put all this back together, but that's another day. I moved on to the next possible culprit: the climate control system.

OBD-2 Issue Diagnosis: Climate Control

found in climate
computer

The climate control system in these cars is another little computer. In some models, it is held in place with a couple brass clips. In Nemo, I had to remove the center console cover plate / face and found 2 Phillips screws holding it in. Once threaded out, the unit removes through the front. I unplugged the unit and checked the OBD-2 for a signal. Nope. I did, however, find a soda/beer can pull tab inside it (picture on the right, here, laying on the carpet after I removed it from inside the climate control computer thing). So, that was interesting. Next.

OBD-2 Issue Diagnosis: ABS (Brakes)

The fine folks on the interwebs have found that the ABS sometimes causes K-Line problems. The way to identify if it is the problem is to disconnect the plug. The ABS unit is on the driver (left) side, next to the washer bottle. You simply pull up on the silver metal tab and the plug lifts out of the socket. I found a piece of electrical tape floating around in there. Another question-mark from the prior owner. Neat. I checked the OBD-2 for a signal. Nope. I shot the socket and the plug with DeOxit and left it disconnected for the rest of my tests. I figured I might as well leave it better than it was (DeOxit, not leaving it unplugged). Next!

OBD-2 Issue Diagnosis: Dash Cluster

Moving on, we consider the dash cluster. The entire thing is held in by 2 Torx-head screws from the front, hidden behind a cover plate just above the steering wheel. Pull the cover plate, remove the screws and it pops right out. I unplugged the various cable plugs and checked the OBD-2 again. Nope. Grr... Next!!

OBD-2 Issue Diagnosis: ECU

example A4 ECU 

It seems like every system on the engine that has more than one wire into it delivers some signal to the computer. So, this seemed like the next logical step. I figured if I could get a signal after unplugging the small plug on the ECU, I would have shown that the issue is in the engine compartment and I could put everything in the cabin back together again. If the issue remains, then it could be the ECU. So, I disconnected the small plug from the ECU and we still didn't have a K-line signal. Grr...

So, I plugged the ECU, ABS and the dash cluster back in, turned the key to RUN and heard the click-snap of some relays firing, but no fuel pump nor fan spin. I could not remember if I heard the relays before, but this changed my thinking. If at least some of the relays are firing, then the ECU is telling them to. If there is a Check Engine Light, then the ECU must be at least partially working. Perhaps the K-line / OBD-2 issue is completely unrelated and this is just a simple fuel supply issue. So.. new plan: get the fuel pump to fire.

Fuel Pump Test

As is so often the case in laboratory settings, the pre-work for the experiment is where all the time is taken. Such is the case here. I started by removing the plate covering the fuel pump. This sits behind the rear seat in the trunk on the passenger (right) side, and is held in place with 3 very short Phillips screws. Once the plate is removed, you can see the top of the fuel pump. There are 2 fuel lines, one supply and one return, and a single electric plug. I found that slightly wiggling the plug allowed it to pull off the pump. YMMV. Once removed, you will see 4 pins. 2 of them are for the fuel level and 2 are for the pump. I started my tests with basic resistance and continuity-to-ground. Things seemed fine, so I shifted focus to test-firing the pump by applying 12V to the pump.

This is where the experiment set up took some time relative to the actual test execution. I ran a pair of wires from near the battery (not hooked up) back to the fuel pump. At the battery, I taped 10A fuse to the "red" wire and alligator-clipped the other side of the blade to the positive battery post. I alligator-clipped the "black" wire to the negative post. Back at the fuel pump, I applied the red and black wires to the fuel pump and it fired right up. I held the wires there a few second to demonstrate that it would not just run for a second and die. So, we have a good pump, but the pump won't fire from a relay signal. So, next we check the voltage from the relay, after we put the experiment wiring away.

Fuel Pump Relay Test

A4 Fuel Pump Relay

Back up front, I took a red wire, stuck it into the voltage-supply pin in the wiring plug at the fuel pump and tossed the other end through the cabin, over the outer edge of the driver seat. My plan was to compare the voltage sent to the pump at the pump. Since the relay only pops for a second when you turn on the ignition, I had to have my test equipment near the ignition key. I stuck my black lead against the metal fuse box mount, held the red lead against the wire I tossed through and turned the ignition to "RUN". I got 5V. I checked other spots around the fuse box and got 13V, so I started thinking that the relay was bad, dropping the voltage from 12/13V to 5V which, of course, is not enough to run the pump. So, I swapped out the relay... and the fuel pump still would not run. Great. I concluded that the 5V I read was actually the base charge for the fuel level sender and not the supply for running the pump. 

