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280z #6 cylinder not firing


SmokeyRoach

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All,

For some reason my #6 cylinder is not firing. To start the plug is wet when pulled out after running on the remaining 5. Injector is firing, spark is good on #6, compression is at ~178-180 on all, timing is right on. All my checks so far check out but it is still not right.

Any ideas how to further troubleshoot this?

Thanks

76 280z

Stock motor

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I know it sounds dumb, and I don't mean to sound like a patronus, but is your firing order correct?

It's been printed wrong in the past (esp. in the Haynes manual) ... so when you're doing your "checks" what are you using as your resource?

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Perhaps you should switch two plugs and see if the problem stays with #6. I'm not sure if the #5 wire will reach #6 but if so you could also try swapping wires. Admittedly I know next to nothing about fuel injection but is it possible that an injector can get stuck open such that it's always spraying? Can you also swap injectors and see what happens?

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How do you know the injector is good? Even if you're getting a signal to the connector, the injector could be just dumping gas instead of opening and closing. BTDT. You say you have good compression at that cylinder and you're getting a signal to that injector so the only thing that could be at fault is the injector itself. Can you hear it clicking? Is it the same sound as the others? I use a mechanics stetoscope to listen to them. That coupled with a little apparatus I came up with that consists of a 9 volt battery, some wire, a momentary push button switch, and an injector connector.

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And as for #6 not firing. It can only be one of a few things.

1) a bad spark plug wire

2) a bad spark plug

3) bad cap or rotor (more towards the cap)

but you said that #6 IS getting spark. So which is it? Even if your injector is bad (stuck open or dumping too much fuel) a sparking spark plug should fire that fuel.

If it's NOT firing that fuel, it's time to upgrade your igniton system to a set-up that puts out some better fire power than what you're currently running.

I personally use a Mallory Unilite Distributor with a Mallory Promaster Coil and an MSD 6A. The coil puts out around 60,000 volts, or so I read somewhere and it puts out a bolt of Lightning each and every time if fires.

Something to think about.

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Even if your injector is bad (stuck open or dumping too much fuel) a sparking spark plug should fire that fuel.

I also disagree with that statement having been through that. Same scenario and a new injector solved the problem.

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And to that, I still dissagree......

If I fill a METAL gas can with gas, connect a ground wire from the spark plug to the can, submerge the end of the spark plug into the can and connect it to a 60,000 volt coil, IT WILL BLOW THE HELL UP!!!! PERIOD.

Fouled or not, it the spark is sufficient, the fuel or extra fuel will burn or ignite.

Not trying to be stubborn but facts are facts. Fill your whole house with fuel, if lightning strikes the house, it WILL blow up.

JM2CW but not worth fighting over.

Dave.

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And to that, I still dissagree......

If I fill a METAL gas can with gas, connect a ground wire from the spark plug to the can, submerge the end of the spark plug into the can and connect it to a 60,000 volt coil, IT WILL BLOW THE HELL UP!!!! PERIOD.

Fouled or not, it the spark is sufficient, the fuel or extra fuel will burn or ignite.

Not trying to be stubborn but facts are facts. Fill your whole house with fuel, if lightning strikes the house, it WILL blow up.

JM2CW but not worth fighting over.

Dave.

Not if it doesnt have air it wont burn

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Gents,

I will finally be able to get back to this over the weekend and give you guys an update on what I find.

Just a note, firing order is correct, all plugs, wires, dist cap/rotor etc are new and replaced in an attempt to solve this. Based on everyones comments here "which btw is great feedback" I will replace the injector and go from there. From what I have troubleshot on this so far it is the only thing left that I have not changed and makes sense if its stuck open. The good thing is that I have a spare fuel rail and injectors. I will change out #6 injector and update you on my findings. As for upgrading the Ignition/EFI system...I would love to one day and probably will, but there is no reason to do that now and drop $ before finding the root problem.

Thanks

Bill

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And to that, I still dissagree......

If I fill a METAL gas can with gas, connect a ground wire from the spark plug to the can, submerge the end of the spark plug into the can and connect it to a 60,000 volt coil, IT WILL BLOW THE HELL UP!!!! PERIOD.

Try it, I bet it wont.

Fouled or not, it the spark is sufficient, the fuel or extra fuel will burn or ignite.

I guess you've never heard of flooding an engine then. Thats when there is too much pertol in the engine for the engine to fire.

Not trying to be stubborn but facts are facts. Fill your whole house with fuel, if lightning strikes the house, it WILL blow up.

No it wont. I don't know where you are getting your facts from. Petrol vapour is explosive, petrol as a liquid, without the right amount of air will not ignite.

Some science homework for you:

http://en.wikipedia.org/wiki/Flooded_engine

http://en.wikipedia.org/wiki/Upper_explosive_limit

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Not a chance, Dave. Not enough oxygen=no boom. Believe it or not, liquid gasoline is not easy to combust. I've put cigarettes out in gasoline before. It is the VAPOR that ignites, and only in the presence of enough oxygen for the reaction to take place.

You most certainly can "drown" a cylinder with too much fuel and not have it fire. Spark a 100,000 volts if you want in a cyinder full of raw fuel--without enough O2 all you'll have is...spark.

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FIXED!!!

Changed #6 injector and bamm! Runs like it should now. The injector WAS stuck open thus causing the cylinder to flood out thus killing the spark. This is the black and white fact and proof this can happen.

Changed it out for now with a GP Sorensen P/N 800-9208...AutoZone $44.

Looks like eventually I will upgrade all the injectors and fuel system since I am in the full restore mode.

However thanks for all the help and the healthy discussion!

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I knew that because I'd been through it myself as I stated in post 7 and 10. You stated the paramaters, I gave a solution, based on actual experience. But, as usual, things like the combusibility of gasoline and the internal workings of the internal combustion engine had to be debated along the way.:)

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...as usual, things like the combusibility of gasoline and the internal workings of the internal combustion engine had to be debated along the way.:)

It wouldn't be the same around here if we didn't have people getting 'enlightened' all the time (myself included).

I'm glad you got this fixed, I guess I never realized an injector could get stuck open enough to "flood" a cylinder... but I guess I do now.

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I guess I never realized an injector could get stuck open enough to "flood" a cylinder...

Oh yeah. A leaking injector will dump gas into the cylinder as long as you have fuel pressure even with the car turned off.

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Oh yeah. A leaking injector will dump gas into the cylinder as long as you have fuel pressure even with the car turned off.

Well, I have a hunch that all of the injectors in my car are leaking a bit, so that's why I wasn't sure.

I guess that would make the rail depressurize into the cylinders more uniformly though, instead of dumping it all into one.

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