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No, it means with the sensors plugged in, the engine should be getting the amount of fuel that is needed, assuming accurate real time data is being delivered to the ECU. When the sensors are unplugged, the ECU no longer relies on any of the sensor data needed to efficiently fuel the engine and follows a pre-set program to determine how much fuel is needed to run the engine. The result will be over-fueling to ensure all bases are covered.
To test the oxygen sensors you would need something that could read the oxygen sensor data in real time, while driving the car. Since that data flip flops constantly, you would need an output similar to an oscilloscope to read the wave patterns. The short answer is essentially no. The only basic test to run is to operate the car, plug in an OBD2 reader capable off seeing the oxygen sensor data and make sure that the numbers are constantly shifting from 0 to 1, which is different from most other oxygen sensor setups. These cars use titania sensors which work differently. You can search the forums and learn a lot about these, but basically the only thing you can diagnose is a failure of the sensor, lazy ones are less obvious.
RockAuto will probably have your best prices on these sensors. If theyre originals, they are most likely past due for replacement anyways. They aren't supposed to last more than 60k miles?
Hi Vee; thanx again for your explanation. Today i was on the highway for a long time so i tested out driving conditions again a bit better. other than i experienced yesterday; the hickups did also occur when i unplugged the two upper sensors on the exhaust manifold.no difference at all. i was not able to testdrive with the lower two sensors disconnected; the engine was too hot to unplug those.
the problem only occurs when the engine is running between 1800 an 2100 RPM without accelerating. it looks like its becoming worse. the only reason i am thinking about those sensors is because the 'car scanner' OBD app gives me sometimes a -99,8% LTFT reading, and then next time 54% or so. all not moving; and very high.. Other users told me not to trust the obd capabilities of the 95 xjs, but i think its very strange since the SFTF readings are looking fine.
You also mentioned that the ECU is going into a preset mode when one of the sensors or the air temperature sensor is disconnected; and that the mixture will be richer; the app tells me the ecu currently (with sensors unplugged) is working in closed loop, and there's also no check engine light on when those sensors are disconnected. Could it be that if the sensors are bad; they have the same effect on the ecu as being unplugged; and going into the preset mode; which gives a too rich mixture, that makes the car hick at 1800 RPM? or is that not logical... the sensors are about 60 euros; so changing four is a lot of money...
here two screendumps of the car app.
The LTFT readings on your model year are a mystery. They are not directly tied to a sensor, they only relay the long term effects of the STFT. There should be nothing you can do to immediately affect the LTFT, short of using the PDU to reset it. The only way to change what the LTFT is showing, is to change what the STFT is doing, for a period of time. Unfortunately, I don't know enough about your model year's programming on how its reporting the LTFT, and I don't believe anyone here on the forum does either. It's an absolute mystery. As I mentioned before, as long as both LTFT numbers match, that should clear up any theories on a problem with your exhaust...including the oxygen sensors. They would both have to be failing at the same time, in the same way, in order to throw off fueling at both banks. I don't believe that's your problem here. That's too much of a leap for me, but still plausible?
Unplugging these sensors are not going to help identify a problem. I understand that you want to unplug it and see if it makes a difference, but the only result should be testing the ECU by forcing it to go open loop. For some reason, I remember one of the programs I use, Yhasi Movi, actually indicates whether the car is in open or closed loop. That program is an Apple program, run on a laptop, not phone. I don't have access to that right now, but I will next week. That might help. Figuring out which PID tracks that, and whether or not your program can do it. (It should)
In the meantime, read this, just be careful to read the relevant AJ16 parts.
To me, the low LTFT numbers just reflects something in the basic structure of the math equation set up for it. The number makes no sense, so I assume that the math behind it wouldn't either. There's clearly an unanticipated error here. I don't believe it provides us with any useful information.
I understand that 60 euro is alot, especially times 4, but I don't believe you have an issue there, I think it might be a costlier part. My suspicions would be the coils, which I believe you mentioned you changed already, and then the TPS, which has been known to cause strange issues on this engine. The TPS is particularly problematic because it is (a) expensive and (b) capable of being faulty while bench testing perfectly fine! I had a long standing issue with my 96MY where the LTFTs were both stuck at 10 for a long time. After bench testing the TPS, I basically replaced every other part until I finally decided to spend the money and replace the TPS and it cured the problem!
It is indeed strange that your MAF sensor is reporting 0.26 g/sec when the throttle plate is at 10.59%, or idle, I presume (which is low, I thought at idle, the butterfly should be closer to 12.9%) versus 0.24 g/sec when the throttle is at 17.65%, which means you're giving it some gas. Shouldn't the g/sec be higher when you have your foot on the gas?
hi vee, thanx again....the car scanner app also indicates that the car is in closed loop, although the sensors were disconnected. I will try your app tomorow also, i already downloaded it.
its a good thing you noticed the throttle position not behaving accordingly to the MAF air flow rate. i will test that specifically tomorrow..!
it does react to pressing the gas pedal more, the throttle position does go up, but it also might be that i took the screendump exactly in between the refresh intervals of the app; but again, i will test that some more tomorow. is it possible to clean the tps sensor; i saw the prices and indeed it doesnt make me happy. i will also ask my garagist, he might have some spares.
Yes, most likely took snap as you pressed the gas pedal, so the MAF number did not have time to adjust.
The TPS acts wonky because it gets worn out, so cleaning will not help. (They also get damaged from cleaning fluid for those who lazily clean the throttle body without removing the throttle body. The TPS is at the underside of the throttle so any solvents used to clean the throttle butterfly collect at the TPS)
06-03-2020, 06:54 AM
