1978 280Z Runs rough? - Page 6 - Nissan : Datsun ZCar forum :Nissan Z Forum: 240Z to 370Z
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post #51 of 56 (permalink) Old 07-17-2019, 07:19 PM Thread Starter
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Sorry have not had time to do additional tests and won’t have time until next week. I’m going to redo the compression , do leak down and check on some of your other suggestions. My vacuum seems ok but I may try the smoke test again. I tried it before but don’t think I did it correctly.
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post #52 of 56 (permalink) Old 07-17-2019, 08:26 PM
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Vacuum leaks can easily cause rough running. Good idea to check thoroughly.
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post #53 of 56 (permalink) Old 07-17-2019, 09:31 PM Thread Starter
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Yes I’m still not 100% on how u check for leaks using smoke. So I remove the rubber boot between the air cleaner and the air flow meter. I seal up the open end of the air flow meter with something like a plastic cup. I then pump or blow smoke into the intake manifold top right port that connects to the brake booster?
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post #54 of 56 (permalink) Old 07-19-2019, 12:50 PM
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You got me. Seems like you'd want to apply smoke on the outside of hoses and look for it to be sucked in, but how to do that with the engine running is beyond me.. (I have learned that I'm not good at finding vacuum leaks.)

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post #55 of 56 (permalink) Old 07-19-2019, 02:24 PM
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Originally Posted by ctfisher View Post
Yes Iím still not 100% on how u check for leaks using smoke. So I remove the rubber boot between the air cleaner and the air flow meter. I seal up the open end of the air flow meter with something like a plastic cup. I then pump or blow smoke into the intake manifold top right port that connects to the brake booster?
That's correct.


common areas include cracks in the boot from the AFM to the TB, disconnected hoses, missing or damaged O rings on the fuel injectors. Harder to see is the EGR stuck open if used. it would leak into the exhaust manifold. its something to test but not with the smoke test. Other things to look out for is damaged PCV hose, and PCV valve. best to just look at the hose (disconnect it and examine) and just replace the PCV valve if no history on last done. In a pinch you can shake and see if it rattles (good) if no rattle some brake clean can be used to clean out the gunk. I prefer to just replace, but get a good one, Nissan OE if you can.
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post #56 of 56 (permalink) Old 07-22-2019, 08:30 PM
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That's correct.


common areas include cracks in the boot from the AFM to the TB, disconnected hoses, missing or damaged O rings on the fuel injectors. Harder to see is the EGR stuck open if used. it would leak into the exhaust manifold. its something to test but not with the smoke test. Other things to look out for is damaged PCV hose, and PCV valve. best to just look at the hose (disconnect it and examine) and just replace the PCV valve if no history on last done. In a pinch you can shake and see if it rattles (good) if no rattle some brake clean can be used to clean out the gunk. I prefer to just replace, but get a good one, Nissan OE if you can.
Yes, this.

Also (and this was my prob) the bladder in the vacuum advance pod on the distributor was cracked so smoke was coming out of my distributor cap haha. After capping that line, the car wouldn't even idle because the PO cranked the idle screw up so high to compensate for the leak.

1978 280z - stock L28 engine - Dallas, TX
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