QuestionI have a 2000 Discovery II with 69,000 miles. The O2 sensor problem started after I had the 60,000 mile check up performed by the dealership. I have had the O2 sensors replaced twice in the upstream bank B. The first time it was checked at the dealership and the fault it was the right front O2 sensor. The second time it was checked at the dealership also and the fault codes they gave me were as follows: P1050/0442/0174/1300/0302/1415, plus multiple misfires and the O2 sensor connector was oil soaked in bank B. The car also idled rough and the tail pipe had a black ring around the edge. The exhaust also smelled like sulfur. The dealership said that it was most likely a valve problem that was causing all the O2 problems and they wanted to do a valve job on the engine. I took to another mechanic and had the valves pressured tested and they were all within recommended allowances. The second time, I had two O2 sensors changed in bank B and the spark plugs changed because they were running too hot and 3 of them were covered in black carbon. The first time the sensors went bad occurred at 60,296 miles and it was the right front O2 sensor. After it was replaced it ran just fine, idled fine and the black ring around the tail pipe disappeared. The second time, 64,855 miles, I had the two upstream bank B sensors replaced along with the spark plugs and they cleaned the fuel injection. It ran just fine again. Now at 69,000 miles the same problems have returned, plus the engine sounds rough when it starts.
Jared Morris
Des Moines, Iowa
AnswerHi Jared,
it could very well be the sticking exhaust valves that is common with Disco II engines. In your case, it may be complicated by failed O2 sensors. An O2 sensor covered in oil is an oddity, especially a 2000. My '95 has 324000 kilometers and the O2 sensors are dry as a bone.
The valve problem that the dealer may have alluded to concerns series II Disco exhaust valves sticking. This can throw off your engine to various degrees, depending on how severe the deposits and conditions of the valves. It can appear as early as 50000 miles and can repeat itself even after a valve job is performed.
I always thought that when the plugs are covered in black soot it meant that the fuel:air ratios were too rich. It could be caused by the faulty O2 sensors and the ECU interpreting and adjusting the mixture to compensate.
Pressure testing may not reveal that the valves are sticking. The best time to test is on hot humid days when the engine has been running hot for some time.
I am having the same problem with my Disco. Even though I too am seeing the O2 sensors acting up, I know that its due for an overhaul. The difference between your Disco and mine is that yours does not tolerate slight variations in its sensor readings while mine does not give a ___ care. The 3.9 just ploughs right on through. When it gets to the point that you hear ticking on acceleration, that's when you know its time for service.
My plugs, for the first time in years, are covered in black soot and I have little I can do to adjust the mixture. Its all in the ECU. I can reset the gap on my plugs from .032 to a max of .038 but the ECU will probably compensate for that. I've seen this trick done by a LR dealership. It helps for a while but its avoiding the problem.
The misfires on your Disco is a concern and the sulfur-like odour is 'rank'. Did you know that most general mechanics could perform the valve job at a fraction of the dealer's price? You'd probably have to supply the parts (better this than having he gen.Mechanic mark them up) AND you can get the parts from various sources other than the dealership.
I've had TPS problems that have affected the timing on my Disco. The throttle position sensor was faulted and as a result the idle was never smooth. The dealership replaced the TPS and reprogrammed the ECU. Rough idle (wild swings from 500 up to 1000 rpms) were brought down to 750. O2 sensor was acting up at that time and dealer wanted to change them. Long story short...he replaced the TPS and the idle came back into control.
In your case, it just sounds like a mechanic has to open up the engine to see whats going wrong. Usually, the LR testbook reveals these problems but your note does not mention if the dealer did an complete analysis. I once took my Disco to a dealer with a problem and asked him to 'check it out'. Two days later, he told me that they flushed all the fluids and could not find any trouble. I asked "what did the computer tell you?". The service manager's reply "OH? You did not ask for a computer diagnostic!". ARGGGGGH.
If you can find a mechanic you can trust, have them perform the tests. Some euro-mechanics (BMW, Volkswagen,) have experience with LUCAS electronics. In your case, I think BMW redesigned your engine when they owned LR.
The only problem with that is the investment on the diagnostic tools. LR has a 'reported' $10,000 testbook system that can diagnose your LR from intercooler to tailpipe (almost). Most euro-mechanics won't have this on their benches.
I wish you luck with this, Jared. Let me know how it turns out.
Regards,
JohnMc
