TPS issues

[unreal-]

Hi everyone, long time lurker, first time poster.

First off the specs:

- 1996 s14 240sx obd2 model with obd1 (95 240sx) nistune board.
- KA24DE
- z32 maf
- Five-0 Motorsports 580cc Injectors
- gt2860rs @7psi
- new Coolant Temp Sensor, o2 sensor/TPS sensor/IAT sensor.
- all grounds checked and replaced/cleaned
- new battery and alternator
- Only CEL is for the disabled front o2 sensor (disabled due to a part throttle lean spike issue thats been brought up in this forum)

- 440 K-Value/ 0.500 latency (according to injector information)


Ive been trying to figure out this problem that has been going on for the past year or so. Every few days the ECU will refuse to read from the TPS (idle flag not lit) and the car stalls easily and the injectors don't turn off while decel in gear. In order to fix this I have to turn the car off, wait a few seconds, and turn it back on. Then the tps will read properly for another 1-4 days. This is regardless of outside temps, and whether the motor is hot or cold. The tps is a "standard motor" OES part from rockauto.

Is there any way I can solve this issue? Ive tried everything and nothing seems to make the tps set for more than a few days at most. Ive set the voltage to 0.48v warm and reset it several times using the directions in the fsm and KA-T.org. Could it be because im using a obd2 tps on a obd1 ecu? Or some sort of weird glitch due to using a non-oem tps?

Thanks

[Matt]

Definitely sounds like a glitch. When the problem occurs, do you see it straight after starting or does it occur after driving for a while. I'm wondering if NVRAM got corrupted on the board (or is getting corrupted) and then causes the glitch

What is the ECU part number showing in Nistune? What is the TPS voltage showing in Nistune when you do and dont have the issue?

[unreal-]

Definitely sounds like a glitch. When the problem occurs, do you see it straight after starting or does it occur after driving for a while. I'm wondering if NVRAM got corrupted on the board (or is getting corrupted) and then causes the glitch

What is the ECU part number showing in Nistune? What is the TPS voltage showing in Nistune when you do and dont have the issue?

- It occurs immediately after starting

- 23710-70F00 is the ECU part Number

- Under normal circumstances my TPS voltage is 0.48v closed, and ~4.14v WOT (Engine running) When i shut off the car and try it again, my TPS voltage decreases from 0.48v down to 0.44v and WOT voltages start off at 4.14 and drop to around 3.88-3.90.

Is it Possible that the voltage drops (which i just noticed when i went out to the car to check out the info you requested) are causing the ECU not to read the proper voltages since it falls below the minimum threshold? Then when i cycle the key, it gets a voltage bump, and then the ECU can read it again?

I havent been able to see the TPS voltages when the problem occurs, as EVERYTIME it happens, my laptop is not in the car with me

Just wondering.

[unreal-]

update: The car has been doing it more often lately, with the colder and sometimes moister temps.

Going to try the TPS learn procedure outlined in the FSM. Hope it helps.

[unreal-]

Reset the TPS learn as per the FSM (warm up, turn off, unplug TPS, Turn back on, and plug TPS while motor is running. Shall see if it helps or not.



Matt: Here is a screenshot of how it looks when the car is started when the problem presents itself

[Matt]

You can email me for a board swap over and we can try another ECU program on the board. I can test that one to see if the ECU ROM image is affected at all

[unreal-]

Thanks for the offer matt, does that swap require downtime on my end? I want to exhaust all my options before I would go through with that.

I reset the tps accoring to the obd2 instructions on my FSM. It's been a few days with multiple starts and the problem has not presented itself. Im going to keep track of it for a while to see if it comes back.

I do have a minor problem with my warm start, as my afrs go lean for a bit and then settle back down to normal levels. It sometimes does this on cold starts too. I think I have to play with my crank enrichment and warm start tables?

[UNISA JECS]

I've also had a similar problem with my P11 Infiniti G20, there were a few things I had to sort out to remedy the problem, first off:

Does your TPS Sensor match your Nistune ECU?

Secondly:

With my P11 I found that I had a voltage drop on my TPS sensor and I had to disconnect and actually remove some pins at my ECU (This were mostly smog related devices that my (99 ECU harness was wired for) but since I am using a 97 B14 ECU I had to make my harness satisfy the needs of the B14 ECU, I think your problem will probably very similar to the issues I had.

Attached is a screen shot of the TPS part number and years of use with ECU 23710-70F00

[UNISA JECS]

This is the TPS part number a 96 S14 as you can see they are different I had this problem like I said on my P11 and yes you may thing that they are the same because you can adjust them and get the same volt readings but I would keep droping the TPS memory for whatever reason until I had to actually swap TB so that the correct TPS sensor could bolt on and ever since no issues.

p.s. with the TPS is not entered at idle it usually resulted in a HIGH IDLE by about 800rpm or so.

p.s.s. I know the most popular thing to do is when you have a double plug TPS type sensor is to plug in the 1 plug that fits but that's incorrect you must use the correct TPS, I know cause my 99 used a double plug TPS but my ECU required a single plug style TPS.

