HI guys

It finally happened; my trusty polo has given up on me just 150 miles before its 100,000 mile mark!

Went to college this afternoon; ran fine. Came out in to the carpark to go home and it wouldn't start :(

Luckily the college teaches mechanic so the tutor had a quick look at it. He seems to think it could be the crank positioning sensor. We'll see what they say tomorrow when they are open again and can look properly.

One thing he noticed was there is no spark at the distributor, as if the fault lies somewhere before this>? I can do minor mechanincs and maintenance but vehicle electronics is black magic to me.

Has anyone heard of this problem before?

Fueling should be fine as should plugs, leads, battery, throttle cable etc we had a look at these today.

Anyway.......the point of the thread was to ask if there are any other sensors likely to die with old age that my be worth changing whilst i got it in a workshop? Is there a throttle position sensor? temp sensor? etc.

The idea is I want to replace the things that may go wrong whilst i can so that i don't get stuck in a frosty car park again.

Cheers guys

R

Might help if you put what engine and what car buddy, on the vague info i would day faulty hall sensor or coil.

something like this happend to me and ended up being the fuel pump.

ah sorry guys wrote the last one in a rush to get to work.

Right here goes........1.4 8v 1997

The car has never missed a beat, bee a real trooper. I have serviced 300 miles ago which involved the following:

Oil change

New plugs

New dizzy cap

New dizzy arm

Air filter

Pollen filter

All very basic stuff. I doubt any of these are causing the problem as the engine has run spot on for the last 300 miles since the service. As far as i remember the car has always fired first time.

The car drove to college fine was then parked for say 3 hours and wouldn't start.

It turns over fine just does not fire.

No warning lights come on the dash.

The only fault that happened before the problem (and only happened twice in about 1000 miles); when driving the car at a steady speed, all of a sudden the revs dropped (as if it was stalling for a split second), only to go back to normal almost instantly. Bizzare!

When the mechanic had a quick look he mentioned there's no spark in the cap (did a test with holding a screwdriver over the cap while I turned the engine. He presumed it was a fault from the (sorry i can't remember the technical term) the HT lead? (the one from the centre of the cap to the coil) or the crank position sensor.

Any suggestions?

If the mechanic students can't fix it, I'll get it towed home and have a quick look.

I was really just looking on here for some pointers that will save me having to take the car to a proper garage and pay (I'm a cheapskate student :p)

Thanks guys

RUss

More than likely a faulty hall sender in the distributor, or the ignition coil i reckon.

cool

I've just been trying to learn about crank and cam sensors.

Would my polo have a crank and cam sensor? or just crank?

The hall sender is the cam sensor, its just built into the dizzy, its the black 3 pin connector on the top. Pretty sure the 1.4 8v doesnt have a crank sensor.

remove the dizzy and the cap and see it there is alot of free play in the bearing. if there is its probley that just remember to mark it before taking it off.

thanks lads.

just looked in Haynes and can't see any crank sensor in the wiring diagrams so you must be right; there isn't one lol.

I didn't realise the cam sensor was called the Hall sensor. I'll look to see if these can be replaced seperate to the whole dizzy

I'm not 100% but i think it can but i think if the bearing on the shaft goes it damages the sensor so if yours in worn i wouldnt mess about and just get a good second hand one or a new one

pretty sure u cant buy a new hall sender seperate

hall sender vw part no 030 905 065 B there about £60 from vw :-)

Yeah these engines don't have crank sensors, that reading for the ignition timing is taken from the hall sender in the dizzy.

Not sure exactly why cam sensors are on newer cars, I just thought it was a form of misfire control but either way your polo won't have one either!

It makes more sense that your coil has died as this is more of a service item, try plugging on another known-working coil if you can get hold of one, same for the HT lead from coil to dizzy. If not then could be dizzy problems, try switching with another known working unit

cheers guys

you're all right regarding the diagnosis. I rang the mechanic tutor; he's saying the cam sensor (attached to the dizzy) is kaput.

What I need to know but can't seem to find online is can the cam sensor be changed seperateley from the dizzy, or as the mechanic tutor says, does the whole unit (dizzy and sensor) need to be changed?

Looking for prices online, new dizzys are coming in at about £80-100 new (Eurocar parts) does this seem right to you guys?

I'd really like to replace the whole unit with a new one as the dizzy shaft is wobbly/worn anyway so a new sensor may be false economy.

Russ

Just been reading the Haynes.

If I can get the dizzy myself I should be able to fit it no problem, although surely when I've fitted a new one it will affect the timing?

I can see the trick of marking the dizzy body in relation to the mounting/head if you are removing the dizzy, only to put it back on later. But how do you know which position to put a new one in so that the timing isn't buggered?

R

Price sounds about right for a new one, Id stick with bosch tho, iv had endless poblems with the cheaper alternatives (sensor wise) in the past, so much that id rather get one from a scrappy than buy one .

You can get it roughly right by ear by rotating it with the engine running, how ever a timing light should be used to get it spot on.

TBH i would be suprised if the college dont offer to do it for you, most of the cars in there will be fucked anyway so will be good practise for them.

Cheers lads

All done. I got a new dizzy complete with sensor today and the college fitted it :)

I learnt quite a lot from the tutor about ignition systems which was a plus too!

When i was googling 'cam sensors' I was getting confused.......

The Hall sensor on my dizzy is basically a modern(ish) replacement from the old types of mechanincal points in dizzys. The tutor mentioned people often call the Hall sensor a 'cam sensors' when in actual fact a true 'cam sensor' is different (only found on modern engines, often with variable valve timing and dizzyless ignition etc). Confusing hey?!

Anyway I just need to pick the car up tomorrow providing it doesn't get nicked over night. Fingers crossed.

Thanks for your help lads

R