TPS diagnosis, continued. Help.

[elwesso]

k.. Ive finally had it with my transmission acting up.. This is REALLY strange...

Symptoms: Transmission will not shift from 1-2 below 3000 RPM... simply wont do it. It WILL shift if you completely let off the gas.. if you let it go above 3000 RPM it will shift but its firmer than normal.. At about half throttle, its fairly normal, but still not normal...

So heres what Ive done. Ive been fighting this all afternoon.... Heres what ive done for starters. First off, i know the TPS is good, i bought a used one from a known good Q and it also did not change any when I swapped it for my old TPS... I however did get ahold of a known BAD TPS and it definitely was worse when it was installed.

I have the TPS pins on the TCU already probed and ready to look at voltage... I pulled the voltage from that, as the FSM dictated, ignition on, TPS plugged in (obviously).. Between pin 34 and 35 on the TCU. Its supposed to read around .5 volts.. I set it to .44 a long time ago (what tech recommends), so I know my method worked fine...

Anyway, i checked the voltage and I got 5 volts.. what it is at WOT... for kicks and giggles, i checked the resistance, set the ohm meter at 20k and got 2.65 ohms, so that means to me its pulling 2.65x10^4 ohms or 26,500 ohms... interestingly enough the resistance OR voltage does not change if the TPS is plugged in or not.... What surprised me is that I got continuity between the 2 pins, i didnt know if I should or not, and I suppose the only way to find out would be to check on a known good Q.. Not really important at this point.

Onward we go, i just checked the continuity between the respective pins on the TCU and the TPS harness... I get continuity, albeit, not FULL continuity between the 2 respective pins and the corresponding pins on the TPS harness.... There doesnt seem to be a short in that circuit.... because when I test it, say between pin 34 on the TCU and pin B on the TPS harness, I get continuity but if I switch to pin 35 on the TCU and pin B on the TPS harness, i get no continuity. I think that if there was a short, that I would get continuity between both of them. I tried every combination and was able to achieve "good" results.

So then I checked the integrity of the connection between the ECU and the TPS harness, as dictated by the FSM. I was able to get great connections there, full continuity where there was supposed to. The TPS harness is getting a good ground, and a good input signal of a little over 5 volts (where it is suppose to be.)

So I checked the TPS voltage at the ECU between pin 38 and pin 48 and got 5 volts, a I think I got 5.10 volts vs the 5.08 volts i got at the TCU. makes sense, because the ECU apparently gets the TPS voltage first, and then sends the information to the TCU...

The only thing I have yet to check is the continuity between the ECU and TCU, but I suspect that will be ok....

The thing that confuses me and I think is causing my problems, why am I getting 5 volts (approx) when I should only be getting .4ish at idle? as stated earlier, the wiring integrity seems that there isnt a short, however the voltage readings seems like there IS a short....

[maxnix]

Sorry I can't help, but one of my neighbors diagnosed a faulty TPS via FSM procedure, bought another used one, and shows the same symptom. I think it was an open though.

[elwesso]

See normally when you have a bad TPS it shows no voltage where I probed, or the voltage changes but is either incorrect or not linear, but mine is constant regardless..

[FarFetched]

You are right about idle V on TPS. It shouldn't be more than 1.0V (some cars have +- .3V variance).If TPS operates in "limp" mode then you will nt get correct TCU-ECU read-out. Everything will be mixed-up and won't make sense. I've had similar problems in some GM cars/trucks. 5.0V is the reference voltage and most components will modify (you know that ) output voltage under various conditions. Try to get resisance check on TPS (with a good shop scope) I bet you will se drop outs you couldn't see with multimeter. Good luck.Cheers!

[elwesso]

Thanks for replying, farfetched. Glad to see you still lurk even though you are not of the Q owner bretheren anymore.

Anyway, i dont understand what you mean about the "limp mode". Even if I unplug the sensor, the voltage should go to 0!

Im going to play around with it more tomorrow and check more for shorts.

I really need to buy a scope sometime, ive been eyeing them down on ebay...

[FarFetched]

The reference V should remain 5.0V, however, if it doesn't modify REF voltage according to its movement then it in "limp mode". That doesn't mean it has dead spots, it's just potentiomemter part is csrewd up. Like you've said, once you are NICO member you're always NICO member. I still like Q45 (even love it). However, open roads becon me more these days. I ride even now when temps are in teens (brrrrr) I can kill pretty much every car on the road with my "HO" . But then again you cannot compare apples to oranges - right? Cheers!

