Codes PO171 and PO174?

ARTENDER

MEMBER
2003 FORD WINDSTAR
3.8L
6 CYL
AUTOMATIC
167 MILES

I was wondering if my car does not have a visible vacuum leak, if there is a way to know based on symptoms where to go next with a PO171 and PO174 code? I know a problem with the intake manifold gasket is common, but it seems so is a mass flow air sensor that may need cleaning. Or perhaps an O2 sensor issue. The car starts up fine, seems to accelerate okay, but when stopped at a light it kind of bucks back and forth a little and one time it stalled.

I appreciate any assistance you can provide.

5 Replies

JACOBANDNICKOLAS

MECHANIC
109,885 POSTS

Hi,

It could be any of the things you mentioned. Additionally, a partially plugged fuel filter or weak fuel pump can cause it.

If you were to bring the vehicle to me, here is what I would be checking. First, I would confirm there isn't a vacuum issue related to the PCV valve hose. Additionally, I would test for vacuum leaks. Here is a link that explains how it's done.

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

If I determine there are no leaks, I would next check fuel pressure. You will need a fuel pressure gauge to do this, but most parts stores will lend one to you. Here is a link that explains in general how it's done:

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

At this point, testing of fuel flow through the injectors, engine compression, a faulty oxygen sensor, and the list goes on can cause it.

Let's get through checking the PCV, checking for vacuum leaks, and fuel pressure. I have a feeling the problem is with one of these things.

If you look at pic 1 below, it shows the PCV valve. Check the hose and the grommet that the PCV presses into for leaks. That is on the driver's side valve cover. Pic 2 provides the manufacturer's fuel pressure specifications. Make sure to pay attention to how quickly the pressure drops when the key is turned off.

Let me know if this helps or if you have other questions.

Take care,

Joe

See pics below.

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Thursday, August 25th, 2022 AT 7:32 PM

ARTENDER

MEMBER
3 POSTS

Hi Joe,

I cannot even begin to explain how appreciative I am that you have taken time out of your day to give me such a thorough explanation. This is truly so kind of you. I will definitely go through the steps you mentioned. Would you suggest at least cleaning the mass flow air sensor just in case it is part of the problem? I bought a specific cleaner for it, but it doesn't look like the easiest item to access.

Also, a friend of mine was not able to access the 3 spark plugs in the back but said the ones in the front were in bad shape. These have been replaced and I was wondering if this can be part of the problem. If so, I guess I should hire someone to check the inaccessible ones too. Again, I am so thankful for your help and will try to pay it forward and help others in the areas I know.

Thank you again,

Art

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Thursday, August 25th, 2022 AT 8:33 PM

JACOBANDNICKOLAS

MECHANIC
109,885 POSTS

Art,

You are very welcome. As far as the spark plugs are concerned, they should be replaced, but they wouldn't cause a lean mixture.

As far as cleaning the MAF, here is a link that explains how to do it:

https://www.2carpros.com/articles/mass-air-flow-service

If you look below, I attached the directions for replacing the MAF. I'm not saying to replace it, but the directions will help you with accessing it.

Let me know how things turn out.

Take care,

Joe

See pics below.

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Thursday, August 25th, 2022 AT 10:02 PM

ARTENDER

MEMBER
3 POSTS

Thanks so much again Joe! I guess now I just cross my fingers and hope it is not a weak fuel pump. To replace that might cost me more than the price of the car! I am so thankful to you. Art

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Friday, August 26th, 2022 AT 7:01 AM

JACOBANDNICKOLAS

MECHANIC
109,885 POSTS

No problem whatsoever. As far as the pump is concerned, make sure before spending the money. I have directions if you want to do it yourself. Let me know and I'll help you through it.

Take care and let me know what you find.

Joe