1998 Ford Explorer XLT P0171 and P0174 codes

[fast_dave]

Thank-you for the information, it is greatly appreciated.
I have cleaned the MAF sensor twice so I don't think that is the issue.

@CynthiaK

The Upper Intake Manifold is a 12 pound piece of plastic (and coil pack) with a LONG rubber snorkel connected to it, all on top of a vibrating engine - that goes through countless temperature extremes...

Only three very thin thin rubber gaskets seal the plastic Upper Intake Manifold to the Lower Intake Manifold.

In the "dry heat" of the PRK, I'm lucky if I get about 3 years out of a set before I get a Check Engine Light code.

Seriously - I keep a set of (3) extra O Rings in my tool box and can change them in my sleep

 

[Cuco]

@CynthiaK

Hope this helps

BELOW is a picture of what you need.

This is a very common repair, about every 3-4 years, and if you plan on holding on to your Ex for any length of time you should really consider doing this "on your own" as it's not too extreme a repair. It's a little tedious at first, without feeling rushed/stressed, it might take you 3-4 hours start to finish. By the 3rd time you do it, you're looking at 1 hour. The parts cost almost nothing - it's an "all labor" job - and it's not hard labor - only tedious (at first).

OK - so what you need is called "Upper Intake Manifold Gaskets"
Note: Sometimes guys call them "Upper Intake Manifold O Rings".

They are NOT Lower Intake Manifold Gaskets (which is something totally different).

You need to purchase Quantity (3) in TOTAL @ $2.88 Each at Rock Auto

Click on this link in BLUE for more details: 1998 FORD EXPLORER 4.0L V6 OHV Intake Plenum Gasket | RockAuto

OR,

You could purchase Genuine FORD gaskets off of this Ebay dealer for $12.40 for Quantity (3) with Free Shipping & No Tax

Click on this link in BLUE for more details: Genuine OEM Ford Manifold Gasket F57Z-9E436-AA (PACK OF 3) | eBay

and here's a pic of the bottom of your OHV Upper Intake Manifold, so you get an idea of where the (3) Gaskets/O Rings go!

It's only a 6 bolt job.

What about 5.0 engine?

 

[410Fortune]

do not forget about the larger green EGR O ring....it should also be replaced and can cause the same codes as if it does not seat properly it will cause a large air leak
I use vaseline or assembly lube on the O ring when installing to ensure it slides into the correct position inside the intake plenum

If you are anywhere near North Idaho I would be happy to help with this repair

5.0 Engine uses metal upper and lower intakes, no O rings to leak.
If you have a 5.0 and these codes then its a totally different story of where to look

 

[fast_dave]

do not forget about the larger green EGR O ring

@410Fortune

+10 ^^^

Never even thought of that part - then for the first repair, order this kit to get the EGR O Ring (which is hard to get by itself, outside of a gasket kit).

When properly lubed up, an EGR O - Ring lasts a looooooooooong time so buy a "upper intake gasket kit" to get it.

In fact, each time you take off the upper intake, you'll be cursing that O-Ring, as it holds on to the upper intake pretty tight - even when properly lubed up from the previous repair. It's a heavy duty o-ring, made of Viton (type) heat resistant rubber.

Getting off that o-ring is the last step in the upper intake removal process and a pita due to the height & angle of the dangle needed to clear the underside of the hood. Heck, now that I think about it, getting it back on with the EGR tube in place (on the egr valve) is also a pita

A way around this tedious "dance" just described - I get around this by removing the two bolts holding the EGR tube to the EGR valve, and thus remove the Upper Intake AND the EGR TUBE as a complete assembly. I have extra egr gaskets in the toolbox as well since they're .25 a pop. Once the two EGR bolts are removed, threads cleaned up w/ a wire brush, and nickle anti-seize liberally applied, you can take them out pretty easily every three years or so. They're pretty heavy duty bolts.

