one can of bg44k on the way. i'll post back with numbers after that tank (shouldn't be too long at my current 12mpg average!)

 

Great! I think you will see a difference....

 

Hi Guys, Having been through the lean codes and high fuel trims, I thought I'd offer my 2cents. My vacuum leak turned out to be where the intake elbow joined the composite intake manifold... faulty o ring seal... so double check this area. It's been 2 yrs. since and no more codes. My stft's are low, sigle digits while the ltft's are aroung + 10... maf #'s are in spec., car has 142,000 miles. Can one explain why a blocked or damaged CAT can cause ltft's fuel trims to go + ? I wish to learn all I can about this and just want to make sense of it all. THANKS GUYS!

 

Blocks exhaust flow, ruins what the O2s see and the back pressure is all wrong.

 

Thanks JagV8, I get it...so, do you suspect Kreyszig has an O2 sensor isssue or a missfire issue? I would lean toward the O2 sensor malfunction on bank 1. I know I've heard of this before but, I wonder as to how a faulty MAF sensor can infuence one bank more than the other...maybe just one of those things... just seems as though it would affect both banks more evenly as it is common to both.

 

02 makes more sense to me as when the head gasket went the sensor could have become caked in crud. This is how the original misfire code was sold to me, but I think that was a separate issue (wrong bank for starters).

(edit: Note that the misfire I mentioned was only evident when cold and did not last long - & I think it was due to moisture in the coil cover and now seems to be cured)

I imagine (I don't know for sure of course) that the sensor could be faulty without throwing a code. I.e it could be giving incorrect readings but still functioning well enough to not alert the system.

The thing is, it would have to be reading high, and I'm not sure a dirty sensor would produce more voltage (unless these aren't voltage based sensors?)

Then there's the leak option of course...

 

You may wish to take one or more O2s out and peer in with a borescope. I'm working on the basis this isn't a 4.0 with timing that's out i.e. has updated tensioners etc.

 

yep the tensioners were all upgraded along with chains following the head gasket blowing - new (to the car) head that side too. One of the cylinders was replaced too. (all by designxkr in andover)

 

I believe an O2 sensor can be at fault here and not throw a code. The ecu is set up to see an acceptable range of voltage from the sensor. if the voltage is near one end of it's range, due to being old or damaged, no code will be set. Example; when the O2 sensor failed in my jeep, it was an internal short to the heating element which caused the reference voltage to be very high, hence the O2 code. The sensor you have may be functioning at near one end of it's range so the ecu adjusts the trims accordingly.

 

are you using fuel with ethanol?

in north america where ethanol is mandated as part of the overall total fuel sales by a refiner, switching to Shell V-Power non-ethanol can drop LTFT by about 5 points as confirmed by obd-ii monitoring.

it won't solve your left and right bank imbalance, but it will drop LTFT on both sides

the cost is offset of the switch is mostly offset by the increase in mpg.

ps. the above has a good explanation, but a further drop in LTFT was observed after long term use of TC-W3 added to the fuel. don't know why ... maybe less blowby, maybe freed up the egr ... no idea

 

Has the bad coil been changed?

It could be a bad MAF, as the LTFTs get worse in a similar way as revs go up. Anyone else have ideas?

 

No ethanol here for me. Coil-wise, I don't know that there was a faulty coil. My cover was missing a couple of bolts so my theory is moisture was getting in and evaporating once warm. That fits with the symptoms (restricted performance for a short while when cold), and swapping two coils (both at the end with the bolts missing) resulted in misfire codes for both rather than moving with the "bad" coil. Anyway misfires no longer an issue (after replacing the cover), I'll run the additive through, see if that helps and use maf cleaner to try and find a leak if the weather picks up. I'm feeling like 02 fits though.
Really appreciate all the feedback by the way guys, thanks!

 

Quick update: I got about half way through the tank full of additive and there's been no change in trim values.
I have a new o2 sensor about to go in but the cars up on jack stands in the garage while I sort out some body work, so won't be able to warm her up without gassing myself.

I'm repeating myself as I've just tacked on the end of another thread, apologies for that.

 

well I've replaced my bank 1 02 sensor and no change.

I then sprayed everywhere I could reach with wd-40 as it seemed less volatile than carb cleaner and I haven't got any MAF cleaner. (I have cleaned my MAF sensor with electrical contact cleaner already)

No change in rpm or fuel trim, but I couldn't get a clean shot at the injectors on bank 1 with the intake and supercharger in the way. I sent plenty in that direction, but still no change.

I do think I can hear a hissing noise near the throttle but a) that would affect both sides and b) no change when sprayed.

So, I'll be following RaceDiagnostics lead and building a smoke machine. Any other suggestions?

 

By way of an update - I found a pretty bad leak in the full load breather. I'm not sure the pipe itself is broken, it seems the seal into the intake tube just isn't any good. I ordered a new pipe anyway and it will be going in tonight. Could just be the o-ring but none of mine seemed any better than the one that was in there.

My smoke machine is a large plastic paint tin type thing (actually for holding mortar) with a pie tin glued to the bottom; this stops a plumbers smoke bomb from burning the bottom out of the bucket.
The tough bit was getting a good seal on the lid; I hot-glued the inside of the lid and put it on the container with some cling film to stop it sticking.
Its not perfect but good enough. A proper paint tin would be better but I didn't have an empty one!
I pressurise with a bicycle pump; it's easy to control the pressure that way. A bicycle valve cut off an old inner tube (presta) screws into a 5mm inner diameter flexible tube perfectly (which was a surprise!) with no leaks.
The smoke bomb burns for a minute and gives probably 4 or 5 minutes worth of searching time before it's all gone. I lose a fair bit out of the seal on the bucket but can still put 20psi into the intake without popping the lid loose.

I noticed a smaller leak from a small hose somewhere around the TB but will find that once the breather tube is good.

 

Any updates to your findings kreyszig, I have a simular problem on my XJR8, No codes, new CATs new Lambdas and still high fuel trims and emissions on both banks, smoke test done no leaks.

 

Hi there. I changed the breather tube for a brand new one and no change. I haven't retested but suspect there's still a leak at the connector. So I'll try a silicone hose next.
I've put new coils in 7&8 and still get a misfire.
I should have tried swapping the plugs first; that's what I'll do today.
If yours not getting leaks then maybe you're MAF is dodgy; and if you're not getting unmetered air, perhaps you're not getting enough fuel - I'd check/change the filter and fuel pressure.