The TR8 TPS (Throttle Potentiometer Switch ERC 3619 NLA) My TR8 Efi had been running odd for some time with on occasions a very strong HC smell. Unfortunately with its MOT looming it was fairly obvious it wasn t going to pass so I was going to have to do something about it. Strange how when a cars performance and driveability slowly deteriorates over time you tend to instinctively live with it. In this case driving the car was becoming increasingly less pleasurable with often a jerky ride and fuel consumption becoming horrendous. The heavy rains here in Yorkshire seemed to make the issue worse having driven back from Manchester on the worst day of the rains. I d previously moded my TR8 to run with a piggy back ecu to improve its performance so I decided to take the car back to Denis Vessey who did the mod to put it on his rolling road. It took less than 20 mins to see the fuel was all over the place and then another two to find that when you moved the TPS (Throttle Potentiometer Switch) plug it all changed. That immediately pointed to either a faulty plug or the TPS its self. Changing the plug didn t fix it so we were left with the TPS which is now no longer available. Two options then remaining; take it apart and try and fix it, or try and find a new TPS that would fit in its place. We tried option one first. The top of the TPS has been sealed where the screws are so we carefully drilled out the plastic sealant as it s a quite hard material. Then the screws can be easily undone.
What you see next when the two parts come apart are the carbon tracks that the wiper arm moves over to indicate to the ECU what position the accelerator is in. You ll note from this picture we found that the carbon tracks had in effect almost worn through the carbon. This isn t always the end of the story as it s possible to remove the plastic welds on the wiper arm and move it to a new piece of carbon using small screws to re-secure it. See picture below. Unfortunately in this case the RED wire we discovered after cutting through the plastic sleeve was in fact only hanging on by a thread. We had a go at re-soldering it to the remaining stub and sealing it all back up with some sealant but in this case once back on the rolling road it wasn t successful.
So to plan B Denis has a motor sport TPS that he uses as a generic replace all sort of part made by Lumenition part number TPS001. Main problem is that the spindle holder is set recessed as opposed to the original TPS spindle holder that sticks out (See picture below) and the TR8 adaptor plate is modified for this with a raised circle platform. So two choices here make a new adaptor plate or machine the original to fit the new. Given I had a spare anyway we machined the original down by 4 millimetres off the face (not including the raised platform that fits in the circle recess you can see above which was removed prior). Two new adjustment screw holes need to be tapped plus one cable holder screw hole as well. Point to note when modifying the original plate is that it s actually two metals, aluminium and a steel circle in the centre. The wires are exactly the same as the original RED, YELLOW and GREEN.
So all you have to do is to fit the new style plug to the harness. The spindle is a very tight fit so to avoid breaking the new spindle holder you will need to gently file a very small amount off to make a snug fit as opposed to a tight never get it off again fit. See Picture below. Notice it s about 2/3rds the size of the original!
Once back on the road WOW what an improvement very very responsive now a totally different car to drive very very smooth! Nice neat fit and works so much better than the original! Richard Connew. World Wide TR7 TR8 Owners Club