loose Distributor CAP = Perfect idle

[ira]

2 hours ago, Zed Head said:

Does injector #6 work with the cap up?  Can't tell if you're saying that you got boost and up to 70 on 5 cylinders or something else.  How does spark plug #6 look after boosting to 70 mph?

i don't have a way to confirm if its running on 5 cylinder.  i can only confirm that idling is perfect, and it drives a lot smoother.

i tested all spark cables resistance from with in the CAP, and its sitting the same across all cables of about 8200 ~ 9200 ohms.  According to FSM it needs to be less than 30,000 

i do see an improvement in spark plugs when cap is elevated.  #6 still looks a little rich compared others.  the reaming plugs look a lot better than prev pics.

 see attached n let me know what you think PLS

i also did a dry compression test.

 

[Zed Head]

#6 looks wet and like it has not been firing much.  The strap should be grayish-white like #5.  Does it smell like gasoline?

Something is not quite right.

[ira]

30 minutes ago, Zed Head said:

#6 looks wet and like it has not been firing much.  The strap should be grayish-white like #5.  Does it smell like gasoline?

Something is not quite right.

i couldnt tell if i smelled gas.  given the exhaust smell in the garage and on my clothing my nose is shot

 

I can confirm the new injector is spraying.  so if the rest of spark plugs are looking better now, isnt that a good indication that the Dist Cap may be the issue?

 

i still dont know what would cause plug 6 to look like that if the wiring is good, compression is same across, and the injector is working, and the valves have been set to .008 & ..010 across the board

 

you didnt tell me, whats ur take on the compression being 125.  i heard it should be close to 150~180 

 

[Mark Maras]

Was the throttle wide open during the compression test? If not, that would account for the low numbers. If it was wide open, I'd adjust the valves and test again.

Edited November 5, 2020 by Mark Maras
C.R.S.

[ira]

2 minutes ago, Mark Maras said:

Was the throttle wide open during the compression test? If not, that would account for the low numbers. If it was wide open, I'd adjust the valves and test again.

Hey Mark,

yes i made sure to push down all the way on the throttle, while my son cranked it over about 10 cycles   i noticed all pistons  it would get to that 125 range by 2nd cycle 

[Zed Head]

Turbo engines have lower CR's.  And gauges vary.  It's the comparison of all six cylinders that really matters.

[ira]

looking back at the pics, mine reported 130.  so i should im good there correct?

Q1, are the distributors for the turbo charged 280zx diff from the non-turbo? 

Q2, what route should i take now to figure out why plug #6 is wet and looking diff than others?

 

[dutchzcarguy]

Q1 - Yes..  non turbo has D6K7-02 OR D6K7-04 OR D6K8-02   And turbo has D8K81-07 According to my serv.manuals..

Q2 -  If your CR is 130 Psi on all cylinders thats OK.  You could exchange injector one of 1-5 and 6..   the problem is now in cylinder 1-5 ??  then the new injector is faulty.. get a new one.  (i understand your sparkplug is, as the cable to cyl. 6 good/new..?)  As i sayd before the new part can be dead..  it happens.

You better test the injector with a  small ordinary 9v battery.. with a 12v battery you could burnout the coil of the injector very easely..  the 9v bat can deliver just enough power to let the injector open.. maybe the new injector you put in cyl.6 is stuck.. put it overnight in a cleaner solution like injectorcleaner stuff.. maybe that helps..

Edited November 5, 2020 by dutchzcarguy

[ira]

45 minutes ago, dutchzcarguy said:

Q1 - Yes..  non turbo has D6K7-02 OR D6K7-04 OR D6K8-02   And turbo has D8K81-07 According to my serv.manuals..

Q2 -  If your CR is 130 Psi on all cylinders thats OK.  You could exchange injector one of 1-5 and 6..   the problem is now in cylinder 1-5 ??  then the new injector is faulty.. get a new one.  (i understand your sparkplug is, as the cable to cyl. 6 good/new..?)  As i sayd before the new part can be dead..  it happens.

You better test the injector with a  small ordinary 9v battery.. with a 12v battery you could burnout the coil of the injector very easely..  the 9v bat can deliver just enough power to let the injector open.. maybe the new injector you put in cyl.6 is stuck.. put it overnight in a cleaner solution like injectorcleaner stuff.. maybe that helps..

Hey Dutch,

i already ruled out that the new injc#6 to be in a working condition.  i posted earlier that i raised the fuel rail far enough to see it spray when cranking over the car.

do u still think i should alternate inject 6 w lets say  injector 5 or 4 ? are you aiming to see if the spark plug would end up showing rich on 4 or 5?

[ira]

Folks, 

im considering a Compression test while car is running for a min or so to see if i have any loss during operation.  What are ur takes on that?

also, i came across the below.  what if carbon build up is causing valves to get stuck or not open/close properly

 

 

[Dave WM]

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.

 

 

 

 

 

 

Edited November 5, 2020 by Dave WM

[Dave WM]

oh forgot to ask, does the turbo model have the throttle plate position enrichment sensor (idle mid full switch mounted to the throttle body). On non turbos this adds fuel at idle. Its an adjustable series of micro switches that has a 3 prong plug. Small box on the side of the TB.