240Z not running right

[soundmasterg]

Hello all,

My 1972 240Z with original 2.4L was sitting for 20 years in a chicken coop when I bought it in 2008. It only had 87k original miles on the engine, and I spent some time getting it running well. I drove it without incident for several years until the summer of 2012 when I went to start it and there was a very bad valve train clatter. I didn't have time to look at it for awhile due to school and work. When I did get a chance I discovered that one of the lash pads had fallen off the rocker arm, so I put that back on, but I also noticed that the timing chain was badly stretched, and the tensioner had broken too. So I had a friend who is a Datsun mechanic help me replace the timing chain and all the associated parts up there. I adjusted the values cold to the recommended values in the specs, and I tuned it up with new plugs, cap, rotor, etc. It uses a Pertronix instead of points. I started it up and reset the timing and mixture etc. By the time I was able to do all of this, the car had been sitting a year. The carbs were overhauled in 2008 by me and they are stock Hitachi SU's. It ran great for about 250 miles, and then started fouling the plugs and running on less than 6 cylinders. I found out this was due to the chokes sticking on. So I fixed that, replaced the plugs and it again ran well for about 200 miles before running on less than 6 cylinders again. Now however, the plugs are not fouled. When first started it runs on 4 cylinders, then after it warms up, it runs on 5 sometimes. The cylinders that are not firing are consistently number 3 and 5. If I pull those plugs I can see they spark just fine with good strong spark. I've adjusted the carbs to hell and back and can't get those two cylinders to fire for some reason. I've tried adjusting the timing from 6 degrees to 10 degrees BTDC and at 10 it pings badly, even though that seems to be what the book suggests to set it at. I am using good fuel and have tried super in addition to regular. Compression is good and even in all six cylinders....around 150-160.

I can't figure out what is going on here....I seem to have fuel and spark yet it just doesn't want to run on all 6. Does anyone have any ideas I can try as the weather gets better?

Thank you!

Greg

[Mark Maras]

Wow, This one is going to a be more difficult diagnosis than the average repair. I'm going to have to dwell on this for a while. Anyone out there got any ideas to throw at the wall and see if they stick? I'm baffled. Although, you might try switching sparkplugs to different cylinders and see if the problem is the plugs.

Mark in Portland

[mlc240z]

Could be a couple of bad plugs. Not fouled but are they wet with gas? If not, follow fuel system.

If getting gas then check wires. Spark, tho seen might not be strong enough to fire the mixture.

Then work your way back to the cap, check terminals, connection of plug wires etc etc.

Also, maybe 3/5 valves too tight so when it warms up lash goes out of spec and won't allow intake valves to open enough.

Edited February 3, 2014 by mlc240z

[madkaw]

Valves still sticking. If you had one of them stick bad enough to come off of lash pad, there is probably going to be more problems. Maybe try some Marvel Mystery oil in the valve cover and gas to see if that helps

[Mark Maras]

Tell us what color the spark was & could you hear it. It should be blue, loud [for a spark] & and jump about a 1/2" to ground. If it's lazy and yellow, it won't jump a 1/4". Does the spark look the same on 3 and 5 as the others ? If you have an ohm meter, check the resistance in the wires and cap assembled. They should all be relatively equal. To get it running well, I think you'll have to take a look at both carbs & elec. again but I think this specific problem is electrical, based on the info.

Invest in Ztherapy's DVD on SUs[it's worth it & they're in Salem]. Plugs-NGK BP6ES. There has been some nice Z days this winter, at least here in the Pac.NW & you've got fantastic roads close to your home. Keep us posted, we want to see you on the road again too. Mark in Portland

[madkaw]

Could be a couple of bad plugs. Not fouled but are they wet with gas? If not, follow fuel system.

If getting gas then check wires. Spark, tho seen might not be strong enough to fire the mixture.

Then work your way back to the cap, check terminals, connection of plug wires etc etc.

Also, maybe 3/5 valves too tight so when it warms up lash goes out of spec and won't allow intake valves to open enough.

If the valve adjustment was too tight then the valves would not want to close when warned up.

[Stanley]

Pertronix starting to go? Just a guess. Read a post that they get fried if you leave the ignition on. Pertronix works good in my Chevy, though.

Edit: but you said good strong spark so no. Can't see how carb adjustment would only affect #3 and 5. Runs a little better when it's warmed up?

Edited February 4, 2014 by Stanley

[Mark Maras]

madkaw, Right you are, but why is the compression OK? I don't know how far a valve would have to be open to have a no-fire condition but surely you'd hear it in the intake or exhaust. No mention of that in the history. If it was barely open wouldn't it be the same symptom as a burned valve? Poor combustion & loss of power?

Mark in Portland

Stanley, I know little about pertronix, Why just two no-fire plugs?

