2002 Jaguar XK8 - Fuel Trim at 19.5%
 

Hello All. Been a while.

I recently swaped my 215k engine for a 37k engine and all went well, well, almost...

Im getting a lean code on the bank 2, p0174... The LTFT is reading 19.5% steady with no fluctuations. Is that a leak or a dead downstream O2 sensor? At one point (and maybe it will return) I had a p0160 saying that there was NO reading from the O2 sensor. It's since disappeared. I'm wondering what the heck might be going on and am completely open to suggestions. I don't wanna get under the car again (spent way to much time underneath recently, lol) to change a sensor if I don't have to - if ya know what I mean?

The lower O2 sensors did take some bumping and scrapping during the trans sliding in and out part of the swap. Damaged wires?

I mean, 19.5%? Crazy.

Check for vacuum leaks and replace the oxygen sensor. Also, check for exhaust leaks around the manifold and catalyst.

Hey, NB... Understood.

I had also considered (fearfully) some sort of leak between the manifold and cat/down pipe, but thought about it thinking that exhaust would blow out,,,, would outside air work it's way, in?

Also,,, is it possible to get a socket on the down stream sensor from under the car? Maybe with a looooong set O extensions and a flex joint? Not looking forward to it.

On the earlier car, these can apparently be reached through the A/C drain holes from inside the cabin.

If you can get to the o2 sensor plugs behind the T.B, try changing bank 2 sensor to bank 1..
If the code moves to bank one then its the o2, if not then look for the air leaks on bank 2..
Unfortunately you could have a bad air leak and a damaged sensor on bank 2 but hopefully not..
Good luck..

Love it! What's considered early? 02?

I can, and good idea. I'll swap them...
Thanks for that!

Nothing good to report, yet. I fear something bad.

Still with the P0174 code,,,, only...

For the reason of not wanting to just throw parts at it, I removed intake and re-placed 8 intake gaskets just make sure nothing got bound up or went sideways when I did the swap. Seemed fine. I checked all ports with o-rings - and such. Nothing seemed a-miss and went around with a huge bottle of carb and choke cleaner at idle, no idle changes.

The LTFT on bank 2 remains at 19.5. Doesn't budge no matter how much throttle play. STFT and LTFT bank 1, fluctuate and seem "normal" or to be working. OBD says I am operating in "closed loop"... No O2 sensor codes at all... Guess I gotta git under there.... See if I can get the sensor off somehow.

I'm sorry, I still haven't swapped sensor wires for fear that if there is a short in frayed wires at the sensor, it could create a short or an arc that may damage something. I'll try it after inspection of the wiring, better. From below.

I was under the impression that it was the upstream sensors that were responsible for fuel trimming and O2 sensing. My

You have a way to smoke test?

In the process of making one.

I can't understand:

No fluctuation and a steady 19.5% on one bank.

No "apparent" leaks in the intake system up top (though it can't be ruled out, just yet) and a leak that size only effecting one bank.

That the O2 sensor status is in closed loop (if it is a dead sensor)

And no sensor codes?

My fuel MPG is thru the floor. Abysmal...

I'm in the twilight zone in this.

Steady 19.5% is all you get. It's saying it can't compensate for the lean condition any better (or extra air if that's what it is). Looking glass half full, since it's only on one bank, halves the leaky things to look at.

Good luck.

Right. Thank you.
It's what I was thinking.
Which has kind of produced as much a mystery in itself.
A clogged injector? But what about a misfire code?
The engine runs smoooothly...

So, all the intake plenum ports/connection points in the bank in question were checked - seals replaced... All the injectors not exactly tested for firing,,, except the ol screwdriver to the ear listening for clicks, test... 4 seats were inspected and sprayed all around - no change in engine idle... In the engine swap I simply took the entire intake assembly off the old engine, stored it carefully, and popped it back on the "new" engine...

I'd better pull all the injectors. Bit if I pull coil plugs I get a definite idle change.

I've been thinking (until I can actually get back to it) what else is left on the ONE bank, to only create a problem, in the one bank? Trims on bank 1 seem normal/fine. I don't get the combo p0171 and p0174. Just the p0174

PITA.

Just to eliminate one more possibility, check the fuel pressure. It should be between roughly 3 bar (300 kPa) at idle and 3.8 bar (380 kPa) during WOT.

I don't understand why you haven't done the simple test of swapping upstream sensor connections, then downstream if necessary.

Thanks RJ...

Been at work, and finishing up the engine change in a 2000 S Type (can't say it been fun). I appreciate your wise suggestion and advise, I do, but as I stated above I need to get under the car and inspect the wiring of the bank 2 downstream sensor first looking for frey or damage from rubbing against the side of the trans when I placed the "new" engine in her,,, about a week ago. I'm afraid there might be damage - maybe damage that caused this problem in the electrics? There is a fuse to protect things, but a high amp 12v up a line to the ECU that deals in milliVolts is something I've been worrying about.

I'll do as you say, no doubt. Right now, I'm kinda in a "thinking" phase (all I can do during the work week) and, always dangerous, lol

Possibilities below. Obviously, some of these things will likely cause lean codes in both banks. If you really think you damaged the electronics, you can swap connectors, as mentioned by RJ, but you also could go down the more capacious rabbit hole of doing the pinpoint tests from the Workshop Manual on the ECT, MAF, IAT and TP sensors.

A little story. I recently put off the easy smoke test because I had already replaced everything that I was previous leaking and I thought would leak in favor of the electronics pinpoint tests in the Workshop manual (must be the electronics, I reasoned, for my both bank lean codes, and wife hates the burning mineral oil smell). This wasted much time when the apparent failure I found doesn't apparently cause lean codes (confirmed on one of the other cars). So, the workshop manual is not particularly helpful there...

When i smoked it, i found the leak i in a few minutes that I had apparently induced by disturbing the dipstick tube when i replaced the cam cover. I would have saved a lot of time smoking it first (and telling my wife there must be a refinery fire somewhere nearby), especially with no other codes.

https://cimg8.ibsrv.net/gimg/www.jag...be251b8110.png
Possibilities

Could be an exhaust leak. And it doesn’t take much of a leak to throw the code. So don’t discount a leak just because you cant see one. I had 5 I couldnt see

Help me out,,, Post CAT leaks will throw lean codes p0174 and 0171?

I placed new manifold to CAT seals (pre-sensors) on the engine swap... Afaik I have no leaks further along, but I don't understand. What about folks who make dramatic changes to there exhaust systems, lowering compression post CATs? Are they left to live with lean codes?

Bass,,, thank you, as usual, all good ideas. You must know by now that I DO NOT have the expertise or experience with the electronics... It's a serious deficit. I will try to keep inspecting and figure out some kind of DIY smoke test... Imma have a look at some injectors on that side as well... Something's gotta give,,, or not.

I haven't done anything due to work and early sunsets... This weekend it is.

Thanks y'all

Leaks after the cat wint throw codes. But a leak at the manifold to engine or manifold to pipe will. If the manifold isnt flat or if you overt or under torque the bolts is can leak. Pipes can have a welded seam thats mot flat. Cracks. Etc

Got ya. I'll break out the mirror and see if I can have a look see. I don't hear that familiar sound of a leak that high up on the exhaust. Ya know, that poppy kinda sound of a leak near or around the manifold. But I'll have a look.

Again, I get NO O2 sensor codes, I will have a look, but I'm thinking I damaged a vac line, cracked the housing of the intake, it's gotta be something like that. Fingers crossed.

If it can be a simple fix,,, I have to say this being my only issue after swapping this engine, first EVER, will make me happy. Gotta solve it.