Battling my 2005 X-Type which has not managed to make it more than 5 miles in the last year without misfire codes... I present a hypothesis.

My X-Type was driven into a garage for the state emissions test a year ago. They are supposed to turn the car off, open the gas cap, close the gas cap, then restart the car. My car would not restart. Car gets pushed out, no inspection. I google and find out maybe the gas cap is not on solidly. Check the gas cap, close it solidly, then get my state inspection, no problem. Since that day the car runs like crap. I get misfire codes on bank 1, cylinder 1, cylinder 3, cylinder 4,.. I replace all the coils and plugs. Get misfire on cylinder 3. Replace coil, spark plug, and injector. Finally can run the car for 300 feet without a check engine light. Then I get an ABS light and an air bag warning light. Disheartened I leave the car alone for 3 or 4 weeks. Then I go out and try and start the engine, the engine that started fine 3 weeks ago,.... nothing. Cranks and cranks but no start. Put some starting fluid in the engine jumps to life. Clearly a fuel problem.

Hypothesis 1: fuel pump is dead
Hypothesis 3: fuel pump has been bad for a year so runs but does not provide enough pressure. All the "misfire" codes are a result of a bad fuel pump.

How does the ECU decide something is a misfire? Could the fuel pressure be low, resulting in this error?

 

There's a long list of the usual known possible causes in the workshop manual / OBD codes files - free downloads from this site or JagRepair.com - Jaguar Repair Information Resource - and a LOT of threads about this kind of thing.

Reading the free doc is quickest

 

Thanks JagV8. I know there are a lot of threads about misfires, I have been reading them and creating my own for months. I must have missed any that concluded with a bad fuel pump, but there it is in black and white in the "Powertrain DTC Summaries-OBD-II" (the link called Engine Management from the JagRepair.com site JagV8 linked in). Low or high fuel pressure can create random misfire codes. RTFM!

 

dh53, if you find that the car cranks and cranks, but will not fire, try this: roll the key back to OFF, then roll the key to the RUN position, let it sit there for 3-5 seconds, then finally roll it to the START position. If the car fires up, bad fuel pump. As for what causes a misfire, in short, it is a bad reading on an O2 sensor. A properly running cylinder will have a very small amount of oxygen left in it. This oxygen causes the O2 sensor to have a very small voltage created in it. If you have too little fuel/bad spark resulting in unburt fuel, the oxygen left over goes up, making the voltage on the O2 sensor go up, triggering a code. Kinda like if you add too much fuel (fuel pressure too high, stuck open injector), there is no left over oxygen and the O2 sensor drops to zero volts. The computer is smart enough that it knows where in the rotation the motor is and knows that at a certain time after a cylinder fires, that cylinders exhaust is going to be going past the O2 sensor. So, as the O2 sensor voltage jumps around from good cylinders having just a little bit of oxygen left and the one cylinder having none, it can figure out the cylinder that is not running right.

 

Thanks Chris. I did wonder how on Earth bad fuel pressure would result in a misfire code. I am happy to think that limping home all those times it was not enough fuel rather than no detonation so I probably didn't damage that catalytic converters. It amazes me they can pick out individual cylinder problems with the timing of the O2 sensors while at the same time they can't figure out to put an access port over the fuel pump like Jag apparently did on other models.

Anyway, I went whole hog on the bad fuel pump problem, decided against cutting into the body, and in about 7 hours today managed to drop the drive shaft, the exhaust, lower the differential, disconnect 100 wires and hoses, and get stuck with only the filler hose connected to the tank. There is a section of rubber hose a few inches long between the tank and the steel filler tube. Mine was held on by 2 worm gear hose clamps. Stainless clamps, but mild steel screws. The heads of the screws were completely rusted off, nothing to even try to turn. I ended up cutting the hose so I could get the tank out. Probably regret that tomorrow when I look for a replacement, but the fuel tank is out and first thing in the morning I'll be at the pump itself.

 

Lol, a few months after cutting under seat to replace my pump, I got a persistent evap leak that finally wouldn't clear and reset. Had local ex-Jag tech owned shop find problem (smoke test). It was THAT RUBBER hose piece between filler neck and tank leaking. $50 part (not bad) $800 labor (as you found out = quote 6 1/2 hours), smfh.

 

That had to hurt. My 7 hours was just to get the tank out but I could have cut a couple hours off if I had a lift instead of crawling around on the ground.

I expect an evap leak at what I believe to be the "evap canister close valve", pictured. Thank goodness for SNG Barratt diagrams, I can't quite make out the part number on this one.