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PostPosted: Fri Jul 13, 2012 8:10 pm 
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OK got the readings

Spare tps Mk2: 5.912K Ohm
Original tps in car Mk3: 4.361k Ohm

both are in spec i guess, 3.5 to 6.5k

moving the tps doesn't have any affect on the resistance


i used my fluke meter to measure it
i have a crappy multimeter that i guess refuses to test K Ohm


Hope that helps
Amer

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PostPosted: Fri Jul 13, 2012 11:29 pm 
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crnolic wrote:
OK got the readings

Spare tps Mk2: 5.912K Ohm
Original tps in car Mk3: 4.361k Ohm

both are in spec i guess, 3.5 to 6.5k

moving the tps doesn't have any affect on the resistance


i used my fluke meter to measure it
i have a crappy multimeter that i guess refuses to test K Ohm


Hope that helps
Amer


Thanks man you really helped, now I know for sure what the problems is. I'm gonna explain the whole thing cuz it seems like this is a sticky topic and people WILL have problems with these sensors (20 years old) even though the ECU is not giving codes.

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PostPosted: Fri Jul 13, 2012 11:45 pm 
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So here it goes:
I currently have two sensors for testing and one that I opened to see what was inside(just for fun cuz it was completely useless).

Comparison (negative things with bold letters) :
TPS No.1 (the one that was originally on the car)......................................TPS No.2 (the one used to make the first video)
trouble-codes..................................................................................no trouble-codes
resistance between C and D: changes from 0 to 2k+..................................from 0 to infinity
between C and B: 680 @ idle, 5k+ @ WOT................................................700 @ idle, 5k+ @ WOT
between C and A: just like between C and B............................................steady @ 4k+

The problem with TPS No.1 is the hard starting of the engine (have to push and release the throttle while cranking for a couple of seconds), probably cuz the adequate resistance between terminals C and A is only reached almost @ WOT. Because there is always continuity between terminals C and D I was able to adjust the afr as desired, so I turned the sensor @ idle position of the throttle until 450 ohms was reached between terminals C and B. At this point, the engine is running perfectly, except for the check engine light and the hard starting. Can make a video if necessary.

Using TPS No.2 will eliminate the hard starting but will on the other hand cause a rich mixture as soon as the throttle is touched (previously shown on the video). This is because of scratches on the contacts inside the sensor, as a result of wear during the years. So if after adjusting TPS according to manual, resistance-readings between terminals C and B are above 500ohms, the engine will run rich (the higher the reading. the richer the mixture). You will probably not notice any difference, besides less MPG.


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Last edited by elbola on Sat Oct 06, 2012 11:46 am, edited 2 times in total.

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PostPosted: Sat Jul 14, 2012 12:51 am 
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So I adjusted TPS No.2 just like No.1 and fastened the sensor when a ohm-reading of 450 was reach between C and B @ idle. This made the engine run bad til 2500rpm, because of the change in resistance from 0 to infinity at that point (this should actually happen at a 0.6mm throttle-opening). I'm gonna try to run the car without the blue wire, to eliminate the idle position- signal from the TPS to the ECM. We'll see how it goes.

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PostPosted: Sat Jul 14, 2012 7:07 am 
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Everything is written in manual what should be resistance between what values.

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PostPosted: Sat Jul 14, 2012 9:38 am 
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deluxor wrote:
Everything is written in manual what should be resistance between what values.


If you read my posts carefully you will understand that after 20 years of use, even if you get the proper resistance- readings, you won't get those readings at the adequate degrees of turn of the tps. The proper way to adjust the tps is by inserting a 0.6mm feeler gauge and turning the sensor until resistance between C and D changes from 0 to infinity, but than you should get less than 500 ohms between C and B @ idle. if that's not the case and you get higher resistance, you WILL run rich, which is why I'm trying to use other adjusting-methods.

