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'99 Windstar Running Lean

08-09-2004, 05:41 AM
The check engine light came on and the code is saying both bank one and bank two are running lean. What would be the things to check for this condition? I was told by a co-worker to change the rear oxygen sensor but that has not helped. IT was however a Bosch aftermarket sensor which I heard after buying are unreliable.
Thanks for any suggestions.

08-09-2004, 06:02 AM
What year is the Windstar?

A lean condition can have a lot of different causes. Often a Vacuum leak which is addressed in a TSB for particular modle years can be the problem.

08-09-2004, 06:04 AM
Sorry I see that it is a 99. There is a TSB for these codes. It is a lot of work but if you are comfortable with a wrench then it can be done in about 4 hours and $100 for parts

08-09-2004, 06:05 AM
me again...................what exactly were the code numbers?

08-09-2004, 06:30 AM
I'll have to borrow the reader again as I lost the paper the code was written on. All I remember is it was lean on both banks. What exactly is TSB? I'm not to good with abbreviations.

08-09-2004, 07:28 AM
I had the same problem with my 96. I changed the O2 sensors, a day later the Check Engine Light came on again. Turned out to be carbon buildup on the EGR Valve.You can either clean it or just buy a new one. I think you can buy a leaner for removing carbon.Since cleaning the EGR, the light has never come on again, and that was over two years ago.

08-09-2004, 07:44 AM
A TSB is a Technical Service Bulletin that is issued by Ford to their mechanics. They cover various items including fixes to known problems (read "design flaws").

There is a specific TSB for lean codes on the 99 (up to 2001 I think). It requires that the Upper Intake manifold be removed and the EGR ports cleaned. It also requires the bolts to be replaced with a new type. The TSB also mentions replacing a fuel line vacuum hose and one of the valve covers.

I think you need to know your codes for sure. I would not do the work unless you know it is required.

08-09-2004, 07:55 AM
Also take a look at this link, it shows the valve cover that needs to be replaced (if yours is black) and the fuel pressure regulator vacuum line. Check that line first thing to see if it has loosened up and disconnected from the intake manifold. If it has buy a new one at the dealer.

08-09-2004, 09:08 AM
If the codes are P0171/0174 on a 99, it is most likely a contaminated intake manifold as a result of the PCV line from the left hand valve cover. It will require removal of the upper intake, cleaning of the intake, IRMC runners etc and replacement of the gaskets and intake manifold bolt isolaters as well as the left hand valve cover to prevent future fouling. Total is about 100-150 in parts but would cost around 700-900 at the dealer to have it repaired.

08-09-2004, 09:58 AM
A lean condition is caused by:
1) A vacuum leak
2) Malfunctioning MAF sensor (dirty or bad)
3) Bad oxygen sensors (dirty or worn out)

The very first thing to do is to check for any vacuum leaks. Listen under the hood for any hissing with the engine at idle. Then spray around the inlet tubing and maniflold where it meets the heads with carb cleaner. If the RPM changes abruptly, you have a leak.

I didn't see where the mileage is mentioned, but oxygen sensors typically are good for 100,000-150,000 miles. Some more, some less. I would NOT just go and replace them, since it is quite a coincidence that they would both go bad at exactly the same time. Very unlikley.

I would be suspicious of the MAF being dirty. With the proper "tamperproof #20 Trox" bit, (or a small vice-grip) you can remove the sensor element from the MAF sensor and inspect/clean it. This will very often solve lean conditions where no vacuum leaks exist. No, a dealership will NOT do this.

There is an excellant tech article with photos of the sensor at

08-09-2004, 10:51 AM
Here's the part#s for the TSB if you confirm the error codes and the vacuum leak. The vacuum line is the fuel pressure regulator vacuum line I mentioned and the LH valve cover needs to be replaced if it is the old design (pull the PCV and grommet, hole at five-o-clock position indicates old valve cover design, new one should be silver).

