Jump to content

240sx TPS ADC range?


Recommended Posts

Twelve weeks back I dropped off a well running car to the body shop for paint.

What I got back is less well running.  I don't blame the shop, I suspect based

on a data log that show TPS dropping well below zero and stalls or near stalls

when the drops occur, that dust from the sanding process got in the TPS.


I still need to pop the cover and clean it, but I have been confounded by trying

to calibrate the TPS.  There are two issues, one I have found referenced here,

but not solved, and not reference to the second.  The first is that the calibration

drifts, and the running ADC values can be 8~10%  below the off values, which

matters only that trying to calibrate with the engine running causes a stall.

The second issue which compounds the first is that the calibrated range seems

limited, from around 750 to 1000.  I plan to investigate the connections and

measure the TPS signal, but I wonder if other installations of this TPS have

seen similar limit signal range.  If it is normal for this model TPS, I can consider

trying to adapt a different model TPS (assuming I can find one known to

support a wide ADC range)


Also worth mentioning is that all sensors, TPS, CLT, MAP, IAT are all located

within six inches of each other and connected to the common leads  (sensor ground

and VREF) at the same point next to the sensors, and no other sensor is exhibiting

noise or odd readings.  The way I twisted, soldered and crimped the weatherpak

connector pins would make is unlikely that just the TPS has a faulty connection, but

I will check for that.

Link to comment
Share on other sites

I don't think I have noise, as the pattern is constant, either at idle or part throttle cruise the signal

will drop below zero for a fraction of a second, triggering decel fuel cut and then AE when the expected

signal returns.  At idle the result is a stall and while cruising a 'hiccup'


I did not get a chance to work on it this weekend, and I will consider adding shielding, but I suspect

the recent issue is crud in the sensor.  Longer term I was hoping to find a better TPS unit, unless

other installs using this unit had different results.  The lack of resolution (250~ish ADC between idle

and WOT), and the fact that calibration drifts has me unimpressed.  I've tried two of the 204SX sensors

and one was new, with consistent results, but a sample size of two less than compelling.

Link to comment
Share on other sites

I am still wondering what folks are seeing for a their TPS calibrations, but I think

I fixed the signal drop out.  I decided to start with the only connector in the harness

that I did not terminate and assemble myself, the TPS pigtail on the 'new' TPS.


I was thinking maybe bondo dust or moisture snuck in while it was at the paint shop.

Well as soon as I started to unplug it I noticed the TPS signal pin was pulled out

of the connector.  The first inspection showed the pin lock had not been pressed out

far enough, but after fixing the simple little tang, I determined that either the connector

was mis-aligned or the lock catch damaged in the 'new' TPS, since every time I

put the ends together the pin pushed back out. 


After addressing the floppy pin I have not been able to reproduce any off the issues, and

as an extra perk I think it solved a problem that appeared to be a failing fuel pump relay.

I only have a couple miles on the repair, but the problems had been easily occurring multiple

times in the same span before the repair, so hopes are high.

Link to comment
Share on other sites

  • 1 month later...

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

  • Create New...