P0174 system too lean, bank 2. What's the cause?

[SD1too]

Thanks for confirming that Ian. So it's back to the filter then.

You may have read T-Cut's posts on the subject. He advises against unscrewing the housing since there is a seal between the two parts which he says is easily distorted. Perhaps that's what the RAC did.

Simon

[ianM]

Yeah, that's what I'm assuming has happened (probably the o-ring at the top). So we need to get it apart to fix the problem. But try as we might, we simply cannot get the fuel filter housing apart. It will not budge when trying to unscrew it.


Are there any instructions anywhere for how to get filter out of the car, so we can get it on a workbench where we might be able to get a better grip on it? I have all the bits needed to basically do a renovation on the filter and all its rings to see if we can fix the problem, but we've rather fallen at the first hurdle by not being able to get it apart!

[ianM]

Wanted to post an update after a productive Sunday!


We bought some new rubber strap tools to try and give us a bit more leverage, and it worked! We got the fuel filter to pieces, and discovered that (as we expected) the o-ring at the top was split in two, hence the lack of fuel pressure. We fitted the new bits following T-Cut's guide, and put it back together.


Started the engine and it fired first time, no cutting out, no backfiring, running smooth as anything. Engine light went out - job's a good 'un!


The only issue we have is that we now can't get the fuel filter to go quite back together in order to fit the fabeled orange (or in our case white) clip. It's almost there - we are perhaps 2mm out - but it can't quite fit in.


Putting all of our strength on it seems to be getting us nowhere - I'm quite amazed at how stiff this fuel filter seems to be. Even having put WD40 everywhere when trying to get it back together, we still cannot get it to line up enough. I'm at a loss as to what could be causing it, but it's another job for another week now...

[SD1too]

That's great news Ian, well done!

As for the difficulty reassembling the filter casing, this is why T-Cut urges people not to separate it. In your case, you had no choice thanks to the RAC!

As you say, the answer is to leave it for now, pour a glass of wine or a beer and come back to it at the next opportunity. You'll probably have more success then. The clip does need to be fitted to prevent future breakdowns.

Simon

[ianM]

Right, an update!

On Saturday I finally had some time to look at the car, so I got stuck in. Before our repair, we could see that the fuel filter was visibly leaking, so in order to test our repair, we went to get the fuel filter out to dry it off, in the hope of then starting the engine to see if it ended up soaking again.

Surprisingly, when I detached the fuel pipe from the top of the filter this time, petrol sprayed out everywhere obviously under pretty considerable pressure. I've never had this before, but seemingly this is a good way of telling if you're suffering from fuel filter syndrome - if there's no fuel spraying out when you take the pipe off, it's because the system's no longer under pressure because the fuel filter isn't doing its job!

Happy that in the week since we'd left it, the pressure had stayed, I had another go at tightening the fuel filter cap those last few mm with my bare hands, and managed to get it to line up! Hooray! Clip fitted, engine started, all working fine, revved up to 5k no issues. All sorted!

Or is it?

Today I took it for a test drive, and again, all looks good. Fires fine, no lack of energy at all. But on the third test loop round the estate, at the top of a little hill, I hear a whooshing sound from the fuel filter area, which sounds very much like the sound the fuel pipe made when it sprayed fuel everywhere the other day (and kind of similar to the noise you hear if you put your head near it when it's priming, only audible from the driver's seat with the engine running). Fearing the worst, I turned the car round and got it into the garage, expecting a sudden loss of power - but it never comes.

Starting the car a bit later, it still fires fine. It revs fine, there's no sign of fuel starvation, and the pipe is still properly attached. The million dollar question, then, is what the heck did I hear? Any why did it sound just like the system depressurising?

I'm wondering if it was some air trapped in the system. When we put it back together, the fuel filter was completely empty of fuel, as we stripped it down and put a clean filter etc in. I was expecting when we started the car, that would then lead to it running a bit rough, or failing to start as the air came out of the system. But that didn't happen - when we first put it back together, it started fine first time without even a hint of a hiccup.

What I'm wondering is if what I heard was the air finally being sucked out of the fuel filter, for whatever reason - maybe because I was on a hill, so the compressed air could be sucked through the nozzle at the top of the filter, or maybe just a coincidence. When the filter was first primed, the air would have been compressed up at the top, and the engine feed doesn't suck fuel in from the very top of the fuel filter - it's a few cm down at the end of the spiggot, so the stars aligning to empty the compressed air out of the filter might make sense. There are two problems with this theory though - first, when I disconnected the hose yesterday, I presumably depressurised the filter, which I'm guessing would have let a lot of that air out (not to mention that I had it at all sorts of angles too), and secondly, the engine didn't even think about going to stall, which you might expect if it's just had a load of air pumped to it - unless there's some sort of return system that sends any air back to the fuel tank (or bleeds it out) rather than letting it into the engine.

It's a bit of a mystery. but with the problem looking to be solved. I'm hoping there's a good explanation for it... I just have no idea what it is!

[ianM]

Another day, another update!

After the odd hissing noise yesterday, I decided to try starting it again today, but was fully expecting to have exactly the same thing happen when I broke down the first time - if what I heard yesterday was the seal going, I was fully expecting it to fail to start.

So imagine my surprise when it starts no issue at all. A few goes and up and down the drive, then round the estate suggest no issues at all. And no more gurgling/hissing either?

I have a fuel pressure gauge on the way (although am a bit unsure of how to attach it without spraying fuel everywhere), which will give us some quantifiable data. But if the seal has popped again, somehow - despite the renewed o-ring and the clip attached - there was no sign of it today.


(On a related note: why does the workshop manual not suggest measuring fuel pressure using the schrader valve? It wants you to disconnect the inlet hose from the rail pipe and then fit your gauge in between!?)

On flicking through the Haynes manual, I noticed they say that when you've done anything with the fuel system, you should expect it'll take a long time to start when you first try and turn it over, as the system gets up to pressure. It also suggests you might want to repeatedly prime the fuel filter to build up the pressure before starting.

With that in mind, it's weird that even though the fuel filter was completely empty after our repair, it started pretty much instantly - no longer than it usually takes at all (and did the same yesterday, even after I'd detached the fuel hose from the filter and sprayed petrol everywhere).

I do wonder if what we heard yesterday was a bubble of air in the system - but where it's come from, and why it took until yesterday to make itself known is beyond me... Hopefully any experts on the fuel system might have some more theories!

[gnu]

If it’s running ok, and you only heard the whooshing once, after restarting with air in the system, I’d be tempted to leave it and see how it goes in the longer term.

[ianM]

Originally Posted by gnu

If it’s running ok, and you only heard the whooshing once, after restarting with air in the system, I’d be tempted to leave it and see how it goes in the longer term.

Indeed, I think that might be what I end up doing! The only problem is, I thin it breaking down so suddenly, going from driving to just coasting and ending up stuck in a layby on the A34 (which I only just managed to get into) with a wife and toddler has seemingly put the fear of god into me, so that I want to make sure that, to the best of my abilities, nothing like this ever happens again...

Also, with the fuel system apparently being returnless, I'm still not 100% sure how the air would stay stuck in the system until I was on the incline on my last test trip round the estate of the day... I just don't fancy it happening again when the car really only does big motorway journeys...