Chased this cat all around, still at a loss. PO171, &174, & R P are gone with fuel filter, 4, O2 sensors, O'rings on P V C valve, & hose, air filter, as well as M A F sensor. Car runs great, passes E check's tail pipe test, but PO 101 keeps coming back

 

So this code is telling you that the MAF sensor readings are out of the range of expected values.

First step is to look at freeze frame data for when the code was set. Then look at MAF live data and see what values the PCM is seeing in real time. At idle, hot, in gear, should see 5.0 g/s. There's a spec for 2500rpm as well, I believe, will have to dig for it.

The PCM uses other engine sensors (RPM, MAP, TPS) to double check MAF readings and see if they make sense. It's also possible you simply have an air leak after the MAF letting unmetered air into the engine.

 

Believe there may be a slight leak in intake manifold gasket, as everything looks to be in great shape. The wife says she thinks she can hear a slight hiss that stops when i push down on the left rear portion of the intake manifold, after the car is well warmed up. Would like to make sure this is what is needed, before i tear it apart to find it was not the issue

 

Hi Wingrider,

The Diagnostic Trouble Code Summaries Guide gives some of the more common possible causes of each DTC. You can download the manual here:

X350 DTC Summaries Guide

Here's the page with the details for P0101:



Cheers,

Don

 

If there may be a leak, watch fuel trims to check and be sure.

Even a tiny leak will be a problem and unlikely to make a hiss you can hear.

 

Thanks for the responses guys. Have been looking for this slight leak for some time now, (only my guess) as do i not understand what the trim numbers really mean. Going to change the intake manifold gaskets, that's why i'm trying to get all necessary tools, parts, and know how to go about it b4 one jump's in. Hope this handles the last code as the car runs great, with good fuel milage for such a big luxury car. I guess if this does not fix my code issue , i'll have to buy a smoker to find it. Hate to think of buying yet another tool used only occasionally then gathering dust for years, till needed, if ever again.

 

[QUOTE=Wingrider;1681702]Thanks for the responses guys. Have been looking for this slight leak for some time now, (only my guess) as do i not understand what the trim numbers really mean.

If the fuel trims both short term and long term are at 0 the world is perfect. Since that's rarely the case the car's computers do there best to manage fuel flow and air fuel mixture to maintain as near a perfect 14.7 to 1 air to fuel ratio as possible.

So if you have an air leak for example AFTER the MAF sensor the short term fuel trim (STFT) would show a positive number on a graph of between 0 and 25+ which indicates that it is "trimming" (adjusting the fuel flow) to be richer to compensate for the air that is entering that was NOT measured by the MAF but is being detected by the O2 sensors in the exhaust. (The numbers indicate the percent of increase or decrease and not an absolute number)

The long term fuel trims (LTFT) on the other hand 'learn' from what the computer is doing to adapt over time to the increased (or decreased) fuel being metered into the system and will continue to keep that 'extra" fuel being injected until such time as the 'lean condition' persists while the STFT's will now act as if there's a new normal and slowly go back to zero. (Remember that the STFT's get there info from the downstream O2 sensors and not the MAF).

When the 'lean' condition is repaired the STFT will initially record what it sees as 'rich' condition (0 to -25+ because the LTFT's are still dumping extra fuel in) and like a good dog it will reduce the fuel flow to compensate and over time the LTFT will now 'learn' the new normal and adjust fuel flow accordingly and the STFT will soon drift back up the graph to 0 and the world will be perfect again.

Clear as mud now.....right<G>

 

A very clear explaination but I will never remember it!

Thanks

 

Yep, clear as mud!!! Will keep on trying, & eventually figure it out. Appreciate your effort to explain how it works.

 

FAQ

https://www.jaguarforums.com/forum/g...ed-quiz-49317/

 

O K guys, used my reader today, got some info, but clear as mud still. short term fuel trim, bank # 1=2.3 to 5.5, long 10.9

bank # 2= short 2.3 pretty steady,long9.4, fuel rail prime 378 kpa.

intake manifold 36.0,

mass air flow rate 4.7

Vac leak at intake manifold? W T F

 

Maybe try tightening the intake manifold bolts a bit before tearing it all open?

Trims on both banks are a bit high, especially Bank 1. Bank 1 is passenger side I believe. Might be the intake gasket on that side.

Also check the air intake tube from MAF to throttle for damage or loose clamps.

 

Tried all that several months ago, everything looks intact, the car runs great with good gas mileage.Well looks like the set of intake manifold gaskets hanging on the wall, will get used after all. Want to try smoke testing it first, before taking it apart, to see where to look, and hope if it's leaking at the manifold, it's only the gasket, & not a crack in the manifold itself.

 

After sleeping on it if my understanding is correct, the numbers on # 1 bank S T are my biggest problem. They should be @ 0, & steady, instead of jumping around, indicating an air leak, what about the L T T, is it about right? Trying to get my head around what these numbers mean, thanks for the assistance!

 

LTFTs are too high.

Follow advice in (the many many) other threads.

 

They adjust to match the S T fuel numbers, & they should be at 0, or a lot closer to 0??? What are L T numbers supposed to be?

 

Ideally they should be as close to zero as possible. Codes will be flagged when you get around +15. High positive numbers indicate lean (air leak). High negative numbers indicate rich (too much fuel).

They won't be absolutely steady. They'll fluctuate up and down where you're at idle or speed. But they should fluctuate within the specified range.

My trims are usually between 0 and +5.

 

So my short trims are fine, making my long trims go to 10, is air leaking past the M A F sensor? Is this the basis of my problem?

 

Could be any of the vacuum lines - see the other threads for how to find out etc.

 

Agreed, have tried to eliminate all the obvious possibility's, want to be sure b4 i start, if possible. Do not really want to replace the manifold gaskets, unless they are needed.