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Discussion Starter #1
For a long time now, I have not been able to figure out this issue. I used to get pretty decent mileage, averaging about 16MGP. Now I get 10-11, and something is clearly wrong, but no real codes. I have a bad cat, constant P0420, which is probably due to a bad tune on that bank, related possibly to this issue. The RPMs under constant steady load say on freeway fluctuates 100-150 RPM, and the instant mileage readout bounces all around. I heard of similar issues with the torque converter lock up going bad, but that is much more pronounced.

Any guidance appreciated..

https://youtu.be/VbYxP-r4i30
 

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Would not hurt to boroscope your intake runners, check for excessive carbon buildup.
 

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Discussion Starter #4
How many miles on your car?

Rob
130k. at around 100k, I had full timing chain guide/chains, and practically any other part that was came off replaced, all new injectors, rebuilt supercharger snout, everything.. except for these variators, unfortuantely. Performed flawlessly for a while.
 

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Might be worth pulling the supercharger and taking a peep, and be ready to turn the crank and clean the valves chemically or walnut shell blast.
 

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With that mileage it'd be worth doing a cylinder leak down test to determine the efficiency of each cylinder.

In all likelihood, and a common issue with direct injection technology, it's possible you have a couple of less than perfectly sealing valves, especially at that mileage.

The good news is that a head rebuild is relatively affordable vs an engine rebuild.

Also, SDD allows many measurable parameters to be selected with the engine running.

If you don't have access to that diagnostic equipment it may be worth spending an hour or two on JLR shop labor to more acutely diagnose the problem in advance of heading off down a potential rabbit trail.

Lastly, is the transmission shifting correctly and are you getting "normal" RPM at highway speeds?

Rob
 

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Meant to include this in the above post...

VVT's can "stick" with advanced age and extended oil change intervals.

If you do go the diagnostic route, this will be easily determined.

Rob
 

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Discussion Starter #9
Meant to include this in the above post...

VVT's can "stick" with advanced age and extended oil change intervals.

If you do go the diagnostic route, this will be easily determined.

Rob
Thanks for all of the info. One of the VVTs is definitely really noisy, and going to replace them next week (all 4). Will have him pull the intake again and inspect the intake valves. If a timing chain sprocket was off by a tooth, wouldnt it throw a code? I just want to make sure it wasnt an error when the chain was done 30k miles ago.

Another symptom - I can hear light engine knock when motor is warm, under light accel/loads when in 5th/6th gear at RPMS under 2K.

I really hope I can get this sorted out, as its already killed one 1300 dollar catalytic converter, and I dont want to put the next one in just to have it die too :(
 

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I see two potential issues: one is the bad cat code, which may be restricting exhaust. This will reduce mileage. The other is the trace knock at low rpm and heavy load. Though this could be due to the VVT, it could also indicate a timing or fuel issue. Either way, it may be an issue of ignition ping causing the ECM to retard timing due to the noise (knock sensor.)Valve timing could cause this, but so could a restricted exhaust. One cam tooth would likely cause a real driveability issue, not just noise. One thing to note here is the mileage being over 100K miles, which might indicate oil usage causing the ignition ping and the cat failures. Ray
 

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Not sure if you have High pressure fuel pumps on that engine But if you do Check your engine oil level and smell inside the oil cap for fuel. If levels are high and or smell fuel than check for this.

In some cases the high pressure fuel pumps can leak fuel into the engine oil and even throw the Cat code and even cause uneven rpms. Could also be the cause for the vvt being thrown out of wack. the reason for this is the fuel that is leaked into the oil when hot will cause vapor to recirculate back into the into manifold causing an imbalance.

This of course is only if you have high pressure fuel pumps..
 

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Not sure if you have High pressure fuel pumps on that engine But if you do Check your engine oil level and smell inside the oil cap for fuel. If levels are high and or smell fuel than check for this.

In some cases the high pressure fuel pumps can leak fuel into the engine oil and even throw the Cat code and even cause uneven rpms. Could also be the cause for the vvt being thrown out of wack. the reason for this is the fuel that is leaked into the oil when hot will cause vapor to recirculate back into the into manifold causing an imbalance.

This of course is only if you have high pressure fuel pumps..
So some 5.0 engines have hi pressure pumps, and some do not?
 

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Discussion Starter #13
I think any DI motor has to have a high pressure pump by design, so yes the 5.0s have one.

