Confused by RAVE and Throttle Position Sensor

[AndrewClarke]

Hi. I'm new to the world of RAVE. I've downloaded the ISO, fired it up in VMware on my Mac, and been brought back to the bad old days of 1990s computer software. I've found rave.zip which has versions of the PDFs that have been decrypted, which is was a beautiful discovery.

My 1995 Discovery is throwing code 17, Throttle Position Sensor. I could just buy a new sensor, but I'd like to test this one first to narrow down the fault. I've read everything I can, and see that there are or ought to be test procedures to test all this by reading resistance at the sensor and at the ECU. There are apparently continuity tests I'm supposed to be able to refer to for this.

HOWEVER, I can't find any of this in any of the manuals I have. I've got fragments of tests I've found, for example, for a 1987 Range Rover in section 19 of the fuel injection system. However, in the 1995 Discovery manuals it just seems to say "not serviceable, here's how to replace".

Partially I'm asking if I can use the procedure I found for the RRC to test my 1995 D1 TPS even though the RRC had an adjustable TPS and mine isn't. Mostly though, in the "teach a man to fish" vein, I'd really like to understand where in the RAVE (or elsewhere) I'm supposed to look for these test procedures so I can start to work through this stuff on my own.

 

[robertf]

I'm not sure it's in the rave manual. It's a linear potentiometer. Measure the resistance from open to close between the wiper and either end and make sure it doesn't jump because of worn tracks. When TPS wear (all, not just Rover) it's usually at the cruising angle from fretting

 

[AndrewClarke]

Thanks. Most places that list the codes, like http://www.robisonservice.com/servicedep/rover_trouble.asp, say something like

Refer to test 17, continuity test procedure.

If these tests aren't in RAVE, where are they? Are there other technical documents for these vehicles that nobody has?

 

[AndrewClarke]

I measured voltage at my TPS plug and got around 0.16V with the throttle closed. It seemed pretty smooth with my digital multimeter up to around 4.55V, and then popped up to 4.93V when I opened the throttle completely.

According to the fragment of 1987 Range Rover document I found, it's supposed to vary from 0.29 -> 5.0V. Does this mean my TPS is fine, or is the extremely low voltage at closed throttle potentially an issue?

I tried testing resistance but I couldn't measure resistance at all, getting 1 ohm everywhere I tried. Maybe I'm an idiot, or maybe my multimeter isn't sensitive enough.

Thinking at this time that the voltage range was acceptable (not having checked the low number against the document yet), I decided to pull the cable off the ECM and test voltage across the pins on that to see if there was a problem somewhere between the TPS and ECM. However, for the life of me I can't figure out how to disconnect the ECM cable. So from here on I'm asking how to disconnect that cable, but if anyone feels like taking a step back and weighing in on my TPS voltages, that might obviate the need to check at the ECM.

I stuck my camera in under the plug and it seems like there's a tab at the back (pink circle). The tab at the front (blue circle) seems too heavy to be moveable, so I assume there's a trick at the back. However, I can't manoeuvre my hands into any position to both press that tab and pull the cable out. What's the trick to this? To be honest, I'm not even 100% sure this is the right cable to be testing. It certainly doesn't look anything like what the workshop manual says it ought to.

 

[AndrewClarke]

I was thinking about this a bit more. When I reset the codes, code 17 comes back as soon as I turn on the vehicle. It happens before my foot touches the throttle. Therefore, any fault has to be with the throttle closed. This seems possibly consistent with the ECM reading low voltage from the TPS on startup. I'm just not sure if 0.16V is low enough to throw a fault.

 

[AndrewClarke]

I've ordered a used TPS from a wrecker, so I'll update here if it helps or doesn't.

 

[4Runner]

I elongated the mounting holes so I can adjust it. It doesn't take much. If you want to prove your theory then take the mounting screws out of your tps. Using a meter with the ignition on set it to something less than .40 volts, hold it there and have someone clear the code and then start it and see if the code still pops up. I do not know for a fact what the bottom limit of the 14CUX tps voltage is but .16 sounds low to me, in my experience. You could also clear the code, step on the gas slightly and then start it and see if your code comes back. I would shoot for .3 to .35 for a base voltage. Your ECU will learn what you set it at. Good luck.

 

[AndrewClarke]

I elongated the mounting holes so I can adjust it. It doesn't take much. If you want to prove your theory then take the mounting screws out of your tps. Using a meter with the ignition on set it to something less than .40 volts, hold it there and have someone clear the code and then start it and see if the code still pops up. I do not know for a fact what the bottom limit of the 14CUX tps voltage is but .16 sounds low to me, in my experience. You could also clear the code, step on the gas slightly and then start it and see if your code comes back. I would shoot for .3 to .35 for a base voltage. Your ECU will learn what you set it at. Good luck.

Good idea. I thought about that but since the manual says the ECU is supposed to learn, and it's no adjustable, I guess I just shut my brain off at that point. If I have time over the weekend while I'm waiting for my "new" one to arrive, I'll give it a shot.

 

[Buddy]

Good idea. I thought about that but since the manual says the ECU is supposed to learn, and it's no adjustable, I guess I just shut my brain off at that point. If I have time over the weekend while I'm waiting for my "new" one to arrive, I'll give it a shot.

It's not supposed to be adjustable but you can make it adjustable. It helps to fine tune them. I spent a lot of time researching the 14CUX system after I bought my first '95. there were some of the more helpful pages.

http://www.britishv8.org/articles/rover-14cux-efi.htm
http://www.v8engines.com/carbs-2.htm

I also got the RoverGauge and built one of the serial cables.
http://www.g33.co.uk/fuel_injection.htm
https://github.com/colinbourassa/rovergauge
https://github.com/colinbourassa/libcomm14cux/blob/wiki/HardwareInterface.md

One other thing to note is that the TPS are NLA so they are getting harder and harder to find. I came across this thread one time but the original vendor no longer makes the adapters and I've not had time to try and create one myself.
http://www.aulro.com/afvb/showthread.php?p=2501331#post2501331

 

[AndrewClarke]

The throttle position sensor the wrecker sent me was from a 1997, so I sent it back. I then used the drill press to elongate the screw holes on mine, and just guessed an amount to twist the sensor when refitting. I reset the computer and after a short test drive my check engine light is out and the readout is blank. Who knows how long this fix will work for, but for right now it's perfect.

Thanks everyone for your help.