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PostPosted: Sat Jul 14, 2012 10:53 am 
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TPS No.1 (450ohms between terminals C and B @idle)




Hard starting :(



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PostPosted: Sun Jul 15, 2012 8:39 pm 
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TPS No. 1 is not causing a rich mixture anymore. It was calibrated to 450ohms between C and B @ idle-position, just like TPS No. 2.
I removed the blue wire after starting and the engine ran beautifully at around 14 afr till 3k+ rpm and got a little richer after that, which is normal. I do have a lumpy idle without the blue wire, so I'm planning on adapting a switch to the throttle-body, to interrupt that wire when not @ idle.
Still running rich on deceleration though, but I think it has nothing to do with the tps, gonna check fuel pressure regulator and vacuum lines later.

So this is what I've learned so far:

When you install a TPS according to manual (Step A):
-Be sure there are no inconsistencies or flat spots in resistance-readings throughout the whole throttle-range, between terminals C and B.
-Be sure there's less than 500ohms between C and B @ idle. If not, go to step B.
-Resistance between C and A should be continuous on any position of the throttle and between 3.5 and 6.5kohms.
-Make sure ohm-readings between C and D change from 0 to infinity, there should be no continuity at all.

When TPS is calibrated according to manual, but there's more than 500ohms between terminals C and B @ idle, causing a rich air-fuel-mixture(Step B):
-Disconnect battery's negative cable and sensor coupler.
-Make sure throttle-stop screw is all the way in.
-Lose mounting screws and turn sensor fully clockwise.
-Turn sensor counterclockwise until resistance between C and B is around 450ohms (less than 500 anyway) and fasten sensor at that position.
-Disconnect blue wire from coupler.
-(If you get a lumpy idle) Make your own switch to somehow allow continuity through blue wire only @ idle-position and connect blue wire back to coupler.
-Connect sensor and battery cable.


*Please be advised that this "fix" is only applicable if the only issue with the sensor is a high resistance between terminals C and B @ idle, all other resistance- and continuity-tests to the sensor should pass, in order for this to work.
*It's also important to add that this high resistance will only cause a rich mixture, you will probably not get any codes from the ECU or notice any difference when driving. It could only be spotted with an afr-gauge.
*And last but not least, this only applies to swift gti's without a stock 02-sensor, which is probably the reason why the ECU can't spot the problem.

So after buying 3 TPS before coming to this conclusion :( , I wouldn't recommend anyone to buy a secondhand TPS without testing it yourself on your throttle-body. I mean they are 20 years old and most people sell them without even knowing they're bad, because the ECU is not giving codes! Of course you can always buy a new one for $250 :D

I hope my struggles can be of help to anyone who has a similar problem with his swift.

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PostPosted: Tue Jul 17, 2012 11:34 pm 
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I just read an article about the CTS mod... maybe a similar mod can be done to the TPS to correct the resistance values, using a potentiometer . I'm too busy to try it myself at this moment but I think it could be done in theory. It's easier than adapting a switch to the throttle-body anyway :) .

edit: nope, resistors can only be used to increase resistance, when used on a series circuit. Using them on parallel circuits can reduce resistance, but than the increase of total resistance (when pressing the throttle-pedal) won't be linear. Will have to think about something else :roll: .

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PostPosted: Mon Sep 03, 2012 6:31 pm 
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Finally figured out a way to make the switch. This is just for testing and of course it will have to be perfected so it's reliable and durable. I will try to explain how it works, as I didn't make pictures of the process.
Anyway I over-bored the hole of the throttle stop-screw and made a threaded one next to it. Than a 3mm-bolt slides freely (but straight) though the first hole and is isolated. For the isolation a typical wire connector was used(red one at the right-bottom corner of the pic), by removing the metal piece from the inside and screwing the bolt through the plastic cover(it makes a thread on the inside and it's pretty firm). Only half of the insulator was used though.
Plastic/hard rubber washers were used on both sides, and a spring to maintain tension. Than a spacer to hold the spring. Important is that the washer right under the spring must be the exact size of the 3mm bolt, so the spring can push it down by pressing on the top of the insulator, which has like a 5mm diameter.
A 5mm bolt was screwed into the second hole, holding the spring-spacer at the height needed(depending on the springs size/strength) by using a "plate" made out of non-conducting material as well. So the tube around that bolt was cut last, after the height of the spacer was determined.
Because of the spring pushing down the 3mm (stop)screw, a normal washer and 2 nuts are used on top of the plate to regulate how far the stop-screw will be pushed down(insert a 0.6mm feeler between plate and washer with throttle lever fully closed).
Than 2 more washers and 1 nut is needed to connect the blue wire (from the wiring harness not the TPS) to the stop-screw.

