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Hi everyone, really need some help solving this problem.
I’ve got an X300 3.2 which has, until recently been running sweet as a nut. It started with a couple of stalls at junctions, I would be in drive and the revs would drop, it only stalled a couple of times (99 times out of 100 it would pick up before stalling) but I’ve had the throttle body and stepper motor cleaned; I thought and hoped this had sorted the problem.
After a few days I noticed the mpg had dropped significantly on short trips or trips where I don’t go above 30 mph down from around 20 mpg to 14 mpg, but this was only on journeys where I wasn’t pushing the car, on long journeys averaging 80/90 mph or more I was still getting about 26 mpg which I consider to be normal compared to previous X300s I’ve had.
It’s stalled once since, also when stopped but in drive you can feel a slight wobble in the car like an uneven idle perhaps. I’ve read on line about changing the coolant temperature sensor as even though the temperature gauge in the car reads normal it could be that on short journeys/ low speed journeys the car is over-fuelling because the sensors reading cold?
Any help or suggestions would be very much appreciated!
Sorry we missed any replies yet, Jagguy. Have you put in new spark plugs anytime recently? it is prudent to replace them every 20k miles or so, with the inexpensive Champion RC12YC plugs. Occasional stalling and/or stumbling is known to be caused by old plugs. If in doubt, change em out!
I'm not sure this would improve mileage, but perhaps it will to a small degree, by making combustion more efficient. 26 mpg on the highway is a good number. Also if you get a scan tool you can read the fuel trim readings which give an idea of the fueling efficiency.
Correct about the coolant temperature sensor. Your new scan tool will display the coolant temperature that the ECU sees from that sensor.
Beside using the OBD - II connection port to retrieve the standard recorded failure codes ( free service from some auto parts stores ) you can use a device yourself that goes beyond the check engine light failures and that is the values like the LTFT amd the STFT . These 2 LTFT and STFT values are not sensor values per say hut are values derived by the ECU as a result of the sensor values as a final regulation ( target of 0.0 ) from the O2 sensors .So you have 3 things / failure codes , sensor values , and regulation values .This information requires purchasing a $ 12 US ELM - 327 device and some time to learn how to use it .. In the mean time you can retrieve any CEL codes for a sensor failure . The codes are on page 111 for a 1995 and on page 121 for a 1996 and above on the 801s document linked to above .To see a video on how the ELM - 327 device works see below video .
Without this device with a volt meter some of these sensor values can be obtained and referenced with the information from the Jaguar wiring guide printed your meter table of voltage or resistance values . The LTFT and STFT can not be obtaned in this way
This is the best way I can explain this iand how I understand n laymens terms and corrections welcome
One thing I failed to mention is the difference between a your meter seeing a reading in voltage or resistance vs, a ELM - 327 seeing a value . An example is the coolant sensor in post # 3 . With your meter seeing a physical thing like resistance and the ELM - 327 giving you a temperature value for that sensor . .
Hi, thanks for your replies, the plugs were changed about 2000 miles ago so probably not connected to this issue, although saying that I did use NGK plugs instead of champions.
It passed the MOT test, initially it showed up as 8 % on emissions but after a minute of revving at 3000rpm it dropped to normal emotions and passed the test.
The mechanic said a couple codes came up, one code, which he can’t remember now was due to a slow response from the lambda sensors he said so that could be the problem I’m having with low mpg perhaps? He put a bottle of fuel additive in tank to maybe help, he said to come back after a few hundred miles to see if code is back.
The other code was p1621 which I can’t seem to find on the link above, when I looked it up on search engine there was some mention of a transmission problem.
Thanks everyone and if anyone can help with these codes that would be fantastic.
The Jaguar CEL codes are on page 111 of the 801s doc linked above .
Notice there is a list fot 95 and 96 - 97 for whatever reason .
the 8 % value us probably the STFT and it changing verifys the ECU shifts to closed loop mode ( more economical )and is a function of your ECT sensor working correctly and hitting a certain coolant temp .
The slow response may be the heater element in the sensors that bring the sensors up to operating temp before the gasses do and is powered by a fuse and the heating elements can be verified with a meter .
Note the X300 uses a different titanium based technology and work differently then normal .
Some world regions use 2 O2 sensors and others like US use 4
The O2 sensors are not used until the closed loop mode is triggered..
The O2 sensor values can be monitored with the ELM - 327
The O2 sensor connectors can get corroded and cleaned and is important that they be placed in the proper position and effects the MPG if wrong .
The O2 wires are shielded carrying sensitive intelligence signals so the shield grounds are important to be cleaned and maintained. on the firewall . Tthe 2 for this are the small multi wire terminals on the left and on the right side of the firewall .
There was a good Youtube video explaining how the O2 sensors work in engine regulation if I can find it .
Last edited by Lady Penelope; 09-21-2018 at 09:15 PM.
My 95 4.0 has the same faint miss at highway speed. Not a full on miss, just a little noticeable stumble.. Not discernable on my logging tools. O2 sensor voltages are cycling as they should and within ranges that are reasonable. Not enough to make me try to fix it....but it is there. Will pay attention to coolant temps next drive. New plugs last week. Oil on two coils so also did all valve cover gaskets. Slightly improved the situation. Could be a coil I suppose , but not throwing a code.
I do get a cat efficiency code but only infrequently.
107000 miles
I'll take better notes next drive and maybe it will help. I use Torque pro. Lets you set up pages of graphed data so you can see trends in real time. You can also record and down load to review later. https://play.google.com/store/apps/d...orque&hl=en_US
With your Torque Pro you may see your EVAP system cycle at the by design highway rlike egime .
This assuming a % 100 working correctly working ignition system .
By it cycling the STFT may go too low forrotting a adiquit fuel mixture for cylinder fire off .
By the EVAP lines cycling open it may expose a leak like the shell of the charcoal canister seen in some bad environments of the world ( mine is fine )
Just a guess
Al Roethlisberger has a situation where the voltage regulator ( or alternator as a whole assembly ) fails at times after he changed it and this I believe causes the ECU reference voltage to be off until the ECU adjust or the alternator comes back on line as can be seen on his ELM - 327 device . This reference voltage being off puts the many different sensor values out of wack including the reference voltage to the different in how they operate titanium O2 sensors
I'll try to find the graph someone else noticed and marked of his drive log that shows this
You can see how when the blue line voltage goes astray the O2 sensors go astray and bottoms out on what he has stored in his battery, other sensor not on this graph can be doing the same having ill effects on his engine regulation he is feeling as a stumble under his bonnet as the British might say .
Editing
Last edited by Lady Penelope; 09-23-2018 at 08:17 PM.