I have a 2003 S-Type 4.2 with a problem that has been annoying me for awhile. I am getting a Restricted Performance message and it is throwing a P0171 (lean) code. I checked the easiest thing (cleaned then replaced the MAF) and looked for a vacuum leak. I can't find anything, but have not done a smoke test yet.

But the engine only hesitates when I hit 2900 rpm. Does this fact provide any clues to what the problem may be? Any thoughts on what I should do? Am I on the right track? Throttle body? Any problems with IMF rings on a 4.2?

Thanks for everyone on this forum. It is a fantastic community!

 

Did you ever get answer to this problem? Have exact same issue, but restricted performance message clears in a few minutes and vehicle runs fine. Thx.

 

Did you check fuel trims?

 

I did a little test drive and recorded them on my Torque app on phone, but not sure how to interpret them. Just wading into this.

Idle: LTFT1 19.5 LTFT 11.7

5000 RPM LTFT1 3.9 LTFT2 4.7

STFT genrally +- 5

Thanks

 

my profile is still not fully active, i thought i put vehicle info in. 2004 s-type 4.2 with 98,000 mi Thx

 

Based on the values above, it appears the PCM is compensating for a possible vacuum leak. If the leak is small, it may be difficult to find without performing a smoke test.

The condition you describe can also be caused by a faulty coil unit that could be fouled by oil in the spark plug well.

 

Thanks, man! I just love this vehicle and actually am enjoying learning about it so I can take care of it myself as much as possible. This forum is great and a godsend for those of us new to vehicle

 

That's a fair size air leak I reckon - go hunting.

 

Thanks! It's only throwing P0171 bank 1 lean code. (It did throw P0105 MAP code a week ago, but that hasn't come back after a lot of driving. It has never thrown a P0174 bank 2). I'm just curious if P0171 is thrown when LTFT1 goes over 20% (I heard 20% was trigger point for code). I haven't seen myself yet 20% yet reading trim, but it's very close to 20% at low RPMs. So I bet it goes over 20% occasionally. But it never throws P0174 code for bank 2, and I've never seen bank 2 anywhere near 20% LTFT. Does that narrow down where to look for leak, etc? Also is the 19.5% vs 11.7% difference between banks LTFT at idle significant, i.e. is problem isolated to bank 1, or common to both? I watched great YouTube 2 part hour video on fuel trim by so I have a little knowledge.
One mechanic said to replace MAF. But it seems like MAF would affect both banks equally? The vacuum leak diagnosis makes sense to me. Air leaking in is much more significant proportionally at idle than when throttle is wide open. So LTFT trim drops Dramatically at 5000 RPM. Could it be leak close to bank 1, that also affects bank 2 just to a lesser degree. Questions. Questions. Questions .....

Idle: LTFT1 19.5. LTFT2 11.7

5000 RPM LTFT1 3.9. LTFT2 4.7

STFT genrally +- 5

 

<iframe width="560" height="315" src="https://www.youtube.com/embed/fwNF8wzWYUc" frameborder="0" allowfullscreen></iframe>

 

This was NOT a vacuum leak. It was exhaust leak at manifold flange pulling air in right before wide band O2 sensor on Bank 1 cat. Should have figured this out sooner!

 

That is VERY odd. I can't see why it affected BOTH banks. Any explanation?

 

JagV8, my only explanation is that perhaps I had two (or more!) problems. I did a bunch of vacuum leak troubleshooting at your kind suggestion and some routine maintenance: dip stick O-ring, re-seating all vacuum lines, a couple cans of BK44, fuel filter, plugs, cleaned MAF, and a hard reset. After all that, fuel trims improved gradually, but Bank1 remained substantially lean (+10-14 at idle, correcting at speed/load), and Bank2 was pretty close to normal. (Data and video above was before this improvement). When I recently fixed exhaust leak on Bank1 at flange right before cat and wideband O2 sensor, Bank1 LTFT went to 0+-immediately, matching Bank2. So in the end, I think Bank1 exhaust leak was affecting only Bank1 fuel trims. I still have a very intermittent P0105 MAP code I am trying to figure out. And P1000 still hasn't cleared out yet to P1111. So I'm not out of the woods yet! I'm still learning... but having a blast and really appreciate the help I have received here. I am stumped by one thing: Does anyone sell those 2 plastic covered foam pads (Oil absorbing? Sound deadening?) that are attached to 2004 s-type undertray? Or can I substitute something? A diaper...(kidding...kind of). Thank you all!



This makes it ALL worthwhile!

 

It was exactly as Schrodinger explained in thus video by the time I got to exhaust leak.
https://youtu.be/c-uetoVkiQk

 

A continuing P1000 means one or more monitors hasn't run OK. Most OBD tools can show which one(s).

Look for any other pending codes as clues to what may be wrong. The code you get may be the hint, though.

 

For your oil/sound deadening option I replaced mine when I repaired the plastic undertray with this moisture releasing foam pad from McMaster-Carr:

McMaster-Carr

I used the adhesive backed foam but still applied a silicone adhesive. Seems to work well.

Mike