So summarizing here's how it works:
-The point at which continuity exists between terminals C(ground) and D doesn't depend on the position of the TPS anymore. There'll be continuity to ground when the throttle lever touches the throttle stop-crew, the lever being the new grounding point.
-the 3mm bolt is the new throttle stop-screw, but it's not fixed on the throttle-body, it slides through it's hole. The first 2 nuts after the "plate" regulate how far this bolt is pushed down by the spring. Continuity between the blue wire(terminal D) and ground should exist just before the throttle is fully closed and this position is set with a 0.6mm feeler, according to manual.
-It's important to know that the throttle's POINT-ZERO will be changed, as it depends of the size of the head of the 3mm screw(which should be flatted) and the size of it's washer. If either one of them causes the throttle to be too open at idle, the lever should be reduced with a grinder until the throttle closes to normal spec. If it's however too close, it doesn't matter cuz the TPS can now be adjusted as desired and the idle speed can be increased with the idle speed screw.

After doing this mod, I have been able to "fool" the ECU as desired by choosing the resistance-range that I want, finally getting the car to it's normal a/f ratio at cruising speeds. Now the engine starts right a way and the ECU is not showing trouble codes anymore. The fuel efficiency was dramatically improved (now doing 33 miles per US-gallon on city driving and a lot of hard-pulls from stop).
I know it's not a pretty mod and I'm not sure how long it will last, but at least it works, so this is the first step.... besides it took like 4 or 5 hours to figure it out and a new TPS costs $250 :shock: I apologize if my description was confusing or unclear, I did my best.


image_id: 22201 image_id: 22202 image_id: 22203

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Last edited by elbola on Sat Oct 06, 2012 11:50 am, edited 1 time in total.

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PostPosted: Mon Sep 24, 2012 11:57 pm 
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For the ones who might be following, a little update.
So far so good... air/fuel ratio OK, throttle-response OK, mileage dramatically improved as well. A spring washer was added between the 5mm bolt and the black "plate" on the picture above, cuz the whole thing was coming loose with the vibration of the engine.

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PostPosted: Wed Oct 03, 2012 12:48 pm 
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Here's a video of the a/f ratio gauge after the mod was done. As you can see, the air/fuel mixture is within specs @ idle and under acceleration as well. The starting problems were also solved :)
Turning the TPS at will makes this mixture either leaner or richer when cruising, but of course not @ WOT. For that a WTS mod is needed apparently.

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Last edited by elbola on Tue Nov 12, 2013 1:25 pm, edited 1 time in total.

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PostPosted: Wed Nov 07, 2012 2:28 pm 
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I've been thinking about a throttle body upgrade... but I don't want to use the stock TPS cuz when this one fails completely, who knows how long it will take before I can find a good one. Anyway has anyone ever used a 4-wire TPS from another car?

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PostPosted: Tue Nov 13, 2012 11:38 pm 
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jankoelbola wrote:
I've been thinking about a throttle body upgrade... but I don't want to use the stock TPS cuz when this one fails completely, who knows how long it will take before I can find a good one. Anyway has anyone ever used a 4-wire TPS from another car?