So, I checked the voltage at the supply-side of the relay: 13V. I jumpered across the relay pins, and the pump fired up. So, we're back to the ECU is not sending a signal. Fearing it is the ECU, I went looking for any other reason. I recalled that when Dot (the white 2000 VW Jetta 2.0 which broke the timing belt) failed, one of the theories for not starting was a crank position sensor. The thinking is that if the ECU doesn't know where in the revolution the crank is, it doesn't know when to fire, so it doesn't try. It is not as clear whether a failing crank sensor would prevent the fuel pump relay from getting a signal from the ECU, however. As much as I have tried to avoid it, it felt like I was sliding into just-swap-parts problem solving. At $35US for the least expensive part-to-swap (crank position sensors start closer to $60US), this can get needlessly expensive very quickly.

Crank Position Sensor (CKP)

A4 Crank Position Sensor

I have mentioned before my belief that the Audi engineers are sadists. Only someone who takes pleasure in other's pain could arrange for replacement items to be so hard to get to. Case-in-point: the crank position sensor. The crank runs the length of the block (obviously), so given a blank canvas, an engineer could potentially place a sensor anywhere along that axis. Chosen location? Directly under/behind the oil filter so you either have to remove the oil filter (forcing an oil change, which arguably is due) OR you need to perform contortions to get an Allen-head wrench in there. If you go this route, consider that the further the bolt comes out, the closer you get to the oil filter. At least there is only one fastener. These sensors have a long lead on them that plugs into the engine harness... behind the coolant bottle. In Nemo's case, this plug was fairly easy to get to. There are methods for testing the sensor, of course.

The Audi/VW sensor has 3 wires, from pin 1-3: power | signal | ground where the power and signal connect to the ECU and the ground finds its way to the chassis. To test, 12V and ground need to be supplied to the sensor plug (once disconnected from the harness) and a multimeter checking the signal wire for an AC wave signal while the engine is turning. No signal = bad sensor. Since no local shops had a CKP, I returned to sanding Bondo in Zed while I waited for the part to arrive.

Once I had the part in hand, I checked the resistance between the pins. I got 500ohms +/- between the middle pin and one of the outer pins. Using that as a baseline, I swapped out the CKP and then tested the one I had just removed. Same resistance. So, I concluded there was nothing wrong with the old one and put it in the stash of A4 spare parts (with the fuel pump relay).

ECU Swap

At this point, I had run completely out of ideas fo4r why the ECU was not sending a "go" signal to the fuel pump relay. I hit the local junkyard looking for a just-dropped-off A4 to scavenge the ECU. None of the A4's there had the right ECU, but I did get an ECU box cover: Nemo's had a good-sized hole in it where I thought water might have entered. Without another option, I hit eBarf and found an ECU with the same part number as the one as was currently in Nemo at a salvage yard on the East Coast (with a 30 day return policy!). Hopeful, I swapped out the ECU's which consisted of pulling out the big plugs in the back of the old and plugging them into the new one, since the box was still lid-less. I had some concern that energizing the ECU could fry it if the underlying condition still existed.

Still, I turned the key to "RUN" anyway... and heard the radiator fans and fuel pump cycle for a second before shutting off. This was how things used to work. So, I turned to start and he fired right up. I have concluded that my first guess was the correct one: I had left the hood open a little bit to make room for the alligator clips on the trickle charger, and with the hole in the ECU box lid, water got into the ECU and partly fried it. If I had not had the experience with the chipped ECU for Hapy when the computer semi-worked, I would not have been so quick to accept this. The Check Engine Light lit, so the A4 chat-boards all assume that means the ECU is fine. NOT TRUE. It could be partly damaged, like Nemo's.

The climate control is still in pieces, the lower dash panel is off, and the radio wiring, well, it's the same as it was: a mess. While I can move Nemo out of the way so Oliver can go for a spin, Nemo is not ready for driving around just yet. The re-assembly will wait, and I'll probably post on at least the re-wiring of the stereo plugs that the idiots at CarToys cut apart. I did, however, install the ECU box lid, complete with threading in the screws to hold it tightly shut. No more water getting in there.

