WHere exactly on top of the balance tube? I bought one  a year ago and dont know how to plug it in to measure the vacuum leak?

 A Z engine will run on 5 cylinders. #4 not firing didn't cause the stall. At this point, not enough info to diagnose that.

Compression ratio figures, I don't remember if this engine is new or old but either engine would run fine with these #s. If the engine is new, the #s should be very close if not the same.

 However, the valves MUST be adjusted to specs before ANY troubleshooting including a compression test. If a mechanic has been doing this in the past, IMO, YOU should pull the valve cover & check the clearances. It's the only way to be sure & it's not difficult.

 #4-compression is good, & it is fed by the same fuel supply as #5 & #6. The only reason the cylinder is not firing, IMO, is little to no spark at the plug. The coil supplies elec. to all the plugs through the distributer. The pathway to the plugs is very simple. As the dist. turns, the rotor distributes the elec. to the contacts inside the cap. From there it goes into the plug wires & into the plugs. Fact, there are 5 cylinders firing. The problem has to be located somewhere from the dist. cap to the plug. A quick check with an ohm meter will tell you if have a bad plug wire. Compare it to the others. Other options already mentioned, timing light on #4 plug wire or just trade #4 wire with another one to see if the problem moves with the wire. You've replaced the plug, if the wire is good the only thing left is the cap. Rare, but I recently had one go bad on one cyl. Ohm meter check, inside to outside & double check the connections at the cap & plug.

Mark,

 

To give you more information regarding my 1972 240z: The camshaft installed is a Schneider 274-F,with new valve springs, retainers and .175 Lash Pads. I also changed to new nissan oem rocker arms. The specifications of this cam are the following:

 

 

Intake Duration (gross): 274 Exhaust Duration (gross): 274 Intake Duration (.050”): 215 Exhaust Duration (.050”): 215 Intake Valve Lift*: .480" Exhaust Valve Lift*: .480"     Intake Valve Lash: .008" Exhaust Valve Lash:  .010" RPM Range: 1800-6000

 

2. My car has a  L26 crank which makes the motor 79 mm stroke instead of the stock 73.7 mm

stock bore is 83 mm for the L24 and the L26 motors. My block has been bored out 1 mm to compensate for wear

that makes my  motor a 2.627 liter motor and has a  E88 head from 1972 will give about 8.7 to 1 compression

 

 

I have a pertronix 1761 ignitor installed in the stock distributor.

 

Any other information that can help you diagnose and solve my cylinder 4 issue?

If you do have a leak, the fiber insulator blocks between the carb and manifold have

been known to crack with age. If you put new ones on when you put the new carbs

on then not.

Vacuum Gauge install:

 

http://jarvas240z.blogspot.com/2012/11/vacuum-gauge-installed.html

Vacuum Gauge install:

 

http://jarvas240z.blogspot.com/2012/11/vacuum-gauge-installed.html

You're the best!

Good compression. I doubt that you have much, if any, spark to #4. Check the dist. cap, rotor, #4 wire & the connections. Try swapping #4  plug & wire with # 3 or #5 & see if the problem moves to another cylinder. 

 

Okay Mark. Just came back from the mechanic! We spent like 2 hours inspecting all the valves. Most of them were adjusted to .010 with the exception of the exhaust valve on cylinder 4 which is the one that is not changing the idle when removing the spark plug wire. Mechanic then decided to open it to .012 and now it does change the idle if you remove the spark plug wire. Could one of the rocker arms that i bought Courtesy Nissan be warped or not straight enough? I paid like US$300 for the full OEM Nissan set.

 

Please advise! I am driving the car and dont hear any backfire either on the intake or exhaust!

 You don't say what the clearance was on #4 but I don't think a tight valve was causing your misfire. If that was the case the compression in that one would have been lower than the others. I don't think there is anything wrong with your OEM rockers. I do sometimes question the info you're getting from your mechanic.

 That said. congratulations. You're running on all six. Confirm the clearances for your cam You don't want to run it with the valves too tight. Enjoy

Thanks Mark! Finally i am running on all six! The valve was tight at .008 and in order for the feeler gauge to slide perfectly without pushing it he had to open it to .013

Edited November 8, 20159 yr by jalexquijano

Your Schneider cam comes with a "cam card" that shows the valves clearance recommendations. FWIW

oh oh... I hope that exhaust valve has the same installed length as the others..... i'm thinking it's "different"...

They should all adjust the same way.

What could be the worse scenario? the exhaust valve on the 4th cylinder should be adjusted to .010. If the Porsche mechanic ajusted it to .013 so there could be a change in idle when the spark plug cable is removed and the car ran in 6 cylinders, will the engine suffer any damage?

 

Just took the car for a ride, some backfire on deceleration after releasing the gas pedal. Once at the garage, i pulled out the plugs 4, 5, and 6  and number 4 is getting a Little bit red on the White element.

 

Any opinions?

Edited November 11, 20159 yr by jalexquijano

Those plugs look fine. The red is just an additive in modern gasoline.

 

Personally, I wouldn't worry about a pop, burble or mild backfire on decel. Probably just normal.

 

BTW... a backfire ( from exhaust ) means different things to different people. To me, a backfire out the exhaust is like a shot gun going off. Pops and burbles are normal.....  and most cars with higher compression and larger duration camshafts will do that.  They add " character ".  Shotgun type backfires are not normal.