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Discussion Starter · #1 · (Edited)
* SOLVED * Scroll down to post #17 *

Hey guys, first and foremost, great to be here! So much info and helpful insight!

Having what I believe to be an issue, and was wondering if anyone else had experienced anything similar or could chime in on what it could be. I recently purchased a certified preowned 2018 XC90 T6 AWD with just under 20K miles. When I go full WOT or really hammer it from pretty much any speed, gear or driving mode, the engine builds up power decently but the “ramp up” or torque curve feels rather flat. As I pull 1/4% to 1/2% off the throttle, the engine accelerates faster and the curve (so to speak) spikes considerably faster with much more power. I find if I simply don’t go full throttle, and keep the pedal at no more than 50%, the vehicle pulls substantially better. The difference is not subtle but quite noticeable. I pulled the plugs to see what condition the ignition system was like, and they’re like new.

Only way I can explain it, it feels like the engine is starving for more fuel but not getting it at WOT. My reasoning for that, I had a aftermarket supercharged Denali SUV that did the very same thing. Turned out to be that supplemental in-line fuel pump the supercharger kit came with was faulty, and the engine wasn’t getting adequate fuel to keep up with the supercharged engines demands. Replaced the pump, and the car woke up! Could that be happening here with the XC90? Do these vehicles, like in some of the late mode BMW’s, have hi and low pressure fuel pumps? Perhaps a bad high pressure fuel pump or something in the lines of a faulty fuel pressure regulator?

Being that this is a certified vehicle, the vehicle is under warranty, and I’m certain whatever it is, it can be dealt with, but I was just curious if anyone had experienced the same, or similar issue.

Thanks in advance
 

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Hey guys, first and foremost, great to be here! So much info and helpful insight!

Having what I believe to be an issue, and was wondering if anyone else had experienced anything similar or could chime in on what it could be. I recently purchased a certified preowned 2018 XC90 T6 AWD with just under 20K miles. When I go full WOT or really hammer it from pretty much any speed, gear or driving mode, the engine builds up power decently but the “ramp up” or torque curve feels rather flat. As I pull 1/4% to 1/2% off the throttle, the engine accelerates faster and the curve (so to speak) spikes considerably faster with much more power. I find if I simply don’t go full throttle, and keep the pedal at no more than 50%, the vehicle pulls substantially better. The difference is not subtle but quite noticeable. I pulled the plugs to see what condition the ignition system was like, and they’re like new.

Only way I can explain it, it feels like the engine is starving for more fuel but not getting it at WOT. My reasoning for that, I had a aftermarket supercharged Denali SUV that did the very same thing. Turned out to be that supplemental in-line fuel pump the supercharger kit came with was faulty, and the engine wasn’t getting adequate fuel to keep up with the supercharged engines demands. Replaced the pump, and the car woke up! Could that be happening here with the XC90? Do these vehicles, like in some of the late mode BMW’s, have hi and low pressure fuel pumps? Perhaps a bad high pressure fuel pump or something in the lines of a faulty fuel pressure regulator?

Being that this is a certified vehicle, the vehicle is under warranty, and I’m certain whatever it is, it can be dealt with, but I was just curious if anyone had experienced the same, or similar issue.

Thanks in advance
Check, rail pressure sensor, MAP sensor, TB cleaning, MAF sensor, inspect the upstream O2 sensors, check for vac leaks, make sure charge piping connections are tight…
 
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Discussion Starter · #3 ·
Connections look good, in fact everything looks good under the hood. It’s clean as a whistle. I’ll connect my scan tool later this evening and see what I get in terms of readings from the aforementioned sensors. See if I may be able to logs some runs or something.

One more thing, what kind of MPG is everyone getting? Mine is registering 16.5! No where near the manufacturers claims. There’s gotta be something going on here!
 

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I am getting 21.9-22.1 in my T5, according to the car readout (I know that some argue that is not accurate, but it's accurate enough for comparison's sake, and it is probably how you are getting your reading, as well). I am a lead-foot and definitely not someone who tries to maximize my mileage (sorry, Earth), so I would think that there might be something amiss somewhere.
 

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One more thing, what kind of MPG is everyone getting? Mine is registering 16.5! No where near the manufacturers claims. There’s gotta be something going on here!
I wonder which use case mpg would be most relevant to your question about WOT issue; steady freeway use is probably most easy to compare from one vehicle to another, while stop and go surface roads will likely vary much more depending on the subtle differences in the roads and stop and go timing.
 

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Discussion Starter · #6 · (Edited)
I’ve only put on roughly 500 or so miles since I took delivery. A little of highway and local stop and go use. The majority of the miles have been “babied”, so I would have liked to have seen better MPG’s. I know the onboard system can be a little screwed, but in almost all my cars, the system shown readings have been pretty accurate, not to mention, not too far off from what the manufacturer claimed.
 

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I also have a 2018 XC90 T6 AWD that I picked up about 2 weeks ago. Not sure about the WOT observation you have cause I only drove it maybe once or twice on the freeway to even notice. Then about a week ago I had the Polestar software upgrade, so know I'll never really know. In regards to my MPG it appears to be the same before and after the upgrade but currently show at about 15.7 mpg after about 2 tank fill up so far. Did a long drive last weekend and didn't see to have improved that MPG.
 

