Hellllllllppppppp!!!! Timing / electrical issue!?

[AliK]

So I'm sat here crying that I can't drive the Z to Goodwood tomorrow and park her in the "Special" car park! Been looking forward to doing that since starting the engine project!

Reason why: since changing to the 123 ignition dizzy, the car has not been running smoothly at all. Like it's missing on a cylinder on a regular basis.

And when I go WOT at 3k rpm she sometimes back fires albeit quietly. Unburnt fuel in exhaust is the obvious cause and you can smell it too.

Same issue with vac advance both connected and disconnected.

Timing set dead on 34 degrees all in at 3000rpm

Changed back to old dizzy, same problem.

Changed and gapped all plugs - no change.

Changed all HT leads to no avail.

Changed coil - just as bad.

Checked low volt connectors, all is clean and tight.

Took out each HT lead in turn while engine running at 2500 rpm to see which one had no effect but made no difference on the way the engine is running and she happily runs just as well / badly on 5 cyls.

On the timing light it looks like every 10 or so sparks 1 or 2 go missing but while happening regularly, it's not consistently the same frequency of occurrence, if that makes sense. It does it on all leads.

Anyone seen this behaviour before?

I am utterly lost! Any thoughts most gratefully received.

What I'm gutted about is just a week ago the car was running like a dream before I changed the dizzy. But changing the dizzy back again made no difference so I can't blame 123.

 

[Rob Gaskin]

Try a different dizzy cap.

Don't discount other things like fuel.

 

[jonbills]

What colour are the plugs Ali? Sounds a little lean to me.

 

[Jimbo]

if your loosing spark irratically it sounds like you have either bad earth or power issues to the igntion circuit.
go back to basics and check lives (ie you have 12v where your supposed to have it) and earth points.

 

[slaphead]

I'd bypass the resistor if it's still fitted.

Is the dizzy cap and rotor arm the same on both the old and new distributor?

I'd also continuity check the wiring between the engine and side wall for partial breaks with a resitance meter while gently pulling the wire .

 

[Farmer42]

Ali

Probably a simple one but have you checked the HT leads are in the right firing order? It sounds as though you are firing at the wrong time on the cylinders and its an easy mistake to make when you change HT leads on the dizzy. Get the timing mark to TDC on no. 1 cylinder and work from there making sure the rotor arm is in the right position for no 1. It then moves anti-clockwise.

 

[AliK]

Thanks guys - lots to think about when I get some time next to play.

To answer some questions:

Dizzy cap / rotar totally different on new and old dizzies.

Mix is untouched since engine running well and can smell unburnt fuel when I put my foot down before a pop. Plugs are dark brown or black sooty but not always the same colour on the same plugs - if I run the engine and take them out again. It's definitely randomly missing.

Engine earth and coil +v are all showing perfectly as they should with less than 0.2 ohms on engine and dizzy earth.

I got excited when I found and replaced this connector that was hanging by a thread (coil +v)

But no difference.

I am totally convinced it's an HT breakdown somewhere and more than one problem at the same time.

I buzzed out my magnecore leads and 2 out of 4 jump from 5K ohms to 300+ Kohms when waggled. I will have to try the other leads I swapped them out for and find a set of 6 I trust. The coil to common on dizzy cap HT lead is doing the same but I don't have a spare one of those so will have to make one.

After that I will try feeding the coil / dizzy directly from the battery to bypass any dodgy ignition contacts.

After that I'm breaking it for parts so if you need wings, L28, posh dizzy etc, watch this space [emoji14]

Thanks again for all the suggestions and I will let you know how it goes.

 

[AliK]

Well gang - playing after work earlier in the week I think I've found the main culprit (1 of 3)

Spot the molten away part of my coil side HT lead inner core wire!!!!!

And compare with the other end ...

It kinda explains why the timing light stopped getting a strong enough signal to show any flashes after removing and replugging the leads.

Culprit 2: 2 out of 6 other HT leads dramatically changed resistance when waggled. So I can imagine they were varying in spark intensity.

Culprit 3: my spare set (originals that came with the car) were nearly all bad with intermittent breaks. And it didn't take a lot of looking to find evidence to make me take a deeper look.

Sadly all my investigation time was night work with a head torch so I couldn't see these things that well.

Got in from work to find these bad boys on the door step - Cheapo eBay £25 accuspark 8mm set to prove the concept and get me going while I send the magnecore ones back under their 10 year warranty. Waggle tested with multi-meter and all were solid.

So, just got back from putting them on and test drive / trouble shooting session.

MUCH MUCH better - no more backfire under load and now revs out to 6k without hesitating like before.

BUT - still not smooth and feels down on power with intermittent spark under the timing light on all leads - exactly like a cracked cap would behave, so there is another culprit afoot.

I put the timing light on the coil to cap cable and sure enough it's missing every now and then in time with the beat of the engine changing. There is also a strange wire insulation melting type smell on the coil side of engine, albeit very subtle, so next up I will run a direct +ve (fused of course) from battery to coil and see it that makes a difference.

I will also prove to myself it's not the cap and rotor with my spares. But pretty sure that side is fine - however not discounting ANYTHING at this stage.

Let's see what tomorrow brings if I make it home before day light has gone.

 

[uk66fastback]

Good work - I'm sure that dodgy sandwich you had for lunch means you'll have to take the afternoon off ...

(Weekend tomorrow anyway) ...

 

[jonbills]

How tight is the brake servo hose?

 

[Pete]

Condensor. When they break down they leak current to ground, tends to get increasingly bad and usaually worse when hot.

 

[Rob Gaskin]

Ali, you are unlucky with your leads. I've used 'Taylor' leads without a problem.

 

[AliK]

Good work - I'm sure that dodgy sandwich you had for lunch means you'll have to take the afternoon off ...

(Weekend tomorrow anyway) ...

Thanks dude - the boss is out today so that sandwich is particularly bad but in all seriousness days like this are gold as I can actually get a week's work done in a day without the constant interruptions!!

How tight is the brake servo hose?

Great point and one to check this eve!

Condensor. When they break down they leak current to ground, tends to get increasingly bad and usaually worse when hot.

I'm all ears as that does sound familiar.

Do I need / should I have one of those on a 280zx electronic dizzy? I was under the impression they were mainly used on points dizzies?

Ali, you are unlucky with your leads. I've used 'Taylor' leads without a problem.

Thanks for the recommendation Rob, I will look up the Taylor leads! For £120 and the name I wasn't expecting this but I guess any brand can have the odd failure, so let's see if the warranty works as it should. I expected my Q5 to be trouble free but an electric heater matrix under dash smouldering and a snapped Turbo shaft were completely unexpected of the brand - however Audi fixed both for free when out of warranty by a good year or more and over 70k miles - so I'm still a delighted customer in spite of the issues.

 

[Pete]

Whoops, I need to read things properly, yes, points only.

 

[Mr.F]

Blue Taylor 8mm leads in stock...

 

[AliK]

No worries Pete, I welcome all suggestions as however much you think you know you always learn.

Good to know Mr F. If Magnecore don't come good on the warranty, I know where you live