240sx TPS ADC range?

[Dan_Austin]

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.

[skirkland1980]

I was noticing interference with my tps signal so I shielded the tps wires and fixed the problem. If you look at a 240sx wiring harness you'll notice the tps wires are shielded.

[Dan_Austin]

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.

[Dan_Austin]

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.

[FricFrac]

I've had bad 240SX TPS before - some I've cleaned and rebuilt with sucsess - others were unrepairable and simply need to be replaced.  Symptoms were erratic readings when calibrating, no input, etc.

[Matt Cramer]

If the running value is different from the off value, check the ground. The ground needs to be run to the ECU sensor return and not a chassis or engine ground.

[Dan_Austin]

I've run into other reports like FricFrac's, so I was why I was asking here.

 

After fixing the TPS side pigtail  The results are much better, but not perfect.  I will

recheck the connections near the TPS, although it may be good enough and I

am being too fussy.