Hi!
Im sure this is a common issue, but since im not getting any CEL or error codes, id like to start a new thread.

I noticed some rough idling now and then,
and i lost some acceleration
These conditions got me looking at my fuel trims and i noticed
- bank 2 had a LTFT of +4% at idle
- and +15% STFT at constant load at 2500 - 3000rpm, pedal tip almost half the travel so i keep the closed loop operation and see how the fuel trims react. (Hill climbing for ex.)

i am looking for possible issues
what i have done so far:

-Pre cats O2 sensors are ok (Swapped in between them)
-No obvious vacuum leaks ( will listen again tomorrow with a hose and a funnel to my ear. Might spray a bit of propane too, to check for mixture modifications)
- exhaust leaks must be checked,
- camshaft sensor up to be replaced,
- i will test compression (hopefully i can do it on one bank only)
- injectors were professionally cleaned and tested 4000 km ago,
- imt manifold tuners & manifold itself have new gaskets (changed 4000km ago),

I suspect the injector orings or maybe a leak on the exhaust side.
Or maybe a valve not fully closing.

any experience on this matter?
many thanks

 

Check the inlet plenum from the MAF to the throttle housing for cracks or holes.

Use the search function as this has been covered in other threads.

 

Thanks! I will do just that
I did use te search but these complex scenarios need ideeas and discussion.

update: so far so good

i used a propane torch to spray gas around the intake and had NO results on the Live OBD2 fuel trims (also did a test by spraying on the filter and after a second both STFTs turned -25%. So the propane is reactive enough, so i would have noticed any existing vacuum leaks)

then i did a compression test without removing the manifold on the 4 cylinders out of 6 that i can reach. All 4 rated at 150 psi exactly.
no wonder, as i cleaned this engine and its valves thoroughly before installing it.

of course i cleaned the plugs that had oil on them! I believe its the oil that was spilled on the valve covers cause someone was lazy to get a funnel ( not me, i was under the car lol)

i have changed the camshaft sensor on that side.

i have used a intake and full system cleaning additive that i sprayed into the manifold.

AND i havent noticed any more differences on the short term fuel trims, (but i did a short roll).
i will continue testing

 

STILL NEED HELP
Forget what i just said.
its still doing the fuel compensation (STFT +10%) on bank2.

i did a smoke leaks test, and found two (one at the throttle body sensor, and one where the brake booster line connects to the manifold.
i fixed both. But the STFT problem is still persisting

i will repeat the smoke test in the exhaust too (my smoke device broke down)

I also removed the crankcase breather and PCV. I plucked the intake holes and gave it a run.
Issue persists, so the PCV system is ok.

so
- compression is good
- plugs and coils are good
- injectors are good
- no vaccum leaks in the intake
- camshaft sensor replaced
- both precat o2 sensors are good
- PCV works correctly

exhaust left to be tested

Please give me ideas on what else could create a lean condition on bank 2

many thanks!!

 

If the inlet manifold has been removed for any reason, check the inlet manifold to cylinder head gasket(s) for sealing and check the electrical connectors to fuel injectors to make sure they're fully seated.

 

seals are ok, when i swapped the engine, i made sure everything is fresh. Connectors are good and clean. I must check the exhaust. Could inefficient catalysts create such a condition?
They are not broken or melted, i took a look inside them. but the precat senosors are actually positioned in the middle of the cats

 

Have you checked the variable inlet control valves? I forgot what the proper name for them is. But you know what I mean (the big black round things in the inlet manifold that get leaky seals).

 

IMT orings. There are detailed posts with pictures.

 

Yes of course

what bothers me is that shouldn't vaccum leaks be affecting the fuel trims the worst at idle?

 

Yes - if the leak is there then.

If you have a fairly big STFT it should migrate into LTFT - if it isn't then why not? Are you doing something to prevent it?

 

It does actually, yes correct.
so on bank 2:
-At idle LTFT is aprox +3%,
-At 2500 rpm constant engine load LTFT is + 8% ( plus some more STFT )

bank1 works well. its mostly around 0%

 

My catalysts

 

It sounds good enough.

 

yes but its only on one bank
and LT + ST gets up to +10 to around 15
again, only on bank 2.

something happens there