[UNISA JECS]

Just as I suspected they are different double vs single plug and also electrically different.

96 vs early style TPS (S14)

[UNISA JECS]

You can also see I described this same problem here but all my link are dead cause ran out of bandwidth but when it comes back up you can view it you like


http://www.g20.net/forum/showthread.php ... -P11/page4

[unreal-]

Thanks UNSIA i had thought of that when the problem first started manifesting itself, and feared that i would have to swap TPS's. But it seems that it would require a lot more than just simply swapping the TPS. I believe that i would also need a OBD1 intake manifold and engine harness,which would be a lot of work to acquire . It seems that voltage wise, the TPS's are similar (both stop at around 4.0v output voltage) but the resistance is different. I think as long as the ECU gets the proper voltage, it shouldnt freak out.

Strangely, i do not throw any sort of CEL for TPS at all. Maybe it is because the OBD1 S14 ECU has OBD2 circuitry as well? It is a really strange ECU in that regard. Even though it is technically OBD1 i can still plug it up to my scanner and clear codes, and it plugs right into the same harness as my OBD2 ECU.

I havent been able to get a straight answer as to whether it is required to use a OBD1 TPS on a OBD1 ECU when switching from a OBD2 ECU/TPS. I wouldnt hesitate in swapping, it is just that the plugs are completely different on the two sensors. The OBD1 tps would require me to either get a obd1 engine harness, or somehow ghetto rig some alligator clips together to get it to work.

[UNISA JECS]

Thanks UNSIA i had thought of that when the problem first started manifesting itself, and feared that i would have to swap TPS's. But it seems that it would require a lot more than just simply swapping the TPS. I believe that i would also need a OBD1 intake manifold and engine harness,which would be a lot of work to acquire . It seems that voltage wise, the TPS's are similar (both stop at around 4.0v output voltage) but the resistance is different. I think as long as the ECU gets the proper voltage, it shouldnt freak out.

Strangely, i do not throw any sort of CEL for TPS at all. Maybe it is because the OBD1 S14 ECU has OBD2 circuitry as well? It is a really strange ECU in that regard. Even though it is technically OBD1 i can still plug it up to my scanner and clear codes, and it plugs right into the same harness as my OBD2 ECU.

I havent been able to get a straight answer as to whether it is required to use a OBD1 TPS on a OBD1 ECU when switching from a OBD2 ECU/TPS. I wouldnt hesitate in swapping, it is just that the plugs are completely different on the two sensors. The OBD1 tps would require me to either get a obd1 engine harness, or somehow ghetto rig some alligator clips together to get it to work.

Im not sure in your case but in mines I just had to just swap throttle bodys because the casting were the TPS sensor bolts onto would not allow it. Also in your case it sounds and looks like as per the FSM diagrams that you physically have a very different connector, this I would not be to concerned about I would just chop it off and source the correct end and marry it up to the harness instead of swapping entire harness's.

I also never threw a CEL for TPS either.

Below are just some pics I took of my TB swap but there is more to this issue than meets the eye, the pictures with the DVM are closed throttle and WOT respectively and as you can see here that they are both not in either case hitting 4.1v like they should. I would have to do some research on the 96 vs earlier style harness and pin arrangement at the ECU which can be very time consuming but this is how I figured what was casuing my voltage drop.

p.s. one clue to this problem is the MAP sensor in this pic which had to be disconnected but there is much more to getting everything correct than just disconnecting certain sensors and what not you may actually have to depin and re-arrange some pins at the ECU to satisfy the needs of the ECU you are using.

[UNISA JECS]

To give you an idea of what I went through and had to do here a picture than can show you and I only went from late OBDII to early OBDII but there was some critical difference in my wiring harness arrangement that needed to be correct in order for me to run the early style OBDII ECU correctly

[unreal-]

Wow that seems like a lot of work in your case to swap the TPS between the two ecus. I did similar research with the 95 vs 96 ecus and they seem similar when you compare their functions and how they plug into the harness. There are certain differences in the engine harness (1 wire vs 3 wire o2 and a single o2 plug style tps vs the 2x flat looking plug you have on your tps). But it seems the 95 ecu is like a 96 ecu that doesnt care about a lot of things lol

About the plug: I didnt want to have to cut into the harness to rewire it. Kind of want to avoid it so that a future owner can convert back to obd2 if needed. If it comes down to it I may have to do that

Voltages: after doing the evap canister solenoid trick I read on ka-t.org a few months ago, my tps reads 0.48v closed and 4.10 to 4.12v open when the engine is running. Lowest ive seen it drop is 3.90 which may still be in the range of the fsm values when engine is off.