97 Explorer 4.0 SOHC - Misfire on 4 cyliders.

[XL97]

So I am getting miss fires on 4 cylinders on my 97 Explorer XL. Its the 4.0 SOHC. It DOES have 320000 miles but all of the fluids are fine, I just changed plugs and wires to no avail. It goes 0-60 in about 45 seconds at this state and runs extremely rough. Any ideas or is my engine just toast?

 

[PAExplorerXLT]

I am told I have(or had) misfires but the engine runs just fine. I am not even sure how you remedy a misfire. What is causing it?

 

[drdoom]

I would put a meter on the coil just to rule it out, and check the fuel pressure too. Do you have any other codes other than the 0300s?

 

[Pontisteve]

See what codes are in memory. With that many misfires, you may have multiple problems or one big problem. Check for vacuum leaks and air intake tubing leaks carefully. FYI, these 4.0 engines are known for intake gasket leaks. One symptom would be large positive fuel trims when cold, and they get better as the engine warms up. You may or may not be able to detect them with brakleen or propane.

 

[XL97]

Well I had both codes for O2 sensors. But it really does run horrible. How would I go about checking that gasket leak? Would it cause misfires?

 

[Pontisteve]

Well I had both codes for O2 sensors. But it really does run horrible. How would I go about checking that gasket leak? Would it cause misfires?

It can be difficult to catch intake gasket leaks, because they can leak below or internally where you can't get at the leak. Typically a smoke machine or brakleen or even just water can be used to detect a vacuum or intake leak. Sometimes they simply cannot be detected externally. In this case, the motor is typically sealed, and you could pinch off the PCV hose (to eliminate that vacuum), and measure vacuum on the short block using a vacuum gauge connected to the dipstick tube. If you have vacuum in the short block, and it's not coming from the PCV, the intake gasket is about the only other thing that could cause that.

I would start by looking at the long term and short term fuel trims at idle, cold. Then look at them on a warm engine. Did the trims reduce in size when the engine warmed up? Was the engine adding a bunch of fuel when it was cold, and not adding as much when it is warm? This is a sign of an intake gasket leak. They seal up some as they warm up.

You can also compare fuel trims (long and short) at idle, versus at 2500 RPM in neutral. If trims are huge at idle, and get considerably smaller at 2500 RPM, it's a sign of a vacuum leak.

 

[kevinspann]

Either a coil, or it jumped time.

 

[XL97]

I dont like the way "jumped time" sounds. Lol so should I start looking for another engine/vehicle?