ABF OBD possible crank sensor.

Hi,

I have a mk1 GTI running an ABF from a '97 Golf GTI. It is running standard MK3 management and injection. Car intermittently cuts out/runs badly. Changed plugs, leads, drained tank changed filter. I have the diagnostic port fitted, I have a cheap ELM 327 bluetooth OBD adapter the only app I have on my phone is Torque this does not recognise the protocol apparently. Can anyone recommend an app that works?
The reason for the above is that I suspect the crank shaft sensor is at fault. I have noticed that when the car is difficult to start the tacho does not move when cranking. I believe the ABF takes its engine speed from the crank shaft sensor if someone could confirm that would be great.
Also which crank sensor would anyone recommend?
Thanks in advance.
 

The trouble with a code reader/scanner is it will only give you direction. You really need a scope on it to see whether you are getting a good signal or not.

I have a scope. As above the problem is intermittent so its not always practicable to use this. Also I want to look for any stored codes.  I am going to download VAG COM and get the appropriate lead.
Steve1973 do you happen to know what the correct trace might look like? peak to peak etc.
Can anyone recommend a brand of crank sensor. Or at least the ones to avoid!!!

Many Thanks

By trace, do you mean what the signal should look like on the scope? Well it depends on the sensor type. It could be induction or Hall effect. Induction sensors put out an ac sine wave, hall will put out a square wave. How many wires have you got going to the sensor?

That right Steve, the response shown on the screen is called a trace.
Its a 3 wire hall effect type. I suspect I would see a pattern of 4 square waves. But as the fault is intermittent its a bit of a moot point.

If it's intermittent and you're confident that the wiring to the sensor is sound then you might as well risk putting a new sensor in it. Either that or spend hours waiting for it to play up. I've never worked on mk3 so don't know the system. Is it a 5V pull down sensor? Have you tested the reference voltage, ground and signal wire? I'd go OEM with sensor as the aftermarket are junk.

One more thing to consider is the air gap. Is the sensor adjustable?