Tricky Posted March 15, 2004 Share Posted March 15, 2004 I have a '92 legacy wagon, and just recently started having major loss in power and a very rough idle, acceleration. Right now, I can not even back out of the drive way when the car is cold. Once its warm it runs OK, but still has no low end power. I pulled the codes, and got 3 of them. Replaced 02 sensor, Purge control valve, and finally went to replace the TPS but due to the rediculous price...I decided to at least give a junkyard replacement a shot. According to the manual, using an ohm meter....my readings on both TPS units I picked up were bad. I am still getting the TPS code, not sure if its a big possibility I picked up 2 bad tps units, from the wrecking yard. Any suggestions on how I can thuroughly test these, before I shell out $250 for a new one. any suggestions would be much appreciated....are you good enough to fix this? Quote Link to comment Share on other sites More sharing options...
DerFahrer Posted March 15, 2004 Share Posted March 15, 2004 Is it possible that the TPS just needs adjusting and not replacing? Quote Link to comment Share on other sites More sharing options...
Tricky Posted March 15, 2004 Author Share Posted March 15, 2004 I tested BOTH of the TPS which I bought, one which was from my legacy and another I bought from a junkyard. No matter what adjustments I made, both of them made the car react the same....VERY rough idle, and horrible power in the low end. and pulling codes it is still saying TPS. using the ohm meter, I got a reading of 9.3 kilo-ohms. this was the same reading, no matter what position the throttle assembly was rotated in. Meaning, whether closed throttle or open throttle, it was the same reading. According to my manual, closed should be 12 kilo-ohms, and cull throttle should be around 5kilo-ohm I believe. Is there any other way I can test this??????? any thoughts are much appreciated. Quote Link to comment Share on other sites More sharing options...
Legacy777 Posted March 15, 2004 Share Posted March 15, 2004 how are you testing the tps. This is pretty much the only way to adjust the tps http://www.main.experiencetherave.com:8080/subaru_manual_scans/FSM_Scans/TPS_testing3.jpg Adjust the idle switch and the tps should be good. If you adjust the tps via the idle switch and readings are good....then you might want to look at the wiring. have you tried clearing the codes....if so...what method. Quote Link to comment Share on other sites More sharing options...
Tricky Posted March 15, 2004 Author Share Posted March 15, 2004 After replacing tps, with the one I bought at a junkyard(for testing purposes, it was worth a shot) I reset the codes, by disconnecting the negative battery cable for 30 mins, then put it back on and and start, idle for a few minutes. I pulled the codes again and got the same reading, of faulty tps. the original is BAD, as the car will hardly run with it attatched. I have tested it accordign to the manual, using an OHM meter, and tested it to their specs, which it is not even close to. testing between terminal 2 and 3, it should give a reading of 12 ohm's closed throttle, and 5 ohm's full throttle. Both tps units I have, whether tested on the throttle body or off, have only a reading of either 1 ohm, or 9.3 ohm. There is NO smooth change in reading when the throttle position is changed. According to the manual, there should be a steady change (drop) in ohm reading, as the throttle is opened up. hence the drop from 12-5 from closed to fully open throttle. There is NO reading change at all..it is either 0 or 9.3 Quote Link to comment Share on other sites More sharing options...
99obw Posted March 15, 2004 Share Posted March 15, 2004 What kind of meter are you using? Do you have a known value resistor handy to get a sanity check on your meter? It sounds as if you may actually have a bad TPS, but if you want to use JY parts you may want to be sure that your measurement technique is reliable. The TPS is a potentiometer. A potentiometer is a resistor with a movable tap called a wiper. When voltage is applied to one end of the resistor and ground to the other, the voltage at the wiper will be proportional to throttle position. The two ends of the resistor should be easy to identify. The resistance between these two terminals will not change as the throttle is moved. The wiper is the other terminal. The resistance between the wiper and either end of the resistor will change with throttle position. If the resistor is measured to be 12k ohms, the resistance between the wiper and one end of the resistor plus the resistance between the wiper and the other end of the resistor should always add to 12k, regardless of throttle position. Check the connector to the TPS with the key on to verify that a voltage (probably 5V) is present at one end of the resistor and ground is present at the other. You should then get a voltage out of the wiper proportional to throttle position. EDIT: My explanation assumes the potentiometer is linear taper and no guard resistors are used. Quote Link to comment Share on other sites More sharing options...
