Normal STFT high LTFT

[efnfast]

At idle and driving my STFT seem about right - they range from +/- 5%. Every once in a while when stopped for a while it creeps up to +15%, but most times remain in +/- 5%.

At idle my LTFT is 25%. If I give it moderate throttle (quarter to half) and go 1 through 4, LTFT drops to around +2-3%. If I hold it around 3k rpm in 4th it remains around +2-3%. If I shift into 6th and cruise around they rise to around 20% (even though STFT is staying around +/- 5%).

Car drives and idles fine and no check engine lights or anything unusual. Original O2s with around 275k on them.

Does that seem like a vacuum leak? Or should I parts cannon O2s and a new MAF at it (O2 voltages look normal to me)? Or something else?

edit: the reason I'm logging O2s is because 1,000 miles ago while idling it threw a CEL that was 'lean bank 2'; I reset it and it never came back, so I imagine what happened is the LTFT was 25% and maybe my STFT popped up to 25% too very briefly

edit 2: my evap system has an issue - likely clogged charcoal cannister - because I can only put in like 0.1 gallon of gas at a time before the pump clicks off (so I have to fill stop fill stop fill stop fill stop, etc.), but I don't think that would cause this?

 

[Reaper14]

My lincoln town car just went through this issue from your second edit. Would not allow me to fill & when it did at a different pump it over filled without stopping. Removed the tank vent line & solenoid. Blew it out with compressed air & out came about 15 dead moths. Starting filling fine after that.

 

[hotcobra03]

That lower hose under intake.

 

[decipha]

fill it with the engine running might help

to diagnose any eec iv or eec v you need a moates quarterhorse. Use the fuel error over rpm and airmass to see if its your maf or injectors that are acting up.

your a little past 50k miles on them o2s. definitely time to change them.

 

[efnfast]

fill it with the engine running might help

to diagnose any eec iv or eec v you need a moates quarterhorse. Use the fuel error over rpm and airmass to see if its your maf or injectors that are acting up.

your a little past 50k miles on them o2s. definitely time to change them.

yeaaaa, I'm thinking I don't want to try to remove O2s that have been in there that long unless I absolutely have to

If the O2s were starting to get fouled wouldn't that throw off the ST as well?

 

[decipha]

Its not bad just get it all nice and hot first and it should come out easy.

yes fouled o2s will dump fuel in the fuel trims, in closed loop the o2s control fuel.

At 50k miles you can see o2s start to shift and begin reading skewed.

 

[efnfast]

Could partially clogged cats cause exhaust to back up at lower RPM to give a false lean, and then when you get on it the exhaust velocity pushes through the partial clog? (nb: i've got rear 02s turned off)

I've got a magnaflow catted x; for the last 100k on startup it makes a rattling noise and if I shake it when I remove it I hear something loose in at least one of the cats

 

[01yellercobra]

A cat that's falling apart can cause issues. I can't see it taking 100k miles to completely come apart. It might be best to pull the exhaust and see what's making the noise.

 

[efnfast]

A cat that's falling apart can cause issues. I can't see it taking 100k miles to completely come part. It might be best to pull the exhaust and see what's making the noise.

the rattling noise is from inside the cats - whenever I remove the x-pipe and shake it around I can hear stuff rattling inside the cats ..... but it's been doing that for 100k and hasn't gotten worse so I figured just a little bit broken, not fully broken/clogged up

but I am running more boost than stock (ported/pullied) so brokenish cat plus boost probably not the best combination

 

[01yellercobra]

At the very least you should pull the mid pipe and knock the rest of the pieces out. Clogged cats can cost you an engine. And depending on the mufflers it might clog those as well.

 

[efnfast]

I replaced my charcoal cannister so now i can fill my gas tank normally again.

Purchased a used 03/04 MAF sensor and 2 new O2s to install. If these parts don't fix the issue (normal STFT all the time, normal LTFT when accelerating, high LTFT when idling/coasting) are there any other parts i should consider parts-cannoning at it, or would it probably be a vacuum leak at that point?

Are there any common vacuum leak points that won't be evident - I've looked over the engine and can't find anything obvious like a split hose.

 

[vr4]

I replaced my charcoal cannister so now i can fill my gas tank normally again.

