Help please I give up TPS problem.

[metsuki]

For two years, i have Still the same issue.
Hesitations at partial throttle in any gears
I am searching for a solution since then
I replaced many parts

O2 sensors
Plugs
Coils
Decat pipes
Cambelt
filters



Last day I found a fellow primer with a TPS issue sounding like what I endure for so long.
I disconnected my TPS and beside the CEL light coming on, I can tell that the car seems to ride perfectly. I reconnected it and the problem came back directly. It seems consistent with what I endure for so long I ordered a new TPS with confidence it will solve my issue at last

I changed my TPS today (5,02v VCC, 0,48v idle 4,45v wot), I clean my throttle body and check the idle at the same time (little too low eacv disconnected as the engine won't idle )

And for God sakes the issue is still there

I now that the car runs open loop when the TPS is unplug, so what else can cause my problem

I am sorry but here I feel upset and hopeless

Please help me

[goldnsx]

Year/mileage? Could you describe more under which conditions it hesitates? Below or above 4k rpm?

Did you check the fuel delivery?

Short test: did you disconnect the o2 sensors and see if it's any better? Two plugs on the cylinder head.

[metsuki]

1993
145000 kms
Manual
Hésitation at very little throttle but i think all the way up
I already bypass the fuel regulator with no effect at all, but did not go forward checking fuel delivery precisely
Both O2 sensors are New ans did not change nothing

the only thing i cannot understand is why TPS unplug everything Come back to normal. Can a bad fuel pump work fine acter unpluging thé TPS?
Actually i already went far beyond what i thought i could troubleshoot:D

[goldnsx]

I'd bypass the fuel pump resistor and see if it makes a difference. Done in 1 minute.

[metsuki]

You can ses Just above, i already done that without result

[goldnsx]

Did you also clean the injectors and replaced their o-rings, esp. the lower one?

Did you also check for 'wrong' air?

[metsuki]

no i did not
but if i had a problem with those would'nt i have a problem all the time even when i unplug the TPS?

what other sensor can i unplug putting the car in open loop, just to check if my problem is solve by unpluging the TPS or just by running open loop?

[goldnsx]

Open loop: runs richer. The effect of a small air leak could be masked.

[metsuki]

how can i check that easily?

[goldnsx]

Install a wideband o2.

[metsuki]

I post my issue on prime too and this where i am now to keep you up to date:

if i try to explain my issue more clearly:

- when the TPS is plug in: i can feel like a very very light stop and go thing when i accelerate moderatly (not when i am steady at speed). i am the only one to feel it in the car, if i do not tell it to my wife she do not bother. i fell kind a lack of power but i think it is only due to the intermitent throttle or at least it is what i think. at WOT i have no problem

-when i unplug it i have the feeling the car just runs great, more torque, i cannot tell anything else (but i did not try WOT, i don't know how trigering the CEL can arm the engine in WOT condition)

injector are standard as ECU
injector not cleaned (but i will do it one day)
fuel filter changed (and i already bypass the fuel regulator with no effect at all, but did not go forward checking fuel delivery precisely)
valve clearance done with timing belt 3 years ago can't say if it as been done the right way but i think so
i have to check for leaks but i really don't think it is my problem as it was already there before i changed all the exhaust thing (and i changed everything just beacause of my issue...)

i can tell that when i first plug back the new tps i did not adjust it to test. and it trigger the TCS. when i adjusted it correctly the TCS went away. so i think it cannot be reverse polarity.

- test TPS AT THE ECU, got VCC 5V , min 0,53 max 4,37V, very linear all across no peak at all (i have a video to confirm)
- Test second TPS (under the trottle body, for TCS use i think), VCC 5V, min and max ok (more close to the 0,5v 4,80v than theTPS i changed though) and linear too
- if i disconnect TPS: Engine CEL and TCS light up but car runs good just high idle (1200 rpm)
- if i disconnect the second TPS and the top TPS stay connected: engine CEL+ TCS light car get the issue

We can maybe consider that there cannot be conflict between the two as it would have runs good with the second one disconnected.
we can consider that The ENG CEL do not triger a limp mode solving the issue every time. is there multiple limp mode????

