Long overdue update

On the bright side, the seven continues to provide a rich learning experience, so to speak. The less cheery way of looking at it is, it still doesn't work, and in fact has even regressed in some ways.

After the failed MOT, much time was spent looking over the brakes and trying to figure out why they were seizing. The most significant factor turned out to be insufficient slack in the pedal: since the pedal (and hence the master cylinder) couldn't return fully, once pressurised, the system could never release fully, leaving the brakes dragging somewhat. As they dragged, temperatures rose (considerably), raising the pressure... which is why the car didn't make it to MOT without a rest; nothing to do with the handbrake, which was adjusted just fine.

A secondary factor, which Will and I spent quite a bit of time looking at, was the fact that even with this sorted, I still got about 3 ft-lbs of drag from each rear wheel. (For perspective, the diff on its own, being an LSD, takes about 7 ft-lbs to turn, which is just about turnable by hand using the discs, or not too hard to turn using the bigger radius of the wheels - so this roughly doubles the resistance at the rear). We tried winding back the pistons (no improvement); checking the callipers could slide freely on the pins (they could); checking the discs were central in the callipers (a washer was added on one side as a spacer to achieve this); with no improvement. Eventually I got the bench grinder out and ground the pads back by 1mm or so, trying not to inhale too much, and now they are fine.

Unfortunately a slight mishap occured while up on axle stands fixing the brakes: after everything was sorted, I started lowering the front of the car... and the rear fell off its axle stands. Happily, Emily's bike and Chris' lawnmower took most of the hit and absorbed a lot of the impact, but one rear wing of the car was damaged. It's an easy replace, but very, very annoying.

Brakes sorted and wing gaffer-taped up, I tightened up a couple of loose-ish unions that had leaked under the high pressure, topped up the fluid at the last minute, and had another go with Will following, and Becky looking nervous in the passenger seat. No issues getting there this time, but on arrival Will told me he was seeing big clouds of black smoke every time I put my foot down...

As half-expected, the engine indeed turned out to be running very rich. So rich that I hope the cat hasn't been destroyed - I don't think it's been run enough to seriously damage it, but we'll see; it was certainly another MOT fail (along with some a couple of loose nuts which will be trivial to sort out).

I've spent this week trying to figure out why the car is running so rich. I thought I had found the answer when I looked through the throttle body and saw this:

Oil in the inlet manifold.

But unfortunately, inspection of a friend's healthy 328 revealed the same thing, so I don't think this can be the issue. I've ordered a new CCV valve (the bit that's supposed to separate out the oil vapours before feeding back into the manifold) anyway, which I will fit anyway, as this is probably on its last legs at 100k miles (as indeed the state of the manifold suggests).

I had a bit of a poke around the fuel rail and discovered that all the injectors click at a sensible rate, so it's unlikely that one is stuck (and all the spark plugs are equally sooty anyway, so I don't think it will be a particular cylinder that has issues). Unfortunately I don't have anything suitable to measure fuel pressure, which, if too high, would explain things, but I will look into this.

Finally, last night, I had a bit of a breakthrough. After much research into lambda sensors, I removed mine, and tested them by heating with a blowtorch (which gets them to operating temperature - about 500º - and deprives them of oxygen since it's being consumed by the flame), and measured resistance as I did so (multimeter needs to be set to read at 200kΩ). Initially it should read infinity (lots of oxygen = lean conditions), then, when lacking oxygen (rich conditions), a finite value. One of mine just reads infinity, so it's always telling the ECU that there's not enough fuel...

Fingers crossed a replacement (£80!) will sort the engine out. I'm tempted to not bother and just wire up the working one so that the ECU reads it twice, but I suppose I might as well get it right. Also there's the possibility that the ECU fuels each group of three cylinders differently, as each one feeds its own lambda sensor.

This weekend's plan, then, is to replace the broken lambda, do a lot of tests to see if the engine is functioning properly, tighten up the loose nuts, and then the car should be in a fit state to pass MOT. Assuming, of course, that the cat is still OK - it will be expensive if it isn't.