26 minutes ago, Dave WM said:

I doubt a running compression test will add any light to the issue. If you are worried about a loss of seal in rings or valves a leak down test will isolate. OR just do a wet/dry compression test.

However all this seems moot since lifting the cap fixes the issue.

a few things you should do

a simple power test to see if #6 is causing a drop in rpm when disabled. do this with the cap tight vs loose since that is the title of the thread. It would seem to be the issue based on reading the plug, but the power test confirms.

This will confirm the issue is #6 and the cap is the fix.

If that works go simple, try switching a plug and wire with one that seems to work (cause a power drop when pulled).

That will clear the wire and plug.

do a wet/dry comparison of compression from a known working cyl to the suspect cyl, if the same that will clear the compression.

Next try a new cap and rotor if the problem persist. If new cap and rotor have no effect, I would HIGHLY recommend you pop for the color tune. that will comfirm the fuel mix.

That should show if the issue is a lean vs rich, swapping an injector should prove this out.

The only thing that  that I can think of (given the stated issue) re the loose cap deal is a poor air fuel mix that is hard to ignite coupled with a ign that is just on the edge of working with a lean idle mix. the color tune will show the mix and if its lean that maybe the issue. adding a spark gap to the cap maybe just enough to compensate for a poor air fuel mix and lets it fire.

I would start with some brand new standard (cheap) ngk plugs, not sure about those fancy tip plugs (could be adding to the ign just on the edge of dealing with a lean mix).

Pure speculation of course on all the above, but remote diagnosis is very hard since we don't even have a video to see/hear what is going on. Sometime there is a tiny clue missing like seeing a spark in the ign wires a night, or some other odd thing that gets overlooked.

 

 

 

 

 

 

Got u , i will make several vids as i test each scenario

i will also grab a colortTune cause its another cool tool to have

i'm aware of throttle valve, but not sure about throttle plate

as the plate pivots it activates two micro switches. they are located in a small plastic box on the throttle body in line with the rod that the throttle plate is screwed to.

the on/off position is adjustable, one switch should be closed at idle, then off as throttle comes off idle, then another switch comes on again at about 2/3 throttle, so both switches are off at just over idle thru about 1/3 throttle. At least on the NA 280z efi.

Edited November 5, 20204 yr by Dave WM

Turbo different

1 hour ago, Zed Head said:

Turbo different

alright going to inspec that now...

here is how the injectors sound on the stethoscope.  in person injector #6 sounds a lot lower/subtle than what u hear in the recording.

 

 

I only posted that to clear things up about the switch.  I'm not really sure what problem you're working on.  Trying to change the appearance of a spark plug or make an injector sound louder is not a good target.  If you're planning to just leave the cap propped up and run it that way then maybe removing and cleaning all of the spark plugs, or buying a new clean set would be worthwhile.  Do that and see how things look now.  You might be trying to fix a problem that doesn't exist anymore.

Does it have running or performance problems with the cap propped up?  What are they?

If you're still worried about cylinder #6 then measure pressure on all six cylinders.  It's easy to do and will tell you if the cylinder, piston and rings, are the same as the other 5.  If 6 has low pressure then injectors or plugs won't help much.

1 hour ago, ira said:

alright going to inspec that now...

here is how the injectors sound on the stethoscope.  in person injector #6 sounds a lot lower/subtle than what u hear in the recording.

 

 

results of resistance measurements ....  Keeping in mind that my Klein MM300 indicates .3 or .2 when the 2 leads touch, i will assume that's my zero.

1) pin 18 & 25 at the harness,

results when depressed  = infinity

when released = i get anything from 1.9 to 2.2 to 2.5.  but nothing less than 1.9

2) testing at the valve looked better.

when depressed =  infinity

when released = .3 or .2 

 

Looks fine.  They got a little too specific I think on continuity and open circuit.  A problem there would be more noticeable while driving anyway.

