L24 won't run properly (video). What can cause this?

[Tomzern]

Hi

 

 

A friend of mine has some problems with his Z, and is about to give up so I want to give him a helping hand

 

He was out driving when suddenly the engine went sour and stopped. This was about a year ago. Since then we have tried lots of things, like new plugs, new plug cables, different distributor, new coil, ignition adjustment ++

 

When we changed the distributor we got it running good, but it only lasted for a short trip and then back to the same starting point.

 

Here's a video of how it is at the moment: 

 

https://youtu.be/7Jx_rV4Z62s

 

 

Can this be carb related? All the plugs are getting wet, but it sounds like it's only igniting on one or two plugs.

 

 

Regards,

 

Tomzern

 

 

[siteunseen]

You can lift the pistons in the carbs and disable them to see if both are functioning. Or push that pin up, whatever's easiest. If you disable one and it has no effect on the running of the car you may have carb problems.

I'm assuming you have SUs. Can't watch video on this device.

Edited May 25, 2015 by siteunseen

[Mark Maras]

What year is your car & what ignition system do you have? The more details you can include the better. I'd first check that each plug is firing. We'll take it from there.

[siteunseen]

I got to watch the video this morning, sounds horrible like the timing is way off.

[Tomzern]

When the problems started, the car had a 280Z distributor with a GM HEI ignition module. The first thing we did was to change the plug wires, but that did not help at all. We tried changing plugs, but that didn't help either. The problems started out with the car running OK at idle, but started spitting and misfiring alot as soon as we tried revving it a little. Then it got worse, when it wouldn't even run at idle.

 

We tried changing out the 280Z distributor with a stock 240Z distributor with point ignition. This got the car running seemingly good. Good enough for us to believe that the problem was fixed. He left my workshop that day as a happy man, but it lasted for about 1 mile and we had to tow the car from there... Since then it has been more or less like in the video. In the video we have switched back to the 280Z electronic distributor.

 

We will try to buy a new set of plugs and confirm that every plug fires!

I got to watch the video this morning, sounds horrible like the timing is way off.

 

That is what I think as well! Is there any possibility that the chain has skipped a tooth or something like that?!  Seems impossible to me, but I feel we have tried almost everything now

[siteunseen]

Anythings possible I've always been told, I don't believe it though.

Get TDC and pull the valve cover to see if the chain sprocket notch is lined up with the cam plate mark.

[Mark Maras]

Agree with Site. Start with a the basics.

You mentioned previously the plugs were wet. The question is, too much fuel, weak or mis-timed ignition or a combination of both? Have you tried pushing the nozzles up on the carbs? These can become stuck & stay in the choke position. If the mixture is already set rich, adding choke (dropped nozzles) can make it blubber.

I kinda doubt it's cam timing. It seems if that was off the engine would still be firing on six cyl. It sounded like it was firing on one maybe two at the most.

[Tomzern]

OK, so today we looked further into this, and we have confirmed that all the marks are lined up perfectly at TDC. We have also more or less confirmed that the problem is with the ignition. I hooked up an ignition wire tester on a couple of plug cables and it showed sporadic and very weak sparks. Just to rule out the cables, we took the cable set from my car (which is running good) and tested them on his car with no improvement. I then hooked up the wire tester between the coil and distributor and even then the sparks were sporadic and weak. We tried changing the brand new coil with another brand new coil with no improvement. The points gap has been adjusted and controlled several times. We tried a positive wire directly from the battery to the coil, and a negative wire directly from distributor to coil, but no change.

 

We have not yet checked for the same symptoms with the 280Z electronic distributor installed, but the points distributor installed now has new points, new rotor and new cap so I doubt the problem is there.

 

What else can cause this?

Edited May 29, 2015 by Tomzern

[Zed Head]

The condenser is an important part of the points system.  If it is shorted, it will cause a weak spark.  Probably easiest to just get a new one, although they can be tested if you have the right meter.

 

The ballast could also be a problem.  You could try rewiring the ballast to bypass it, just to see if it fixes the problem.  Put both power wires on the terminal that does not pass through the ballast.  It won't hurt to run it that way for a short while.

[seerex]

i have lived this a few times and I would guess the points , or possibly a loose wire somewhere , if you tested the plug cables and they are of good quality then you can narrow it down closer to the distributor , make the assumption  that every 40-45 year old electrical connection is bad till you test or redo to prove otherwise , very odd that you would have the issue with the zx unit, as mentioned before back to basics and just take your time

[Zed Head]

Those are some good points. Don't forget that the system grounds through the distributor body.  Coil > points > distributor body > ground to engine block.  You might just have a bad ground.

[gundee]

Check the continuity of this ground wire also.