I recently replaced the distributor Hall Sender on my GT, so I thought I'd put a little guide together on how to do it, a few pictures included.

* This FAQ is based on a 1991 VW Polo GT (Mk2f), with the 3F engine. It will be the same procedure for all other Mk2f's, and I'm pretty sure its the same on Mk2's as well - and probably the later Mk4 lumps, but don't take it as gospel *

First off - what is the hall sender? Well basically its an electronic device that replaces conventional points in order to determine when the spark is generated for the engine. It uses a notched trigger wheel inside the distributor, which has four notches - this is driven by the camshaft. When the notches pass by the hall sender, a signal is sent to the coil and the HT spark is generated - a lot more to it but that gives you an idea!

General symptoms of Hall Sender failure is very rough running, misfires, low fuel consumption, the engine shaking at low rpm in a high gear, erratic tacho behaviour and eventually the engine will die and not restart. Before spending the £55-odd quid on a new Hall Sender, make sure the car is properly serviced and you've eliminated other things such as the lambda, blue temp sensor, throttle position sensor and AFM.

The hall sender is the same for all Mk2f's, it is the trigger wheel that varies. So if you have a GT thats not performing well, it'd be worth checking you have the correct dizzy (with the right trigger wheel) - have a look here .

The entire job to replace it took me about half an hour, its not the awful job that people make it out to be.

Tools required:

A decent timing light

10mm spanner (or the tool to undo whatever holds your dizzy on)

A 3mm punch and small hammer

Small phillips screwdriver

The normal clean working environment

The job itself:

1 - First of all, find yourself a car that needs the Hall Sender replacing. (Pretty much any poor running Mk3 where you're scratching your head as to what it could be!):

2 - Open the bonnet, find the dizzy. There it is:

3 - Take the dizzy cap etc off, unplug the hall sender plug, remove the bolts that hold the dizzy on, take it off:

4 - The dizzy will now look like this:

You can see the black plug for the hall sender, the trigger wheel with the four notches in it etc. You can't gain access to the hall sender itself until you remove the trigger wheel and shaft, which is held in place by a roll pin through the drive pinion on the back of the dizzy - this:

To remove the roll pin, place the dizzy in a soft jawed vice, clamp it gently, and using the 3mm punch, drift out the roll pin. You need to make sure it is lined up with the slots in the dizzy body.

Also, make a note of which way the drive pinion is mounted in relation to the rotor arm slot on the other end of the shaft for when you put it back togeteher:

Once the roll pin is out, remove the drive pinion. Then withdraw the shaft gently through the dizzy body, as there are shims behind the drive pinion - don't lose these. It'll look like this:

Now - turn the dizzy over and you should be able to see the Hall Sender easily. Its held on with three small phillips screws. Undo these and gently pull the hall sender up and out of the dizzy body - it comes out level, so be gentle:

You should now have all the component parts, looking something like this:

Open the box for the new Hall Sender. Inside you should find the unit itself, and a small bag with all the components in, include a new roll pin, drive pinion, o-ring for the drive shaft and shims:

So, replace the o-ring on the end of the drive shaft:

Now would be a good time to clean the dizzy body up inside and out. Once its clean you can start putting it back together.

So put the new hall sender in place, sliding it fully home into the body of the dizzy:

Put the screws in, tighten them up (no torque setting). Next, make sure the drive shaft and trigger wheel are perfectly clean, as well as the inside of the distributor body.

Put a small amount of high-temperature grease on the drive shaft, then slide it through the dizzy body.

You will now need to fit the correct amount of shims before fitting the drive pinion. Its important that there is a small amount of movement in the shaft, to allow for expansion when the dizzy gets hot - shimming up may take a bit of time, but its worth it. You will need to fit the drive pinion and roll pin, see if its right, take it off if its not, re-shim etc - longest part of the job.

Make sure the peg drive pinion is the right way round. I didn't the first time, put it all back together and it wouldn't fire. The timing was 180 degrees out! So make sure you get it right.

Once its all back together properly, re-fit it all to the car. Plug it in, fit the rotor arm and dizzy cap, then see if it'll start.

If it doesn't, then read the above paragraph and make sure its right! Then just try swinging the dizzy a bit while someone cranks the engine, eventually it should fire.

Once its running, let it warm up and then set the timing properly using the right method for your car before driving it. Don't forget the GT/G40 Digifant engine managment system has a different system to the Monotronic for setting the timing - make sure you're doing it the right way for your car.

Thats pretty much it - you should find it'll run a lot nicer now

Edited 30 December, 201411 yr by mark_crox

pm a mod to make this faq so its not deleted. good work mate

Done and done, I tip my jimmy-hat to you.

