I've had some trouble with my '99 Ranger 4x4 with 5-spd manual and 4.0L V6.  First, it would not want to start.  Changing gas seemed to help, from Diamond Shamrock to Chevron.  This came and went.  I've experienced some rough idling from time to time, but never predictable or constant.  It is slow to return to idle, also, though not all the time, often hanging at about 1,200 rpm before finally dropping down to 800 or so.  Now I get a "Check Engine" light.  So far this has happened three times, and it won't go away until I have the dealer check the code and reset it.  All three times it's occurred, I've been driving at a steady speed of about 45-50mph.  The diagnostic every time has been a "lean code" (I haven't seen it, and am unfamiliar with Fords OBD codes.)

I recently replaced the oxygen sensors, and while this seemed to improve the way the truck ran (start-up, throttle response), it didn't prevent the third incident of "Check Engine" light.

It's in the shop now, and the mechanic says he's checked everything and he thinks it's the fuel pump.  My cost to replace the pump is over $400.

So, hive mind, any thoughts?

I would yank the fuel injectors and clean them. Maybe check the Fuel Pressure Regulator. Clean the MAF sensor, air filter, IAT sensor, etc. Which set of O2 sensors did you change?

If that model has a TPS, get that checked out as well. That can really screw up the works.

Did he get that conclusion from the fuel pressure?

Is it throttle body fuel injected? (1 Injector spraying fuel into the carb body) Is injector clogged? Or do you have a bunch of water in your tank?

Hope you find out without spending $400.

catalytic converter maybe?  Im just guessing because I had a ford explorer which ran fine, but the check engine light stayed on until the catalytic converter was replaced (emissions)

Fuel pump? Maybe. I'd like to know how the mechanic determined this, though. What's the pressure on the rails? Have the injectors been tested? What's the measured flow rate?

For $400 he should be dropping the gas tank and replacing the in tank pump. There are two fuel pumps on the 4.0 ranger. The one in the tank is the volume pump, the pressure pump is located on the drivers side frame rail near the bell housing. If he only "thinks" it is the fuel pump is it because he doesn't know? $400 is a lot to pay for "I think" sometimes it is good to bite the bullit and go to the dealer, they have testing proceedures in their service manual.
Has anyone changed the fuel filters (two) if a filter is partialy clogged this could cause a lean mixture because not enough fuel is getting to the injectors.
Do you have a buddy that is good with tools? Dropping the tank is not that hard and the pump is about $80.

It's sequential port injection.  My suspicion is a bad injector, but it passes a power-balance test.  I don't think the dealership (where my daughter works, so I get a discount on parts & labor) is equipped to flow-test the injectors.

The discount isn't that helpful if I spend $400 that doesn't fix the problem, though.  The filter has been changed.

I'm sure that your mechanic has checked the "short term" and "long term fuel trim" and found them both to be trending toward RICH?

Checking fuel pressure at the rail under acceleration is a must.

I vote start small, and work your way up.  Fuel filter is where I would start.  Check the injectors, pull the plugs and look at em?  Do they look like they've been running lean?  Check engine light is emissions related 99% of the time.  Check your cats.  How many miles on the truck?

The truck has about 67,000 miles.

Quoted: It's in the shop now, and the mechanic says he's checked everything and he thinks it's the fuel pump.  My cost to replace the pump is over $400. So, hive mind, any thoughts?

How can I put this as nicely as possible .......

If the shop you're using said they " Think " it's the fuel pump .
Well then , my best advice to you is to find another shop .

Basically , if you are a professional tech and have the correct tools
then there is no guess on this one . This is a common code on V-6 fords
of that vintage with a few easy to test causes . If you want the list
here it is :

Vacuum leak , usually the o-ring gaskets in the intake manifold .

Mass airflow sensor , possibly defective , but most likely just dirty .

Defective O2 sensor

Exhaust leak upstream of the O2 sensor , usually the EGR supply
tube .

And last but not least a dirty fuel filter or failing fuel pump , but
I strongly doubt it because of the mileage and the symptoms .

