Poor Running ?

Wyn

Wyn

Club Member
Trying to sort out a misfire/ poor running on me 260z
Hot or cold it starts ok, ticks over reasonably well if not a little lumpy but seems acceptable
Under load in any gear it will misfire badly at approx 4.5k/5k n not rev much more
If reved at stand still it will do much the same so to me that seems more like ignition?
As the engine warms fully the misfire will happen at lower rpm. Ie 4, 3.75k, almost as if something is getting hotter and breaking down.
I changed the coil today as I had one spares but that made no odds.
Feathering the throttle at high rpm will see it rev a little more but still mis badly
Pulling the choke on seems to make no odds at all.
Turning it off when warm will result in it running on for a few secs more often then not.
Thinking its a dizzy/ ignition prob so I tried retarding and advancing the dizzy either way just to see, but it still missed just as bad at high rpm.
Had a look at the dizzy shaft n it seems the rotor arm/ spindle has excessive movement? Ie I can manually advance retard it but then it moves a little more as shown.
As far as I know its a 280zx dizzy, but are they known to break or cause like running faults if the module/ dizzy fails?
I took a short vid in the hope someone could say if it looks norm or not?
Your thoughts as I’m running out of ideas now.

Short Video Link

I don't think its fuel as surly pulling on the choke sould ease it?
 
tel240z

tel240z

Club Member
I think its a faulty plug ,try pulling one lead off at a time hold it about an inch away from the plug but not to far to make it miss at tick over ,then rev sharply, do this to all of them to see if the missfiere goes away, what this does is let the energy build up in high tension side of the ignition which gives the plug a stronger bolt of energy. im sure u have a spark problem somwhere as u need a quality spark when the engine is under load
 
Wyn

Wyn

Club Member
Mr Ex said:
That play is normal.
It could be HT leads breaking down.
Click to expand...

I would assume the same, but its the fact the rotor arm/ shaft can be moved a few more deg after the shaft stops that puzzles me. Maybe thats accepable?
Leads and plugs are reasonably new but that’s the next to try.
 
Mr Ex

Mr Ex

Inactive
900ss said:
I would assume the same, but its the fact the rotor arm/ shaft can be moved a few more deg after the shaft stops that puzzles me.
That is where you get your advance from when it's running.
Click to expand...
 
Wyn

Wyn

Club Member
Mr Ex said:
That is where you get your advance from when it's running.
Click to expand...

Sure you can see it adv and ret, but right at the beginning and just at the end you can also see the shaft can be retarded with very little effort even more
Maybe its not as obvious as over the net or not an issue in any case
Would retarded ignition cause a high-speed misfire or just flat running?
 
Mr Ex

Mr Ex

Inactive
I had the same problem as you last year when the car came out of hibernation & as I run a 280 dizzy I didn't know if it was coil or dizzy at fault so I got both at once to speed up a fix. After fitting both it still misfired, thought I had got the timing right but as my strobe light is only a cheap one it wasn't throughing enough light on the marks.
The bottom line is I took it to the electrician who said the timing was way out, so to this day I don't know it it was the coil or dizzy as they both got changed 1 at a time.
 
Rob Gaskin

Rob Gaskin

Treasurer
Staff member
Site Administrator
Always start thinking of the simple things. If the car was running ok recently what component has changed, anything?

My car runs-on and it's fine so I think that may be a bum-steer.

How bad is the misfire, if critical it will not be a plug or single plug lead?

I think the rotor arm movement is ok, i.e. normal spring advance.

So it may be the dizzy cap, coil-dizzy lead (breaking down or not pushed in fully), loose low tension lead etc.

If you haven't touched the timing then that should be ok.

I'm sure you know most of this, just gradually work through each component looking for basic faults, don't assume anything. It could still be fuel related of course, if it's not getting enough the choke will make no difference.

Good luck!
 
Wyn

Wyn

Club Member
Rob Gaskin said:
How bad is the misfire, if critical it will not be a plug or single plug lead?
I think the rotor arm movement is ok, i.e. normal spring advance.
So it may be the dizzy cap, coil-dizzy lead (breaking down or not pushed in fully), loose low tension lead etc.
component looking for basic faults, don't assume anything. It could still be fuel related of course, if it's not getting enough the choke will make no difference.

Good luck!
Click to expand...

Cheers all
tbh I've not looked any more atm as its to dark n cold when I get in lol but can only guess of possible causes whilst twiddling me thumbs lol.
So you know the leads appear reasonably new as do the plugs.
The plugs are all running the same colour with a indication of hot running therefore I can't see it being a single plug or lead fault, unless all 6 are at fault which is very unlikely?
As for fuel I thought about that but assumed it couldn't be that? As again the plugs appear all the same colour? Obv i'm assuming the 1st 3 and 2nd 3 cylinders are individually feed from their own carb? I see the manifold is linked but can also see a bleed screw is fully closed so assume the 2 aren't linked? If they are then that may well pi55 on that theory lol
Sure I'd like to try another dizzy but finding one isn't as easy any more lol
Still onwards n upwards n roll on the sunny weekend of joyous Zedding :D
 
Wyn

Wyn

Club Member
Could be, but as I say I can't say I've seen them like these?
But then I'm not that old either lol :D

Was thinkin ol Jag of a sort :confused:
 
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