- if I disconnect an O2 sensor and both TPS stay connected: engine CEL car get the issue

I tried to see if another type of engine CEL/limp mode will act like the one i get from disconnecting the TPS but No.... big disappointment there

- if everything is connected properly: Very good idle 800 rpm steady and all no cell but same issue as before

- drove the car traction control Turned off TPS pluged in and the issue was still there.

I will work again on the car tomorrow.
when i unplug the O2 sensor the car runs as bad as before. we can conclude that unplugging the O2 sensor do not trigger the same fail safe mode as unplugging the TPS. and i think if unpluging the TPS was acting on close or open loop, unplugging O2 sensor would do it too.
i will test the O2 for rich VS lean condition as you told me
i read elsewhere on prime that the car has 5 different map for different issue but really do not know much else.

so what that TPS limp mode can change to blur my issue like this

if you have any other ideas on what i can troubleshoot tell me, i ll have some time for it tomorrow.

thank you sooooo much for helping me on this

[goldnsx]

If I understand correctly you only have hesitation while going from throttle position 20% to 30% (for example). While you hold the throttel constantly at 20% or 30%, the cars runs smoothly, no hesitation, right? If so it sounds like a bad communication between the ECU and the TPS. Just wondering, is the ECU modified or stock?

I've found this here: http://www.nsxprime.com/forum/showthread.php/140528-Throttle-Position-Sensor-(TPS)-replacement-howto
Not sure what you mean by the modification that is needed to make it work.

Also, there are two versions out there, one for 95-00 and one for 01-05 AFAIS. Which one did you use?

Not a serious proposal: let your wife drive the car, problem solved. :D

[metsuki]

the ecu is stock as far as i can tell, the car was totally stock when i bought it. i think nobody would modify the ecu without modifying anything else on the car.
the only tps i found wad the 95/00 and my car is a 93.
when the TPS arrived it was turning the wrong way (as i already read on several prime post), all i done was swapping the spring inside with the one on my original TPS to make it turn the good way. the parts is exactly the same apart from that. i was planning to reverse the plug too but it appears that the voltage was going the right way from start .

and my wife already drive the car!!!! sadly i drive it too some times:D

[goldnsx]

Did the modification work for the guys on prime?

[Pride]

As you've already replaced almost everything except ECU why not remove the fuel tank and replace the old and weak fuel pump.

[metsuki]

Did the modification work for the guys on prime?

on prime i only found the information that the 95/00 one turn the wrong way. the guy has not modified it

[metsuki]

exactly because i already replaced so much thing for nothing (and in fact sometimes for worst).
i know the pump will have to be change at one point, but i do not think it is the culprit because bypassing the resistor did not change anything and i do not see why tps unplug the car would run good with a bad fuel pump
but an easy way would be too check fuel pressure and i am planning to do so

[Pride]

My 92 has developed similar symptoms when away in Spa last weekend (strangely enough when giving it some beans on the 3 parade laps) and the consensus of opinion around a lunch table general chat was to replace the fuel pump as apparently they are known to get weak over time and in your case 25 years now.

[goldnsx]

Not sure if it's a weak fuel pump. Could be but I'd monitor the fuel pressure before taking out the fuel tank. Fuel pressure gauge and small camera while accelerating.

FPR ever changed?

[metsuki]

Not sure if it's a weak fuel pump. Could be but I'd monitor the fuel pressure before taking out the fuel tank. Fuel pressure gauge and small camera while accelerating.

FPR ever changed?

FRP= fuel pressure regulator?
no i don't think so

[Pride]

For the new low price of a more powerful upgrade is it worth worrying about measuring.

https://www.scienceofspeed.com/index.php/walbro-255-lph-high-pressure-fuel-pump-nsx-fitting-kit.html

Honda book time to instal is just 1.6hrs, by the time you've tried measuring it you could have replaced it.:)

[goldnsx]

FRP= fuel pressure regulator?
no i don't think so
Sorry, typo, yes FPR.

@Pride: Replacing the fuel pump takes much more than that stated time...
I had bad luck with a Walbro 255 once, excessive noise, very annoying, I'd choose another brand.

[Pride]

Pride: Replacing the fuel pump takes much more than that stated time...
I had bad luck with a Walbro 255 once, excessive noise, very annoying, I'd choose another brand.

