I purchased a 2005 XJ8L with a misfire and shifting issues. It has 80K miles and looks immacalate inside and out. Prior to my purchase, it sat for 2 years because of these issues. I found the following codes: P1000, P300,P302, and P1316.

I proceeded to replace all the spark plug with OE plugs. I also replaced the #2 coil. I then added 16 ounces of sea foam to the tank and drove it around for a few days.

The idle is slightly rough, but not lumpy like a vaccum leak. The car drives mostly normal till about 2500 rpm. At 2500 rpm, it bucks and studders when I mash the gas pedal. However, if I gently accelerate it is fine. I can go from 70 mph to 100 mph in 20 seconds without an issue, but it I try to do the same in 10 seconds it will buck and studder violently.

The short term and long term fuel trims are both in the -5% to -10% range. The ECU voltage is 13.7 - 13.8 at idle. At 2000 rpm it is 14.0 -14.2.

I'm at a loss for the solution to this problem. It it was a vaccum leak or lean issue, I would expect to see alot more fuel being added. I have the opposite, its very rich and the ECU is taking fuel out. If it were a electrical connect issue, would expect to have codes 354, 356 and 358 on the same bank. I don't have those.

Any ideas?

 

Hot engine parked. What are all the trims at idle & when revved to about 2500?

 

In park, at 2500 RPM, the short term is about +5%.

In park, at idle, the short term is about -10%.

 

Should have 2 STFTs & 2 LTFTs at each revs - do we guess the others?

 

I have a 2005 4.2 XJ8 Sport. that has done 165,000 miles. Although it has a high mileage it is in excellent condition with FSH and very clean MOT emissions and minimal oil consumption. It is pretty smooth but always seems slightly rough with a throughout the body "rumble" at 50 + mph which is no longer noticeable over 80. I replaced the nearside rear wheel bearing which was causing some of the rumble / shudder but it did not completely cure the problem. I put the roughness down to transmission vibration which these x350s have a bit of history for intending to investigate it in future, trying weights on prop shaft etc after a gearbox oil change. I know old oil can cause transmission vibration on XJ40s. Because of corona virus I took the car off the road at end of March. I warm it up every few weeks and run it up and down the drive. Whilst warming it up in neutral I revved it a bit and notice a roughness that peaks at about 1400 rpm, the same as the vibration when driving. I have had a warning light on the dash at times, usually after filling with Morrisons (supermarket) petrol which I no longer do. Although it says restricted performance the car drives normally. One of the codes I got was knock sensor but this has not reoccurred for some time whereas the vibration / roughness is constant. I suspect that one or maybe more cylinders are not getting quite enough fuel, not such a shortage to cause a full misfire, just enough to make it or them fire differently to the other cylinders. Any comment or advice welcome. I am too busy to work on the car at the moment but intend to check the plugs and coils, and maybe back flush the injectors when I get time.

 

In reply to the original post, a faulty air flow meter can cause the symptoms you describe. Diagnosis can be difficult as in garage tests are often inconclusive. You need to connect a PICO scope or similar and drive the car whilst someone monitors the scope. I am not familiar with the throttle position sensor (TPS) on an X350 but on an xj40 (and other cars) wear or oil contamination on the TPS can cause the symptoms you describe.

 

Both sides are identical in their fuel trims.

 

How many miles are on the vehicle? It may be wise to replace all the spark plugs and coil units as often misfiring coils do not set a DTC. Continuously operating the vehicle under conditions that lead to misfires results in damage to the catalysts with the resulting P0420 and P0430 DTCs being set.

 

I replaced all of the spark plugs already and the coil that was misfiring. That cylinder still has a misfire, along with an open coil circuit fault.

 

Have the injector and coil connectors and wiring looms been checked for damage and poor connections? If necessary, perform a pin test for continuity back to the PCM.

 

I was hoping that would be the last thing since that's pretty involved. That might be the next thing to do.

I notice that via the Torque app, the ECU voltage is around 13.3 - 13.8 when going down the road. Is that enough voltage to keep the ECU happy?

 

Yes. With the ignition in the OFF position, there should be a minimum of 12.6 volts across the battery terminals when checked with a voltmeter.

 

I may have fixed the problem. New fuel filter and new #2 injector. The car runs like it always should have now.

The old fuel filter was so clogged that it was only flowing maybe 1/4 of the volume of the new filter.

 

Great news that you've got it sorted. I had two injectors go completely open circuit within months of each other but I found that testing the injectors and replacing them was actually a surprisingly straight forward job.

 

I love a happy ending. Thanks for taking time to keep us informed, now I can relax and enjoy lockdown.

 

I spoke too soon. After two days of running around town, the same faults came back. P0300, P0302, P0352, P01316. So new plugs, new coil, new injector, and new fuel filter didn't solve the problem. Initially, the problem was resolved for 20 miles and now its back.

I'm baffled why the codes are only on cylinder #2. What ever is happening is triggering limp mode.

 

How infuriating. Surely it can't be much Motoneil. I wonder if it's a dirty or loose connection, the challenge is of course to find it. My Bro in law bought my last X350 off me and it ran fine until he drove it through a flood and now it has similar symptoms as yours. Just wondering, is there a chance that it could be dirty or contaminated fuel? Interesting that it ran fine after you worked on the fuel side.
Good luck with it. You'll feel great when you find it.

 

Something else is wrong then as realistically that never happens with cars of this age.

 

I have ran multiple tanks for fuel through it and also ran 16oz of SeaFoam in a 1/4 full tank. My next step is to swap the coils around to see if I have a bad "new" coil. I wasn't getting the P0352 , "open coil circuit" fault before I swapped coils.

 

Sounds like a plan. Maybe even try the original coil back on. I wonder how much the previous owner knew about it and what he had tried. At least you aren't paying garage fees for them to experiment with coils etc.
Seems that it's giving us a clue when it switches from bad to good then back again.