Club 80-90 Forums

Hi all

I have a 2l cu Aircooled T25. I need some advice please.

I adjusted the tappets and planned to adjust the timing. I connected the timing gun to no 1 plug lead, it also has earth and +ve leads, these were connected to an engine bolt and the +ve feed for the coil.

Having connected up the gun, I turned the engine over but it wouldn't fire. Disconnected the gun and checked for a spark, nothing. Prior to this the engine had been running fine.

I held the coil HT lead near a bolt and shorted the hall sensor middle connector and got a healthy spark on the HT. Also checked the voltage across the outer 2 pins and got 10.8v.

Does this mean I need a new hall sensor? If so how did connecting up the timing gun cause it to fail. I've clearly cocked up and don't want to make the same mistake twice.

Cheers all
Myles

The hall sensor is just a magnetic switch, so short of a wire breaking between it and the plug on the dizzie there's sod all that can really go wrong with it. Check for the more obvious problems first.

Did you leave the rotor arm in your pocket?
Did you fit the rotor arm properly, does it turn when the engine turns over?
Check that the spade connector on the ignition loom by the dizzie is on tight?

Hi Boxy

Thanks for the response.

Rotar arm deffo fitted and turning. Do you mean the connector at the base of the dizzy, on the clamp?

If you got a spark when you earthed the centre terminal then that proves that the coil and amplifier are working.
The voltage across the outer terminals powers the hall chip in the distributor, if you have voltage and the distributor is turning that then the problem is between the connections to the chip or the chip has failed.

Well I checked all connections, and all appears fine. The wires to the chip look fine and intact. So I guess that means the chip is fried. How would connecting a timing gun cause this? A voltage surge maybe?

I suppose the most cost effective option is a dizzy from a scrapyard. Does anyone have a part number, there is a scrappy in Chelmsford with dizzys listed by part number.

Cheers

Here's a circuit diagram showing how the Hall sender connects to the ignition control unit. If you wire in a supply & LED as shown you can test the sender. You need to take the dizzie off the engine and turn it by hand. As you turn it the LED should switch on and off. Because the wires inside the dizzie are such a light gauge it's easy for them to break up inside the insulation or at a joints at each end. I got a dizzie off e-bay that would work fine for a few minutes and then no spark. When I tested it using a LED I found I could stop it working by just touching one of the wires in the dizzie.




http://www.brick-yard.co.uk/VehicleSpec ... lnmbrs.htm" onclick="window.open(this.href);return false;

Here are the dizzie part numbers in case the sensor is U/S

Cheers Boxy

Removed the distributer this morning connected a feed and my multimeter, turned it and nothing.
So I've order a new sender from ignitioncarparts.co.uk for £48.

Will fit tomorrow and let you know how I get on.

Thanks again
Myles

Just to update,

I fitted the new hall sender and it fired up first time. I had to change the socket over for the old one but it was fairly straight forward.

Thanks all, for your help.