260z misfire woes

[Markb]

Hi guys,

 

I have a UK spec 1978 260z 2+2.

 

A friend of mine took the car out one day and called me after parking it up for an hour saying he couldn't get it started as the battery had drained. We jump started the car but it was misfiring and barely running. I drove it home where it languished while life, work and other cars got in the way.

 

Recently, I got some enthusiasm to get the car back up and running. I've done the following with some significant improvement, but it's still misfiring:

 

New condenser

New spark plugs

New coil & ballast resistor

New points (in bad need of replacement)

Set timing

Checked Valves move up and down as they should

All HT leads are sending a spark to the plugs (although they don't look the freshest)

Dizzy cap looks fine and is clean inside

Rotor arm was a little bit burnt but I cleaned it up with some fine sand paper

 

I know I need to do a compression test (which I will be doing as soon as my compression tester gets here) but is there anything else I should check for? Are there any other common problems?

 

I really want to get it back up and running so all help greatly appreciated!

 

Mark

 

[Scoota G]

We is all here to help (Yes lurch i'm talking to you) Some more stats on the car would help, type of Carbies, Ignition system ... blah blah .. and photo's are even better. Check and see if it's got fuel, what condition it's in or if it is getting to where it's meant to go.

 

Sounds like your friend has been giving it the "Buscuits"

[Markb]

Hi Scoota,

 

Thanks for the quick reply.

 

It's running 240Z SU carbs, retrofitted by previous owner. I'm going to be honest and say I have no idea what distributor it has! It is definitely getting fuel, I have checked fuel filter, and took out the fuel pump to clean and check it - seemed fine. I put 25 litres of fresh fuel in it last week (it was very low).

 

The only thing that's a bit strange is that I was told that the 260Z had 2 fuel pumps - one mechanical at the engine and one electrical at the fuel tank - is that correct? I only have the mechanical fuel pump!

 

I'll see if I can dig up some photos (car is in my workshop 30 miles away).

[Zedsabbath]

Check the tappet clearances Mark, not just your valves moving up and down, correct clearances are important

for smooth running

 

Check the level of coolant in the radiator, a cracked head or block can cause misfiring from water finding it's way

into cylinders

 

Replace the spark plug leads

 

Pete

[Markb]

Hi Pete,

 

Thanks for the reply. I forgot to mention that I also checked coolant level and it did not move during 30 mile misfiring drive from my house to workshop!

 

I will check tappet clearances and replace the leads as the next port of call!

[Riceburner]

Hey Mark, if you have a Multi meter You can check the resistance of the leads, they should all be similar  Check the coil lead too.

[Zedman240®]

Is it popping out from the carbs or exhaust? Check for any moisture in the dizzy cap..

[gav240z]

If it's running too lean it could cause it to misfire as it gets too hot and then pre-ignites, I wonder if the fuel bowls in the carbs are at the correct levels. It would also be good to see the manifold the 240z carbs are on.

 

Are you running vacuum advance? Remove the distributor cap and suck on the rubber hose that feeds into diaphragm, if you suck hard enough (not being dirty here), you should see the advance arm move a bit. If it's not moving your vacuum advance is stuffed in the distributor.

 

Since you are running points, I'd also double check the points gap and make sure it's correct. If you removed the distributor make sure it's still correctly aligned, if it's a tooth out it could cause a timing issue. You did mention you set the timing though.

 

260z's should have come with an electronic fuel pump located near the fuel tank. It's a low 3-4psi unit and quite noisy. If you are running mechanical pump that should be fine provided it's getting fuel as it should they are pretty unbeatable.

[chris240]

If it's running too lean it could cause it to misfire as it gets too hot and then pre-ignite

Gavs on the money....

Check your timming, you should be "hovering" around 7-9deg advance..

[Markb]

Gav - I think you need to have a look at the car - you're the guru!