FREELANDER TD4’S MAF PUZZLE
Can you help with a problem on my friend’s 2003 Freelander Td4, which has covered 156,000 miles? He had it diagnostically tested and found that the air pressure sensor was blocked, so he cleaned it out and it was running within parameters. He tried running without the MAF (Mass Air Flow) sensor connected for a while but, when he re-connected it, the car wouldn’t run without spluttering at about 2000rpm. He disconnected it again and it revved well and ran great, but used 5mpg more than it should.
So he fitted a new Bosch MAF. It started fine, but still wouldn’t rev above 2000rpm. He was advised to take it to a specialist recommended for resolving this kind of thing. They used a Pecoscope, checked all wiring and sensors, but still couldn’t get it to rev. It was noticed that the new Bosch MAF read low (260), so another new Bosch MAF was fitted and the readings were spot on, but it still wouldn’t rev with the MAF connected. He thinks it may be a fault in the ECU, but he’s not sure.
The crankcase breather filter has been changed by a Land Rover dealer some while ago (this whole engine issue has been going on for a couple of years). It’s also had a new set of injectors and he was then advised to have it chipped by Quantum in case it was a fuelling/ecu issue. It has since been put back to standard mapping. Initially, the problem was hesitation between 2000 and 2500 rpm, but has now developed into the problem described above.
Steve Haywood, Cornwall
This really ought to be a really straightforward problem to solve, but I suspect it is not going to be. As a general rule I would always suggest a new fuel filter and, possibly, a new low pressure fuel pump to solve the symptoms you have described, but unplugging the MAF (Mass Air Flow) sensor should not mask faults in these components.
I would suggest a filter change as a matter of course, unless it is a very recent one. The next obvious thing is that the new MAF sensor must be at fault if the engine revs freely with it unplugged, but you have already tried a second one and proved it is running within parameters.
This really leaves the wiring or the ECU. I know your garage has tested all the wiring with an oscilloscope but this is not an absolute guarantee that there is not a fault. If there is even one wire in the loom that has fractured most of its strands, it will still allow enough current through to run an oscilloscope, but not feed the correct readings to the ECU. Obviously, with an engine that has over 150,000 miles on the clock, everything has done a lot of shaking and has been through enormous numbers of heat cycles, so there is a fair chance that the wiring loom is not in the first flush of youth. This can be checked a little more accurately by testing resistance on each wire between the given sensor and the ECU. You will get a good idea of an average resistance, and any that are reading low will be at fault. Start with the MAF wiring and work your way through all the sensors, it sounds like hard work but, realistically, it will not take much more than an hour.
If this test of the wiring proves all is good, then you must suspect the ECU, although they are not known for being unreliable on the Freelander. I have not mentioned mapping because you have reverted it back to a standard map, though it is a common fault that people suggest ‘chipping’ an engine to try and get around an existing fault.
This is not correct, and any savvy garage will insist that an engine is running completely as it should before doing any tuning.
Sam Clarke