I just figured out why the car was running rich on deceleration (full release of the throttle) with all the TP-sensors I tested... apparently when the blue wire shows continuity, the timing is backed out to the base-setting, causing un-burned fuel to mess with the a/f-ratio readings, so that's actually normal. Removing that wire should fix that but the idle gets a little lumpy.

Anyway same question again: anybody tried a different TPS from another car?

I'll try the one from the SR20 throttle-body I intend to buy from a friend, but will have to check the specs first... time to sign up at a Nisan-forum! :P

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PostPosted: Thu Nov 15, 2012 8:32 am 
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jankoelbola wrote:
.. apparently when the blue wire shows continuity, the timing is backed out to the base-setting, causing un-burned fuel to mess with the a/f-ratio readings, so that's actually normal. Removing that wire should fix that but the idle gets a little lumpy.



That would be the idle switch/closed throttle position switch then, at idle the ECU runs different maps.


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PostPosted: Thu Nov 15, 2012 10:14 am 
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Rhinoman wrote:

That would be the idle switch/closed throttle position switch then, at idle the ECU runs different maps.


I've gotten a little confused about the mapping.... a lot of different posts in the forum :roll: Some people say there are four maps, two for below 4k rpm and the other two for above that point. Some others say the different maps are for open/closed loop operations and now the ECU runs different maps for the idle as well?
I think you are the most trusted member to answer that question, if you get some time though :) , I don't want to take time of that emulator-project you have been working with. Yes, I've been watching.... waiting for the emulator to be ready.

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PostPosted: Thu May 02, 2013 10:32 pm 
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update: the switch has been holding up pretty good, but it comes a little loose in intervals of like 3 months, due to the tube bending when tightening the bolt that holds it in place. I luckily found a stainless steel replacement for it, so I don't expect anything to come loose anymore. The old pics seem to be missing, so here are some new ones.
image_id: 22779 image_id: 22780
Put everything back together and basically adjust the TPS to any position without affecting the ground-wire signal 8)
image_id: 22781

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PostPosted: Tue Nov 12, 2013 12:27 am 
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Dude this thread just blew my mind.

I am still chasing an intermittent lean condition that exists when the throttle is just cracked a little bit and the car is allowed to accelerate gradually without much throttle--or if the load on the car increases gradually going up a hill, for example. A little more pressure on the foot and there's fuel again, but the lean condition can persist into the high 16-17 AFR range for longer than I'd like when the ECU is forced into open loop. It's not a huge problem because it doesn't happen often and if I'm really worried about it I can mash the gas just a bit more to fix, but it obviously isn't right.

Because it doesn't seem to be related to the tune (worse on a leaner tune, but the lean spike is still there sometimes no matter what I do to the fuel table).

I had though about the problem being TPS related earlier, but I just now decided to go ahead and check my TPS to see if that might be the problem. Everything is fine except I get a little more than 500 Ohms across B and C at idle (which is what this thread is all about and yet I see that there was a TSB correcting the value to 2000 Ohms, so my TPS is actually well within spec there and now I'm really confused :huh: ) and I get 3,400 Ohms at WOT, which is just a bit less than spec.

Everything else checks out, so it seems to be adjusted properly and my problem is not at WOT even if the resistance does test slightly low. Also, the sweep between idle and WOT seems to be smooth with an analog meter, so no problems there.

What do you think is going on?

This only happens during forced open loop operation, by the way, so I've almost come to the conclusion that the ECUs were simply not designed to run that way and I might as well just keep closed loop unless I am racing, where the lean conditions never occur in open loop.

And then I read about you changing the AFR across the rpm range with the TPS on a stock ECU that never looks for an O2 sensor in the first place and then my head hurts.

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PostPosted: Tue Nov 12, 2013 8:49 am 
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Teeth wrote:
Dude this thread just blew my mind.

I am still chasing an intermittent lean condition that exists when the throttle is just cracked a little bit and the car is allowed to accelerate gradually without much throttle--or if the load on the car increases gradually going up a hill, for example. A little more pressure on the foot and there's fuel again, but the lean condition can persist into the high 16-17 AFR range for longer than I'd like when the ECU is forced into open loop. It's not a huge problem because it doesn't happen often and if I'm really worried about it I can mash the gas just a bit more to fix, but it obviously isn't right.

