[Tom131]

Hi Folks,

I'm in real need of some forum wisdom today. Apologies, but there's fairly long story to this one; please bear with me, some of the info may even be relevant.

So, I'm a long time MG-Rover driver / owner, having run no less than 14 different examples over the last 20 years, including 3 x 75 / ZT diesels. I'm also an aerospace engineer by trade, so I consider myself pretty technically competent, but this one has got me scratching my head.

The current problem child was acquired via ebay auction around a month ago. Its a high spec 54 plate ZT CDTi, with a tad over 100k on the clock. It would appear that during its life it has seen at least some attention lavished on it, with several of the common faults apparently already having been rectified (eg intercooler O-rings), albeit with a distinct lack of mechanical sympathy (read bodged). I was told it had been service religiously through it's life, though no receipts could be produced to confirm this. Once I got it home I gave it a damned good service myself to be sure, and whilst the air filter must have done less than a thousand miles, I doubt if the PCV filter had been changed in the last decade, as it had a huge quantity of thick tar-like muck all over the filter and housing.

Anyway, on to the important stuff. At the time of viewing / collection it was clearly down on power, but disconnecting the MAF instantly improved the situation, so I assumed that to be the culprit. Other that this, the car has always started and run well enough. Having previously enjoyed positive results from the Pierburg MAF & Synergy combo, I duly order one of each from Ron and fitted them.

Now things start to get interesting. With the new components fitted, the car developed the most appalling turbo / power lag. Between each gear there was a 5+ second delay before you got any power at all, after which it came in one almighty chunk. Even when the power did come, it didn't seem constant and you could kind of feel it pulsing or surging a little as you held the throttle down. I ran if for a couple of days in that condition to see if it improved, but it did not. I did however notice that it got very much worse the longer I drove it / the hotter the car became.

Next I turned my attention to the EGR valve and manifold, as I wondered if that could be fouled & sticking. However, a quick check revealed both to be unusually clean (though certainly not spotless) for the age of the car. I'm pretty certain both have been cleaned relatively recently. Never the less, I decided to prove the EGR was not sticking by blanking it off altogether. As expected, it made no difference at all.

I wondered if perhaps the Synergy box, or new MAF might have been U/S on fit, so I transposed them with the examples already fitted to my wife's 75 to check them. The fault however, stayed with the ZT, whilst the 75 continued to drive beautifully.

For the last couple of weeks work commitments have prevented me from doing very much more with the car, so I've been running it with the MAF disconnected, which has left me with a driveable / tolerable motor, but it is certainly not ideal. Obviously with the MAF disconnected I don't get the performance that I should, but even accepting that, it still seems a little more hesitant than it should be, so I suspect something else is going on. Performance definitely seems to degrade as the car warms up, and now I have also noticed that once it warms up I get a tinny / metallic little rattle from the engine bay under acceleration. It also feels to me (though I could be imagining it) that it is starting to get ever so slightly lumpy at idle, sounding a bit more chuggy and clattery than I would expect from the BMW engine and more like the old L-series diesels.

There is one more point of note with the car though. Independent of the performance problems, I have also had trouble with the steering wheel controls. Whilst changing the rotary coupler I did notice that a couple of the ignition wires has been cut and spliced, then routed through into the engine bay, seemingly disappearing into the battery box; I have no real idea why, but it may be relevant as I continue.

So, my current train of though goes like this:
1) Could my turbo be on the way out? I am doubtful, as I do eventually get some boost, and it seems sort of ok-ish when running with the MAF disconnected. However, I am getting that rattle, which whilst not the usual screech you get from a failing turbo, might just be related. Anyone had any similar experiences?
2) Is a different sensor (other than the MAF) causing me problems? I have read on this forum talk of HP/LP fuel pressure sensors and regulators causing trouble, but the descriptions I've read don't seem to quite match what I am experiencing. What about crank / cam sensors, map sensors or air temp sensor? Are any of these likely culprits?
3) Could the ECU be at fault in some way? I am extremely suspicious of those 2 ignition wires being altered and I seem to vaguely remember once reading somewhere that ECU faults can sometimes be bodged by bi-passing certain relays in this way. Anyone have any idea what I'm talking about here, or am I just making that up?

I'd be hugely grateful of any assistance which would save me having to systematically replace every possible component.


Tom