Quoted: Quoted: It's in the shop now, and the mechanic says he's checked everything and he thinks it's the fuel pump.  My cost to replace the pump is over $400. So, hive mind, any thoughts? How can I put this as nicely as possible ....... If the shop you're using said they " Think " it's the fuel pump . Well then , my best advice to you is to find another shop . Basically , if you are a professional tech and have the correct tools then there is no guess on this one . This is a common code on V-6 fords of that vintage with a few easy to test causes . If you want the list here it is : Vacuum leak , usually the o-ring gaskets in the intake manifold . Mass airflow sensor , possibly defective , but most likely just dirty . Defective O2 sensor Exhaust leak upstream of the O2 sensor , usually the EGR supply tube . And last but not least a dirty fuel filter or failing fuel pump , but I strongly doubt it because of the mileage and the symptoms .

Ok I guess I was bouncing around all of these, your answer was much better than mine as I was trying to remember all of the things that I check on my two. One is stock the other highly modified.
I could never see paying $400 for a fuel pump job. But most people have not their Ranger in their garage in multiple pieces, body here, bed there, engine and tranny over there.

If it has lean code(s)? I would check for a vacum leak first, especially if you get lean codes for both banks.

It's definitely not good business practice to change parts unless they were found to be the cause of the problem. Unfortunately we see this more and more today from what is known in the industry as 'parts changers,' and without hesitation I would have to include many dealerships in that category.

Hopefully your mechanic already went through the proper diagnostic process -thoroughly- before coming to that conclusion.



Good Luck, let us know how it turns outs.

Same thing happened to my Dad's Mazda (same truck).  Was idling oddly, sometimes would fail to start.  I suggested he replace the fuel pump relay to isolate the problems before dropping the tank and testing the FP.  The relay fixed it.  

Most likley intake manifold gaskets(between upper and lower). This may be more evident when engine is cold.
The mass airflow sensor could be throwing off the barometric pressure reading in the PCM. The "tech" at the dealership should be able to easily check this as well as the gaskets. I do not know your altitude but around here(1000 ft) 155Hz is normal on the Baro Pid.
Also, check the PCV line at the front of the manifold were it makes a 90 degree turn into the manifold. These are bad to collapse and leak there. It is hard to see the first time you look. This on SOHC engines.
If I think of anything else I willl try to post it.
Cartech, Ford Senior Master Tech

My 97 ranger with 4.0L had idling issues, and all it was the IAC, the idle air control valve, if you havent replaced that do it, it solved alot of problems i was having. Boone.

Quoted: Most likley intake manifold gaskets(between upper and lower).

+1.

The 4.0L has a reputation for leaking intake gaskets.

Quoted: Quoted: It's in the shop now, and the mechanic says he's checked everything and he thinks it's the fuel pump.  My cost to replace the pump is over $400. So, hive mind, any thoughts? How can I put this as nicely as possible ....... If the shop you're using said they " Think " it's the fuel pump . Well then , my best advice to you is to find another shop . Basically , if you are a professional tech and have the correct tools then there is no guess on this one . This is a common code on V-6 fords of that vintage with a few easy to test causes . If you want the list here it is : Vacuum leak , usually the o-ring gaskets in the intake manifold . Mass airflow sensor , possibly defective , but most likely just dirty . Defective O2 sensor Exhaust leak upstream of the O2 sensor , usually the EGR supply tube . And last but not least a dirty fuel filter or failing fuel pump , but I strongly doubt it because of the mileage and the symptoms .

What he said.

What Dealership? I know you said your daughter works there, but when the "mechanic" uses words like "I think it is this". He better be damn sure what it is.

Take the truck to Autozone and they will read the codes for free and go from there.

Next time the light comes on, do not take it to the dealer. they keep as much info about the repair to them selves as they can. If the light is on, you can go to your local Autozone, they have a OBDII scanner which will tell you the code number and a small definition of the issue. If its an inconclusive code they at Autozone can call ACTRON, the maker of the scanner and see if there are any Ford service bullitins on the vehicle, known issues, and the most likely cause of the issue.  If the person at autozone says they dont have a number for ACTRON< tell them to pick up an ACTRON package, its on the package, i use the number every day. Im a store manager at a local one there are several different codes for a lean condition. Did they tell you if bank 1 and bank 2 both set a lean code? If they did id first look for a vacuum leak, next suspect the mass air flow sensor or dirty air filter. If none of those check out, have your fuel presure checked.  did your dealer say if it set any other codes such as a specific cylinder misfire? I worked on a 98 ranger, 4.0 and it threw out lean bank 2 as well as cylinder 3 misfire. ended up being a faulty injector.

