Explorer, Sport Trac, Mountaineer & Aviator1991-1994, 1995-2001, 2002-2005, 2006-2010 Ford Explorer
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I've found this problem posted a lot but haven't found a solution. I have a 1998 Explorer Sport, 4.0 EFI (Not SOHC). It has 106,000 miles and runs perfectly, cold and hot.
The MIL light comes on all the time. I got a codes scanner and it shows P0171 and P0174. I clear the codes and can go from a couple hours to a couple weeks before the codes flag the light on again.
I took it in for a required smog test (California) and the emissions all pass but the car fails only because all the monitors have not run. I check the monitors every time I start it up to see if they have cleared. This last time all cleared except the catalyst monitor when the light came on again. The P0171 and P0174 codes stayed pending a few days before the check engine light actually came on.
I have cleaned the engine and examined all the vacuum hoses with no luck. I checked and cleaned the MAF sensor as some suggested with no luck. I checked and cleaned the PCV valve and hose with no luck. I've sprayed carb cleaner and starting fluid around the lower intake manifold but didn't notice any change.
I'm not sure how to diagnose the O2 sensors. There is no surging at idle, cold is around 1100 RPM and hot around 800, both are steady. I don't have the cash to just replace them without being fairly certain what the problem is.
I visited my dealer last month with the same problem and he quoted $1000 to repair. I took it home and replaced the upper intake manifold gaskets (o rings), injector o-rings and egr gasket. Runs great, no errors, and about 10% better gas milage. All for a total of $300 plus my labour. That includes the OBDII tester I have now added to my toolbox. (4L pushrod)
Thanks for the reply. I already have the code reader so hopefully that will cut my cost down. I've replaced the PCV valve and air/gas filters, re-cleaned the MAF, to no avail. I'll try the gaskets this weekend. Any tips on changing them?
(I just ran over to AutoZone. They only show throttle body manifold gaskets, no upper manifold. They don't list any o-rings for the injectors. I couldn't get over to Napa due to roadblocks for some reason. Will try tomorrow or the Ford dealership.)
Last edited by canyonbreeze; 09-21-2004 at 02:01 PM.
It's embarassing but I'll confess, when things went back together I mixed plug wires 5&6. Look carefully at the numbering cause it just doesn't follow any logic. Loosen your a/c compressor to give you room to thread the egr pipe when lifting the upper manifold (runners) off. The runners require 3 seals (paired). It takes a good steady pull to lift the fuel rail off the injectors. If I recall I did end up using a pry to assist. Much easier on assembly side. I used some petroleum jelly on the injector O rings (2 for each injector) which helped. The rail to lower manifold gasket is a thich heat shield unit, easily placed. If I had worked steady it probably would have been a 4 hour job. Good luck.
The parts stores list a lower manifold gasket and a fuel rail to plenum gasket. Is the fuel rail to plenum gasket the one you are refering to as the upper gasket? Also, no one lists injector o-rings. Did you have to go to the dealership for that? (There is not a Ford dealership near me so I haven't checked there).
I replaced all the above parts yesterday. Didn't find a need to move the a/c compressor as suggested. Lost about one hour due to my clumsy hands dropping a nut into the intake manifold. This wasn't all that bad as my wife was eventually able to fish it out with a couple steel welding rods bent as hooks. Watching her, an ex-professional dancer, hunched up under the hood in her shorts for about 40 minutes made me feel life is good.
Got it all back together and let it idle about 10 minutes. Went to road test and it dies about halfway down the block. Wouldn't restart so I looked under the hood, all seems ok. Then it restarts fine after about 5 minutes. Did about 10 trips around the block and then the 40+ freeway miles to work this morning.
No errors flagged yet. Will have to see if all the monitor flags in the driving cycle clear without any errors. This can take a few days.
There is a pronounced howl sometimes now that stops when I tap the gas pedal. From other posts I think this may be the Idle Air Control (IAC). I did remove and clean this when changing the gaskets. Is this noise a problem or just an annoyance?
Let it go without resetting the codes for a couple weeks as I had no money to do anything. Went to clean the MAF again, this time under a microscope. It looks very clean.
When putting it back I notice the oil filler cap is gone. It was there when I changed all the gaskets and the IAC. Bought a new one for $5 and am hoping that maybe this little part will fix the issue. There is an air tube from the oil filler pipe to the air intake just after the MAF, an obvious air leak if the cap wasn't sealing good, more obvious with the cap gone.
Reset the codes and will wait and see. The C and EV never cleared in the last few weeks. When there are codes flagged and the MIL on, does the drive cycle stop doing the checks?
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