Multiple misfire?

Tiny
RUSSLYONS
  • MEMBER
  • 2009 INFINITI G37
  • 3.0L
  • 6 CYL
  • 4WD
  • AUTOMATIC
  • 235,000 MILES
The car began having a misfire under load. I checked the plugs and a couple had a lot of oil on them. Cleaned them, misfire went away for about 15 minutes of driving then returned. Suddenly it got very bad a would barely run. It now misfires very badly at idle. I changed the valve covers, plugs and coils but the problem persists.
Monday, February 26th, 2024 AT 11:41 AM

16 Replies

Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 52,356 POSTS
It sounds like the fuel pump is getting weak but to be sure we can do a pressure test which you can rent the gauge from the auto parts store for cheap or free. This guide can help walk you through it and I have included how to test your car in the images below:

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

Fuel Pressure

At idling .................... Approximately 350 kPa (3.57 kg/cm2, 51 psi)

I have also included how to change the fuel pump out as well. Check out the images (below). Please upload pictures or videos in your response to the problem so we can see what's going on.

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Monday, February 26th, 2024 AT 12:32 PM
Tiny
RUSSLYONS
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  • 9 POSTS
Is this what would be expected with low fuel pressure? Or is there a different direction I should be looking?
Video (Click to make bigger)
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Tuesday, February 27th, 2024 AT 7:49 AM
Tiny
RUSSLYONS
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Also, there is a very pronounced smell of gas while running.
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Tuesday, February 27th, 2024 AT 7:52 AM
Tiny
KEN L
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Thanks for the video, it helped. It sounds like you have low compression in one or more cylinders, let's do a compression test on the engine before we go any further. This guide can help:

https://www.2carpros.com/articles/how-to-test-engine-compression

Please go over this guide and get back to us.
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Tuesday, February 27th, 2024 AT 9:21 AM
Tiny
RUSSLYONS
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I’m struggling to do the next tests. The picture shown looks like you are tapping into the fuel dampener for the fuel pressure test, but it is a solid line with no way to disconnect and insert the fuel pressure gauge. I tried to do a compression test, but my tester is too big and won’t screw into the spark plug hole.

One thing I have noticed is that there is a very strong fuel smell when it’s running but I’m not seeing any fuel leaks. Given the strong smell, would you dismiss any fuel delivery issue? What would cause such a strong fuel smell?
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Monday, March 4th, 2024 AT 3:21 PM
Tiny
KEN L
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  • 52,356 POSTS
It could be the timing jumped, does the engine have okay power? I would use a compression gauge that has the hose attached.

Here is one for $19.00:

https://amzn.to/3wD3Fg5

Also, when the spark plugs are out does one look different than the other? If so, this will be the cylinder having the issue.
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Tuesday, March 5th, 2024 AT 9:46 AM
Tiny
RUSSLYONS
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I bought a new kit today and checked the compression. Cylinders 1, 3, 4, 6 had 230-240 PSI. Cylinders 2 and 5 had 160 PSI.

The spark plugs in those 2 cylinders initially were oil covered. I assumed it was the valve covers leaking into the spark plug tubes, so I changed the valve covers, plugs and coils.
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Tuesday, March 5th, 2024 AT 2:27 PM
Tiny
KEN L
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Good job, these compression reading seem okay. Did the new spark plugs and valve cover gasket fix it?
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Wednesday, March 6th, 2024 AT 8:34 AM
Tiny
RUSSLYONS
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  • 9 POSTS
There was no change after changing the valve cover gaskets, plugs and coils. That’s why I went further and did the compression test. So, you don’t think 160 on cylinders 2 and 5 is too low when the others are 240? I thought they should all be within 10% or so of each other?
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Wednesday, March 6th, 2024 AT 8:46 AM
Tiny
KEN L
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Yes, they should but it is not low enough to cause the problem you are describing. But with engine noise you may have a valve train issue, I would remove the valve covers for 2 and 5 and check the cam lift and valve springs. Unplug the fuel pump relay so the engine doesn't start and have a helper crank the engine over while you watch the movement of the valve train. Also, on cylinder # 2 and 5 how has the spark plug washed clean?
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Wednesday, March 6th, 2024 AT 10:36 AM
Tiny
RUSSLYONS
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I didn’t clean the plugs, I replaced them.
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Wednesday, March 6th, 2024 AT 10:39 AM
Tiny
KEN L
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Yes, but the old ones, were they washed clean on #2 and #5 this will tell us if the injectors are stuck open.
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Wednesday, March 6th, 2024 AT 10:47 AM
Tiny
RUSSLYONS
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I’m going from memory, because I didn’t really think about that aspect, but yes, they were very clean other than oil on the threads. I was surprised how clean they looked. I don’t know how old they were. The car had 200,000 miles when I bought it. It now has 235,000.

How would I check to see if they are stuck open? That could possibly account for the very strong fuel smell when it’s running?
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Wednesday, March 6th, 2024 AT 11:01 AM
Tiny
KEN L
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Yes, the injector sounds like it is the problem, here is how to test the injectors and how to remove them:

https://www.2carpros.com/articles/how-to-test-a-fuel-injector

If you find the injectors to be bad, I would replace them all with this kind of mileage teh others are right behind. Check out the images (below). Let us know how it goes. BTW the fuel injector can wash the oil from the cylinder wall causing the low compression.
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Wednesday, March 6th, 2024 AT 12:10 PM
Tiny
RUSSLYONS
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Thank you! It was bad injectors! I replaced them all and it is running like new!
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Friday, March 8th, 2024 AT 2:13 PM
Tiny
KEN L
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Glad you could get it fixed, thanks for letting us know. Please use 2CarPros anytime we are here to help.
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Saturday, March 9th, 2024 AT 9:55 AM

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