Spark From The Coil, But No Spark At The Plugs

[James_K 6 1 Cars]

A couple of weeks ago, during a long motorway run, my 1989 1.6gti lost all power, there were no prior symptoms. Luckily it happened near the entrace to Reading services so I pulled in and called the RAC.

The RAC guy spent a long time testing the coil, ht leads and ignition amp and told me that the amp had probably overheated and failed.

There was a weak spark from the coil king lead, but nothing at the plugs.

 

I managed to buy an unused Ducellier amp from ebay, which was a match for the one already on the car. I also bought a new pattern part coil, just in case that was also at fault.

Having fitted the parts, I found they made no difference at all. There is a regular spark from the king lead when cranking, but I'm not sure if its too weak - the spark plug tester bulb didn't seem to glow bright white when I was checking it (more of a red colour). I'm getting 12v across the coil as you'd expect. However, still no spark at the plugs.

 

Not having much mechanical knowledge, I've run out of ideas as to what to do next, I've done many searches and the only things I could come up with are:

 

1. There's a problem with the signal cable from the dizzy to the amp - I don't think this is the likely cause though as it doesn't fit with the sudden failure. I haven't been able to test the cable as I can't seem to separate it at either end and I didn't want to risk damaging the connectors

 

2. Earthihg - the gearbox earths look clean.

 

3. The amp I bought is duff - seems unlikely as it was clearly unused, but has probably been on a shelf for years

 

4. The distribtur has failed - I've no idea whether this could be the cause, given the spark from the coil.

 

 

The HT leads, dizzy cap and rotor arm are all virtually brand new, and look ok.

 

Any ideas what else I can change/check and how I can avoid throwing good money after bad would be greatly appreciated.

 

Thanks

James

[Miles 331 1 Cars]

Could well be the Dizzy, Has the same failings as a amp when hot but when cold and not under load seems fine, There are windings in it which break down so worth a shot

[TT205 42]

+1 dizzy

[M@tt 77]

wouldn't it just be the little pick up lead rather than the whole Dizzy that needs replacing? granted it may be easier to find a whole dizzy rather than just the lead

 

Is the follwoign theory correct? as i understand it the pickup leads on the dizzy generates a little signal based off the cam rotation which is then boosted by the amplifier and sent to the to the coil causing it to generate the main spark on the king lead. The distribitor just does the mechanical "distributing" of the spark to the appropriate HT lead based on its rotational position.

 

Have i got the theory correct there?

[Dizzee stuff 33 1 Cars]

I would try the rotor-arm, just cause its nearly new dont mean its ok. Fit a new one an give it a go.

[DamirGTI 342]

It'll not be the dizzy pick up coil ... cos , when the winding breaks you've left with no spark at all ... so neither a weak one - nothing , dead ignition system . (i've had a pick up coil breakdown once , but not on a 205 , and it was just a two quick shots of strong misfire and an dead engine afterwards .. couldn't get neither "S" of a spark , not even a weak one ..)

 

Id try the dizzy cap , rotor arm , wirings from the amp to the coil and especially - dizzy signal cable (start up the engine and wiggle it about , squeeze , move etc.) ... and check the signal cable ends connectors for oxidation deposits ..

 

Damir

Edited October 26, 2011 by DamirGTI

[James_K 6 1 Cars]

Thanks all,

 

I'll try a new cap and rotor to start with and see if that works. If not maybe a distributor, but they're pretty hard to come by used.

 

Any tips on how to disconnect the distributor signal cable - at both ends. At the amp connector it was impossible to remove, despite considerable force. Is there a simple technique that I'm missing?

At the distributor end I couldn't sse how to remove it - should it slide off somehow?

 

thanks again

James

[M@tt 77]

the pickup lead from the dizzy to the ignition amplifier should just unplug at the big plug end (pull harder ) I'm pretty sure at the dizzy end there's a small screw holding it in place you need to remove before it will come out

[James_K 6 1 Cars]

Thanks Matt, I'll eat some shredded wheat then give it a go.

[James_K 6 1 Cars]

Finally got it running again!

It turned out to be the rotor arm (as predicted by Dizzee stuff - thanks), despite only having done about 1,000 miles it had failed.

As soon as I put the new one on it fired up.

 

thanks all,

James

[Dizzee stuff 33 1 Cars]

Nice to see you got it going again.

[lagonda 42]

Moral of story, never assume that because a part is new or nearly new, that it is therefore OK.

 

Glad you got it going with an easy & cheap fix!