#4 on 1.6 @ 150psi all others 190 - Miata Turbo Forum - Boost cars, acquire cats.

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Old 12-22-2015, 07:01 PM   #1
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Question #4 on 1.6 @ 150psi all others 190

As the title says I have a cylinder reading low.

initial cranks got me to around 150-155 on #4 with all others at 195.

Added oil to #4 and got 180'ish

Notes:

#3 and #4 plugs were dry-carbon fouled (#4 MUCH worse than #3)

#1 and #2 plugs were g2g

My thoughts (fingers crossed) are that #4 is carbon stuck (it's certainly got a nice amount of carbon build up on inspection through spark plug well).

Cause(s): So in order from "hopefully" to "f.m.l" =
leaky fuel injector(s)
Bad coil/wire/plug for a LONG time causing massive buildup
Worn out ring(s)
Damaged cylinder wall(s)

The car consumes NO oil.

It has been sitting for quite a while (about 6 months)

Engine pulls well and there is a slightly noticeable misfire at idle (I know now that it's #4 and mayhaps #3 every once in a while)

Advice?
There's obviously some shade tree stuff I can do to "decarbonize" along with all the other additives that are magic and made of foam and whatever....

I've got a set of new injectors I'm about to install and fortunately the car isn't daily driven...yet...

I'm leaning towards...well basically doing nothing... just install the new injectors (along with new plugs) and drive the car...spiritedly...for a few weeks to see if I can't dislodge some of this stuff.

Any other thoughts?
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Old 12-22-2015, 11:10 PM   #2
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Do a leak down and you will know if it is leaking through the rings inrake or exhaust valves, then youll know if you need a head job or a rebuild
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Old 12-23-2015, 02:33 AM   #3
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Which year? Hydraulic lifters in NA, 99-02 might need a valve adjustment.
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Old 12-23-2015, 08:56 AM   #4
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Quote:
Originally Posted by gooflophaze View Post
Which year? Hydraulic lifters in NA, 99-02 might need a valve adjustment.
Sorry, car is a 91 with long nose crank 1.6. Disregard my user name. Im new at keyboards.
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Old 12-23-2015, 08:24 PM   #5
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Carbon. You probably can't fix it without taking it apart. Just drive it. It's fine.
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Old 12-24-2015, 01:01 PM   #6
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Carbon. You probably can't fix it without taking it apart. Just drive it. It's fine.
Yeah, I let it it over night and pulled plugs on 3 and 4 in the morning and they were wet. Leaky injectors it is. Im gonna just hope some of it blows loose eventually. Thanks for replies!
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Old 12-24-2015, 01:06 PM   #7
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Drive it hard for a while and recheck, i.e. an Italian Tune-up.
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Old 12-24-2015, 03:21 PM   #8
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I tried sea foam in the cylinder, carb leaner, brake cleaner, fed the intake about a half a gallon of water at 3k rpm. Carbon refused to leave.
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Old 12-25-2015, 07:14 AM   #9
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Quote:
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Drive it hard for a while and recheck, i.e. an Italian Tune-up.
Absolutely!
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