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Typically with a turbo you'll get the best acceleration from gradual increase in throttle from ½ to 3/4 throttle until you're at it's peak where full is fine. Recall the supercharger is only for low end fill but once over say 1500-1900RPM it'll be turbo.
 

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Discussion Starter · #9 ·
Yea I get how this marvel of a little engine works, and it’s genius, but what I’m experiencing is definitely something in lines of a component and or a sensor not functioning properly. Hammer the gas, go from supercharger to turbo transfer (which the car does perfectly), and hold the pedal down. The car goes, but it’s just not 100% there (more like 75%). Gently pull off the gas from WOT, and all of the sudden the car begins to pull harder and faster. Step back down on the gas and the power delivery is flat again. If I accelerate from a stand still, and not go WOT, but rather play with the pedal between 50% and 75%, the car is significantly quicker and more powerful.

It’s really hard to explain, but something you can feel immediately behind the wheel. Traditionally, when you ease off the pedal, the vehicles power delivery should begin to reduce, but in this case it’s almost the opposite. I can get from 0-60 quicker by not going WOT, and slower when I’m at WOT, which is the whole issues at hand.

IMO, since they’re no DTC’s, and the car starts and idles fine, the ecu is definitely adjusting and or compensating for some sort of errounous sensor reading and or aging counterpart. The fuel supply on most cars is one of those areas where failing or faulty components could cause drive issues without throwing any codes. Most of the other drive related sensors, when they start to go bad or begin to make changes that are not within normal parameters, you almost immediately get DTC’s. It’s no rule of thumb, but I can say with 90% assurances, that is often the case.

There’s just so much to check and without any DTC’s, it’s hard to focus on one thing or area. Nevertheless, I have an appointment next week. Fingers crossed they’ll be able to get it sorted out.
 

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Connections look good, in fact everything looks good under the hood. It’s clean as a whistle. I’ll connect my scan tool later this evening and see what I get in terms of readings from the aforementioned sensors. See if I may be able to logs some runs or something.

One more thing, what kind of MPG is everyone getting? Mine is registering 16.5! No where near the manufacturers claims. There’s gotta be something going on here!
Average mpg is going to depend on lots of variables not the least of which is average speed for where ever you were driving to get 16.5mpg. On the road at 65mph in mostly steady traffic I can get 30 mpg. In town it drops to low to mid 20s depending on driving conditions.

No surprise that running wide open throttle consumes a lot of gas. You're rapidly accelerating over 2 tons of car.
 

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Discussion Starter · #13 ·
Average mpg is going to depend on lots of variables not the least of which is average speed for where ever you were driving to get 16.5mpg. On the road at 65mph in mostly steady traffic I can get 30 mpg. In town it drops to low to mid 20s depending on driving conditions.

No surprise that running wide open throttle consumes a lot of gas. You're rapidly accelerating over 2 tons of car.
Regardless if I’m driving in and or around town, or out on the highway cruising at a steady 65, the system fluctuates from high 16’s to low 15’s. I’ve tried Eco mode but only saw a .1 to .3 increase over several miles. Haven’t been able to move it much higher.

Heck my Benz, which has a supercharged V8 AMG cranking north of 600 ponies, easily achieves similar MPG’s on the highway. Sure it’s not an apples to apples comparison, but just taking into consideration the parameters and specs on hand, the little 4 banger in the XC90 should do a lot better IMO.
 

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Regardless if I’m driving in and or around town, or out on the highway cruising at a steady 65, the system fluctuates from high 16’s to low 15’s. I’ve tried Eco mode but only saw a .1 to .3 increase over several miles. Haven’t been able to move it much higher.

Heck my Benz, which has a supercharged V8 AMG cranking north of 600 ponies, easily achieves similar MPG’s on the highway. Sure it’s not an apples to apples comparison, but just taking into consideration the parameters and specs on hand, the little 4 banger in the XC90 should do a lot better IMO.
At 65 mph the engine should be turning about 1700 rpm. On a flat surface with steady throttle and in 8th gear you should be showing twice that mpg or better. If so you may have a problem. Any warranty?
 

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Discussion Starter · #17 · (Edited)
Well it appears that I have SOLVED the aforementioned WOT issue I was experiencing. Pulled out my scan tool to see if I could get some in-depth sensor readings, and log a few drive cycles to see if anything was out of the norm. In the mists of doing just that, I decided to dive into the available special functions and active tests for the XC90, which to my surprise, there was a throve of parameters I could test, control and recalibrate. I noticed it allowed me to reset the throttle body adaptations, which I did and after a quick test drive, it absolutely restored and corrected the flat power delivery I was experiencing at wide open throttle! The engine now responds in direct relation to how the pedal (throttle) is being applied. In hindsight, it kind of makes sense now, and I'm just glad I didn't go on a wild goose chase trying to figure out what was going on. I'm also kind of happy that I don't have to drop my car off for service next week.

Ironically, after some digging online, I found that an out of calibration throttle body could also result in poor or incorrectly calculated fuel economy. Won't know for sure till I rack up some more miles, but it's a good and valid starting point. Fingers crossed that I can now achieve low 20's MPG, which I would be content with.

Thanks again for all that chimed in!
 
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