Thats the time my Honda dealer told me he would charge me for, so that's ok.
My biggest concern for them though is releasing the no doubted rusted straps or bolts.
As regards the pump I believe one bad egg doesn't make a bad batch.
In fact I haven't read any bad reviews.

I will report back once installed.
Thanks anyway gold.

[goldnsx]

Thats the time my Honda dealer told me he would charge me for, so that's ok.
My biggest concern for them though is releasing the no doubted rusted straps or bolts.
As regards the pump I believe one bad egg doesn't make a bad batch.
In fact I haven't read any bad reviews.

I will report back once installed.
Thanks anyway gold.
That's a good deal (for you) but not sure if the dealer is happy with it in the end because it takes more like 4-5 hours or so and we did it multiple times. The Honda workbook often underestimates the amount of time and the dealer has to cope with it.

There have been a few reports with excessive noise of a Walbro fuel pump, it really p*ssed me off that I got a noisy one. After two years of bearing it I went with a quality pump, Denso again where you have 100 out of 100 and not 98 or 99 out of 100.

All aftermarket fuel pumps draw more current than the OEM one. Double or more. The cars wiring can't cope with it really. I'd say they should measure the voltage at the fuel pump after installation. There are Denso fuel pumps out there which are said to be a replacement for the NSX fuel pump (also Denso) but the no. of the Denso fuel pump in the NSX is unique and can't be obtained in any shop. You can only buy the expensive full set at Honda... I know have a Denso Supra fuel pump which is 'lusty' for Amperes but I wouldn't have installed it in a non-boosted NSX.

Back to the topic: I would strongly suggest monitoring the fuel pressure while driving to rule out any problem with the fuel pump/FPR.

[Kaz-kzukNA1]

Just returned another NSX to the owner so I have bit more time for this subject although already working on another one.

Based on what you wrote so far on here and on NSX Prime, please refer to the followings.

To prevent confusion, please use the following terms.
TPS: Throttle butterfly/barrel Position Sensor, mounted at the side of the TH body. Used for 'w' mapping described later.
ACP: Accelerator Pedal Angle Sensor, mounted at the bottom side of the TH body. Not much factor for EFI control.


First of all, what was the reason to replace the TPS?
Unless you triggered the CEL or accidentally broke off the connector (I know at least one owner did this....), no need replacing.
Depending on the country spec, the screws are locked or tamperproofed.


Please check your base idle rpm and most importantly, the base IG timing.
You must disconnect EACV during the test and the engine must be able to idle fairly smoothly at 600rpm.
If IG timing jumps around, you have other issues.


Can you always create the same issue at any time of the drive cycle?
In other words, does your issue only happen at the very beginning of the cycle or can you re-create it even after driving for a while, let's say even after 30min in to the driving?


Any specific rpm range?


Does it make difference if you slowly accerelate or open the TH pedal sharply?
ECU uses angular velocity 'w' (omega) of the TPS signal to enrich the fuel timer during acceleration.
It is also used for fuel cut but I'll leave it for now.
The faster you open the ACP, the larger the 'w' of the TPS resulting in extra fuel into the cyl.
ECU has its own mapping for 'w'.
If you open the ECU, you will know what CPU is used and that will tell you the estimated performance.
Also, count the number of trigger teeth on the front intake cam pulley.
That will tell how many INT jobs can be triggered during the 720deg crank cycle and that is the limit of the ancient ECU performance.
O2 sensor has its own responce delay as well.


I think you already tried this but forgot your answer.
If you disconnect both O2 sensors (yes, not just one bank but must disconnect both) but keep the TPS connected, does it make any difference even for a small change?


When the issue happens next time, quickly look at the rear view mirror.
Any white smoke?


If you disconnected TPS, it will trigger the CEL and ECU will disable the 'w' mapping.
For IP reason, I won't tell what the ECU is doing but under this condition, it will explain why your issue is fixed and also depending on the situation, your idle rpm will be higher.


Unless you have data logger with wide band O2 sensor attached to each cyl (yes, all six cyl), monitoring the narrow band O2 signal voltage won't tell you much for this type of issue.


It all depends on your answers to the above but I would first clean the INJ.


I won't go too much in detail with the fuel pressure based on what you wrote so far but it's easy to check so just test it although probably you won't find any issues.


