Vacuum pipes?
 

I have an F Reg 240DL, 2.3. Engine is a B230K. It has a very annoying slight hesitation on gentle acceleration. If you floor the gas pedal it's hardly noticable but on gentle acceleration it is not smooth. It's like it's being held back, not getting enough air/gas. It has been to two garages who were a waste of time. A friend spotted that one of the rubber connectors for the small coloured pipes to the engine body had a split in in. I thought I had found the problem and sealed the split but it was not to be.
Having given up on garages I was thinking I would replace all the coloured pipes and connectors to see if that helps. Does anyone know if these things are specific to Volvo, size wise, or are they just available at any motor factors?
I am not very technically minded so thought this would be an easy change in the hope it sorts the problem. Car is fabulous apart from that ! I am assuming these pipes are some sort of vacuum system.

I notice in your 3rd picture the large diameter black rubber tube from the Pulsair bulb appears to be unplugged from its connector to the air filter box.
Was that deliberate in order to make a clearer view of the small pipes, or what?

it does sound like a lean mixture (rather than weak sparks) and the #1 cause of lean mixture as you describe is an air leak into the inlet manifold, letting 'unmetered air' into the engine. On engines with Oxygen sensors and 'closed loop' running this kind of fault can be masked but on 'open loop' cars (most pre-cat ones) this kind of fault results in lean running.

Often the idle mixture can be artificially enriched in some way to compensate for the air leak, but these adjustments may not compensate for an air leak at part throttle. Note that when the throttle butterfly is wide open, there is very little pressure difference between the inlet tract and the outside air, so there is relatively little (unmetered) air drawn in through any given leak path.

So it is best to check for leaks into the inlet manifold; leaky/disconnected vacuum hoses, cracked/leaky rubber intake boots, that kind of thing.

Some connections to the inlet manifold on some cars are basically a controlled leak (eg some cars have a cabin temperature sensor that has air drawn across it all the time, and that air passes into the inlet manifold), but most of the devices on the end of vacuum lines ought to be vacuum tight.

It doesn't always taste nice (tip; connect the hose under test to a clean piece of rubber hose when checking any given line) but you can test these by sucking on the end of the pipe that connects to the inlet manifold and putting your tongue over the end of the hose. Your tongue should 'stick' to the hose (which has a partial vacuum in it because of the sucking; practice on a plugged length of hose to get a feel for it). If there is no suction on your tongue, the device at the other end of the hose is leaking air, and may be the source of your troubles.

Dunno what exactly is fitted to the vacuum system on your car (lots by the look of it) but possible culprits include vacuum brake servo, fuel pressure regulator, 'warm-up' air divertor in the inlet to the air filter, vacuum advance module on the distributor, other vacuum motors.....

FWIW the narrow (nylon?) vacuum hoses seem pretty reliable but if one rubber vacuum hose/joiner has split the others will be well on the way; on a lot of cars these hoses are amongst the first things to fail (I've seen the same thing on Vauxhalls, SAABs, BMWs and Volvos...). I'm tempted to say 'if in doubt, replace the lot'; lengths of rubber hose can be bought for this purpose.
[When I've run out, in a pinch, I've used, er, similar hose from an old washing machine; in fact this seemed to be much better quality than the stuff used on the car...…]

hth

cheers

You had me worried that I had missed something blindingly obvious !! I have double checked and it is attached, it just comes out the back rather than the top, which appears to be blanked off. Photo uploaded to explain but not very good quality.

Thanks Brucee, lots of good advice there. Will have a suck around over the weekend !
The rubber bit that had already split was a 'T' piece. Are these rubber bits standard size to all cars or are do you have to get special Volvo ones, do you know?

the same size of rubber hose is used for vacuum lines on a wide variety of cars. Because it only sees a few psi vacuum, unreinforced rubber hose is good enough; it just needs to fit OK, be oil resistant, and be thick-walled enough that it won't collapse under the vacuum.


I've replaced 'all rubber' lines with 4mm plastic pneumatic line (as is fitted in many cases anyway), and the rubber hose (for joiners) can be found such that it will fit over barbed spigots of ~5mm diameter, +/- a bit. 'T' pieces meant for windscreen washer plumbing are usually just fine in vacuum lines.

A good trick is that the 4mm plastic pneumatic hose can be heated at the ends (using a naked flame) and this usually creates a sort of flare/barb. Once cool, 4mm line ends so treated are a more snug fit in typical rubber hose.

cheers