Hi all,

 

So to start, it's a 1998 1.6 8v GL 5 door. A few weeks back it was having trouble starting which I put down to battery as I knew it was on the way out. Then it wouldnt start at all. Was getting the odd fire and puff of smoke from the exhaust but wouldnt turn over.

RAC came, checked coil pack said it was fine. Checked rota arm, cleaned it up a bit. Ran fault checker and said it was saying crank sensor. 

Towed to garage who when they started looking at it, said it was in dire need of a service, which it was, so they did that, new battery, plugs filters etc and then called and said it seemed to be fine now.

Picked it up, drove it home. Was fine until yesterday when it wouldnt start again. Called garage and asked if they ended up doing the crank sensor. They said no as it doesnt have one, only a knock sensor. 

Much as I dont like to question professionals, and he is a really sound and knowledgeable guy, I'm sure I've watched a video of a guy changing the crank sensor and without one how is engine speed etc known?

He said it is likely dizzy or leads problem. Does anyone have any ideas or know about the crank/knock sensor question? It will crank just not fire. Battery brand new, plenty of fuel but not starting.

Cheers, sorry for long post

A lot depends on exactly what engine code you have as to if it has a crank sensor (check your V5 the engine serial number will start with three letters, that is you engine code) however most of that era didn't have a crank sensor just the sensor in the distributor (cam sensor G40) but if the Knock sensor ( back of the engine block below the inlet manifold) has gone bad it will stop the engine from running, you need to get the fault codes read with a VAG specific code reader preferably VCDS 

Thanks dude. Some people have said it's the hall sensor in the distributor. Yeah I do need to confirm the engine code, didnt know you could get it from the V5 though, cheers for that.

Probably worth pulling a lead off or a plug out and seeing what the spark looks like. 6n's aren't known for hall sender faults (a lot of people use 6n disis on 2f GT'S because they're more reliable, but its 20+ years old, so anything is possible. 

 

There's an ignition amplifier/transistor pack/TCI stuck to the bottom of the coil. These can be well worth renewing once in a while. Get a decent brand one if you're doing that, something like a febi or Bosch. 

Ok, so. I have replaced the distributor and cap but still no joy. Had people telling me there was "definitely" some sort of crank position sensor under the starter motor and even watched videos of people removing the motor and changing the sensor. But, obviously, after sweating and swearing to remove the starter motor bolts, guess what? No sensor! Or not that I can see anyway. The nearest thing I can find is a plug that looks bolted to the back of the block Absolutely tearing my hair out now and it doesn't run so can't even get it to a garage! Any other ideas folks?

Did you find the engine code ??

 

Did you get it scanned with VCDS ??

 

The sensor on the back of the block under the manifold is the Knock sensor

Hey dude. Yeah its an AEE engine. Yeah looking around managed to work out it is the knock sensor but from reading stuff it sounds like it would still start if this was bad, just run really badly. When I put "1998 VW Polo 6n AEE crank sensor" into parts finders, stuff comes up which makes me think it must have one somewhere!

Looking at the dealer wiring diagrams that engine code does not have a crank sensor only the sensor in the distributor 

 

Any fault codes ?? as that would help with the fault finding 

I've asked a mate to bring his fault reader round, or I might just buy one myself. All very frustrating as it went from fine one day to broken the next and now I don't know what to try. Thanks everyone for your help.

If the knock sensor is telling the ECU that it's sensing a knock the ECU will retard the ignition timing to try and protect the engine and the retard will be enough to make it almost impossible to start 

Oh right, didn't know that, thanks. I'll get my heads on a reader and try and at least narrow it down to a cause.