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post #11 of 33 (permalink) Old 08-21-2019, 11:55 AM
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Originally Posted by GT75Z View Post
'75 Z, in the Dallas area. My cylinder #6 does not seem to be firing. This is after me doing some undercarriage pressure washing. At idle, when I pull the #6 plug, no change. All other plugs I can notice a difference. So this I presume would tell me that 6 is not firing. I have a new distributor cap and rotor. Spark plug wire seems OK, I can't see any problems with it. What else can I look for that would keep #6 from firing.

Thanks!
GT75Z
Hi GT - I am in Dallas too. Are you a member of Dallas's club called "The Z Club of Texas"? I'm curious if we've met before. We hold tech sessions so we definitely could tackle this too.

1978 280z - stock L28 engine - Dallas, TX
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post #12 of 33 (permalink) Old 08-21-2019, 12:18 PM Thread Starter
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Originally Posted by Dave M View Post
if the plug checks out, then yes an injector can become clogged, that it happened after washing the engine means its unlikely. BUT if you want to check it, get a 9v battery and some alligator wire test leads, pressurized the system with a fuel pressure gauge attached, engine off fire an injector with the 9v battery across the injector, watch the gauge, if its working the pressure should bleed off.
Thanks All. I have looked at and compared all the plugs. I do not seem to see moisture/gas on the 6 plug. It looks like all the others. I guess this means the injector is not firing (even though I hear the injector clicking?)
Assuming I have to pull that injector, is it just me or is that a real pain in the arse. Because it is the #6 injector, I think I can probably pull it without pulling the whole fuel rail. But that injector seems to be causing the problem. But as said earlier, a wash should not have caused this and no, I've done nothing else recently to the engine.

Thanks,
GT
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post #13 of 33 (permalink) Old 08-21-2019, 01:28 PM
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if its a 75 it should have a split rail on the injectors, makes pulling #6 a tad easier, but if the fuel line is old (should have been replaced ;by now) it may be very hard and somewhat of a PITA to get loose. IIRC the best way was to loosen 4,5 hose clamps and unbolt #6 to release it, 4 and 5 will partially come off but not completely before you can free up #6 . IF you have not had the injectors out before you may find the screws used to fasten them could be very hard to get out. IF it has OE phillips I recommend you use a hand struck impact driver with a correct fitting bit. Realize there is a medium chance of snapping the screw off in the manifold, which will ruin your day. After you get the injector pulled up with #6 still attached to the fuel line you can test fire and see if the injector is firing. Just re attach 4,5 with 6 injector hanging out to see it. IF you have had the injectors out, replaced the fuel line and used antiseize on the screws its MUCH easier.


All of the above is why I suggest you try the leak down test 1st hooking up a gauge and checking for leak down is not the big a deal, compare #6 to a working one and see if the leak down is about the same. IF it is its prob something else.
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post #14 of 33 (permalink) Old 08-21-2019, 01:32 PM
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https://youtu.be/Gu3JCo0iG9U?t=10




this may give you some ideas. I have a part 2 as well.

Last edited by Dave M; 08-21-2019 at 01:35 PM.
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post #15 of 33 (permalink) Old 08-21-2019, 06:17 PM
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One other thing to check before you start ripping things apart: the injector connector to #6 . I've had these get water in them and cause a misfire. (And again, if it didn't do it before you pressure washed, then my experience tells me it HAS to be something related to that. Injectors don't usually just 'go out' out of the blue. FWIW, the Nissan injector connector plugs were kind of cheapies. If you have a self-serve wrecking yard nearby, look for replacements under the hoods of 80s-90s era Volvos and BMWs. They use the same Bosch type connectors, but theirs are nice and have a little O-ring built in to keep dust and water out.
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post #16 of 33 (permalink) Old 08-22-2019, 01:03 AM
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It would seem that "what we have here, is a failure to communicate".

I'm afraid I did my part by being a bit facetious about pulling the injector. The issue is that "cleaned all the injectors" or "seem to see moisture/gas on the 6 plug" can mean different things to different people, always the fundamental problem with remote diagnosis.

I would suggest that perhaps working thru the basics (air, gas, spark) would put us all on the same page.

Let us assume that the cyl. is getting air. That leaves gas and spark.

Let's start with spark. Pull all the plugs, marking the current #6 plug. Plug #6 plug into #6 wire. While holding (with plastic handle pliers) the plug electrode to the block, spin the engine a bit. No spark? Try another plug, then another wire to identify the problelm source..

No matter what you find, go to the second step below.

Next (with all plugs still out), put a clean, short hose to the #6 plug hole and spin the engine a bit with your nose close to the hose. Smell gas? To calibrate your nose, do the same on another cyl.