Thanks, as always, for following along-

P0121 - the 1200 rpm limp mode - Part 1

Today, I will start to go through my efforts to identify the cause for my P0121 - Intermittent Signal from TPS issue. Yes, I know! Another multi-part series?!? Well, that's how it goes when we need to wait for shippers. Anyway, the process I followed is similar to what I did for the other wiring issues I just resolved in that there is a logical approach, but otherwise, this is about solving a 6-wire circuit and really shouldn't be a big deal. But it was and here we are.

Drive-by-Wire

drive-by-wire pedal

For those who haven't suffered from this code before, or may not even know this is the code you are getting, I'll start with a quick summary of what this is about. In modern drive-by-wire cars, your throttle pedal may not actually control the speed of your engine or vehicle directly. If you have watched some of the car shows on MotorTrend, when an older car (pre-fuel injection) gets a modern engine (with fuel-injection), they need to add a throttle position sensor (TPS) to tell the computer how far open or shut the throttle is. In these conversions, the TPS is usually connected to the throttle cable in the engine bay. This converted the pull/push of the cable (which reflects the push / let-up of your foot) into a signal the computer understands so it can figure out how much fuel to throw in, or how to adjust the timing of the spark. Cool, eh?

 

New cars, whether they are burning volts, waste cooking oil or dead dinosaurs, do not have a go pedal hooked up to a cable any more. They skip the middle man and have a TPS wired up to the pedal, so your pedal works like a big fader (light dimmer) or rheostat. The TPS converts your foot push / let-up into different voltage that gets sent to the computer where it does all the things I mentioned above.

P0121 - What Is It

All this is great. I mean, having something that precisely collecting your speed wishes and implementing them without a mechanical component seems pretty fantastic. And, it is, until that day when you are driving along and suddenly the pedal no longer seems to translate into speed. You notice that no matter how you position your foot, the engine speed doesn't vary. In fact, you note that the engine's speed has become static. I can't speak for other makes and model years, but if you are in a VW TDI circa 1998-2004 the engine will be pinned at 1200 rpm. Adding color to the scene will be the illumination of the check engine light. Your first impulse may be "oh snap, the engine is broken". Not so fast. In this case, you are probably getting code P0121: Intermittent Signal Inconsistency from the Throttle Position Sensor.

That sounds awfully scary, but in cars that were not hacked up like Hapy, this is probably caused by your TPS failing. It happens. In VW's, this is one of those rare parts that do not fail super-often, but when they do they are actually kind of easy to replace. You remove the panel under the dash, unplug the flat-connector, remove 4 bolts and it's out. Replacing the one in Hapy is just as easy, but determining that the TPS is the root cause is not. In Hapy, we have 6 circuits running through 7 meters of wire and multiple connectors. In your car, the 6 circuits probably run for less than a foot and run from that flat-connector to a T10 or something similar. No extra connectors, no super-long wires.

Hapy Diagnosing Plan

Before I pulled out my multi-meter, I gave myself a few minutes to think about the situation. I had intermittent P0121 codes getting thrown since I before swapped out the original 1998 NewBeetle one-year-only TPS for the more general-use one for model years up through 2004. The original TPS had the 6-wire bundle pressed against the underside of the bus, and eventually the plastic wire casings wore through. The wires grounded against the body, causing the original P0121 errors. The general-use pedal threw codes intermittently and was one of the drivers for the replacement of those wires with the front-to-back cable. That cable runs from just after the flat-connector all the way to the blue T10 (through another T12 connector). So, either some part of the wiring was done wrong or it was never the wiring all along, and it had always been the TPS or the flat-connector or both.

 

A side note about the wire sizes. The wires coming out of the VW 6-pin flat-connector vary in thickness from 22 or 24 up to maybe 18 (probably more like 20). Since the resistance of the wire is inversely related to it's thickness (thinner = more resistant), by replacing the old thin single wires with a thicker well-jacketed cable, I effectively reduced the resistance of the front-to-back run. According to this calculator, the wires in the new cable should be around 0.03 ohms. The old wires, being 22AWT gauge were around 0.3 ohms. Noting the decimal point, the old wires were 10x more resistant to current. So, we can exclude any concerns about the new cable wire size being a cause; quite the contrary, it should be delivering electronic messages better.

