#1 cylinder not firing

krazykrames

Original poster
Member
Feb 6, 2014
11
The number one cylinder isn't firing. I swapped ignition coils with a working one and it still didn't fire. I swapped a spark plug with a working one and it still doesn't fire.
I unplugged the coil and with the engine running I probed the electrical connector and got 14 volts to the red wire and 14 volts to the black wire, I don't know what the middle wire is for or what it's suppose to read for voltage.
So I think the coil is good and it's getting power and I think the spark plug is good. What else do I check for???
 

AWD V8

Member
Jan 12, 2015
463
You need spark, fuel and compression at the right times.

Coils often fail on these, but if you swapped the coil and the misfire remains on the same cylinder the coil is OK.

Spark
You can check for spark by attaching the coil to the harness but not the spark plug. You need a grounded wire, or a long screwdriver if you are brave. Start the engine up and slowly insert the grounded wire into the coil. You will hear or see the spark. You can also rest a long screwdriver on a grounded surface and insert that also.

Compression
Just pull that one spark plug out and unplug the other coils so it won't start. Compression on that I believe should be around 170+ psi, somebody can correct me. Once the compression gets to around 100 psi the cylinder will failing to fire consistently.

Fuel
You can try to listen to the injector clicking with a stethoscope, or long screwdriver. You can unplug the injector and use a NOID light to see if you are getting a signal. If the compression and spark are good and you have a signal to the injector, it still could be a clogged injector. In that case you can either pull the injector and swap it, or if you have a fuel pressure gauge you can check it with that.

From what I've heard if it's not a bad coil it is often low compression.

Good luck
 
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seanpooh

Member
Jan 24, 2012
461
The coils are powered by the PCM. Bad ground from the ignition coil? Dead injector? The PCM controls the ground to each injector but the injectors have constant power.

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Mooseman

Moderator
Dec 4, 2011
25,257
Ottawa, ON
While cranking for the compression test, pull the fuel pump relay so you're not dumping a bunch of fuel into the engine.
 
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krazykrames

Original poster
Member
Feb 6, 2014
11
Great info and quick replies, much appreciated, I'll give them a try in the morning and report back.
 

mrrsm

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Oct 22, 2015
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I like @AWD V8 's idea for using the EFI NOID LIGHT TEST KIT to diagnose the EFI circuit and while they do offer a GM specific kit on-line at Amazon … this particular kit has served me well for covering a wider range of possibilities to include earlier model designs and other non-domestic testing applications; the average price being around Twenty One Bucks. If the #1 cylinder EFI circuit passes muster after performing this simple exam... a malfunctioning, clogged or stuck Fuel Injector will rise higher on the list of possible suspects to be investigated.

FWIW... If you intend to use a Mechanic's Stethoscope to listen for the #1 EFI actuating... this video I shot is from a series about using the Fuel Rail and OEM Multech II EFI s from a 2002 Trailblazer for an Off The Vehicle EFI Cleaning Machine I designed and built that will give you an idea of what they should all sound like when they are "clicking" properly inside:


...and about half way through in this video... you can see that a "Lazy Injector" or one with a sketchy connection can also be problematic. Double Checking all of the Multech II Harness Connections might reveal one or two that are too loose:


This what the Noid Kit components and instructions look like via my photobucket:

http://s557.photobucket.com/user/60...LAZERENGINEREPAIR/EFINOIDLIGHTS?sort=3&page=1

This is where to obtain these kits:

https://www.amazon.com/Electronic-Fuel-Injection-Light-Storage/dp/B009V28MU8/ref=sr_1_6?s=automotive&ie=UTF8&qid=1498383507&sr=1-6&keywords=#31098

...and this video demonstrates how easy they are to use for testing EFI circuitry integrity and the PCM pulse signaling… and so the less ambient light under and around the engine and hood… the better it will be for observation purposes:

 
Last edited:

Mooseman

Moderator
Dec 4, 2011
25,257
Ottawa, ON
Just added info to that. You might be able to test the first one but the others are covered by the intake manifold and difficult to reach. Using a stethoscope or screwdriver may also prove ineffective. You may be able to check at the main connector but you would need the wiring diagram with with colours to check each pair with the noid light.

After the process of elimination (check for spark, spark plug, compression, wiring), once you get to the injector as the last piece to check, the best way to check the injectors is an injector balance test using a Tech 2 scanner. Basically, you hook up a fuel pressure gauge, the Tech 2 pressurizes the system and will fire the first injector a measured number of times. You note the final pressure. Then this is repeated for each cylinder. If one cylinder fired abnormally, it will be evident with a higher or lower end pressure than the others. You would need to either find a shop with a Tech 2 or go to the dealer.
 

krazykrames

Original poster
Member
Feb 6, 2014
11
Ok checked for spark with a grounded wire into the coil and there is good spark.

Checked compression on #1 and it reads 155 psi.

Must be a fuel problem. The spark plug has always been dry as a bone if that's an indication of no fuel to a cylinder that's not firing.

I'll try to dig into the fuel diagnosis. Some of the suggestions are a little Chinese to a self taught weekend mechanic.
 

Mooseman

Moderator
Dec 4, 2011
25,257
Ottawa, ON
You might be at a point where you may need to take it to the dealer to confirm an injector issue. Just tell them what you've checked so far and TELL them that you want a cylinder injector balance test. At least this way they won't waste time on other stuff and know they can't bullshit you.

Although not probable but possible, check that the intake manifold bolts are tight. I say not probable because you would usually just get a lean code instead of a complete misfire.

One last thing, do not drive it too much on a missing cylinder or you will kill your cat.
 
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krazykrames

Original poster
Member
Feb 6, 2014
11
Just an update on things. I had a new coil on hand so I tried that on #1 and there was no change. The spark plugs were way past due for a change so I replaced them while I was in there and still not firing on #1. Well in the process of swapping things around trying different things I never ended up having the new coil on #1 after putting new plugs in. Once I put the new coil on #1 with the new plugs she ran smooth as silk. I don't know why that cylinder didn't fire with an old coil on it when the same coil worked fine on the other cylinders but whatever, it works now.
Also on a side not I tried the grounded wire into the new coil vs the old ones, the new one jumped a spark a good inch or more while the old ones jumped a spark a quarter inch at the most.
 
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