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Dave - are you suggesting I try an ethanol free gas?
I seriously doubt that would account for the problem, I just prefer to run the cars on what they were designed for. They have a very primitive EFI system, so less variables the better. Does the problem present only at Idle?
 

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Discussion Starter #42
Ok thought I would check the valve gaps (even though a local guy told me he checked them!!). Counting valves from the front had to correct gaps in 2,6,10,11 out of the first 11. 11th is intake so trying to get it to .008 and it won’t get that tight? The top of the rocker moves freely up and the others do not. I assume something is missing? Tried to show on the photo that I can pull the end of the rocker up? Thanks for suggestions and help
 

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is the lash pad in place? Should not have a problem adj to .008.


I should have asked if you have done a compression test, just assumed that was covered. A leak down test even better.
poor compression will look like a miss, guess its possible to show up as the engine warms up. a Cold and Warm test should be done as well.
 

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Discussion Starter #46
To hard to explain. Maybe just mental fatigue after a long day. I thought that I spun the top nut one way and then the other and if would not tighten either way. I had it so loose that the rocker was lifting off freely so I figured something was wrong. Thanks
 

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Discussion Starter #47
Ok. Worked on the timing and got the Vacuum up to 16-18 range. Got a compression tester and I think I found the problem. Should be 164-178lbs and mine are as follows. 1-108, 2-105, 3-110, 4-113, 5-111, 6-110. There is no doubt that when car warms and runs rough that 1&2 are not combusting. When u pull off those plug wires it runs the same. Sorry I know this should have been the first thing I checked. Realizing my local mechanic does not know what he is doing. He checked them and said they were all about the same. I now know that means nothing if they are all below spec. Can I just assume the only fix is a major engine rebuild. Thanks
 

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those are low but
a few things to consider. You have to be sure your equipment is reading correctly, Cant tell you how many times I have been misguided by faulty equipment or hook up. IF possible check equipment against a known good working engine and see if you get normal readings.


Next, should not mater much but did you have the throttle plate wide open? did you have all the plugs out (helps with cranking speed)?
Did you try putting a little oil in each plug hole (wet vs dry test).


You may want to do a leak down test, this will tell you if you have a ring issue vs a valve issue. they are all the same so I would assume IF they truly are that low, most likely worn compression rings, the leak down test will help know for sure (you will see low % and hear the air escaping thru the block (valve cover/dip stick/from the opening that lead down the front cover where the timing chain goes).


as far as the power test (1&2 not changing RPM). this is where you really should focus. Start with listening to the injectors, make sure you hear them clicking. For spark, pull the plugs out, leave them attached to the plug lead and rest the metal body of the plug on the valve cover, check for spark.


If both check (click and spark) pull the suspect injector and one that seem to be working, check to see if they both spray the same while cranking. Its possible you have a slightly clogged injector. You could even just swap the #3 (good injector) with &1 or &2 (the bad cylinders), and see if the power test fails on #3 after the swap (and passes on the cylinder that got #3 's injector).


Cant overstate the importance of making sure you compression readings are really that low. Also the factory specs are a bit optimistic IMHO, my 75 gets about 150-155 across all, below factory spec yet is runs just fine. I think more typical reading on a engine that has 100k or more miles would be 125-150 and it would run fine, just down on max power. Confirm those low numbers before going to far. a wet test will prove out the ring issue, if you jump up to 170psi from 110psi with an teaspoon of oil added, then yes your engine is worn and would be something you need to consider.
 

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Discussion Starter #49
Don’t want to ask a stupid question but I’m not sure how to open the throttle plate? Is this done by depressing the accelerator??
 

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yes just hold it open any way you can. I generally use a remote starter (push button) that plugs into the solenoid on the starter, and the battery +. this way I can be outside the car while cranking and don't have to worry about disabling the ign or fuel injection. you can just reach over and hold the throttle open while cranking (find the throttle shaft that runs along the top of the intake manifold). Use a good compression tester, the kind that screws into the plug hole is best (vs the kind that you have to press into the plug hole). Generally it will take about 4-5 compression strokes to max out the reading.
 

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Discussion Starter #51
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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Discussion Starter #53
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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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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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?
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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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.
 

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Discussion Starter #57
Sorry it took me so long to get back with an update. After going over everything I could think of I decided to tow my car to the Datsun Doctor in Waterford Michigan. Within a couple hours they found the problem was my fuel tank which was unable to allow good fuel flow. I thought my fuel pressure was where it should be but apparently I had that wrong. Tank had to be cut in 2 and rebuilt but it runs great now so I’m happy. I wasted months going through everything but I learned a lot and I assume they were worthwhile repairs. Thanks everyone for your help. The support trying to help a stranger was amazing. I plan to drive this Z for the next 30 years. Thanks again.
 
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