04 V70 2.5T MAF reads way high, no codes, stalls out Topic is solved

ZachS · Post by **ZachS** » 01 Oct 2020, 07:22

Hey, finally made an account here because this has been a diagnosis nightmare and hopefully I can get further if I make a forum post. My V70 died while I was driving, immediately after flooring it to get up to the speed limit with a blind corner behind me. Lost power, then after about 5 seconds the engine shut off. Now if I try to start it with the MAF plugged in, it idles extremely rough, car shaking, RPM bouncing between as low as 300 and 800 for the most part but occasionally surges past 1000. It usually stalls out at some point in less than a minute, and throttle has barely any response until I press at least halfway usually. It's definitely running rich, there's a sulfur smell and the 02 sensor indicates rich. But as soon as I unplug the MAF, it seems to run just fine aside from running rich in a more predictable way.

Now, I have Vida so I can easily track different values. That's how I know that the MAF reads high. It didn't throw any codes except when I unplugged it. When the MAF is plugged in, it fluctuates between 70 kg/h and 100 kg/h on the reading. If I give it enough throttle, the RPMs will go up and the MAF will climb as well, I've seen it get to 300 kg/h. So it's not just a high reading, but a reading that tracks with engine RPM. Now here's the kicker... This is the behavior regardless of if I use the Bosch MAF sensor that was in my car when I bought it, or the brand new one from FCP Euro that I installed yesterday. Any ideas what this could be?

Post by **chrism** » 01 Oct 2020, 07:52

I only know Just enough about this stuff to be dangerous, but have you put a vacuum gauge on the intake to see if it is wondering up and down. I’m thinking that maybe some how when you tromped on the gas pedal that something on the turbo got stuck like the waste gate actuator so now you either get too much boost when not needed or not enough boost when needed???
Also have you cleaned out the throttle body recently?
Some of these cars have a nipple called a PTC, or something like that, where the PCV system ties into the turbo plumbing. It occasionally needs cleaning.
Another long shot - could the timing belt have jumped a couple teeth due to the engine reaching RPMs that it hasn’t seen in a long time.
Hopefully my rambling will get the more knowledgeable amongst us to put on their thinking caps.

ZachS · Post by **ZachS** » 01 Oct 2020, 08:03

There's a lot of things that can cause the symptoms, but I can specifically see that the MAF reads way too high. It's supposed to be 12-20 kg/h and I think 12.5 at idle. But it reads almost an order of magnitude too high when idle, and spikes even higher if I give it some throttle.

The whole PCV system was done including the expensive bit people like to skip and the throttle body was cleaned in the process. And this isn't the first time I've floored it, it's just the first time it's decided to break.

As for the your first idea about something with the turbo is waste gate actuator, would anything like that cause the MAF to actually read way too high? I haven't actually measured the vacuum/boost but I do have a boost gauge I was going to install after I got it running properly again. I know the boost pressure measurement in Vida normally just shows atmospheric until I actually make boost so not sure if that's helpful. But yeah, the key point is I know for sure that the MAF reads high, so it doesn't make sense to run around looking at other stuff unless that stuff can cause the MAF to read high.

Post by **cn90** » 01 Oct 2020, 08:05

D/c MAF and see what happens.

Also search forum for PEM.

ZachS · Post by **ZachS** » 01 Oct 2020, 08:17

cn90 wrote: ↑01 Oct 2020, 08:05 D/c MAF and see what happens.

Also search forum for PEM.

In the original post I said I disconnected it and it runs fine disconnected. I've read through countless forum posts before I made my account and tried to cover my bases in my post about everything I already tried and all of the readings that I got in Vida. Isn't PEM a fuel controller of some sort? I don't see how that would cause the MAF to read high so I haven't looked into it too much.

Post by **jimmy57** » 01 Oct 2020, 09:04

If you ruptured a hose anywhere between turbo outlet around back to throttle you'd have your symptoms. Intercoolers can split at core to end tank seam also so that needs to be checked. The turbo can pump air out of the leak as it is driven enough by exhaust the moment you start engine to force the air out. You do not have to open throttle to get turbo sped up enough for this to occur on low pressure turbo engines. The MAF is registering that air. If no leaks then failed MAF sensor is possible.

ZachS · Post by **ZachS** » 01 Oct 2020, 09:08

jimmy57 wrote: ↑01 Oct 2020, 09:04 If you ruptured a hose anywhere between turbo outlet around back to throttle you'd have your symptoms. Intercoolers can split at core to end tank seam also so that needs to be checked. The turbo can pump air out of the leak as it is driven enough by exhaust the moment you start engine to force the air out. You do not have to open throttle to get turbo sped up enough for this to occur on low pressure turbo engines. The MAF is registering that air. If no leaks then failed MAF sensor is possible.

Oh, that does make sense. So the leak would have to be after the turbo. I guess that's the next thing to check. Would it make sense that it would run well with the MAF sensor unplugged though?

Post by **cn90** » 01 Oct 2020, 09:16

What is your car mileage?

ZachS · Post by **ZachS** » 01 Oct 2020, 09:23

It's at 110K right now.

Post by **jimmy57** » 01 Oct 2020, 11:08

Yes, when you unplug MAF the computation becomes engine speed and throttle opening so the extra fuel a high MAF signal adds is gone.