Hi, looking for suggestions and advice here.
The car is a 1999 XJ8, ~135000 miles on it. SN 856983.
We have had it since the summer, and it came with no maintenance history, although I did talk to the shop that was used to repair the car when needed and they thought it was running fine. It passed CA smog easily so is in relatively good running condition. After passing smog I replaced the air filter, it had the oil dripping issue, replaced the part-load breather hose (cracked), cleaned (the hole was completely blocked) and resealed the left part-throttle breather fitting. It then threw codes P0172 and P017 - both banks running rich. It did this at idle in drive. Looking at live data, both LTFT and STFT were running at -10 to -14. ECT seems to be accurate, from cold up to ~194F. I checked the MAF and it was not as accurate as it should be. I cleaned the TPS contacts at the plug as well as the MAF, no change in readings for MAF or fuel trim. I replaced the MAF with a rebuilt Denso, and get readings that align with what they should be
Park-idle - 5.1g/s
Park-2500 – 17.7
Drive-idle – 5.8
Drive-1500 - 42.6
I reset the CEL and it threw both codes again. I checked fuel pressure and it was 39/30 PSI with vacuum removed/attached at idle.
Reset CEL again and then it threw just P0172, this time coming off the freeway. STFT was -8.5 and -10.9 and LTFT was -14.8 and -10.1.

From looking on the forum I found this thread https://www.jaguarforums.com/forum/x...h-codes-56028/ very similar, the fix being replacing the throttle body. Is that what I am looking at next? SN 856983
What about the throttle body that goes bad that makes it think it needs more fuel? The TPS? On mine the TPS goes from 3 to 88.6% Is that a normal range?

Is the fuel pressure too low @ 39/30 PSI? I guess a new fuel filter would be a start.

Thanks for any help.

 

Hello;


Check your O2 sensors.
Especially the upstream sensor before the cat.
This sensor tells the ECU how much fuel to "dump" into the engine based on many factors/variables.

My suggestion:
Clean the TB and see if that fixes it. (I doubt it)........
When you changed the MAF, did you do a hard restart/reset????
If not, please do so before checking other items. The ECU needs to reset itself with a properly working/NEW MAF sensor.

I suggest doing an OBD scan of O2 Sensors and report back here, but THIS could describe what your referring to.

 

Hard reset not done. Is that disconnecting the battery for 10 minutes?
Ill check the O2 sensors.

 

Do this before checking anything else.

Hard Reset:
1.) Turn key Off
2.) Remove Negative battery cable from battery
3.) Turn Key ON
4.) Touch Negative battery cable to the POSITIVE battery terminal for at least 15 seconds. (Leave Positive battery cable connected).
5.) turn key OFF
6.) Reconnect Negative battery cable and start car.
7.) Let car idle for approx 5 minutes WITHOUT touching the accel pedal. This allows the car to reset the throttle position. Then drive it so It can re-learn the car/engine. It may take up to an hour for the ECU to relearn the system.

This hard reset should be done anytime you replace any engine parts. (MAF, O2 sensor, TPS, etc....)

 

On my 08 supercharged Range Rover Sport, I would run a can of Lucas finest (or later, SeaFoam or BG44K) in the gas. This cleaned up the injectors which were spitting instead of spraying. Always worked. (All three of my 4.0 Jags had the opposite problem: always seem to be running lean). Your OBD II reader should tell you if the oxygen sensors are enrichening the mixture.

You might reclean the MAF sensor and throttle bore and plate. Then reset the CEL at the OBD reader.

 

Did hard reset then let it idle for ten minutes, STFT stayed around 0, LTFT slowly climbed up to -8 and -9. I'll take it for drive home after work and report back what i get. FWIW EQ ratio is 0.994 and 0.997.

/

 

I struggled for a while with higher than normal trims, must be a thread about it here somewhere.
I did the same as you have done, and can add to check also the following:

- the connector to the MAF.
Mine definitely has/had an issue, and I still suspect this is the main culprit.
I slightly bent all little clips for better contact, and always install it with some contact spray, plus some moving around while installing.
Good or bad connected never showed up on the MAF readings, but it changes the trim values by some 6 points.
I never noticed it changed after connecting; just the luck of the moment during connecting, it is either good or bad.

- Be sure the intake pipe is straight connected to the MAF housing.
I have now seen several x308's where the connection is angled, and tightening the clamp might still leave a leak.

Finally, I still see slightly richer values if the ambient temperatures are high, and on trips below 50 km.
Maybe the ECU adds some fuel for cooling, which is then taken away by the O2 sensor.
Right now, with temperatures around 20C, and on a trip over 50km, my LTF trims are back to around zero.

As suggested, check the above, add a good cleaner, and go out for a nice long ride.

 

Hi,
I thought I should up date this. I ended up pulling the remanufactured MAF, cleaning/bending the contacts on the plug and the original MAF, and reinstalling with the original MAF.
Since then I have had the rich show up once. I do agree that it is likely the contacts.

 

Is it possible to repair the old sensor?
Cut off remains of broken nipple and fit barbed hose fitting.
Test new sensor here:

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