Never hurts to take a step back and see what you've learned since you decided that there was a problem.  The lifted distributor cap is still a very odd thing.

1 hour ago, Zed Head said:

Looks fine.  They got a little too specific I think on continuity and open circuit.  A problem there would be more noticeable while driving anyway.

Never hurts to take a step back and see what you've learned since you decided that there was a problem.  The lifted distributor cap is still a very odd thing.

with my humble experience and seeing what everyone spoke about i will focus on the following

1) confirm the distributor installed 3 yrs ago is indeed for Turbo model

2) get new CAP & Cables

3) use some upper intake cleaner to rule out any carbon build up on the valves.  Specially since the live compression test showed very low numbers.  Piston#6 showed 45psi

4) continue to follow the FSM to chk other sensors & parts

i hope i wont need to look for an EFI Analyzer

 

can you describe the setup that results in the 45psi on #6? I am not sure I follow what a "live compression test" is. 45psi is for sure a problem. I assume the live test on the others was somewhat higher in psi readings? On compression test its all about being even or at least within 10% of the high number.

My standard test is a warm engine, throttle plate open, fresh charged battery, use a remote starter, all plugs out, screw in type tester with a one way valve built in, then crank it till it hits highest reading, generally takes about 4 compression stokes to max out. Do this on all noting pressure, then I go back and squirt in some light oil, maybe a 1/2 teaspoon, take another reading.

Look for even numbers wet and dry.

IF you have an outlier, then do a leak down test, TDC compression stroke, pump up to about 100 psi with shop air,  note leakage (should be no more than about 20% max) if more listen to exhaust pipe (exaust valve leaking) intake manifold (intake valve leaking) valve cover opening (rings leaking). Generally most of the leaking will be from the rings into the crankcase (valve cover opening). Very little if any should be heard from the exhaust or intake manifold (you can use a hose to ear connect hose to brake booster port on intake manifold for listening to intake).

1 hour ago, ira said:

3) use some upper intake cleaner to rule out any carbon build up on the valves.  Specially since the live compression test showed very low numbers.  Piston#6 showed 45psi

You said that you got about 130 psi in your other post.  So, we can't really tell what's going on.  A list of all six pressures would be good.  

 

1 hour ago, Dave WM said:

can you describe the setup that results in the 45psi on #6? I am not sure I follow what a "live compression test" is. 45psi is for sure a problem. I assume the live test on the others was somewhat higher in psi readings? On compression test its all about being even or at least within 10% of the high number.

My standard test is a warm engine, throttle plate open, fresh charged battery, use a remote starter, all plugs out, screw in type tester with a one way valve built in, then crank it till it hits highest reading, generally takes about 4 compression stokes to max out. Do this on all noting pressure, then I go back and squirt in some light oil, maybe a 1/2 teaspoon, take another reading.

Look for even numbers wet and dry.

IF you have an outlier, then do a leak down test, TDC compression stroke, pump up to about 100 psi with shop air,  note leakage (should be no more than about 20% max) if more listen to exhaust pipe (exaust valve leaking) intake manifold (intake valve leaking) valve cover opening (rings leaking). Generally most of the leaking will be from the rings into the crankcase (valve cover opening). Very little if any should be heard from the exhaust or intake manifold (you can use a hose to ear connect hose to brake booster port on intake manifold for listening to intake).

yesterday i did the dry compression test, results were about 130 cross all cylinders

today i did it while the car was running in order to rule out if car loses compression during operation.

i managed to do it on cylinder #6 which recorded 90 at start but then immediately dropped to 45 and remained there.

i couldn't finish testing the rest due doctor Appnt  i wasnt aware of

also one of the spark plug cables was too stuck to plug and ended up going bad.  i have to order new set

22 hours ago, ira said:

u still think i should alternate inject 6 w lets say  injector 5 or 4 ?

no. If inj.#6 works thats fine.

Now you say #6 compression is 90 going to 45 psi..thats the problem.. smells like stuck valves..