Help with a miss

[97ExPxLt]

I've got a 97 ford explorer 4.0 ohv. It idles really rough and has no power. I know its missing on cylinder 6. So I checked the ignition system (plugs, wires, coil) everything was good. Checked the compression and I can't remember but I know it was over 100... So the only thing left woudl be a fuel issue I would think so I change the injectors and still the same thing. So finally I check the fuel pressure and at idle with the vacuum line hooked up on the regulator is was at 30psi with the vacuum unhooked it rose to 35 psi, so I replaced the complete fuel pump assembly, fuel filter, and regulator.. And still the same thing. I'm completely stumped on this one... Anyone got any ideas?

 

[ford33]

This might sound like a stupid question, but just trying to get a little more information. How do you know it's missing on cylinder 6? Are you sure it's not missing on more then one cylinder?

 

[97ExPxLt]

I say its missing on cylinder 6 because If you pull the plug wires off of one cylinder at a time number six is the only cylinder that doesn't not change the way it idles or runs.

 

[ford33]

In my experience having only one cylinder misfire the cause has usually been the spark plug or the wire. Have you tried swapping the spark plug wire with a known good one? Is the number 6 spark plug tightening down properly? My brother-in-law has a ranger with the 4.0L in it and he stripped out the spark plug hole in one cylinder and got a misfire as a result.

You said you did a compression test, but it looked like you only did the 6th cylinder. You should run the test across all of the cylinders. That would tell you if there is an oddity in the 6th cylinder compression.

 

[97ExPxLt]

Yea all cylinders were within spec. I'm thinking it may be something to do with the evap system not letting it build enough fuel pressure because I read in a repair manual that it should have 35 psi with the vacuum line hooked to the regulator and 50 with it unhooked and mine still with a new pump filter and regulator has 30 hooked up and 35 unhooked...

 

[Turdle]

Yea all cylinders were within spec. I'm thinking it may be something to do with the evap system not letting it build enough fuel pressure because I read in a repair manual that it should have 35 psi with the vacuum line hooked to the regulator and 50 with it unhooked and mine still with a new pump filter and regulator has 30 hooked up and 35 unhooked...

HAve you checked for the 12v pulse to the injector? There is 12v on both side of the injector at all times. it is when one side pulses to 0v that the injector fires. You need to verify the signal is there.

 

[97ExPxLt]

HAve you checked for the 12v pulse to the injector? There is 12v on both side of the injector at all times. it is when one side pulses to 0v that the injector fires. You need to verify the signal is there.

Have not but I'll go check that... But this still wouldn't explain the low fuel pressure after having a new pump filter and regulator....

 

[Turdle]

I don;t think that would cause just one injector to fail----

 

[mr2fix2it]

by time your done taking it to someone and getting it checked out will be cheeper than throwing parts at it and so far this is what you have done evap has nothing to do with fuel pressure so spend your money wisely not foolishly