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Mysterious Vacuum Line / Rough Idle Issue

MarVelo

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2000 XLS 4.0L
Hello Forum! I'm a long time lurker and this is my first legitimate post.

I have a 2000 4DR, 4WD, V6 OHV Explorer. I purchased it second hand with 130k miles on it a year ago and have since run it up to 142k.

I noticed awhile back that there was an errant red vacuum line capped with electrical tape and taped off to the oil spout breather tube. No clue where its meant to go. I hope somebody can give me a clue. It looks like it runs from the drivers side connected to the intake manifold, goes under/behind the intake and along the fuel rail. There it splits and one line connects the the fuel line and the other is the mystery hose. Below are a few pictures to illustrate the situation.







In addition to this mystery, I have another problem. I recently replaced my intake manifold upper and lower gaskets and the drivers side valve cover gasket (passenger side was too much work and it was midnight by time I finished the rest). I did this because I was getting a P0174 and P0171, both banks too lean.

When I put it all back together now I have a rough idle where I didn't really before and now I'm only getting P0174.

It may be interesting to note that the idle is only rough while in gear. Park or neutral the idle is fine. When up to speed and reving over 1.5k RPM it also seems fine (though it may be masked by the speed).

So far I have:

-Cleaned the AIC
-Put a new gasket on the EGR Valve/Intake junction
-Checked plugs and wires
-Checked the PCV and hose, both were fine


I'm running out of ideas. Could it be the fact that I only replaced one valve cover? that doesn't make sense to me why I would start idling rough where I had not before. It seems like a vacuum leak which is partly why I bring up the first issue with the mystery vacuum line. Please help, this is driving me nuts.

-Tom
 


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JEastonjr

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its about time for a fuel pump. the mileage is right. check the fuel pressure at the rail.
 




mr2fix2it

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check the egr PIpe It cracks when removing intake sometimes mostly when the intake is removed without taking egr off completely. Fuel pump wont cause lean condition on only one bank! To check tube spray with carb cleaner to see if idle changes you n\may need a scanner to monitor fuel trims to see changes.
 




mr2fix2it

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As far as the red hose one possibility is the fuel pressure regulator ,another some times there is a vacuum storage bottle in the passenger fender for 4x4 solenoids and oine more to the a/c heater plenum chamber that goes under heater box on passenger side also.
 




ranger7ltr

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1999 Sport
Look at the pretty pictures!!!...

The red vacuum line goes to the fuel damper on the fuel rail, not a fuel pressure regulator...Model year 1999 and newer did not have a fuel pressure regulator on the fuel rail...it is in the fuel tank...

Hopefully your red vacuum line still has the rubber fittings on it...One side goes to the fuel damper and the other side goes to the vacuum canister on the passenger side...See the picture for the line...Look in the upper left side of the picture...You will see the vacuum line routing and the branch that it is connected...

Now to the intake gasket question; You changed the lower and upper gaskets on the intake? Did you mean the lower intake gaskets or just the lower gasket between the fuel manifold and the upper intake?

I ask because you said you didn't do the passenger valve cover which has to come off to remove the lower intake...I suspect the lower intake stayed in place and the plenum[upper intake] and the fuel manifold were removed and the gaskets between them removed and replaced...

When you replaced the gaskets, did you torque the bolts evenly and clean the mating surfaces well? I would recommend also checking the fuel pressure at the test port for proper level...It should be anywhere from 55-72 psi..

And how long ago did you change the fuel filter? I would suspect a rought idle in gear due to a vacuum leak, a clogged fuel filter, and/or fuel leak due to the injectors not being sealed by the fuel manifold...
 

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MarVelo

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2000 XLS 4.0L
That explains why I don't have any control of what vent my heat goes to. If I'm not mistaken I will have to take off the passenger side wheel well cover to reach the canister?

I took off the plastic plenum, changed the rubber gaskets that press into that, removed the fuel rail and changed the paper/silicone gasket under that, then reassembled. I'm afraid I didn't get the studs torqued up to spec because I used two nuts locked together and may have loosened all or some of the studs unlocking them. I have since purchased the external torx sockets and am planning on re-torquing this afternoon. When I had the rail off I cleaned it till it shined so I don't think there is a problem there. Is it also possible I may not have secured one or more fuel injectors into the rail completely? Or would I have different/worse problems if that were the case?

Can I use a regular air/tire pressure gauge on the fuel rail test port?
 




ranger7ltr

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Checking the fuel pressure is best done with a proper gauge..NOW...I have used other tools to do so in a pinch...I can't remember on this engine if a tire pressure gauge would depress the plunger well enough to read the fuel rail pressure...

Try it...It just might.. If not, Harbor Freight has an inexpensive gauge setup for $20... http://www.harborfreight.com/fuel-injection-pump-tester-92699.html

If the injectors were not seated I believe you would have seen fuel leaking from the injector...I bet torquing the gaskets will resolve the problem you are having...And I would recommend changing the fuel filter unless you just recently changed it...
 




MarVelo

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Found the other end of the vacuum line inside the wheel well cover. Fixed that issue and I now have control of my heat.

As for the other issue. Torqued everything to spec and noticed some minor improvement. Still have a p0174 and a rough running condition at idle that seems to get worse as I drive it. Acceleration is extremely poor and it stumbles every time as it passes 1,500 rpm. I stalled out once while stopped yesterday as well.

I am taking my explorer over to a friend who is a good mechanic and has many more tools than I do to have him look at it. I will update this thread with my results for future reference.
 




MarVelo

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Figured out my problem. Rather embarrassing really. I had the wires for cylinders 5 and 6 in the wrong order on the coil pack. I want to slap the sucker that decided to make it 1-2-3-4-6-5 instead of in order. Everything runs fine now.

I'm replacing the plugs just for safe measure and because its about time anyway.

Thanks for the help. I now have all issues solved, no CEL, no noises, my heat works, hooray!
 




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