XF2Z-9H486-AA Port Seal-Package of 6(1 Pkg Req. Per Veh)
3F2Z-9S479-AA Isolator Bolt Assy. - Package of 8 (1 Pkg Req. Per Veh)
XF2Z-9E498-DD Vacuum Line
3F2Z-6582-BA Valve Cover - LH

08-09-2004, 05:26 PM
Took my 99 and got the code read today. System to lean on both bank 1 and 2. They said it was a 171 and 174. Same thing as what you were told. O2 sensors. Which I find hard to believe. I'm gonna check out the EGR this weekend and see if its clogged, or has carbon build up. I you find the problem on yours please let me know as mine might be the same.

Also, does your van run rough when cold? have a erratic idle? I'm gonna assume so if you are lean but let me know the symptoms yours has.

08-09-2004, 05:47 PM
I think this will answer all our questions KPVSR.

08-10-2004, 06:25 AM
Thanks all! If I remember correctly 171 & 174 were my codes. They are the ones mentioned in the other post simaronde03 directed me to. It sounds like it is a poor design issue with Ford. I believe my extended warranty should cover this, hopefully. Otherwise I may have to bring it to their attention that I am aware of poor design and should not be responsible for the whole cost. I have a little investigating to do on the van to make sure that is the problem but so far it sounds like what is described in the TSB is the problem.
Thanks again for all your replies,

08-11-2004, 11:27 AM
I borrowed the code reader again and verified I am getting the 171 & 174 codes.
Before going to the dealer ship with this I would like to have as much info as possible. Does anyone have a copy of the TSB for this problem they could e-mail to me? lewisnc100, I noticed in another topic you quoted from the TSB about the valve cover issue. Would you have a copy saved somewhere?
Any help greatly appreciated.

08-11-2004, 05:51 PM
I would be happy to email a copy to you. I don't have an address for you though.

08-11-2004, 06:52 PM
Can you email me one?

08-11-2004, 07:16 PM
Thanks, thanks and thanks again,

08-12-2004, 04:07 PM
One quick test for this vacuum leak is to let the engine idle rough, then press down on the black plastic plenum which will make a seal and smooth out the idle.

Ford is pretty adamant against using Carb Cleaner to test for this type of vacuum leak because of IMRC bearing failure.

09-25-2004, 10:58 PM
I'm a newbie, so not sure if this should be a new thread or not...


I have a 2001 Ford Lighning with the 'Service Engine' light on. Not sure of the code # (friend is mechanic, not me), but he told me that it was running lean on Bank A & B. It sounds just like what everyone's been talking about regarding the Windstar. We did an inspection for a vacuum leak and didn't detect anything. The history didn't show any misfires, so it looks that it isn't vacuum leak related. Is this TSB for all Ford's between '99 and '01 or is it just windstar's?

If you could forward me the TSB for this, I would be GREATLY appreciative!!!

I love my lightning, but I know this is killing the performance.

Great forum, by the way.

Many thanks!

09-26-2004, 06:08 AM
What year and what engine is it?

ask your friend for the code number

09-26-2004, 11:32 AM
A dirty MAF will cause lean conditions.

How? The EEC uses the MAF signal to look up the required injector pulse width. Now, you say that the O2 sensors will correct. Well you are right, but only within limits. If the MAF is reading lower flow than the engine is ingesting, the O2s will feedback lean, and the EEC will attempt to correct but it has limits of about 20-25% of "expected". So, if the MAF is very dirty (or failed), the needed correction based on O2s will be outside the capeabilities of the EEC.

Do you have a K&N air filter? I bet you do.

09-26-2004, 08:25 PM
I have a 96 3.8 and I did have at one time code P0171/0174 and had the lower intake gasket replaced and the MAS senor replaced.I had code P1151 come on when I was on the highway and turned off after a few start ups.P1151 if I remembered was a lean condition.I do have a K and N air filter,I figured the van is running great and I was getting 25 MPG on the highway.I was not going to start replacing sensors. :smile:

09-27-2004, 01:18 AM
DRW1000, Could you please email a copy of the TSB to me at

I just found this board after having similiar problems with my 99 Windstar.


09-27-2004, 07:41 PM

By the way simaronde03 did you ever get a copy????

I don't remember if I sent it your way

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