1998 Ford Explorer XLT P0171 and P0174 codes

[CynthiaK]

Hi,
I keep getting these codes. I have changed out the IAC, PCV valve and hose, fuel filter, checked for vacuum leaks and did not find any. I have used Chevron Techron to help clean the injectors. I have read it could be intake manifold gasket.
The strange thing is that I clear the codes and then can drive about 4 to 5 days before the engine light comes back on. If it was a vacuum leak, would it not show up as soon as I drive it after clearing the codes?
I am getting very bad fuel mileage.

Any suggestions?

Thank-you!

 

[BrooklynBay]

Welcome to this forum! Spray intake cleaner on the side of the intake gasket with the engine running to see if the idle changes.

 

[CynthiaK]

Thank-you for the reply.
Intake cleaner as in carb cleaner or is there a specific intake cleaner I can purchase?
I will try that today.

Also, if it is the gasket, why does it take 4 to 5 days for the code to return? Shouldn't it happen right away? That is the part that is confusing.

 

[BrooklynBay]

Intake cleaner for fuel injection.

 

[CynthiaK]

I forgot to mention, it is a V6 4L OHV engine, not sure if that matters or not.

 

[XLTrunner]

I have the SOHC engine...but, my codes would pop up like you describe. Would clear them and a couple days later they were back. Changed out the upper & lower intake gaskets and haven't had a problem since.

 

[CynthiaK]

Thank-you!

 

[Cuco]

Hi,
I keep getting these codes. I have changed out the IAC, PCV valve and hose, fuel filter, checked for vacuum leaks and did not find any. I have used Chevron Techron to help clean the injectors. I have read it could be intake manifold gasket.
The strange thing is that I clear the codes and then can drive about 4 to 5 days before the engine light comes back on. If it was a vacuum leak, would it not show up as soon as I drive it after clearing the codes?
I am getting very bad fuel mileage.

Any suggestions?

Thank-you!

I would recommend doing a full tune-up using only Motorcraft parts , plugs and wires & even if the engine seems like it’s running good check your fuel pressure

 

[410Fortune]

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............

 

[koda2000]

I'm assuming you have the 4.0L SOHC engine? If so these lean codes are super common. (Oh, I just noticed you have the 4.0L OHV engine, but same issue and cause).The codes indicate un-monitored/un-metered air leaking into the engine. On the 4.0L engines this is often caused by the upper and lower intake manifold gaskets/O-rings leaking when they get old and brittle. They probably need to be replaced. Other possible causes for your codes are a weak fuel pump or a clogged fuel filter.

 

[410Fortune]

@koda2000 her trim level details say 4.0 OHV just FYI

 

[koda2000]

@koda2000 her trim level details say 4.0 OHV just FYI

Yes I know. I corrected myself. Same issue, same fix.

 

[AbbyExplorer]

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............

Know anyone in Toronto that is an expert with this engine that I could go to and get it done? I had these codes today but got them cleared.

 

[koda2000]

Now going into colder weather the symptoms will get worse and you'll see the lean codes daily.

 

[AbbyExplorer]

Now going into colder weather the symptoms will get worse and you'll see the lean codes daily.

Is it bad to drive knowing these codes are on with my explorer?

 

[koda2000]

Is it bad to drive knowing these codes are on with my explorer?

It's not ideal because too much air and not enough fuel (running lean) makes the combustion chambers hotter. This can burn pistons and valves when the situation is extreme. Your situation is probably not extreme yet, as sometimes your CEL goes off. My '97 would only throw these codes when first started during the winter months, but it doesn't get very cold in GA during the winter. Living in Canada will be a different story. You need to get it fixed soon.

 

[CynthiaK]

Thank-you to everyone for your replies! I will have to get the o-rings replaced.

 

[96eb96]

Hi,
I keep getting these codes. I have changed out the IAC, PCV valve and hose, fuel filter, checked for vacuum leaks and did not find any. I have used Chevron Techron to help clean the injectors. I have read it could be intake manifold gasket.
The strange thing is that I clear the codes and then can drive about 4 to 5 days before the engine light comes back on. If it was a vacuum leak, would it not show up as soon as I drive it after clearing the codes?
I am getting very bad fuel mileage.

Any suggestions?

Thank-you!

Buy a can of MAF cleaner and clean the MAF sensor. There are many tutorials. It causes the exact same code as a vacuum leak. Usually both banks indicate this problem.
Do not replace gaskets until you confirm the MAF is clean and working. If the maf was never cleaned...now is the time!

There are ways to diagnose this correctly but I suggest cleaning as a first step. Good Luck

 

[fast_dave]

@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.

 

[CynthiaK]

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.