I'd just like to add a little post script to the bottom of this -

Went to fill up the GT tonight, and the fuel consumption is now 41.9 mpg over an average of 310 miles, mostly commuting, occasional motorway driving, journeys no more than 20 miles.

This is compared to a consistent average of 39 mpg over the last 6 months!

Nothing has changed, its always filled with Shell 95 RON fuel, and the driving is pretty much always the same.

I also serviced it a month ago (new plugs, leads, rotor arm, dizzy cap, oil/filter) which made bugger-all difference to the fuel consumption - so I know that replacing the hall sender is whats saving me money.

I'm not sure if enough emphasis is placed on the hall sender (always seems to be the blue temp sender that people suspect first, maybe because its the cheapest!) - but to anyone with a poor running GT, change your hall sender and see what it does then!! Well worth the money

One more thing, just wanted to show the difference between the trigger wheels on 3F/PY engines and other Mk3 lumps:

3F/PY Trigger Wheel (large gaps):

SPi (AAV, AAU etc), possibly multipoint NZ (smaller gaps):

Put together so the difference is obvious, this explains why GT's run crap without the correct dizzy, the ECU can't accurately control the timing:

hat of to you chap nice easy to follow write up may come in handy for future refference

luke

Wish i tryed this with my old GT.

Comparing, the 3f and 6n dizzys they seem to have the same size slots. I fitted a 6n dizzy to my old GT and it seemed to run a lot better than with the SPi one that was fitted when I bought it. I think these may be a cheap functional alternative to a GT dizzy.

BUMP for an easy find for me later

^^^ this whats wrong with your G then?

He's just trying summit else with the coil pack, everything else has been changed but this could be the the one, well it's the next try anyway *everything crossed*

Hi, this post refers above to the two different methods of ignition timing for each engine management system. Does anyone know what the procedure is for the Motronic system?

I also found that when removing the dizzy it would be best to mark on the top where it sat. This makes lining it back up afterwards so much easier.

hi there.

just a quick question.

got a L reg polo 1.0 aau,

Recently after new head gasket was fitted it was been lacking grunt (i know its a 1 litre) but more than usual, really struggling and drinking fuel and hessitating under load (maybe misfire)! feels like driving through a big puddle!

replaced lambda sensor and fuel econony, power and torque are much better but it is still hesitating under load.

soooo googled misfire and polo aau and this post came up.

just before i think about hall sensor, il try to eliminate the other options, you mentioned blue temp sensor??? do you meen the blue temp sensor in the cooling system. if so how does this cause problems???

any other ideas???

cheers, nick

hi there.

just a quick question.

got a L reg polo 1.0 aau,

Recently after new head gasket was fitted it was been lacking grunt (i know its a 1 litre) but more than usual, really struggling and drinking fuel and hessitating under load (maybe misfire)! feels like driving through a big puddle!

replaced lambda sensor and fuel econony, power and torque are much better but it is still hesitating under load.

soooo googled misfire and polo aau and this post came up.

just before i think about hall sensor, il try to eliminate the other options, you mentioned blue temp sensor??? do you meen the blue temp sensor in the cooling system. if so how does this cause problems???

any other ideas???

cheers, nick

your blue temp sensor is part of the feedback system to the ECU, at different tempretures taken the ECU puts different amounts or fuel in, I have a brand new one boxed up if you want, PM me.

Max

brilliant guide where is the best place to get the hall sender from.

part number etc,

Cheers

Rich

Edited 4 November, 201015 yr by XRrich

This is my first time on this forum.

I am trying to get my daughters 95 1000 6n to start after it cut out last week, I replaced the coil before looking at the forum and found lots of info about the Hall sensor. So reading right through your info. I decided to buy another dizzy from a scrap yard, I found one today after trying several places near Barcelona where we live. they looked the

same there except for the last letter on the part number which ends in AA instead of AD on ours, the guy there and a mechanic who was buying there assured me it would work but the problem is that the plug is at a different position on the dizzy making it impossible to connect the plug up without cutting the wires and making the cables longer. then it occured to me to swap the hall sender out of the body of the new one and put it in the old one.

Can anyone tell me if this will work, or am I waisting my time?

Thanks

Neil

great guide i did mine today easy to do but still no spark

Thanks for this - just used it to confirm what i was doing to repair my Daughters 1997 Polo, it stopped and refused to start ever again - got a hall sensor off a golf - 2 hours at a wrecker finding the part, half an hour dismantling and re-assembling the distributor - all done and on the road again...