Because it doesn't seem to be related to the tune (worse on a leaner tune, but the lean spike is still there sometimes no matter what I do to the fuel table).

I had though about the problem being TPS related earlier, but I just now decided to go ahead and check my TPS to see if that might be the problem. Everything is fine except I get a little more than 500 Ohms across B and C at idle (which is what this thread is all about and yet I see that there was a TSB correcting the value to 2000 Ohms, so my TPS is actually well within spec there and now I'm really confused :huh: ) and I get 3,400 Ohms at WOT, which is just a bit less than spec.

Everything else checks out, so it seems to be adjusted properly and my problem is not at WOT even if the resistance does test slightly low. Also, the sweep between idle and WOT seems to be smooth with an analog meter, so no problems there.

What do you think is going on?

This only happens during forced open loop operation, by the way, so I've almost come to the conclusion that the ECUs were simply not designed to run that way and I might as well just keep closed loop unless I am racing, where the lean conditions never occur in open loop.

And then I read about you changing the AFR across the rpm range with the TPS on a stock ECU that never looks for an O2 sensor in the first place and then my head hurts.

I should have updated this thread, but I thought there wasn't enough interest :P. Since my last post I installed a 60mm 240SX TB and I used the Nissan TPS sensor. That sensor is a 3 wire-type, so I used the same method for the idle-switch. More info here: viewtopic.php?f=11&t=55283&hilit=+throttle+body#p421217.

What you are describing, is something I've been struggling with as well; but my gauge is a narrow-band so I've been in the blind. I do know that the car is running lean, but I don't know how lean cuz the narrow-band is not accurate enough. I assume it's around the values you're getting, cuz I can feel the lack of power with small throttle openings (closed loop); specially when the engine is cold. There are no problems at WOT.

I was actually going to start a new thread about this. I tried a modified fuel-rail with aftermarket FPR, replaced the WTS and tested every single component of the ignition system and the problem is still there (only noticeable when the engine is cold, but still present when in open loop according to my gauge). So I suppose the lean conditions in closed loop are related to the electronics. It would be perfect if we could use the diagnostic connector under the dash, but unfortunately life never makes it so easy.

Anyway I think I could continue to play with the TPS, but I doubt the problem is there. I've tried several TPS's at different positions and from different makes without luck. What do you mean with "This only happens during forced open loop operation"?

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PostPosted: Tue Nov 12, 2013 9:49 am 
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There is a value in the eprom code that forces open loop so that the O2 sensor is ignored without it setting a code or having to unplug it. Every aftermarket chip seems to be made this way, I assume because the engine would be (in theory) more "responsive" if it is always hitting the map rather than dropping into open loop to hit the map only when you step on the gas a bit harder.

In practice I am not sure if I can tell the difference, and, now that I've found the value to force open loop, I can fix it and burn a chip with the aftermarket maps that simply behaves normally and runs in closed loop off the 02 sensor most of the time. The small throttle angle that seems to cause the lean condition is not enough to trigger a call to the maps, so problem solved. Except I feel like it should be possible, if everything is set correctly, to just run open loop without seeing the lean condition. Is it really possible that everyone that has chipped their ECU is having this problem and none of the chip tuners noticed and thought to simply leave closed loop enabled? I suppose if you were tuning with a dyno it might be hard to catch it, though.