Tricky Posted March 15, 2004 Author Share Posted March 15, 2004 Thank you all for your input. I apporeciate it a lot. I have tested both tps units, and in all readings, I would not get ANY change in ohm's whether it was full throttle open, or fully closed. THis can only be that both tps are bad, which is hard to believe that a random chance, even the second one I bought from the wrecking yard is also BAD. I am getting power, to the tps, but it seems, taht my poor throttle response and lack of power until the throttle is 3/4 open, is due to the tps being faulty.... any other input....again, these are assumptions on my engine. Quote Link to comment Share on other sites More sharing options...
Legacy777 Posted March 15, 2004 Share Posted March 15, 2004 I suppose there's a possibility for both sensors to be bad.....even though it's very unlikely Quote Link to comment Share on other sites More sharing options...
Tricky Posted March 16, 2004 Author Share Posted March 16, 2004 Do you know of any other ways, to test the tps? using the meter, both on and off hte throttle body, I got the same readings. Both sensors, tested 9k ohms at closed and 1k ohms at fully open. They weren't exact, but very close. However...there was NO smooth change between the ohm readings when turning the sensor from closed to full throttle. I know this is supposed to occur ( example would be similar, to a r/c car speed control....but in reverse movement) this DID NOT occur. Which....for my porposes, tells me both sensors are bad. I wanted to double check if there are ANY other tests I could do, before I spend 250$ on a new one from 1stsubaruparts.com thank you Quote Link to comment Share on other sites More sharing options...
99obw Posted March 16, 2004 Share Posted March 16, 2004 Again, what kind of meter are you using? An analog meter is the best common tool for this kind of thing. The digital meter takes samples relatively infrequently so the readings will tend to look discontinuous as you move the throttle. The best tool overall is probably a digital storage oscilloscope (DSO), but a good one of those costs as much as a car. I found a diagram of the 1990 thru 1994 TPS in my Haynes manual. It is actually a 4 terminal device, my previous post assumed a 3 terminal. The wiper (signal) is on pin #4. The manual also describes basically what I mentioned before. This is done with the TPS on the car and the TPS connector connected to the TPS. Be very careful tapping into these signals. "Connect the negative probe (of the meter) to the ground terminal (#2) and the positive probe (of the meter) to the SIGNAL (#4) terminal. Turn the ignition ON (engine not running) and observe the meter as the throttle is moved through its [sic] complete range. The voltage should vary from 0.5 to 1.0 volt [sic]at closed throttle to 4.5 to 5.0 volts wide-open-throttle." The resistance readings you mention sound very reasonable to generate these voltages. Say perhaps the TPS was a 10k total resistance with 1k of guard resistance on each end. So minimum would be (1k*5V)/10k = 0.5V. Maximum would be (9k*5V)/10k = 4.5V. Sounds to me like your sensor is good. I suspect the reference voltage (5V on pin #3) to the TPS or the signal (pin #4) to the ECU. Move the throttle very slowly if you have a digital meter and the readings should gradually increase or decrease depending on the direction of travel. If the voltage varies as stated then I would check for the same voltage at the corresponding pin on the ECU. You should also test the idle switch. Test between #1 and #2. At idle 0 ohms, WOT infinite ohms (open circuit). Quote Link to comment Share on other sites More sharing options...
Legacy777 Posted March 16, 2004 Share Posted March 16, 2004 ful testing procedures from the fsm http://www.main.experiencetherave.com:8080/subaru_manual_scans/FSM_Scans/TPS_testing1.jpg http://www.main.experiencetherave.com:8080/subaru_manual_scans/FSM_Scans/TPS_testing2.jpg http://www.main.experiencetherave.com:8080/subaru_manual_scans/FSM_Scans/TPS_testing3.jpg Quote Link to comment Share on other sites More sharing options...
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