Edited February 4, 2014 by Mark Maras
More info

[soundmasterg]

I won't really be able to work on it for a little while still due to school and work, and weather issues. Right now I'm trying to gather ideas to help me when I do get a chance to look at it again. It will probably be until early spring before I delve into it again at this point. I appreciate the suggestions as they will help me when I get a chance to delve into troubleshooting it!

My thinking is that it was running perfectly for several years before the lash pad fell off, and then the car sat for a year....I think the carbs should still be ok with the rebuild I did previously. I do have the Z Therapy DVD's btw. I may readjust the float height though and make sure those are still ok, so I'll be calling Z Therapy for new gaskets if nothing else.

I have gone through several Pertronix over the years....one was bad out of the box and would randomly quit. The other I burned up from leaving the ignition on while working on it, so since then I have been very careful to avoid that. I did readjust all the valves, but I was planning to check them again just to be sure. I know if a valve was misadjusted it would cause it to run badly and the compression numbers would also be off. Incidentally, the lash pad fell off the exhaust value on #5 previously.

I did try moving the plugs around, and the ones in there now are brand new NGK BP6ES. I also have the ones that were fouled from the chokes sticking on that only have 200 miles on them...I cleaned them up, so I can try them if needed. The wires are new in 2008, but I suppose maybe something could have failed....though I moved the wires around between cylinders previously and the problem followed the cylinder. I know it has to be something other than the engine itself, since it ran well not many miles ago....so fuel or carbs or spark...etc. Its just baffling and leaves me scratching my head.

What do you guys run your timing at? As I said above...I have it at 6 degrees BTDC at the moment....I'd like to go more advanced but it pinged when I did that before. Previous to all the issues I ran it at 10 degrees BTDC with no pinging, but that was also with a stretched timing chain too.

Greg

[madkaw]

It's going to be hard to troubleshoot when you can't actually work on the car.

I hope your issue is as quick and easy as carbs and wires, but the randomness of the cylinders tells me that it is valve issue. The fact that the valve seats do not hold up on these heads(original bronze) causes blow by and heat which causes carbon build up on the stems and cause sticking eventually. The fact that a valve stuck bad enough to dislodge your lash pad is a sure sign. I know, I fought this myself. When i took it to the machinist he said the seats about fell out of the head on their own.

It's going to have to be done eventually, might consider yanking the head now and having it freshened up while your waiting for time to work on the car. I know it sucks because was running so well before, but it's just the way these engines are. The reward will be a fresh top end(bottom end should be fine) and some new life in a l24.

What month is your car?

[soundmasterg]

It's going to be hard to troubleshoot when you can't actually work on the car.

I hope your issue is as quick and easy as carbs and wires, but the randomness of the cylinders tells me that it is valve issue. The fact that the valve seats do not hold up on these heads(original bronze) causes blow by and heat which causes carbon build up on the stems and cause sticking eventually. The fact that a valve stuck bad enough to dislodge your lash pad is a sure sign. I know, I fought this myself. When i took it to the machinist he said the seats about fell out of the head on their own.

It's going to have to be done eventually, might consider yanking the head now and having it freshened up while your waiting for time to work on the car. I know it sucks because was running so well before, but it's just the way these engines are. The reward will be a fresh top end(bottom end should be fine) and some new life in a l24.

What month is your car?

I hear what you are saying....I was wondering if it could possibly have something to do with the valves or the adjustment of them, or the seats....I am hoping to get more life out of the L24 without major work like pulling the head though....not to mention I don't have the time or weather to pull the head. 6 inches of snow and 19 degrees at the moment. I am also a senior in an EE program and am very busy with that and working when I can find it. I also have an L28ET that I would like to put any engine work into instead of the L24 if possible. My 240Z isn't a great candidate for a perfect restoration so it will get the hybrid style one with a turbo. My 240Z best I can tell is 6/72...it is missing the mounting stuff for a rear anti-roll bar, and has a 6/72 date on the seat belts. As far as I can tell, 7/72 was when the rear anti-roll bar mounts were put in. Only 87k original miles when I get it in 2008....it was sitting in a chicken coop for 20 years....now it has 98k on it.

The lash pad fell out after a day of driving in 95 degree heat...went to start it the next day and that was when I got the original valve clatter problem due to the lash pad being out, and didn't have time to mess with it until 6 months later. And that was the back valve on cylinder 5...whereas currently cylinder 3 and 5 are the ones that have issues...with cylinder 5 beginning to run along with the others as the engine warms up, but cylinder 3 never seeming to run. I plan to recheck the valve adjustment as the weather gets better.

Any idea where to set timing? Book says 10 degrees BTDC, but if I set it there, it pings like a MOFO. I was wondering what others are setting theirs to?

Greg

[madkaw]

Timing should be close enough, might try disconnecting the vacuum advance and see what happens.

As far as the head, it's not that big of a job to remove the head compared to a complete engine swap and turbo. Might want to make sure you have all your ducks in a row before you go down the swap road or you will be off the road for a long time----meanwhile you could be thrashing the sh!t out of the little L24 and having fun while you sort out the swap details.