vacuum pump testing

vacuum pipe is usually about 3 or 4 mm, just connect direct to the pump only, then you can establish the reading you should get when you reconnect everything

Thank you. I immersed the pipe in hot water from the kettle and that softened it enough to fit it onto the vacuum pump. I found the vacuum pump with a little help from the Haynes book. If I attach remove the hose from the vacuum pump and connect my gauge there instead, it reads

-28 or -29. I couldn't quite tell which as the markings were not very clear on the gauge. I couldn't quite work out which marking was -30; it was just under 30 hence my confusion.

Are these figures inches of mercury? From what I've read here it ought to be -30, so I assume my figure is a good result? There is a lot of writing on the scale about idling, and good and bad - fuel economy?, and overdrive. What are they all about? Are they for if you connect the gauge to a petrol pump?

The hose goes from the vacuum pump to a strange "tee" with four branches. One goes to the brakes; the other two are confusing me. One goes to another tee, this time with the usual three branches, but the branch from this tee goes back to the fourth branch of the first tee, making a loop. What is the point of that?

The final branch continues behind the engine, I presume down to the egr valve. I haven't stripped back all the air ducts etc. to allow me to get down there yet.

The vacuum hose reappears on the other side of the engine where it runs around to the turbo waste gate. The vacuum at the wastegate is

-10. I know nothing about turbo chargers. Should the vacuum be -10 or should it be -30? Is the missing minus twenty what is causing my problem?

To test the egr valve, I presume I need to test it in situ, so do I need to strip all the air ducts to access the valve and them rebuild them to run the engine? Is it any easier to access the egr valve from underneath using ramps?

Thanks in advance for your help. Hope you all had a happy Easter.

Full gauge or nearly so is the right sort of reading to see, inches mercury sounds right for the units. The loop back sounds wrong, but should not effect the reading. You should have the same reading at turbo as you get at the pump, so you need to disconnect/blank bits or move back till you find where the vacuum reading is back up to where it should be. A cracked pipe or connector or vacuum operating unit is the likely cause of the problem. Don't worry about the egr valve till you have found where the missing vacuum is !! get Tee pieces from a car shop for washer circuits or go to a fish place that sells aquarium bits, plus some tubing can then be spliced in to check vacuum at various points.

I am not familiar with your exact vehicle so I don't know where to access bits from, sorry.

The other readings (idle etc.) are for when you use the vacuum gauge to measure inlet manifold vacuum on a petrol vehicle

That's what I thought, at least we know what the problem is now.

I have seen various tees and connectors for windscreen washers at Halfrauds. I am a bit unsure what to do with them. Do I cut into the existing vacuum hose to insert the tees? Once I remove the gauge do I join the two ends with a straight connector or is it dangerous to drive the car with the vacuum hose full of joins? I would think the more joins in it, the more likley one is to leak.

Once I have found the leak do I need to buy a special hose to replace it or will the washer hose do?

Thanks for your continued help.

the way to use a t piece is to disconnect a hose at a junction and add the t piece with a short extra bit of hose and connect the gauge there.

A good car shop will sell vacuum hose, washer tubing will just collapse as it is designed for pressure rather than suction. You could disconnect all the little vacuum pipes and use the car, you will probably not notice any difference and it would not be dangerous, the vacuum pump is over sized enough to cope with a hose off and still give the brakes enough vacuum. the most likely culprit will be a split at a connector or actually in a vacuum actuator. I assume you have a thin hard plastic pipe arrangement with softer hose bits at junctions? rather than long lengths of flexible hose?

The first thing I'd do is block the hose at the waste gate, after the gauge, to eliminate a waste gate leak. If it's still -10 there you know the leak is somewhere between the pump and the blocked end and that it's not your waste gate. Then work back towards the pump and the leak will be somewhere between where you get -30 and -10.

Thanks for the advice. I disconnected the waste gate and plugged the gauge into the end of the hose. It read -10 so the leak is before the waste gate. I realise I should have asked before I started but is it ok to idle the engine with bits disconnected: I won't damage the engine if the waste gate or egr, etc, is not connected to the vacuum will I? Now all I have to do is find where the pipe goes when it disappears behind the engine. thanks again.

That's what I have been doing so far, so good.

Thanks, so it is not vehicle specific; I don't need to go to a main dealer/stealer?

That's what I wondered, thanks.

probably not notice any

So as long as there is no leak before the brakes, I don't need to worry. I am sure that the leak is after the brakes as I have not noticed any problem stopping!

It is a black plastic pipe. I'm not sure whether you would say it is hard. It is more rigid than the window washer and aquarium pipe we have talked about but it is not completely rigid, so it's an intermediate firmness! I haven't found many junctions yet: I know the start is by the brakes and the end is at the turbo charger but the rest is hidden behind the engine. From what I can see though, it is the same pipe along the length and at junctions. Where it gets near anything hot, it is sleeved. HTH?

Thanks again.

it has no effect on running the engine as it is all a separate system, so don't worry about idling it with pipes off.

At least you know something is good now :-)

Didn't you say there were some connecters earlier on, cross and tee ones? If they go off into unknown places you could leave the gauge at the waste gate with it blocked and try removing each of the pipes at the connectors and blocking the connector. If the vacuum goes to -30 at the waste gate you would know that the leak is down the pipe just disconnected.

Hello again,

I did start a new thread but no-one noticed ;(

I have followed the vacuum hose and I can only see that it goes to two solenoids both of which are at almost full vacuum. I am having second thoughts whether there is a leak between the last solenoid valve and the waste gate because I noticed that the waste gate is -10 at idle but if I touch the accelerator pedal the vacuum shoots up to -20 and then slowly comes down again. Is the vacuum at the waste gate supposed to vary according to the revs? If so, I haven't managed to find a leak anywhere. Even when I bypassed the final length of tubing with a length of washer tube I got the same -10 peaking -20 result. help!

I noticed but you seemed to be progressing and there wasn't anything more I could ay so I didn't bother :-)

That just means that the vacuum pump is pulling more than the leak can let in when you rev up. If the system was sealed the pressure would be the same wherever you measure it. You will get the highest vacuum at the pump and the lowest at the leak and beyond. Between the pump and the leak it will fall as you get towards the leak. I don't know the layout so can't suggest where you look or even if it's normal to have a vent somewhere in the system, I'd have thought that unlikely though.

Unfortunately it's just a case of trial and error.

Thank you for the explanation; I don't know anything about turbo chargers, so I wasn't sure whether the pressure, or rather vacuum, was supposed to alter at the waste gate according to the revs. Now that know it should be constant at -30, I know something is wrong in that final section of tube.

I asked at a few motor stores but no-one sold vacuum hose, so I have had to go to the Citroen dealer. They say that section will cost thirty-odd pounds exclusive of vat. The problem is, they won't accept returns if the fault turns out to be somewhere else.

I am wondering whether the leak may be at the solenoid valve itself because the vacuum is ok up to there. I tried to replace the last section of vacuum hose with washer hose and had the same lack of vacuum when I put the gauge on that, which suggests the leak is possibly on the solenoid rather than the pipe coming from it.

Like you say, it probably will be a matter of trial and error swapping things, I only hope I don't have to swap too many things before I fix it, otherwise I could end up with a lot of parts that I cannot return.

Thanks again for your help.