3D Printed Throttle Position Sensor Mount
Joe Angell
Ever since I swapped a 3.0L engine into my DeLorean, I haven’t been able to get the throttle position sensor to work. That’s not entirely true — the sensor itself works, but it won’t spring back to closed when the throttle is released. Multiple sensors show this problem, and the throttle body seems fine, so I simply disabled the sensor and relied on MAP for fuel management.
After my jumper to disable the TPS failed and caused my car to stall instead of idle, I decided to try to rig up a working sensor by designing a custom mount for the valve cover.
I made a video showing the process and how it all works.
Mounting Location
I choose to mount it on the valve cover because it’s in line with the throttle, and there are two unused bolt holes in the cover that I can mount it to. My plan is to operate the sensor via a cable connected to the throttle arm.
Mount Design
I built the mount in modo as three parts:
TPS Adaptor and Mount
This has an opening for the TPS itself, as well as an angled piece that bolts to the valve cover.Arm
The arm is pulled by a cable running to the throttle. The flat end goes into the TPS and actually turns it in a similar manner to how the Jeep throttle body works. I used two washers on the ends pivot to act as bushings and to keep everything lined up.End Cap
This just holds everything together and provides 90 degrees of freed movement for the arm. It has heat set inserts for the long M5 hex cap screws used for this.
This worked pretty well, but the TPS’s internal spring isn’t quite strong enough to pull the cable back, so i needed to upgrade the mount with a spring. This just meant re-printing the end cap and arm with holes for an extension spring.
Choosing a Filament
The valve cover gets to almost 180 F (82 C), so the choice of filament is important here. But I wanted to see how different filaments reacted, so I tried three different ones, checking in on each after 20 minutes of driving:
PLA
This was never going to work, but it was already in the printer, and I wanted to see what would happen. PLA has a glass transition temperature of around 145 F (60 C), but won’t melt until over 310 F (170 C). In my test, the mount became rubbery, both mounting bolts came loose, and one of the assembly screws was loose, which honestly is better than I expected. It’s still unusable here, though.PETG
This is my go-to filament, but it transitions at 180 F (82 C), which is far too close to the valve cover temperature. It actually held up really well in my test, and wasn’t really flexing at all. However, it was also below freezing outside. I don’t know what a hot summer day next to a running engine would do to it.ASA
This was my first time using ASA, which is like a better version of ABS with properties more suited to outdoor use. It worked very well here, and was completely rigid after my test.
Given the glass transition temperatures, this was all pretty predictable even before the tests. I went with ASA for the final mount, ABS would have been fine too. I wonder if PETG would have worked over the summer. There are other higher-temperature plastics, but ABS and ASA are close to the limit of what a consumer-grade machine can do.
Cable Construction
I have to run a cable from my new arm to the throttle arm, which means I need to build a cable. I bought a generic throttle and brake cable kit so that I could build my new cable. The kit came with all the parts I needed, but no instructions about how to actually use them. It took me a bit to find any useful information, but I finally hit on two great videos:
Revival Cycles Tech Talk - Custom Throttle Cable Kits
These guys sell quality kits, but more importantly for me is that they provide a video explaining what all the different parts are and how to use them to build a cable.Wildlife Moto - How to Make Custom Cables - Throttle
This is a very good video about how to make cables, with detailed step-by-step instructions. I found this invaluable for adding a barrel connector to my new cable.
You need to use cable cutters to cut sheath or cable, which I discovered by ruining a set of side cutters. I attached the ferrules on the end by just crashing them with a pair of pliers. I was worried about collapsing the cable, but it’s a lot strong than I expected and didn’t have any damage at all from my crimping.
For the barrel end on the arm side of the cable, I followed the instructions from Wildlife Moto. My kit had slightly different parts, but the basics were the same. I slid the cable through a barrel, made a bloom out of the end, and treated it with flux suitable for galvanized steel. Then dipped it in the solder pot to get a ball of solder and wire. After cutting off some stray ends, I dipped the ball and the barrel together into the solder. I finally filed down the solder to roughly the shape of the barrel, and that was it. I tried pulling the end off, but it’s pretty strongly in there, so I think I’m good.
Attaching the Cable
The cable has to be attached at three points.
First, the arm of my mount. This is simple: the cable just runs through the end hole in the arm, and the soldered barrel holds it in place.
Second, the throttle arm. The problem I had here is that there was only one mounting point left, and it moves in the wrong direction. I solved this by designing a new clip that could support two cables, and attached both the transmission cable and my new cable to the same mounting point. This worked quite well. I used some screw-on cable ends, which made it easy to adjust the cable.
Finally, the sheath has to be anchored. This keeps the cable from rubbing against the bracket, and keeps it from flexing too much, which ensures that there’s relatively little deflection as the cable moves. I could have added another anchor on the other end of the cable at my mount, but it’s so short that I don’t think I really need one.
Anchoring the sheath was a bit trickier than I expected. My original plan was a clamp that connected my new cable to the transmission cable. I went through a few iterations to get one that held the cable without slipping. Heat set inserts lock the two halves together. It worked, but it was possible for it to flip around and cause the cable to bind, which defeated the purpose.
So I designed a new anchor that clamped around the end of the transmission cable and the bracket. This holds much more securely and isn’t susceptible to shifting around like the clamp would. It again used heat set inserts to hold the two halves together and to grab the TPS cable.
Final Results
This whole thing worked quite well. The bit of play in the cable means that it’s not quite as good as a TPS mounted to the throttle itself, but considering the Jeep mounting wasn’t working at all, this is definitely an improvement. In theory, I’ll have better throttle response and wide-open throttle behavior now, and the logs will be more useful.
3D Models
This zip contains the original modo LXO files, and the generated STL files that I used to print these parts.