[elwesso]

i see what your saying... but im not checking the reference voltage, im checking the sensor voltage!!!! and its GIVING me the reference voltage.

[FarFetched]

The Throttle Position Sensor has both a linear potentiometer (sensor) and Quote »Closed/Wide Open Throttle switches. The Throttle position sensor is a kind of potentiometer which transforms the throttle position into output voltage, and emits the voltage signal to the ECM. In addition, the sensor detects the opening and closing speed of the throttle valve and feeds the voltage signal to the ECM.Closed throttle position of the throttle valve is determined by the ECM receiving the signal from the throttle sensor. This system is called "soft closed throttle position switch". It controls engine operation such as fuel cut. On the other hand, 'hard closed throttle position switch", which is built in the throttle position sensor unit, is used for engine control when soft closed throttle position switch is malfunctioning.[/quote]Quote »Disconnect throttle position sensor harness connector. Make sure that resistance between terminals B and C changes when opening throttle valve manually.Accelerator pedal completely released, resistance approximately 0.7 K Ohms . Accelerator pedal partially released, resistance 0.7 to 5.0 K Ohms . Accelerator pedal completely depressed, resistance approximately5.0 K Ohms. If throttle position sensor fails test, replace it.[/quote]I dug it up in ALLDATA Cheers!

[3Q Jay]

Wes, when you are on the 20k scale and you read 2.65, that is 2650 ohms, not 26500. i'm not a big fan of the resistance method, unless the tps is the only thing in the circuit (disconnect tps connx and probe right on the tps pins). for me, this is also secondary to the voltage method. anyway, it sounds like you found the problem area related to the late shift. what happens when you read the voltage at tcu as you wind the throttle open/closed? (any change)? my guess just from the descriptions is the tps is bad, eithr the internal wiper or bad connx at tps. you said you measured voltage/resistance when the 'other' tps was installed? is your idle outrageously high, corresponding to the high tps voltage reading?

[Raxephon]

Not sure if this will help, but...

I disassembled my '91 TPS the other day and found one of the plastic "Chocks" broken.

Ohming it only ended in a consistent 0.4, open & closed.

EDIT: Sorry for the quality of the pic, its from a "camera phone "

[elwesso]

Jay...

The car started idling high (1000 RPM) a while back ago for an unknown reason. I just cleaned the TB, MAF and IAC, and it started doing it... This was a long time ago when it was shifting fine...

now the car does idle even higher, at 1200 RPM.... about 1500 when its cold.

The car has not idled normal since I bought it way back whenever...

I just went out and fiddled with it some more, and now im getting NO voltage at the TCU but the same 5 volts when I read at the ECU..... Could be my pins i stuck into the TCU need some help.... I checked between 2 pins on the ECU (38 and 48 I think, the 2 that are on the bottom row regarding the TPS) and while moving the throttle it didnt changed, stayed at a solid 5.12 volts. When i checked between I think pin 30 and 48, it went down to 5.09 volts as seen on the ECU....

Right now i set it at 700 ohms and it moves smoothly resistance wise read right on the TPS....

[3Q Jay]

unless you have real sharp probes, i would guess you didn't have good contact on the tcu pins. now, you say you get smoothly varying resistance from 700 ohm (closed throttle), to ~5k ohm (WOT), as measured directly on the tps? if yes, sounds like bad harness connx at tps. do you (still--just re-read post#1 above) measure 5V at pin C on the tps harness (reading back into the ecu) when the connx demated? what about continuity from pin A thru the harness to ground?

[elwesso]

unless you have real sharp probes, i would guess you didn't have good contact on the tcu pins. now, you say you get smoothly varying resistance from 700 ohm (closed throttle), to ~5k ohm (WOT), as measured directly on the tps? if yes, sounds like bad harness connx at tps.

1. do you (still--just re-read post#1 above) measure 5V at pin C on the tps harness (reading back into the ecu) when the connx demated? 2. what about continuity from pin A thru the harness to ground?

1. Yes2. Yes

[3Q Jay]

Can't think of any remaining explanation except poor/ intermittent electrical contact at the tps connx.