Halfords prices

My 59-plate 1.6 petrol Astra says 10 years or 100K miles, so that's later this year.

If you get stung/sprung for £903 every year for a worthless pot of grey porridge, then it goes a long way on a £144/month inc VAT new last model Astra lease.

FWIW, I've used Halfords for MOTs the last several times and found them fine. Never failed. The only slightly bizarre thing is they've issued an advisory on the front pads for the current car (2007 Audi A3) for 3 of the past 4 years - they're fine, about half. Last MOT they didn't mention it.

Plus £1300 (plus admin and servicing) for the honour of using it for 2 years, at 5000 miles a year . . . over £5k

What does the 'rentals in 1 month' mean?

Some vehicle manufacturers actually advise against fuel system cleaners and oil flushes and realistically its not something you need if you service the vehicle regularly and use decent fuel

I will have a check on Autodata for this one.

Just wonder about the ignition coil. The high price suggests that it's an ignition cassette covering all 4 cyl. If the cassette fails, that usually means sudden death; the engine can't run. E.g. Saabs.

On my previous car a single combined coil pack only took out one cylinder when it failed.

Most coil "packs" these days on 4 cyl are twin coils running a wasted spark. So if one fails it takes out 2 cylinders.

Ford had a cunning single coil system for 4 cyl. The coil was fired by a bridge of transistors so could be fired +ve or -ve polarity and the HT had diodes to direct the "+ve" spark to 1+4 and "-ve" spark to 2+3.

Transistors and diodes are much cheaper than coils.

But you still need coils to get up to the final high voltage for the plugs. On my saab, there is an electronic module (transistors etc.) giving 400 Volt which is then plugged into the ignition cassette with the four coils. I assume this is usually the system. A burned coil will take the whole cassette down.

Ford used ONE coil, 4 transistors, 4 HT diodes and 1 diode + resistor snubber. Wasted spark uses 2 coils, 2 transistors and 2 diode + resistor snubbers. COP uses 4 coils, 4 transistors and 4 diode + resistor snubbers.

If you have ever priced a wound component you would know that even a wire wound resistor costs much more than a transistor.

SAAB ionization detection system is unique to SAAB. No other car maker uses it as it's expensive and I think patented (but now over 20 years old so expired?). Additional cost 2 capacitors, 4 SCRs, 4 resistors, 3 DC-DC convertors (pulse transformer, chopper transistor, driver circuit), one for 400V feed to coil primary, 2 at 70V for knock detector connected to secondary.

Seems to work well on my 9000 Turbo. Always starts instantly, runs smoothly and never had fuel cut out even under hard acceleration.

That's interesting, I wasn't aware of the system, it's a neat way to detect ionised gas before the spark. I would have thought the same system would work with wasted spark as well as inductive discharge systems. I think EU patents now last 25 years?

But there's the cost in sensor, drilling and tapping of a hole and some fancy amplification and filtering. Plus another cable.

We're talking of pre-ignition or pinking. I suspect UK fuels are such it's not something you would hear in your Saab.

The ignition cassette was for the old" generation Saab engines, these engines were later replaced with GM derived engines for the later 9-3 and also the latest 9-5. I don't know how it works on 'modern' Saabs.

The latest 9-5 is now very rare since Saab was already in trouble when it was launched. But the old B engines had timing chains rather than timing belt.

It was well known in the Saab community :) that you should never be tempted to use any other spark plugs than the specific NGK type, the ignition system was designed around that plug.

The ignition cassette can fail as it sits in harsh environment with heat and vibrations. When it fails, then there may be little or no advance warning, the engine just stops and you're stuck. I took mine apart, and you could immediately smell burn from one of the coils, enough to take the whole system down. Some Saabists keep a spare cassette in the boot since they are straightforward to replace if is happens. However, the cassette normally lasts 100k miles or so.