Possible Vacuum Leak, With Graphs

Alright I’m back. It’s finally gotten cold enough to really replicate the symptoms I had been having earlier.

There’s a bad misfire on cylinder 3 and sometimes 1.

Wanted to post the misfire history. I’ve already changed spark plugs on cylinders 1 , 3 and 8 twice in the last 30,000 miles. I also changed spark plug wires at the same time as well. That was the summer of 2023. I started having issues that winter when it got cold.

Pulled the spark plug of cylinder 3

Is the intake air temperature from the mass air flow sensor at startup about the same as the outside air temperature? If the sensor is off it could make the computer think it's getting more or less air than it really is.

houstontaylor said:

Is the intake air temperature from the mass air flow sensor at startup about the same as the outside air temperature? If the sensor is off it could make the computer think it's getting more or less air than it really is.

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I checked this morning. Was 42F on the air intake temp sensor and it was 42F outside.

Probably going to have to take her to a mechanic before something catastrophic happens.

2001LSHoe said:

I checked this morning. Was 42F on the air intake temp sensor and it was 42F outside.

Probably going to have to take her to a mechanic before something catastrophic happens.

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So after the engine warmed up and the outside air remained stagnant, the intake air sensor read 57F. Obviously part of that is the engine heat.

Decided to buy a fuel pressure gauge and at the rail after priming it, it reads 53-54 psi. However, leaving it on after turning the car off the pressure quickly drops. So it’s leaking somewhere.

I’m going to first try the fuel pressure regulator. After that it’s either the pump or injector.

No dice but it does hold fuel pressure. Still below spec, however. Hoping someone reads this and can point me in a direction. Going to be taking her to a mechanic this week.

2001LSHoe said:

I did new plugs and wires, fuel filter and cleaned MAF all within the last year. I initially had this issue last winter on a morning when it got down to -15F. In the winter time the symptoms are much worse. The car had 90,000 miles and was a one owner when I purchased it in 2022. It now has 150,000 on the clock. It was garage kept its entire life and was very well maintained.

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Have you ever cleaned the fuel injectors?
I agree with @B-train, they need to be cleaned.

Another thing you can do is remove the spark plugs and inspect the cylinder w a endoscopy camera for wet spots.

ivin74 said:

Have you ever cleaned the fuel injectors?
I agree with @B-train, they need to be cleaned.

Another thing you can do is remove the spark plugs and inspect the cylinder w a endoscopy camera for wet spots.

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a.co

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When you say clean do you mean running a fuel injector cleaner through the gas tank? Or physically taking the fuel injectors out to observe them? It's been a while since I've ran injector cleaner through them IIRC. So I'll give that a shot.

Okay another question is the temperature on exhaust port on cylinder three was double the temp of the others when I ran it for about a minute this morning. Increasing RPM smoothed the feel of the engine out but the misfiring is still there. Would this mean an issue with the spark? IE it's not getting enough spark to burn the fuel correctly? The only confusing thing to me is that it's also happening on cylinders 1, 2 and 8. So cylinders 1, 2, 3 and 8 are the primary culprits. Especially number 3. I changed the wire from cylinder 4 and 3 and that didn't make a difference.

Also, the air to fuel ratio on start up is below 14.7 so that means it's not getting enough air, correct? So, why does the PCM want to keep dumping fuel into the combustion chamber?