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Z22S Engine Issues


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Hi Everyone,


I have a 1982 Datsun 720 with Z22S engine. It has this engine problem: it 'lopes' on idle and misses in mid range.

So far, I've done the following tests and repairs (engine wise):

  • replaced all vacuum tubing (15ft or so)
  • replaced all spark plugs, cap, rotor, wires, air filter.
  • cleaned and rebuilt a stock carburetor
  • replaced a tvv (I did an EGR test and it failed, EGR is getting a vacuum signal and works fine now)
  • replaced a vacuum motor (it was stuck open)
  • replaced a PCV valve
  • adjusted timing (it was like 30 degrees, back to 3 now)
  • checked valve clearances (per Haynes 81-82 engines method)
  • did a compression test (150 to 160psi all) on the exhaust side only (throttle wide open, coils grounded, did not remove the intake plugs)
  • checked both coils with a spare spark plug (ok)


Further, the auto-choke is closed when cold. It opens when hot, but not every time:mad: Anyway, adjusted a throttle cable linkage, etc. Fuel is getting to the carb, it is on the level and accelerating pump is working fine now. Played with a/f mixture and idle speed screws, it lopes nevertheless. I tightened intake and carb bolts and sprayed carb cleaner around when the motor was idling; there was no change in the idle speed. The engine sounds like valves are out of adjustment.


I am out of ideas, please help me, anyone:confused:

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The correct hot valve clearance is 0.014" for both sides. Some manuals are wrong. Be sure to warm engine up first. If too noisy you could maybe drop back to 0.012".


Pull both wires off the number one cylinder place an old spark plug in each end. Lay on a grounded surface like the valve cover and have someone crank the motor. Make sure both are firing. If only the intake is firing, replace the first fuse on the left side of the fuse box.

Edited by datzenmike
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Two little pipes with rubber stops are missing (next to the accelerator pump). I will have to block the holes somehow. I'll do it tomorrow and update the results.


Thanks Mike for the input on this one. The valves are quiet (for now):D

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I put two pieces of rubber hoses with bolts at the ends and it plugged both pipes. It runs better, but still lopes:mad: I also have a problem with the choke closing on me while driving. I will browse the forum for the solution.

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The choke heater (above) has a Blue wire to it, (may have a black sheath over it) and should have 12 volts when engine is actually running. If not, make sure the wire is plugged in properly at the connector just behind the carb that it shares with the Red idle cut wire. The Red idle cut solenoid wire should have 12 volts only when the ignition is ON.

Edited by datzenmike
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I did my own smoke test. It cost me 5 bucks:D Here is how.


I bought a cuban cigar at a gas station, disconnected a blow by (PCV filtered) and AIV hoses from the air cleaner assembly and put it aside. I put a rubber glove with an elastic band over the carburetor's choke chamber (the very top), disconnected a brake booster vacuum hose and blew cigar's smoke inside the hose. Smoke came out of VVT valve, accelerating pump (i blew really hard:blink:), gasket btw the throttle body assembly and some thick spacer and another gasket btw this thick spacer and the intake manifold.


Obviously, I will have to replace the gaskets. I checked the VVT valve and it is ok (although I forgot to pump air into the exhaust back-pressure hose and attempt to suck air from the vacuum signal opening). Excited I started to disconnect every vacuum line at a device and sucked air to see if it holds vacuum. A carbon canister, a distributor and a vacuum break diaphragm did not hold the vacuum. The first two released slowly while the last one let go abruptly. The distributor advances when vacuum is applied, but comes back if I do not continue sucking the air out of it.


Is it normal for the three things to leak vacuum?


Unfortunately I did not check vacuum at a boost control unit and a vacuum switch, but the by-pass air control works fine.


Previously I thought that the choke was closing on me when engine was warm. However, it appears to be a fast idle cam not wanting to drop all the way down after pressing on a gas pedal while driving. The RPMs drop when I abruptly kick a gas pedal. So I drove and stopped; my idle was high; I kicked the gas pedal and idle came down; I drove again and stopped; my idle was high; I kicked the gas pedal and idle came down, and so on:D


I wish I had some rum with that cigar:D

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