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Discussion Starter · #1 ·
Hi all,

The other day I was on cruising in my '09 XC70 on the highway at 105 km/hr and I could feel something wasn't right. It was like a pulsing or a surging in power, and I initially thought maybe the fuel pump was acting up, but my RPMs were staying stable, at just above 2k, so that wouldn't make sense for a fuel pump issue. It felt a bit like I was driving into a headwind, and it was intermittently gusting, and the car was fighting to stay at 105, as I did have it set on cruise, but there was no wind.

I stopped after a few minutes, and checked the tires, to see if any were low, but that wasn't the case. I pulled back onto the highway and floored it, and it was as responsive as it has always been, and it was fine for 20 or so minutes, and then the surging resumed. I turned off cruise, to see if that had anything to do with it, but it was still doing this, and eventually I lost all power to the transmission, yet the engine didn't stop, but rather the revs jumped up to 3k! I was coasting to get off the highway, and had no response from the accelerator, no matter how shallow or hard I depressed it, and after a few seconds, the revs dropped back down to 2k and I had power in the transmission again and was able to get it home without it losing power to the drivetrain again.

And all of this was happening with no CEL or any warnings on the dash, so it's not like I can run it through a code reader or VIDA (I don't have VIDA, but have wondered if I should get a 3 day subscription to check it out myself). Does the car need to have a CEL on before it drops a code? I certainly don't feel like taking it to the dealer and having them start replacing things without knowing what is actually the issue. I did have my dad, who is mechanically inclined, drive it for 20 minutes to see what he made out of it, but like anytime you want to show someone the problem, the car acts normal. Should I continue to drive it until I do get a CEL, and risk stalling out again in traffic?

At this point I'm wondering if it's a transmission issue, which is terrifying, or if it is the 'lurching' that characterizes an issue with the fuel pressure sensor on the fuel rail.

Just wondering what others figured before I get swept into the abyss of dealing with the dealer. Thanks!

I'm currently at 148,xxx kms.
 

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having been one of those people bitten by a wonky fuel sensor I would suggest you get a new one and make sure that's not the problem first. It's cheap, it's easy to replace, and at 10 years and 150k kms it seems likely that things like this are going to fail. I was lucky when my fuel pressure sensor died for good I was in the driveway - being far away from home sounds far less pleasant haha.

If you know that sensor is original I would replace it without hesitation and go from there.

https://forums.swedespeed.com/showthread.php?512305-I-think-my-fuel-pump-just-died
 

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Discussion Starter · #3 ·
having been one of those people bitten by a wonky fuel sensor I would suggest you get a new one and make sure that's not the problem first. It's cheap, it's easy to replace, and at 10 years and 150k kms it seems likely that things like this are going to fail. I was lucky when my fuel pressure sensor died for good I was in the driveway - being far away from home sounds far less pleasant haha.

If you know that sensor is original I would replace it without hesitation and go from there.

https://forums.swedespeed.com/showthread.php?512305-I-think-my-fuel-pump-just-died
Thanks jadnhm, this makes a lot of sense. I recently picked up a DiCE and VIDA pair, and did a live-time diagnostic test of engine RPM and fuel pressure, and I got lucky and the 'surging' did in fact occur, which corresponded to a spike (normal pressure is about 400kpa and it jumps to over 900kPa) in fuel pressure on the graph in VIDA. I am planning on running it again to grab some screen shots to upload for the rest of the community, and then compare these results after I install the new sensor when I receive it from FCP Euro.

I will post a link to the new thread when I've got it up!
 

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holy cow! 900 spa is roughly 130 psi! I doubt the fuel pump in these cars is even capable of 130 psi... This seems like reasonable proof of a bad sensor to me.

It seems most 'modern' fuel systems work by reading fuel pressure into the computer and then modulating the fuel pressure using a PWN signal to the pump controller (which I guess then either pulses the pump or alters the voltage it receives? something like that). Honestly I see /why/ manufacturers would choose this for assembly reasons, probably fuel control reasons, maybe even costs? but mechanically pressure regulated systems seem a LOT simpler.
 
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