o2 sensor or fuel pump that is the question

[mharris1980]

Hi. I have a 97 expedition eddie bauer 5.4 4wd and I'm trying to figure out what's wrong with it. A couple months ago my check engine light came on and I had a local shop take a look at it and was told I had a bad o2 sensor. They told me not to worry and it just means getting more air than gas but shouldn't be a problem. Here's the problem. So for the last few weeks the truck has been idling and shutting off only when I'm at a stop or in park. What I have to do to prevent this is rev it up with my foot on the brake at a stop until I can go and it'll hesitate a little then take off. If I don't rev it up it dies cuts right back on though which I thought was wierd. A while ago I had a similar instance take place with a Ford Taurus and it was resolved by changing the fuel pump. The only difference was when that car died it stayed dead for hours until the pump cooled and then it would run again for a little. So I took the car back to the same shop and was told it indeed was my fuel pump causing this issue. However after running this problem by many other mechanics an actual Ford mechanic and a few friends I kept getting the o2 sensor. Also when I bought the truck it had a bad manifold which has been replaced and still sounds like gunfire when I accelerate. The same shop that "fixed" the manifold is providing me this diagnosis. I've been on this forum a few times and you guys seem to know what your talking about so I was hoping you'd be willing to help. Any would be appreciated. Thanks in advance.

 

[Bedrck47]

I assume that you are getting a check engine light. At least you should be If so get the codes read and post them here

Just saying you have a bad O2 sensor doesn't give enough information as you have 4 O2 sensors on the expy Having the code will narrow it down to which sensor is bad or its possible that you have other codes that will show up.

 

[mharris1980]

No other codes whatsoever just a bad o2 sensor. I know there's 2 located on the exhaust passenger side front and rear I don't know where the other 2 are. That's why I mentioned I had to have the exhaust manifold fixed when I first got the truck and it still sounds like a Harley when I accelerate. Nevertheless, does the issue I'm having sound more like an o2 sensor or a fuel pump failing?

 

[Bedrck47]

as stated above the expy has 4 O2 sensors 2 0n the passenger side exhaust and 2 on the drivers side exhaust. Normally a bad O2 sensor will cause a check engine light and throw a code. As far as you thinking you may have a fuel pump problem I would check you fuel pressure at the fuel rail. Also if you haven't changed the fuel filter I would suggest you change it.

You stated that a couple of months ago you had a check engine light come on and was told that it was a bad O2 sensor Again I'll ask what was the code that came up at that time.

How many miles on the expy?

 

[mharris1980]

Not sure the exact code itself but was told it meant bad o2 sensor by the shops mechanic. My question is if any of the 4 o2 sensors can cause my vehicle to respond like its been? Idling, stalling out, hesitating etc. Or does that sound more like a fuel pump? See I can easily go back to the shop and have them pin point which sensor(s) it is and have them replace it/them but does that resolve my problem if its the pump?

 

[mharris1980]

Oh yeah the Expo has about 170000 on the odo. Sorry

 

[Bedrck47]

You need to find out what the fuel pressure is at the fuel rail. However my opinion is your problem is not with the fuel pump for if it was you would notice it anytime the expy was running not just at idle.

Take the expy and have the codes read or see if any codes are present.

 

[mharris1980]

Thanks Bedrck. I kinda figured the same thing but wanted to ask around 1st. I do believe the shop I went to tested my fuel pressure and that's when they told me it was in fact the fuel pump. However, again as far as what I know of fuel pumps when your vehicle stalls from it it normally doesn't cut right back on since the pump cuts off. Once I found out an o2 sensor (which is the code my check engine light is showing) can cause the exact same thing that's when I got curious. I know it could be other things like the fuel filter or multiple o2 sensors or even a relay(s) but I wanted to know if anyone has encountered the same issue if so what was the cause or if anyone might have any ideas. So thanks again bro.

 

[GAINMOB]

welcome to the site