Not a problem- my own initial thoughts blamed the immobiliser but tests with the "dead" key disproved that.

Many thanks for your diagnostic approach. The fact that it starts so vigorously and then dies does suggest that something electronic is cutting the sparks. I would say that here's too much fuel around for it to cut so quickly due to lack of.

Many posts/clips point to the cam or crank sensors but if there's no signal from any of those, again- it wouldn't start. And there are no OBD codes relating to those. As they are a known problem area, I will probably replace them at some time anyway.

I've received a suggestion from outside this forum to check that the ignition switch is still "on" and passing volts once it's turned back from the start position. The fact that the light show upon start-up looks correct argues that it's probably OK. That would mean that a downstream electronic something is doing the cutting. I'll wait until it has stopped snowing before confirming that.

Just had an AA man round to look at the Z300S. His super Panasonic laptop diagnostic device pointed to an immobiliser fault. A guy at my local car spares shop gave me the details of an auto lock specialist so I'll contact him and get a new key programmed.

Hi Ian

Ive had this exact problem twice on Z3's

On a 3.0 facelift it was the MAP sensor, bought a cheap replacement off ebay. Fixed it but only lasted 2 months. Bought a Bosch one, to my knowledge still going strong years later.

However as yours is the pre-facelift going by the type of immobiliser this is what happened. Start but not run. BMW technician said he thought it was the KWS II box,charged £125. Not that.

Had an auto locksmith came out and cut two new keys and got all the keys to match the ring and immobiliser, all talking the correct language to each other. Cost £150. Not that.

Towed the car to BMW Grosvenor in Reading (BMW specialist that the main dealers use when they cant fix an electrical problem). They had it 4 days and it turned out to be the camshaft sensor. Car will start but the computer does not know where the camshaft is positioned so cuts the fuel. Cost £462 (OUCH)
If that had not cured it the crankshaft sensor was next to be replaced as that would cause the same reaction.

Hope this helps

Many thanks for your perspective.
I've posted on a number of forums and checked with some ECU specialists but yours is the first reply with direct experience.
OBD is not throwing any codes to point to the cam sensor which has obviously confused the situation but they are a known problem.
Your advice about cheap replacements is well taken- I don't relish stripping the VANOS gear repeatedly for the sake
of a £30 difference between the oriental ones and the Bosch/Delphi/Bilstein equivalent. That experience is repeated on several BMW forums.
Thanks again.

One ECU option that does sound interesting came from EndTuning-
"I can delete the immobiliser, but that doesn't sound like the immobiliser to
me. You should have the M52TU engine, and they shouldn't fire up at all if the
immobiliser has gone out of sync. It's possible a throttle problem could
cause an issue like that, or maybe cam or crank sensor.
It is possible for me to read the stored codes on the ECU, so if you do want
to go down the un-immobilising route, I'd be able to look for codes.
Immobiliser deletes are £50, and they come with raised rev limiters and
there can be options like a harder cut limiter, over-run burble etc."

I like the sound of that last bit !!!

So he agrees with my experience.

Cam or crank does not show when plugged in with the non ODBII cars (yours) or the BMW dealer or specialist would have found it straight away.

I would not advise raising the rev limiter, its there for a reason. Modify the exhaust if you want the snap and crackle sound.

Agreed. It was the "hard" limiter that appealed- they rev so easily.

My short exhaust crackles and pops nicely already but I love the character it adds to the car.

Cut the pipes and push them through the bonnet for that real in your face sound

https://www.dsmtuners.com/attachment...df-jpg.330382/

Nice one. There was a Mk4 turbo'd Escort at Castle Combe the other year with the pipe exiting through the wing in front of the NSF wheel.

I am actually tempted but not sure how that works with MOTs

I've put an edit at the beginning of this thread pointing out that the fault had nothing to do with the immobiliser.

Having replaced the cam sensor and filled the engine with oil I started it up and went for a blast. It was a real blast as well- high revs through the gears and a full 70mph on the local dual-carriageway.

The next day it came to me that I hadn't reconnected the MAF sensor so I did that. Went away for a week. Came back and started the car today.

FFS- it started but would not run!!! I disconnected the MAF and it started and ran. Plugged in the MAF and the engine stopped.

Off to EuroCarParts again I think.

As a friend has just pointed out- I needed to replace the cam sensor in order to leave the MAF unplugged.