Anyways - here's what you need to get the EGR O-Ring

FEL-PRO MS90732 for $13.47 @ Rock Auto

Click on the following BLUE Link: 1998 FORD EXPLORER 4.0L V6 OHV Intake Plenum Gasket | RockAuto

 

[donalds]

I have re seated that green egr o ring a few times I used rubber o ring silicone lube ....just for o rings.. something like this I bought a tube of it
https://www.amazon.com/Silicone-Lub...uPWNsaWNrUmVkaXJlY3QmZG9Ob3RMb2dDbGljaz10cnVl

 

[410Fortune]

nice!
When I remove the upper plenum on a OHV I undo the wiring to the PCM and the ground wire. This gives you room along the fierwall to move the intake up over the fuel rail studs and twist off of the egr hose and O ring.
I install it the reverse way, no need to mess with the EGR bolts as some of the trucks I have built use headers and there are no more EGR bolts...since I had to fabricate the entire EGR tube from the header up

You can buy that O ring separate
fel pro 71202

https://www.amazon.com/Fel-Pro-7120...?keywords=fel+pro+71202&qid=1570727475&sr=8-1

 

[fast_dave]

I have re seated that green egr o ring a few times I used rubber o ring silicone lube ....just for o rings.. something like this I bought a tube of it

I have a tube of this that I use on the EGR (and other rubber gaskets).

It's so old (approximately 2007) that it's been re-branded for Radio Shack - good for up to 400 degrees

It will be unveiled in all it's glory in an upcoming write up I'll be posting to the forum

 

[fast_dave]

Just for future reference - here's the Mahle (OEM) offering for the "green" EGR O-Ring

MAHLE Original G32745 EGR Tube Gasket

$2.09 @ Rock Auto: MAHLE G32745 EGR Gasket | RockAuto

$3.33 @ Amazon: https://www.amazon.com/MAHLE-Origin...02EQCGD7528&psc=1&refRID=BMDW9F2N002EQCGD7528

 

[CynthiaK]

Thank-you sooo much everyone!!!

 

[CynthiaK]

Hi,

I know this is an old post but I wanted to update it.
While replacing the thermostat, I noticed that the housing was not sitting flush when I removed it.
I cleaned it off, applied some Permatex gasket maker and voila, no more error codes.
Quite by accident, but extremely happy it is fixed!!

Thank-you so much for all the replies!

 

[CynthiaK]

Hi,

I know this is an old post but I wanted to update it.
While replacing the thermostat, I noticed that the housing was not sitting flush when I removed it.
I cleaned it off, applied some Permatex gasket maker and voila, no more error codes.
Quite by accident, but extremely happy it is fixed!!

Thank-you so much for all the replies!

Well, so much for that. It went a few days without codes and now they are back. I had thought maybe when I replaced the thermostat that
I moved a hose somewhere and it tightened back on somehow.
I just did a smoke test and smoke poured out the IAC valve from under the black knob.
Is this normal?

Thanks!

 

[fast_dave]

@CynthiaK

1) Just an observation; what codes is your EX CURRENTLY throwing or is it still 171 & 174?

2) Also, please clarify your Feb 4th Post: With regards to your thermostat - when you write that you "replaced it" - please specify; did you swap it out with a new one or did you reuse your old one. I ask this because I understand that you felt that you found a problem with the mounting of the housing wasn't flush, so I'm thinking that you might have possibly "replaced" the used one.

Smoke Test Answer:
And to answer your question, during a smoke test, it is normal/OK to see smoke coming out from the "black knob" that is attached to to he IAC Valve. When that black knob is removed and disassembled, you will find a mini air filter the size/shape of a Bayer Aspirin. In fact, seeing smoke emit from the "black knob" is a good sign - it means that the air filter inside of it is not clogged.

HTH & Good Luck!

 

[CynthiaK]

@CynthiaK

1) Just an observation; what codes is your EX CURRENTLY throwing or is it still 171 & 174?

2) Also, please clarify your Feb 4th Post: With regards to your thermostat - when you write that you "replaced it" - please specify; did you swap it out with a new one or did you reuse your old one. I ask this because I understand that you felt that you found a problem with the mounting of the housing wasn't flush, so I'm thinking that you might have possibly "replaced" the used one.