Other observations - the throttle seems to hang a little after letting off the pedal for decel.. the MPG shows roughly the same as my cruise MPG. I used GAP tool and logged the TPS to look into it, and it does not fluctuate at all. stays put when i let off.. but it takes 2-4 seconds for the car to actually go into decel/fuel cut mode, and to feel more drag from the engine braking. It seems the hang is related to ignition timing/fueling. While doing this, I noticed there are two TPS sensors - "Absolute Throttle position" and "Absolute Throttle position B" - one was linear from about 13% at idle to 91% at WOT. the other one never got below 32% and was on average a much higher percentage, unless I got up to 50-60% then they would get closer to matching.

Next, I have noticed that there is "Engine Coolant Temp" and "Engine Coolant Temp 2". does anyone know what these correspond to? the main one rose as normal with engine temp, leveled out to 87-89C. The Temp 2 stayed aroudn 10C then went up to 35C and stayed there after warming up. I know a bad coolant temp sensor can cause rich conditions.. but I don't know where this "temp 2" is pulling info from. I dont think it can be the outlet for the radiator, seems too cold still?

Same basic thing with "intake air temp" and "intake air temp bank 2" - usually a 20C- 30C difference, which does not seem feasible if both bank are drawing from the same atmosphere..

Lastly, LTFT for bank one is about -2 to -3%. Bank 2 is about -10 to -12%. Bank 1 has the dead cat. I swapped MAFS from left to right, nothing really changed for the fuel trims.

I have basically been watching various parameters with the GAP tool, looking for anomalies that could lead to the diagnosis of this thing.

If anyone has any other recommendations to watch/log/try, or knows what all of these "sensor 1 vs sensor 2" things correspond to, I am all ears. Next week it goes in for replacement of the VVTs, and hopefully further inspection/scoping of the intake valves.
 

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Did you check the oil as i suggested? Many of the things you mention including the fuel trims and the hanging throttle are symptoms of this.

The reason your fuel trims are so out of wack is the one side is trying to lean fuel, the very side that fuel vapors are entering the combustion chambers without passing through the throttle body they are entering the intake manifold on that side. the engine doesnt know this and is trying to balance this out by cut fuel delivery but it cannot control it.

Dont over think it, the The two tps signals will not read the same one recieves half of the voltage as the other and they are designed to be averaged out by the computer, this is normal.

The temp sensors are normal they monitor two different areas one on the hotter side the other on the cooler and return side. they are needed to monitor the vanes and coolant fan. this is normal.

I strongly would suggest looking into the fuel pump issue before spending money on the vvt. the unbalanced fuel vapor load can cause the vvt problems. Remember if fuel is entering the cylinders at a time when no fuel is supposed to you will get combustion at the wrong time and will be very uneven there is only so much the ecu can do it cannot stop something it cannot see.
 

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no you would have two one for each rail. But either way the vapor would be reentering through the breather to intake manifold.

Keep in mind that in your case it may not be this, I was only going on several of your symptoms
 

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The high pressure fuel pump delivery circuit works in a "compound" manner.

Both pumps are driven by an auxiliary cam, which is also common to the oil pump. The high pressure (HP) fuel demand is regulated by the ECM, using multiple measured inputs.

The HP pumps are plumbed through conjoined delivery pipes and thus the high pressure fuel is measured as a combination of the two, not individually (or per rail). The psi at high HP demand can be in the 2000 psi range (yes, two thousand psi).

Usually, if experiencing HP problems both pumps are replaced. Although an individual pump may fail, that would require "guessing" or tossing a coin as to which one was faulty, replacing it then running through the diagnostic procedure again. They are a pain to replace.

If you "guessed" wrong you'd have to go through the exercise again. That gets expensive for the labor portion. I get that if someone's on a limited budget that that may be worth their time. Their car, their choice but the combination for labor and parts is probably a wash regarding replacing both pumps at the same time (like most good shop practice, although replacing "paired" systems at the same time may mean a slightly shorter service life than expected for the non-faulty part, paying twice for the independent replacements is usually a little more expensive in the long run).

Rob
 

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Discussion Starter #20
Ok has all 4 VVTs replaced. Had to be done, one was clearly problematic. So opted to do them all. Nasty noise is now gone, engine quiet. But still have the negative LTFT on bank 2 under idle / low load conditions, even at highway spead. High RPM or higher loads evens out the LTFT.

I did did my homework on the fuel system, and learned a bit, but some things are unclear.

Am I understanding it correct that each bank has its own separate pump and rail? Could it be possible that one side is over-supplying? I think the other possibility is a leaking injector but all 8 are new.

another symptom: idle ignition advance is only at +2-3 deg. I think usually it would be much higher. As I understand it, ignition timing can be used to control and or smooth out idle, bust mostly for non drive-by-wire. Not sure if relevant here but seems very low for no load at idle. Seems normal under all other conditions.
 
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