I suspect that ideally there's even a way to change the threshold where the ECU will drop out of closed loop map thus making the ECU more "responsive" without completely eliminating the ability to trim fuel at fixed throttle angles. That would be even better! Eagle Talon/Mitsu Eclipse ECUs run the same size program on the same size chip as ours, and simply because there are lots more people working with them, all of these parameters are known :(

I haven't the slightest clue what your Euro-spec ECU is doing, but in past discussions it seemed like you still had some sort of closed loop operation because I seem to recall that you wrote that adjusting your fuel trim only seemed to affect your AFR at idle and cruise, not at WOT or anywhere else :huh: Otherwise I would have guessed that the aftermarket chip tuners figured out that value to force open loop from the Euro-spec ECUs to begin with, but maybe not. If that is what's going on, I can't believe Suzuki would sell all those cars with ECUs that would intermittently let them run lean like that--the motor seems to be quite tolerant of the problem, but it still must have some effect over time.

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PostPosted: Tue Nov 12, 2013 12:27 pm 
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Teeth wrote:
Dude this thread just blew my mind.

I am still chasing an intermittent lean condition that exists when the throttle is just cracked a little bit and the car is allowed to accelerate gradually without much throttle--or if the load on the car increases gradually going up a hill, for example. A little more pressure on the foot and there's fuel again


I was sort of scanning this thread until I read this sentence. I've had this same problem on my car in EU for past two summers. When just cruising steady speed all is well but when you need more power and you slightly depress throttle nothing happens , so you press little more and then , BAM , there is all the power you been calling for for past few seconds. Now, Euro car does not have any emission stuff on it out of the factory , and that includes O2 sensor so I was not able to find out what is going on with AFR .
I will re-read this whole thread slowly again to see if it will give me some ideas where to start looking for a problem


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PostPosted: Tue Nov 12, 2013 12:38 pm 
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The Euro-spec has an a/f-ratio knob that replaces the O2-sensor. In my car it can make the ratio leaner at idle and I suppose it gets even leaner than it already is while cruising, but it doesn't make the ratio richer if you turn it to the other side. It doesn't affect open loop operations of course.

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PostPosted: Tue Nov 12, 2013 2:26 pm 
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jankoelbola wrote:
The Euro-spec has an a/f-ratio knob that replaces the O2-sensor. In my car it can make the ratio leaner at idle and I suppose it gets even leaner than it already is while cruising, but it doesn't make the ratio richer if you turn it to the other side. It doesn't affect open loop operations of course.


We've gone around on this before, but I can't imagine how a Euro-spec car would run in closed loop at all without an O2 sensor. Closed loop implies feedback, so without O2 readings, what would it trim to? Presumably it trims to where you set the knob, but that doesn't really make sense either--how would it know that AFR has moved away from where you set it? If there's no reason to keep everything so close to stoichiometric with the O2 sensor to make the catalytic converter happy, why wouldn't the ECU simply be set to call the maps and be done with it?

I wish I had an I3 or similar Eurospec chip just so I could read it and check whether the "force open loop" variable is set, and if there was anything else I could figure out about what it's doing. On cars with O2 sensors the difference between closed loop and open loop operation is impossible to miss if you watch the wideband. During closed loop the values are constantly shifting slightly lean then slightly rich as the ECU trims back to 14.7--if it had a needle instead of a bunch of LEDs you'd describe it as "walking back and forth". As soon as the ECU drops into open loop (or is forced into open loop by the switch in the code or simply unplugging the O2) the behavior is very different. The numbers do change fairly quickly, particularly with lots of throttle input or changes in speed, but at constant throttle and rpm the numbers can stay static for just a little while--much longer than in closed loop, when the ECU is constantly trimming.

I am kind of dumbfounded that so little is known and documented about our ECUs.