+1 on Viper5194.  We need the code to correctly diagnose the SYSTEM that is causing the fault.  You can do the shotgun approach and throw parts at it but that gets expensive.
And very important info from Mr. Bluegrass at F150online.com
:
The lean meaning refers to the computer tables only and not to the engine condition directly.
The code comes from where the computer tables are shifted to. In this case the "tables" are lean set, not the engine.
The other side of this is that the engine is running on the 'rich side' causing the "tables" to shift lean trying to correct for a 'rich' engine condition.
Mis- interpetation causes you to look for the wrong hardware faults.
Look at this from still another point.
If the fuel is too rich, the O2 senor will try to set the injection leaner via the computer tables in an effort to correct the rich condition. As the tables go too far out of range, a code is set and a CEL light is turned on telling you about a lean table condition and not lean engine itself.
The code and the report stays within the computer realm and not the outside hardware it knows little about. The program is used on many different engines with different hardware so it can't be linked to anything outside in a direct manner.
Look for a faulty fuel regulator, leaking injectors, bad MAF, bad hoses etc.

Fritz

The collective knowledge present on this site will never cease to amaze me. You guys are something else.

Thanks, guys.  I'm going to hold off on replacing the fuel pump and try to check some of this stuff myself.  The dealership is the closer of the two Ford dealerships in town (both owned by the same guy), and I'm not all that impressed with their "factory trained" personnel - even with employee discount.

I don't believe it's a fuel pump.  Vacuum leak I could believe.

Oh, and it's not the OHC V-6 (I wish).  They didn't put that in the '99 Rangers, only the Explorers IIRC.

UPDATE:

Codes recovered are 171 and 174, left and right bank lean.

MAF sensor reading, 148Hz; a little low (we're at about 2k' altitude) but not enough to be concerned about.

No vacuum leaks, no exhaust leaks.

Fuel pressure seems OK, but fuel volume is a bit low, apparently.  Fuel filter was recently changed (after the first "Check Engine" light incident..  Didn't help.  

He can't get it to duplicate my problem (naturally.)

I'm going to get it back WITHOUT a new fuel pump. Next time it does it, I'll take it straight in for a diagnostic - again - but at no charge.

Appreciate the help.

Quoted: Thanks, guys.  I'm going to hold off on replacing the fuel pump and try to check some of this stuff myself.  The dealership is the closer of the two Ford dealerships in town (both owned by the same guy), and I'm not all that impressed with their "factory trained" personnel - even with employee discount. I don't believe it's a fuel pump.  Vacuum leak I could believe. Oh, and it's not the OHC V-6 (I wish).  They didn't put that in the '99 Rangers, only the Explorers IIRC.

Yes the 4.0 has a rep for intake manifold leaks. Most of the time this leak manifests it's self in the use of oil between changes (3000 miles) of 1 to 1 1/2 qts and a small puddle can be seen at the rear of the passenger side head. At least this is what I have learned in my experiance.
Now do you want me to tell you about the first engine in this line the 2800cc v-6 that was made in germany and put in the capri and a very few 1978 pintos? Oh my god what a screamer, no gas milage but could smoke tires like a 350 nova ss. A least the one I had that was a ford test vehicle that was not supposed to leave the factory. Sold it back to ford for every thing I paid for it after three years. Damn I wish I had that engine for the old 89 ranger

I would definately pull and clean the MAF sensor-that is a common problem area w/the 4.0.

Nick

171 and 174 are both EXTREMELY common problems in Rangers and Windstars.  Still never did answer my question about the air filter. Is it new , and if not check it. I get on average 2 Ford windstars a week into my local store with 171 and 174 both set. Ive gotten into the habbit of pulling the customers air filter to find it extremely dirty, sometimes so dirty that the engine has sucked holes into the filter to ventilate itself. check first for vacuum leaks, next change the air filter and clean the MAF....   In most cases, well nearly all cases at least with the Windstar when I see these two codes set together it usualy ends up being a neglected air filter causeing the engine to run rich, in turn causeing the ECM to try to over compensate and run the engine lean. the computer then detects its trying to run lean too long and set your light off.

Just two days ago I had two windstars the same day with the same codes. i replaced the air filters for the customers and erased the OBDII codes and one of the customers came back today to let me know the light was still off.........

Supposedly the air filter was changed with the last oil change, and I'd have expected the Ford tech to check that, but I'll look at it tomorrow.