You may need checking the amount of oil trapped at the VVIS chamber if the issue only happens at the very first hard acceleration or if you see white smoke at the back when the issue happens.



Kaz

[metsuki]

Thank you Kaz for the timely you are according to me and my car.

First of all you have to understand I always drove the car with this issue, and most of all this is the only nsx I drove. It is very hard for me to know what is normal and what it is not. I even found a note on the buying honda bill from the last owner (bought used ten years ago from a honda dealer) refering to an issue similar as mine. They wrote something like "cleaning and tuning" to resolve the issue but I think they did not do anything. Maybe this car do not runs perfectly from years and years ago

I replace the TPS because:
it seems logical with my issue
I red many honda thread where it solved similars issues
When I unplug it everything comes back to normal
The part is pretty cheap
When I turned it it made a very light squeaking noise

When the EACV is unplug I have a good 600 rpm idle
If by it timing you are refering at injection timing, I do not understand how to check that

I can replicate the issue any time even after two hours driving. The only moment I do not feel it is maybe the first 5 mn when the car is warming up.

There is no rpm range, I can replicate the problem at light throttle above 140kmh feeling the car going like slightly back and forth. Maybe there'is even a rythm to it I am not sure

I do not feel it at WOT but it doesn't mean it is not there unfortunately.
I do not WOT the car very often because i feel the car is not at ease. It is just a feeling, maybe I am just dreaming...

I do not understand the "trigger teeth" thing sorry

TPS plugged in , I disconnected one O2 sensor and feeled the same issue
TPS plugged in, I disconnected both O2 sensors and the issue seems to be gone

I never saw smoke coming from my car

Monitoring the O2 I was just surprised too see how it jumps from one extrem to the other all the time

From what I saw when I cleaned my TH body , VVIS seems pretty clean an I saw most of the plates was there and tight.

I am waiting for exhaust seals to arrive now. Then I will clean injectors and check fuel pressure (even if disconnecting the fuel regulator did not change anything for me)

I am so happy you took some time to help me. I am hating this car right now and feeling like selling it would make my life easier. But every time I see it I love it again and I cannot sell it

thank you so much

[goldnsx]

Monitoring the O2 I was just surprised too see how it jumps from one extrem to the other all the time

I am waiting for exhaust seals to arrive now. Then I will clean injectors and check fuel pressure (even if disconnecting the fuel regulator did not change anything for me)
Narrowband o2-sensor are designed that way. See here in comparison to a wideband o2 sensor: https://www.drive2.com/b/478329065720250675/
If the exhaust is leaking they jump even more.

[metsuki]

I understand
I will be able to seal the exhaust the first week of September. I will check fuel pressure too
If you have any more ideas until then, I am always listening.:)

[goldnsx]

I'll wait with more comments until the exhaust leakages are fixed. :)

[metsuki]

It is a good start, but I don't think it will solve the issue as it was there before I change all my exhaust.
Maybe the original exhaust had a crack or leak too?

[goldnsx]

Well, if you do it right and change ALL exhaust gaskets chances are still there.

[Kaz-kzukNA1]

Wash INJ and replace o-ring, please.


Kaz

[metsuki]

Wash INJ and replace o-ring, please.


Kaz

Will do!
I can only trust you, you know everything possible about this car.
But I really do not understand why a bad injector would not be an issue when the TPS or the O2 sensors are disconnected?
Just this year my nsx cost me around 3000 euros in parts and repairs and 1500 euros in insurance. and I nearly never drove it...
I am just a little bit exhausted changing parts for nothing, throwing money again and again

[goldnsx]

I understand your point but an injector cleaning can be done by DIY and the seals don't cost 1'000. :)

More fuel is the cure of everything. If one injector is not working properly more fuel (like both o2 sensors off) will mask it.

The main fault people do is letting the car sit for months (over the winter). That's a perfect scenario for injectors to become 'strange' (spray pattern, dripping ...).

[metsuki]

So be it!
i will try to do this as soon as i can

[metsuki]

drove the car yesterday and , god i love this car!
i will continue the work on it!

[goldnsx]

drove the car yesterday and , god i love this car!
i will continue the work on it!
???
Does that mean that your problem is solved? I guess no.

[metsuki]

no no, the problem is still there, but i love the car anyway:D