Not starting.. Resolved

[mikeybjettaman]

Hi all.
My van was starting fine but I came to it one day and all it will do is turn over. I was cleaning some earth's and today I was trying to find out what the voltages were like. The earth between the ignition amplifier and the engine block is reading 12v! Well, 11.6. All of the wires that should be live were reading 11.4-11.6. The voltage dropped whilst I was testing. The battery was reading 12.6 at the start and 12.4 by the time I had finished testing. My testing only involved checking voltages with the ignition on. It sounds like I've found the cause of the starting problems but what do you guys think? Faulty amplifier?

[chewbacca]

Hi all.
The earth between the ignition amplifier and the engine block is reading 12v!

Hmmmm, can you explain what you are measuring here?
I'm a little confused.

[mikeybjettaman]

The earth wire held in by a 10 mm nut in the left hand cylinder head right next to one of the spark plugs

[chewbacca]

Sorry, I must be missing something.

I read you post as you're measuring voltage.
One probe connected to the earth on your ignition module & the other on the earth on the engine block.
Measuring voltage between 2 earths is a valid test, but you should get virtually nothing.
If you're getting 12 volts, an earth has failed big time!

[mikeybjettaman]

The earth I used for my true earth was the block. The earth I measured was the wire that was connected to the block. I agree that something has failed badly. Any ideas? What is in the ignition amplifier that could do this? I had also been checking the coil voltages and they were 11.6 at both sides.
With no other loads on the system but the ignition, there can't be something else trying to earth through this wire. I attached an additional earth from the starter to the bodywork just to see if it improved matters but made no difference as far as I could tell. I did that yesterday. It has not been starting for two months. Not had much of a chance to look at our until now.

[chewbacca]

From your explanation of the tests you've done, it sounds to me as though your ignition modules earth wire has failed. Start by checking that is good.
I'm far from an expert though.

[MidLifeCrisis]

The earth I used for my true earth was the block. The earth I measured was the wire that was connected to the block.

If you are able to measure a large voltage between the engine block and a wire connected to the block - then that wire isn't connected to the block!!! (however it may look!!)

[chewbacca]

& don't worry about just under 12 volts with the ignition on. That's fairly normal with everything turned on, especially things like the cold start heaters

[chewbacca]

The earth I used for my true earth was the block. The earth I measured was the wire that was connected to the block.

If you are able to measure a large voltage between the engine block and a wire connected to the block - then that wire isn't connected to the block!!! (however it may look!!)

Wouldn't the additional wire he tried from starter to body rule out an engine earth fail?

[mikeybjettaman]

I hope this image I took this morning helps to clarify things a little. I have been reading that both sides of the coil will read 12v when not running as the ignition control unit prevents the coil from earthing to prevent the coil burning out. I am suspecting it may be a hall unit fault. What are your thoughts? Anyone had a similar issue?

[marlinowner]

Remember that if you disconnect the earth wire of any electrical component and measure the voltage on the wire when the component has 12v on it, the measured voltage will be very close to 12v because the meters internal resistance is many times higher than that of the component.

[MidLifeCrisis]

WHS ^^^^^^ (Beat me to it!!)

I hope this image I took this morning helps to clarify things a little.

OK - the picture helps (I think)

So are you saying that you disconnected the earth wire that ran from the 'ignition unit' to the block - then measured the voltage between the end of that disconnected wire and the block??
If so, then the fact that the disconnected earth wire has a voltage on it is not surprising as it is no longer grounded - this is to be expected (and unfortunately is not a useful test).

Maybe start back at the beginning - with everything connected back up as it was - have you tried checking to see if you have spark at the spark plugs when the engine is turning over?

[marlinowner]

Great minds think alike.

[MidLifeCrisis]

Great minds think alike.

Yeah - but you won - must learn to type faster!

[mikeybjettaman]

The earth lead was sparking when earthed so I presumed it must be taking some decent current.

I will need to use something to see the spark while I turn the engine and I'll report back. I was thinking of using my timing light but some have reported using a video camera works ok.