It's not rocket science; it has to be one or/and the other.

Let us know what you find out.



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post #17 of 33 (permalink) Old 08-22-2019, 01:22 PM Thread Starter
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Originally Posted by ensys View Post
It would seem that "what we have here, is a failure to communicate".

I'm afraid I did my part by being a bit facetious about pulling the injector. The issue is that "cleaned all the injectors" or "seem to see moisture/gas on the 6 plug" can mean different things to different people, always the fundamental problem with remote diagnosis.

I would suggest that perhaps working thru the basics (air, gas, spark) would put us all on the same page.

Let us assume that the cyl. is getting air. That leaves gas and spark.

Let's start with spark. Pull all the plugs, marking the current #6 plug. Plug #6 plug into #6 wire. While holding (with plastic handle pliers) the plug electrode to the block, spin the engine a bit. No spark? Try another plug, then another wire to identify the problelm source..

No matter what you find, go to the second step below.

Next (with all plugs still out), put a clean, short hose to the #6 plug hole and spin the engine a bit with your nose close to the hose. Smell gas? To calibrate your nose, do the same on another cyl.

It's not rocket science; it has to be one or/and the other.

Let us know what you find out.
First off, Chaseincats, I am a member of ZCOT, just recently rejoined with the group. I use to be a member 15 years ago and then let it slip. In the meeting last week, I believe I saw that the tech sessions were temporarily on hold.
Moving forward, I have had the fuel rail and all injectors out of the motor within the last 2 months. I cleaned all the injectors and got them working fine/consistent. And yes, fuel/air/spark is the key. I seem to be lacking fuel due to the plug not being moist when I pull it. It all may be a coincidence but I can't see the pressure washing clogging up the injector. Also, I only pressure washed the bottom of the engine and transmission. No pressure wash went on to the top side of the engine.
As far as testing for spark... Thank you Ensys. So to be sure, I pull all the plugs and find a helper to turn the engine over and check for spark. It still seems like a lot of fuel might be going to the cylinders and a spark near by may not be good. I like the hose thought and smelling for gas to check the injector.
My wife is working from home today so maybe I will have my helper.

Thanks all,
GT
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post #18 of 33 (permalink) Old 08-22-2019, 01:57 PM Thread Starter
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Originally Posted by GT75Z View Post
First off, Chaseincats, I am a member of ZCOT, just recently rejoined with the group. I use to be a member 15 years ago and then let it slip. In the meeting last week, I believe I saw that the tech sessions were temporarily on hold.
Moving forward, I have had the fuel rail and all injectors out of the motor within the last 2 months. I cleaned all the injectors and got them working fine/consistent. And yes, fuel/air/spark is the key. I seem to be lacking fuel due to the plug not being moist when I pull it. It all may be a coincidence but I can't see the pressure washing clogging up the injector. Also, I only pressure washed the bottom of the engine and transmission. No pressure wash went on to the top side of the engine.
As far as testing for spark... Thank you Ensys. So to be sure, I pull all the plugs and find a helper to turn the engine over and check for spark. It still seems like a lot of fuel might be going to the cylinders and a spark near by may not be good. I like the hose thought and smelling for gas to check the injector.
My wife is working from home today so maybe I will have my helper.

Thanks all,
GT
Okay I pulled all the plugs (I LOVE a car that you can pull and replace the plugs in under 10 minutes) and I am getting spark and it sure as heck smells like I am getting fuel. This is what I was afraid of, now what the heck do I look for.

I will repeat from early on, when I pull the plug wire from #6 the engine idle does not change at all. When I pull every other cylinder, it will cause the engine to slow down a bit - a noticeable change. Seems like this tells me 6 is not firing.

It's a poser.

Thanks,
GT
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post #19 of 33 (permalink) Old 08-22-2019, 02:37 PM Thread Starter
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Okay I pulled all the plugs (I LOVE a car that you can pull and replace the plugs in under 10 minutes) and I am getting spark and it sure as heck smells like I am getting fuel. This is what I was afraid of, now what the heck do I look for.

I will repeat from early on, when I pull the plug wire from #6 the engine idle does not change at all. When I pull every other cylinder, it will cause the engine to slow down a bit - a noticeable change. Seems like this tells me 6 is not firing.

It's a poser.

Thanks,
GT
Oh, and for Dave M, Thank you for the video. What is a colortune plug? I have not heard of that before. Where can you get one and is that it's proper name?

Thanks,
GT
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post #20 of 33 (permalink) Old 08-22-2019, 05:29 PM
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Got a plug wire laying around anywhere. .02c

zippityzda
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