Question for petrol-heads

Dear old Gothilda has a minor fault. I know how to fix it, and it will cost me a few pence and a few minutes of time.

The small hose that runs from the induction side (after the throttle body but before the manifold) to the fuel pressure regulator has split and now snapped. It means two things:

1) The fuel pressure is not regulated, so the ECU has to adjust injector timings based on readings from the MAF and O2 sensors, which it has to do anyway, but now it has to do it more to take into account the loss of regulation of fuel pressure. It just means that any sudden change in load or throttle position leads to a second or two of lumpy running as the mix goes lean or rich because the pressure isn't regulated at source.

2) When decelerating with no throttle, she'll be sucking filth in through the now open hose and worse, when flooring it, some of the pressure generated by the turbo will simply escape, which would explain the new whistle/hum that she does under load.

I only replaced the hose a few weeks ago with brand new hose, which obviously doesn't stand up to the temperature changes experienced in the engine bay.

So two questions really.

How long will she live if I leave her like that for a while?

And where can I get some decent hose that will take the conditions of the engine bay without perishing? The last hose came from the generic motor factors shop, and it was generic rubber hose, sold by the metre.

 

I guess so yes. I've realised I might have mis-remembered where abouts in the induction side it connects. I can't remember if its before or after the MAF now, but in essence, yes, vacuum in the inlet manifold transfers via the hose to the fuel pressure regulator, which then adjusts the rate at which surplus pumped fuel is allowed back to the tank, thus keeping the relative fuel pressure constant regardless of air pressure at the injector nozzles.

Its kind of fine tuning in a way. The ECU does a good job of adjuster injector opening time based on feedback from the MAF and O2 sensors, but of course any sudden change in load, such as if I floor it, or when she changes gear, the sudden change in relative air pressure at the nozzles means the injectors will squirt more or less fuel than the ECU thought. It will of course quickly correct, but not before firing a few cycles on the wrong mix. I notice this mostly when she kicks down, as she hesitates. Exactly as she did last time the hose failed, and putting a new hose on got rid of the hesitation on kick down, but then I noticed the hesitation had come back, so I had a look, and this time the hose hasn't just split, it has actually snapped off completely.

 

You're both pretty much on the money.

As we're dealing with a gaseous pressure or case vacuum and there is no flow as such (just pressure/vacuum difference) the id of the hose is not so important. So a good quality diesel leak off pipe offcut will suffice for now/for ever if it will fit (five minutes in hot water usually does it). Failing that, you'll find something in the local scrappy, or just order a new one from Volvo, although they'll probably want a tenner for it!

 

Thanks chaps. I'll see if I can source an original. Or I might pop to a different local motor factors (the one I used has a reputation, and unfortunately its not as good as the good kind of reputation), and see if I can get some hose intended for diesel 'leak off'.

For the immediate short term though, I think I still have some of the not so great hose left somewhere in my junk cupboard, which I'll stick on just to smoothen her out a bit for now.

 

That's good of you Off the top of my head, I think its about 1ft long.