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PostPosted: Tue Nov 12, 2013 8:43 pm 
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janko, i'll take a stab at describing the tps so it makes sense to you.

it is a resistor with one end at ground and the other end connected to a voltage. there is another pin which is connected to a wiper which moves from one end of the wire wound resistor (or carbon deposited film resistor) which picks off a voltage from the resistor.

as the throttle shaft rotates, the attached wiper travels the wire wound resistor and takes a voltage signal from the tps to the ecu. if you measure the picked voltage it will be from zero at throttle closed to max reference voltage at wot.

if there is a break in the wire wound resistor, when the wiper is below the broken point the signal will be zero between the ground and the break. when the wiper is above the break, the voltage will be something between the max reference voltage and whatever voltage drop is produced by the resistance that's left in the wound wire.

it's pretty common for the wire wound resistance in the tps to break because the wiper moves the wound wire slightly as it travels the arc. that work hardens the wound wire and along with engine vibration, it causes the wire to break.

the max reading of the wound wire is the reading that you measure from end to end. if you put the positive lead of an ohm meter on one end and the other lead on the wiper, you will read a resistance that varies from zero to the max resistance as the wiper travels from end to end. if the wound wire resistance has a break in it, the ohm meter will read infinity (open circuit.)

it's also a fairly common failure mode for the wiper to lose contact with the wound wire as it travels along the arc. when that happens, the wiper doesn't won't pick off any voltage and the ecu reads that as the throttle being closed.

as for the ecu, it provides distinct injection modes for idle and for off idle. there are other tier one level sensors that provide data for the ecu. the maf is one and the clt is another. if you lose the tps signal, the engine will still run (poorly) from the maf data. also, if the tps has a broken wound wire it will provide bad data and again the engine will run (poorly.)

the test procedure as outlined in the fsm checks the overall resistance of the tps and the variable resistance via the wiper. if the resistance doesn't follow smoothly as measured off the wiper with a reference to either end of the wound resistance, if the meter bounces to zero or makes a big jump at any time, it would indicate that the wiper is losing contact with the wound resistance.

any deviation from the readings indicated by the fsm requires that you replace the tps. i have never successfully repaired one.

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PostPosted: Tue Nov 12, 2013 10:41 pm 
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t3 ragtop wrote:
janko, i'll take a stab at describing the tps so it makes sense to you.

it is a resistor with one end at ground and the other end connected to a voltage. there is another pin which is connected to a wiper which moves from one end of the wire wound resistor (or carbon deposited film resistor) which picks off a voltage from the resistor.

as the throttle shaft rotates, the attached wiper travels the wire wound resistor and takes a voltage signal from the tps to the ecu. if you measure the picked voltage it will be from zero at throttle closed to max reference voltage at wot.

if there is a break in the wire wound resistor, when the wiper is below the broken point the signal will be zero between the ground and the break. when the wiper is above the break, the voltage will be something between the max reference voltage and whatever voltage drop is produced by the resistance that's left in the wound wire.

it's pretty common for the wire wound resistance in the tps to break because the wiper moves the wound wire slightly as it travels the arc. that work hardens the wound wire and along with engine vibration, it causes the wire to break.

the max reading of the wound wire is the reading that you measure from end to end. if you put the positive lead of an ohm meter on one end and the other lead on the wiper, you will read a resistance that varies from zero to the max resistance as the wiper travels from end to end. if the wound wire resistance has a break in it, the ohm meter will read infinity (open circuit.)

it's also a fairly common failure mode for the wiper to lose contact with the wound wire as it travels along the arc. when that happens, the wiper doesn't won't pick off any voltage and the ecu reads that as the throttle being closed.

as for the ecu, it provides distinct injection modes for idle and for off idle. there are other tier one level sensors that provide data for the ecu. the maf is one and the clt is another. if you lose the tps signal, the engine will still run (poorly) from the maf data. also, if the tps has a broken wound wire it will provide bad data and again the engine will run (poorly.)

the test procedure as outlined in the fsm checks the overall resistance of the tps and the variable resistance via the wiper. if the resistance doesn't follow smoothly as measured off the wiper with a reference to either end of the wound resistance, if the meter bounces to zero or makes a big jump at any time, it would indicate that the wiper is losing contact with the wound resistance.

any deviation from the readings indicated by the fsm requires that you replace the tps. i have never successfully repaired one.

Thank you for explaining once again how a TPS works, that information was provided previously in this thread. If you read carefully you'll understand what I've been doing and why. This thread already moved past the TPS a few posts back...

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