Possible Vacuum Leak, With Graphs

[2001LSHoe]

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.

 

[2001LSHoe]

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.

 

[2001LSHoe]

Pulled the spark plug of cylinder 3

 

[houstontaylor]

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.

 

[2001LSHoe]

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.

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]

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.

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.

 

[2001LSHoe]

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.