Smoke Test Answer:
And to answer your question, during a smoke test, it is normal/OK to see smoke coming out from the "black knob" that is attached to to he IAC Valve. When that black knob is removed and disassembled, you will find a mini air filter the size/shape of a Bayer Aspirin. In fact, seeing smoke emit from the "black knob" is a good sign - it means that the air filter inside of it is not clogged.

HTH & Good Luck!

Thank-you for your reply!

Both 171 and 174 showed up again.
I replaced the old thermostat with a brand new one.

 

[fast_dave]

@CynthiaK

Look carefully at your Black Plastic OHV Intake Manifold.

It is comprised of two (2) pieces of plastic - a top "cap" that is plastic welded (or glued) to the bottom section.

This assembly of the two sections of the intake manifold is right at eye level, it's a "lip" and it goes all the way around the intake.

As these vehicles get older and go through thousands of heat cycles, sometimes the weld on the seam of the intake between the top and bottom section cracks and or separates, and thus lets in un-metered air. Over the years I've wondered why the aftermarket Dorman sells replacement intake manifolds of this engine,...

Anyways - I live in the hot climate of the PRK, and found this out around the 200,000 mile mark - the last time I replaced the three upper intake rubber gaskets shown in Post 24 of this thread (Post #'s are in the lower right hand corner of each posting). I don't know where you live - so I don't know the climate - but heat cycles are heat cycles, no matter where you live.

I will say this, my Ex wasn't throwing ANY codes - BUT - as many of us have discovered - every Ex seems to have a different "sensitivity level" when it comes for throwing codes for similar problems. With my Ex, and over 15 years of ownership, it seems that a engine related problem needs to be extreme before it throws a code.

OK - back to my separating intake manifold; My solution to the condition - while my intake manifold was removed - was to carefully clean the intake mating seam with a can of aerosol parts cleaner, a clean/old toothbrush, and compressed air. Set the manifold out in the sun for about an hour to ensure that the parts cleaner had evaporated, and then used a tube of Black RTV, and filled in all areas where there was seam separation. The worst areas were on the rear of the manifold, and the passenger side.

In the end, after I made repairs, I noticed that the truck idled smoother/held rpm's better.

I'm always using Cruise Control, and the biggest take away was after the repair my Ex was able to hold onto the set speed on steep/gradual grades in 5th gear for much longer without kicking off. So I got back torque that I was losing due to the lean condition caused by the un-metered air entering the intake through the seams.

Hope that helps and let us know -

 

[Terry Long Sr.]

P0171 and P0174 are almost ALWAYS bad O rings in the intake manifold
Both banks are running lean
What this means is there is air entering the engine after the mas air flow sensor and before the oxygen sensors
This is called "un metered air"
The computer has attempted to compensate by dumping more fuel to match the additional air flow and it cannot accommodate the extra air, so it pops the codes.

Your engine has a plastic upper intake manifold and where it meets the metal lower intake there is a series of rubber O rings.
These O rings (manifold gaskets) dry up over time and shrink and allow air to flow around them
You need to remove the upper intake manifold and replace the O rings
You should also replace the large green O ring that goes on the EGR feed into the upper intake manifold
Somebody who knows these engines can do this job in one hour and that is working slowly cleaning all surfaces
It is a good time to replace spark plug and spark plug wires
Also not a bad idea to check fuel pressure

I cannot count on two hands how many OHV and SOHC 4.0L engines I have fixed with the 171 and 174 codes over the years simply by replacing the $19 O rings............

I agree with you one this, I had a friend replace my intake gaskets on my 4.0l, ran good when I left but before I got home it started idling rough and would quit when I stopped. Turns out when he put the intake back on he pinched the O ring on the on the EGR feed tube, replaced that AFTER I had replaced almost all the other sensors and it's been fine ever since! Much cheaper to check that 1st.

 

[CynthiaK]

I agree with you one this, I had a friend replace my intake gaskets on my 4.0l, ran good when I left but before I got home it started idling rough and would quit when I stopped. Turns out when he put the intake back on he pinched the O ring on the on the EGR feed tube, replaced that AFTER I had replaced almost all the other sensors and it's been fine ever since! Mush cheaper to check that 1st.

Thank-you!