Extreme Negative Fuel Trims -35% to -40% both banks when extended hot IDLE

[duca1991]

Hi all!
I am desperate for some ideas and help
2013 LFX 3.6 185xxx always used 98 octane and serviced always.
Iv started to experience a strange issue that arises when im idling for some time with the engine already at operating temp.
The LTFT on both banks just sits at -35% and dumps fuel into the car, the ECU is trying to reduce as i can see -30ish% on the STFT to try and fix it, but the car just runs rough and theres a bit of after run for 2-3 seconds when i shut the car off.
Upon starting it again, it struggles as there's so much fuel still left in the fuel rails but eventually gets going.

I must mention, on a cold start the next morning the car runs like a dream and the AFR seems pretty normal, around + - 5% on both banks.
at first i thought it was injectors as there was fuel in the oil and thinking it was leaking injectors, big money spent for no fix.

No check engine lights. Fuel pressure is showing 61psi when the issue is happening which seems quite high, usually sits around 43-45 and high pressure fuel reacts as normal.
o2 sensors seem to be operating normal upstream and downstream.

Not sure what to do,
Never seen this issue before with any VE's

Thanks!

 

[uglyoldfatbastard]

Fuel in oil is not a good sign as it can damage the engine quickly.
If you still have fuel in oil get your HPFP (high pressure fuel pump) checked as it runs of the exhaust valve on the rear of the passenger side of the engine and if it is leaking internally that will put fuel into the oil and do a lot of the other things you have mentioned especially the LTFT going crazy.

Cold starts and it runs fine and as it heats up the HPFP starts leaking as the metal slowly expands until the engine is overrun with fuel.
Hard to diagnose and often missed by even the best mechanics.

 

[duca1991]

Fuel in oil is not a good sign as it can damage the engine quickly.
If you still have fuel in oil get your HPFP (high pressure fuel pump) checked as it runs of the exhaust valve on the rear of the passenger side of the engine and if it is leaking internally that will put fuel into the oil and do a lot of the other things you have mentioned especially the LTFT going crazy.

Cold starts and it runs fine and as it heats up the HPFP starts leaking as the metal slowly expands until the engine is overrun with fuel.
Hard to diagnose and often missed by even the best mechanics.

Thanks for the reply!
I will mention this when i get my car looked at, would you expect this to be the case if the engine is warmed up while driving around?
It seems as if driving with regular start stops the LTFT and STFT seem pretty normal, even after driving for 30 minutes.
Just seems to happen when im at idle and the car is sitting for 5 minutes.
If it was a MAF sensor issue or some type of sensor, the issue would be pretty much happening when both cold and hot?

It just stumps me, as long as the cars moving from a cold start without having stopped sitting in idle the issue never seems to happen or at least i can sort of see it starting to happen on my Live data stream.
Bank 2 is always slightly more rich than Bank 1
Its always something like this
Bank 1 -2%
Bank 2 -6%
or
Bank 1 +6%
Bank 2 +2%

Not sure if this is related, but there is a very slight variation in the banks, but that doesnt explain Both banks evenly shooting to -35% (PHOTO ATTACHED)

 

[uglyoldfatbastard]

The VE we found it on had loads of different things happening from fuel trims to cutting out at idle, funny smell out exhaust, white smoke out exhaust once the problem had done damage to the bores. Basically it took over 12 months to diagnose and by the time it was found and pump replaced the engine was in a sad sorry state and has since been replaced with a low km one from a wreck.
Every time the original mechanics looked at it they said "WE THINK" we have found the problem and the owner would pick up and 15 minutes later it would start all over again.
I am not saying it definitely is the HPFP but "fuel in oil" is a classic symptom.

 

[duca1991]

The VE we found it on had loads of different things happening from fuel trims to cutting out at idle, funny smell out exhaust, white smoke out exhaust once the problem had done damage to the bores. Basically it took over 12 months to diagnose and by the time it was found and pump replaced the engine was in a sad sorry state and has since been replaced with a low km one from a wreck.
Every time the original mechanics looked at it they said "WE THINK" we have found the problem and the owner would pick up and 15 minutes later it would start all over again.
I am not saying it definitely is the HPFP but "fuel in oil" is a classic symptom.

Thanks mate.
Just 1 more thing, since injectors have been replaced and there's no possible leaking from them.

It would have to be all the excess fuel in the rails leaking past the pistons after the cars sat overnight?
Or can fuel get past pistons unburnt while car is running?
I believe this issue has been happening for nearly a year, iv just been unaware as I don't sit idle for long too often, until recently when it got slightly worse and decided to do something about it, that's when I started to look into the fuel trims.
Even though it's been happening for awhile, I havnt noticed the oil raising on the dip stick, just a fuel smell on oil cap.
I think I still have time to figure it oit before engine gives in, it doesn run pretty damn smooth when driving from a cold engine. Doesn't even feel like the cars on when stopped at a set of lights.

I didn't actually think fuel could get past piston but I guess if there's such thing as blowby there's such tolerances that a liquid could leak past and into the oil pan

 

[uglyoldfatbastard]

Thanks mate.
Just 1 more thing, since injectors have been replaced and there's no possible leaking from them.

It would have to be all the excess fuel in the rails leaking past the pistons after the cars sat overnight?
Or can fuel get past pistons unburnt while car is running?
I believe this issue has been happening for nearly a year, iv just been unaware until recently when it got slightly worse and decided to do something about it, that's when I started to look into the fuel trims.

I didn't actually think fuel could get past piston but I guess if there's such thing as blowby there's such tolerances that a liquid could leak past and into the oil pan

No if HPFP is leaking it squirts fuel into the passenger side rocker box and then straight down the oil galley into the sump where it mixes with the oil and starts washing out all the bearings and reducing the oils lubrication which starts scoring the bore and then the crank bearings etc etc.

Look at the photo the spring end goes into the engine and the rear exhaust cam drives it.
They start leaking from there.

 

[Immortality]

If there is a strong fuel smell from the crankcase do yourself a favour and drop the oil before you start doing serious damage.

The above is certainly an interesting diagnosis, watching with interest.

 

[uglyoldfatbastard]

Actually forgot to put in the post one easy way to check if it is leaking is to pull the rocker cover off and you will see it will be all shiny and no oil all around down the rear passenger cylinder where the fuel has cleaned everything and it will smell like fuel.

 

[lmoengnr]

Actually forgot to put in the post one easy way to check if it is leaking is to pull the rocker cover off and you will see it will be all shiny and no oil all around down the rear passenger cylinder where the fuel has cleaned everything and it will smell like fuel.

Clean, and no sludge in the lefthand bank...

 

[duca1991]

If there is a strong fuel smell from the crankcase do yourself a favour and drop the oil before you start doing serious damage.

The above is certainly an interesting diagnosis, watching with interest.

**** part is, it's brand new oil after we did the injectors.
Cant believe the issue is still present after spending all that money on genuine injectors.