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Cylinder not firing

4K views 32 replies 6 participants last post by  dumbestone 
#1 ·
'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
 
#4 ·
Yes, I can hear the injector clicking through my very long screwdriver. I have not pulled the plug to check for spark, I use to do that as a kid with my lawnmower but not sure the safest way to do that with the car. Seems I would have to run the engine without the plug in the cylinder and that doesn't seem like a smart thing to do. I have switched plug wires with another and get the same results so it is not the wire.
How can I tell if I am getting power/spark to the plug?

Thanks,
GT
 
#5 ·
Very common after pressure wash for water to get into distributor, which causes all sorts of weird and worrisome running until it dries out. Before you do anything, pop the dizzy cap off and check for water droplets. Also take off the individual wires (at the cap) and check for moisture.

Blow out with compressed air or just let it air dry awhile. Then put back together and try it.
 
#6 ·
I was very careful not to spray the engine. I know the Z motors do not like water. So that is my bad. I popped the distributor and it is as dry as can be but still sprayed compressed air on it and letting it sit for a while. Is there a way to check for spark at the spark plug? or could the injector still be clicking yet not delivering fuel? I just redid the fuel system, cleaned all the injectors and everything was great till I did my little washing.
Note to self - no water near the engine, ever!

GT
 
#7 ·
Okay, just saw that this happened after a pressure wash, so thought it might be the culprit. Is there ANYTHING else you did before this problem popped up? At any rate, if #6 is not firing, it could be the plug or the injector. I would first look at the plug. I've had them just 'go bad' for no good reason. Switch out #6 plug with any other one. If no difference (#6 is still dead), then it's likely the injector. If #6 all of a sudden works but the other cylinder is misfiring, then it's the plug. Good luck and let us know what you find!
 
#9 ·
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.
 
#12 ·
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
 
#10 ·
Which is easier: spudding a fuel press gauge in the line, or just pulling the injector and firing it into a bottle?

Besides, the gauge method will tell you nothing about just how the injector is firing. It's possible that the valve is opening without spitting much fuel.

By the by, one gets a better picture of plug wire condition by checking (with a VOM) the wire's resistance value against the others.

Another by the by; have you yet actually pulled all the plugs to read/compare the tips? This is a better/easier/safer way to check plug operation, no? For example, after running, a wet tip on no.6 would tell you whether the injector is firing and whether the plug is not.

Just a thought...
 
#13 ·
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.
 
#15 ·
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.
 
#16 ·
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.
 
#17 ·
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
 
#21 ·
"Seems like this tells me 6 is not firing."

Not necessarily.

To verify your earlier statement, hook everything up a start the engine, letting it warm.

Now, shut it off and remove all the plugs, laying them out in order. Carefully examine all the electrodes. If they all look the same (as you alluded earlier), you're problem is not a "mis-fire".

If they are not identical, note the cyl. and the difference.

Report your results.
 
#23 ·
I will try to be more definitive. With the engine idling, when I pull each plug wire, all of them affect the idle except for 6. There is no change when I pull 6. That is why I suspect #6 . I know I am getting spark in #6 . Besides it shocking me, I do have spark from the block. So assuming I have air, seems like the injector is failing. I'm about to pull it out, I think it is my only option.

Thanks!
GT
 
#25 · (Edited)
My dear Mr.GT:

Do you really think you're in a position to blow off those who would teach you something?

I would remind you that you also (thanks to suggestion) learned, by experience, that you are getting gas into that cyl. as well. Or did you forget.

You also stated that you looked and the #6 plug "looks like all the others".

There is a thing called The Scientific Method of problem solving. Considered very reliable. All the Method requires to work is an inquisitive mind, some logic, and above all, patience.

Throw up your hands and start dismantling if you wish (and have plenty of time on your hands), but without truly understanding the nature of your problem, it's likely you'll be wasting your (and now our) time.

But first, consider this: you may have the right cyl., but very probably the wrong diagnosis of the problem.

But hey, it's your time, so have at it.

Adios, and don't forget to write.
 
#26 ·
Ensys, I do feel like I have the wrong diagnosis. That is why I am having this discussion with others who might can help me with the proper diagnosis.
* First off, I have power going to the injector connector and I have spark at the plug.
* Currently, I have removed and cleaned the injector (blowing carb cleaner through the injector). It would blow good and strong at first but the more I continued doing it, the stream got weaker. That makes me question the injector.
* I idled the engine and pulled the 6 plug right away. There was a result from that. Yay. But after a minute or two that changed and pulling the 6 plug made no difference
Is this possibly I just need to replace the injector? And can I buy an aftermarket injector that works happily with the original ones?
And truly I am looking for a diagnosis, not trying to waste anyone's time.

Thanks,
GT
 
#27 ·
You did all this since Sat. afternoon?

More importantly, at some point, you had the injector out, on the bench, "cleaned" it, and then put it back in knowing you weren't finished with the job? And without trying to find out if there was something that could yet be done before hooking it back up?

It would seem you've figured things out on your own after all. I guess I'm the one wasting your time; my apologies.
 
#29 ·
the injector should not allow any cleaner thru it unless you had it opened with an electrical current. I presume you had some setup to energize the coil of the injector? Or was this done on the car with the engine cranking? more details on exactly what was done.
 
#30 ·
I clean the injectors by blowing CRC carb cleaner into the injector and firing the injector off of a 3 volt battery set up. Nothing comes through the injector until you apply the voltage.
Looking at the injector before I put it back in, it did not appear to have any type of fine screen.
And ensys, I appreciate everyone's comments no matter, but I am not sure what you mean about me putting the injector back in without finishing the job? If there is something more I could have and should have done, I would have if I knew what that was. Could you please tell me? And yes, I did all this in a day.

Thanks all,
GT
 
#31 ·
there should be a screen, looks like a tiny sock screen, generally you pull them out with a sharp wood screw, like a drywall screw. twist it in, it bites the edge and give it a sharp tug, should pull out the screen. IF its missing then likely someone has been in there before, and did not replace it, Not a good idea since then any tiny bit of junk that goes in will likely block the injector.
 
#32 ·
So this screen would be on the output side of the injector, correct? Should it actually be visible to the eye as you look at that end of the injector. I was not looking for anything like that but it sure was not obvious when I had this one out as well as all the others when I had them out.

Thanks Dave
 
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