A failing TPS or a bad flat-connector sound like great theories. Let's prove it. I chose to start at the flat-connector and work back to the ECU. I have a second flat-connector in the heap of spare or removed TDI stuff in my garage that is also 6-pin, so I can swap-out the in-Hapy one if necessary. This also provided me the resistance values for a 6-pin flat-connector that is otherwise "normal". With the multi-meter at its most sensitive setting, I tested the resistance of each pin -to- end-of-wire. After the plug was warm in my hand, the resistance value was "3". Prior to that, when it was cold from the garage, the resistance was closer to "8". Since they were all within the same order of magnitude, I wasn't too concerned. That's our baseline: less than 10 on the most sensitive setting. With that, we bundle up and head back out to the bus.

Hapy Wiring at TPS

6-pin to
front-to-back cable

First, I unplugged the flat-connector, peeled back the plastic wire protector to where the wire splices were and then, with a razorblade, cut a small slit in each cable wire just past heat-shrink so I could touch metal with a probe. You can see the repairs to the wires in the picture on the right. The blue wire is probably the best visual example. Then, from 1 to 6, I checked the resistance to make sure they were all less than 10 on the most sensitive setting. To keep variables down, I held the flat-connector in my hands for about a minute first. It is still cold (4*C) here, even if I'm not complaining about it in every post. Apparently, its not a cold winter, I'm just a sissy working outside in it. So be it. Anyway, they were all very low, like at or below a "2" on the most sensitive setting. This told me that the flat-connector was good and the wire connections between the flat-connector and the cable were good. Very good, actually.

 

While the 6-pin flat-connector was out, I addressed the TPS plug socket with DeoxIt D5 according to the instructions on the can. I figured that if our problem was a simple case of the contacts getting worse over time, we would see a some improvement from this. I covered the little slits with electrical tape, and took a picture so I could reference the color-to-color later. I re-wrapped the wires in the plastic covering and moved to the back of the bus. I left the 6-pin flat-connector disconnected so the contacts could air dry.

Hapy Wiring at Engine Bay

T12-to-donor (T10 blue)

In the engine bay, I confirmed that the blue T10 and grey T12 plugs were snug. I would have had other issues if they had not been, but diligence wins electrical issues. Then, I pulled back the plastic cable wraps and took a picture of the T12 wires from pins 1-6 and then a picture of the color-to-color connections from the T12 to the wires which run to the blue T10. I compared these pictures with the wiring diagram I had constructed and believed all of the wires were routing to the correct partners. So far, so good. The next test was to confirm continuity between the blue T10 pin and the originating pin on the 6-pin flat-connector. This would demonstrate that the wiring from end to end is clean.

 

I was not really sure what to expect, resistance-wise. Before I could do anything, I needed to close the circuit, so I grabbed a long solid-core wire I have used to test with in the past. My testing process: I would gently insert a bare wire into the pin-hole in the flat-connector, and run the rest of the wire spool back to the engine bay. There, I measured the resistance between that wire end and a pin in the blue T10. I had difficulty figuring out which pin was "1" versus "4" in the blue T10 and the pattern from wire to pin seemed illogical. Unfortunately, had I really internalized that, I would have potentially found the root issue. When I found a connection, the resistance was down in the single digits in all cases. So, we can rule out the new wiring... ish: I discovered later that when I wired up the blue T10, I crossed up 3 of the wires. I didn't realize this until later (hence the 2-part post as I lost a bunch of time going down a wrong road). So, I continued forward believing that the wiring was right. Since I learned a bunch about the pedal along the way, I felt it was worth retaining all of this content.

 

Hapy TPS

Since I thought there were no wiring issues, I figured that the TPS went bad. I first thought that maybe I broke it by stepping on it all the way to max, and it needs a movement stopper or something. I looked at the way I installed it; the floor and the carpet would have acted like a prevent against over-pressing the pedal. After doing some research, it seems like these pedals are prone to failure if they get wet. Since Hapy is parked outside, and last year his fancy BusDepot cover effectively held water in rather than out, if the pedal had been steadily degrading because of the damp conditions over the winter (and sometimes in the Summer around here), then this seems a fairly reasonable explanation for the persistent, recurring P0121 code. I figured that last winter's super-damp caused the pedal to finally fail so I ordered a replacement.

 

That's it for today while we wait for the replacement pedal to arrive. More next time about resistances, voltages, etc as I examine the pedal and the pedal wiring and, ultimately, fix the P0121 error.