Non starter - no sparks

[Colin RedGriff]

Griff has been sat in the garage for about 6 weeks now while I got the exhaust system sorted out. Finally finished fitting it this morning but when I came to start up, it won't start.

The engine turns over but isn't firing at all. I pulled the main HT lead off the dizzy and held it near the alternator and I'm getting no spark when I crank over the engine.

I can only think I've disturbed something somewhere but I can't find anything loose or disconnected.

The only things electrical I've touched are

The battery to disconnect the earth while I was working on the car
The starter motor to get to the manifold bolts
The low tension wires which I put new spade connectors on because I noticed they were looking knackered.
I took the coil and amp out to clean off the crap
All the HT leads got disconnected from the spark plugs (but left on the distributor cap)
New Lambda sensors
The air flow sensor connector

These are all connected back up.

I've checked and double checked the low tension wires and they are making good connections. I have 12v coming from the black low tension wire and 0v from the white/black low tension wire
On the two low tension wires coming from the ignition amp I have 0v on both wires. I believe that I should be getting 9v or 12v on one of those wires. Is that correct?

I've replaced the ignition amp this afternoon just on case that is faulty but it's made no difference.

Any ideas on where I should be looking or tests that I can try?

[eliot]

I would disconnect the fuel pump or pull the injector connectors of whilst you track the problem down - otherwise you are just filling the engine with fuel everytime you crank it. This gets into the engine oil and thins it out, resulting in trashed bearings.

[More Steam]

eliot said:

I would disconnect the fuel pump or pull the injector connectors of whilst you track the problem down - otherwise you are just filling the engine with fuel everytime you crank it. This gets into the engine oil and thins it out, resulting in trashed bearings.

Good advice. You could just remove the fuel pump relay. This'll do the same job.

I think I would start by going over all the low tension wires again. I guess the battery and starter motor are OK from what your saying.

[blitzracing]

The signals from the trigger coil to the amp are very small, so will show as 0v, so you wont see the signal without an osciloscope. You can replicate the trigger signal to the amp by removing the distributor cap, and rotating the engine until one of the lobes on the distributor trigger line up with the pickup. There should be a gap of less than 1mm. Then unplug the king lead from the top of the distributor and fasten it so the conector on the end forms a spark gap to chassis. Then turn on the ignition, and use a small screwdriver tip to jump the gap between the rotor lobe and trigger pickup,(tap it on and off) to complete the magnetic circuit. This should produce a good spark at the end of the king lead. If it does not, and the coil has 9-12 volts on the +ve side, then the connection from the coil to amp is faulty, or the trigger pickup is not connected to the amp, or possibly the coil has failed. You could check across the trigger contacts with a test meter on ohms, and it should show a low value as the pickup is just a coil of wire. Nothing else is involved in making the spark.

[eliot]

blitzracing said:

The signals from the trigger coil to the amp are very small, so will show as 0v, so you wont see the signal without an osciloscope. You can replicate the trigger signal to the amp by removing the distributor cap, and rotating the engine until one of the lobes on the distributor trigger line up with the pickup. There should be a gap of less than 1mm. Then unplug the king lead from the top of the distributor and fasten it so the conector on the end forms a spark gap to chassis. Then turn on the ignition, and use a small screwdriver tip to jump the gap between the rotor lobe and trigger pickup,(tap it on and off) to complete the magnetic circuit. This should produce a good spark at the end of the king lead. If it does not, and the coil has 9-12 volts on the +ve side, then the connection from the coil to amp is faulty, or the trigger pickup is not connected to the amp, or possibly the coil has failed. You could check across the trigger contacts with a test meter on ohms, and it should show a low value as the pickup is just a coil of wire. Nothing else is involved in making the spark.

Presumably you could also eliminate the coil by touching the -Ve side of the coil to ground ? (i.e. simulating points)

[blitzracing]

yes indeed.

[Colin RedGriff]

Thanks guys - I'll be back in the garage tomorrow to check some of those things.

Just for reference can anyone confirm the wire colours for the positive and negative connectors on the coil?

It's a serp 500 if that makes a difference.

[eliot]

Colin RedGriff said:

Thanks guys - I'll be back in the garage tomorrow to check some of those things.

Just for reference can anyone confirm the wire colours for the positive and negative connectors on the coil?

It's a serp 500 if that makes a difference.

The coil should have + and - marked on it and you use a DVM to find the + feed.

[Colin RedGriff]

What a muppet.

Had the positive and negative coil wires reversed... Must have put the connectors on the wrong way round when I replaced them but I still don't know how. I thought about making sure I had the right connector on the right wire when I changed them first time.

Anyway it's alive again

No I can concentrate on finishing up and going for a drive........