Purchased a used 03/04 MAF sensor and 2 new O2s to install. If these parts don't fix the issue (normal STFT all the time, normal LTFT when accelerating, high LTFT when idling/coasting) are there any other parts i should consider parts-cannoning at it, or would it probably be a vacuum leak at that point?

Are there any common vacuum leak points that won't be evident - I've looked over the engine and can't find anything obvious like a split hose.

PCV hose under the intake.

 

[efnfast]

Is there any way the hose can be checked without lifting the intake?

 

[hotcobra03]

Is there any way the hose can be checked without lifting the intake?

No.

But issue I found.

This hose will harden,
The nipple it's on Ford DIDN'T put a clamp on it.

This hose will spin on nipple but not come off ,,hence vacuum leak .

There is also 2 elbows on back side of blower which are common to crumble and a hole start which can be seen and heard .

I'm surprised you don't see po171/174 since +25 should set it ,

I did see my handheld would miss code, say no codes found ,yet a better scanner would show 171/174

Fwiw. Pulling the blower and cleaning that inter cooler is a maintenance step we all skip
This thing gets dirty

 

[efnfast]

My handheld and SCT and HP Tuners all say no codes (and no check engine light). I would periodically get a code though when it's like -40*C outside and I lug the engine .... I think the STFT would go up for a split second to like +20 (normally around +/- 5) and since the LTFT would be sitting around +20-25 that then caused the code (i.e., the code needs around +40-50 combined to set)

I really don't want to pull the intake (I've got a hundred projects on the go and because of its age every project on this car grows exponentially in time and it's my daily driver) .... but everything is signalling vacuum leak to me, except it idles fine. I would think if a vacuum leak is enough to cause +20-25 at idle then idle would show some signs of suffering

 

[Roush6018]

i have an idea on where the engine could be getting a vacuum leak. i did some EVAP repairs on my cobra a year ago. First i replaced the EVAP Purge valve and i still had a evap small leak code, so then i replaced my EVAP vent valve on the Charcoal canister. i got the code to go away after that.

the evap purge valve is in the passenger side front fender well and it connects 1 hose to the engine vacuum and 1 hose to the evap system. when at idle this valve should be closed. Under the right condition while cruising the valve will open to draw in the Hydrocabons to be burned in the engine intake. you can remove this valve and check if its leaking inside or just replace the valve and test drive to verify the repair.

 

[efnfast]

I like that idea more than taking off the manifold since it's easier, haha.

I had assumed that if that valve were leaking/etc. an error code would have been thrown

 

[efnfast]

Parts cannon failed - MAF sensor, O2s, evap valve, pcv o-rings on valve covers all did nothing - so I brought it to a shop.

Took them 5 minutes to find with a smoke machine - it was the hose under the intake manifold - note to self, if you suspect a vacuum leak just bring it to a shop that has testing equipment, so much easier.

Can the lower intake manifold be removed with the blower on? I think I've seen some youtubes where people did that, but I'm wondering if I do that, versus remove blower first then manifold, and I going to hate life when I have to reinstall it because of the weight of the assembly?

 

[2003RedfireVert]

Parts cannon failed - MAF sensor, O2s, evap valve, pcv o-rings on valve covers all did nothing - so I brought it to a shop.

Took them 5 minutes to find with a smoke machine - it was the hose under the intake manifold - note to self, if you suspect a vacuum leak just bring it to a shop that has testing equipment, so much easier.

Can the lower intake manifold be removed with the blower on? I think I've seen some youtubes where people did that, but I'm wondering if I do that, versus remove blower first then manifold, and I going to hate life when I have to reinstall it because of the weight of the assembly?

I removed mine all together as one piece. I also installed mine as one piece with a 2.8 KB on it. It can be done. Yes it’s heavy but it can be done.

 

[efnfast]

Tempting ... the less parts I have to undo at almost 300k miles the better my chance of success.

Are there any tricks to make manifold+blower removal easier, like attach an engine hoist to this and that point and use that to lift it up?

I'm not weak by any means - I've been lifting weights for 25yrs - but reaching into an engine bay to pick up a 60lb deadweight doesn't seem easy.