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Vectra vacuum loss.

Hi,

I come to the well again to call on your experience.

I have a ~100K miles '98 2.0L DTH Vectra deisel which has recently started illuminating the management warning light on light load e.g. overrun in slow traffic. I have replaced the mass airflow device in the last 12 months and cleaned the EGR valve recently. I suspected the vacuum pump and attached a guage to the vacuum line to monitor it and found it varies between about -5 to -15"Hg of vacuum although that drops under certain conditions like taking the foot OFF the accelerator when changing to a higher gear.

That seemed rather flabby so I detached the output line and just the vacuum from the pump alone. That showed a drop to 20 to 25"Hg vacuum within about 15 seconds of starting the engine and letting it just idle. (In case you use a different measure of vacuum, complete vacuum is -30"Hg.)

That reading from the pump alone seems fine and I don't think a replacement is the likely cure. What is your view? Could the lack of good vacuum in the overall system be due to a faulty solenoid valve or individual items leaking or leaky pipework joints? Have you any service experiences of common problems here?

As always, your thoughts are appreciated and have helped me shorten many problem fixings.

Tony.

Reply to
Tony
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The vacuum supply to the air recirculation solenoid on the heater box is taken from the vac pump, as well as a line to a coolant cut-off valve if your vehicle has air-con. IME, either of these can cause a leak on the vacuum system. The other check to make is on the EGR actuator - sometimes the diaphragms leak. Connect a tube to it, the suck on the end of the tube. If you can pull air through constantly, then the actuator is shot, and you need to replace the whole part of the manifold it is joined to. Not cheap I'm afraid!

HTH

Anthony Remove eight from email to reply.

Reply to
Anthony Britt

"Tony" wrote in message news: snipped-for-privacy@4ax.com...

Do you actually know the fault codes that are bringing the MIL light on?

If you don't then i would suggest you find out.

Regarding the vacuum. The vacuum pump should be able to deliver 70-100 MPa (not entirely sure about units could be mBar) vaccum. One thing you have to remember about this particular engine, is that all actuators are controlled by vacuum (Turbo wastegate, EGR valve & Inlet Manifold Swirl Control). If you were to lose vacuum, the car will enter limp home mode (reduced power + limited to 3500 or 4500rpm). Provided you are getting the required vacuum at the pump, the next major thing to check is the brake servo. Easiest way is to connect the vacuum gauge to the small vacuum pipe on the pump. You should get full pump vacuum. If you press the brake pedal the vacuum should drop them return to the full pump vacuum. If the vacuum doesn't return to what the pump alone produces, then i'd suspect a leaking brake servo. (I've done quite a few of these recently) The next thing to try is disconnecting and blocking the vacuum pipe at each individual solenoid, and seeing what effect it has on the vacuum reading. There should be 3 solenoids 2 just inside the nsf wing (1 for egr valve + 1 for inlet manifold swirl control), with the other near the osf strut tower (turbo wastegate control - just follow the vacuum pipe back up from the turbo). There will also be a slight loss on these solenoids as they are working most of the time. To check the solenoids themselve requires the use of a Tech2 to individually activate the solenoids and check the vacuum.

Regarding the vacuum drop during gear changes, this is caused by the turbo wastegate being pulsed to limit the boost pressure, along with the other solenoids working.

Moray

Reply to
Moray Cuthill

I had the same symptoms with my Astra. The warning light would usually come on whilst idling with a hot engine. The air mass meter was replaced by a vauxhall garage free but the symptoms persisted. As it was out of warranty anyway they were unwilling do do any further work (they weren't even obliged to replace the air mass meter - but they did it anyway). It was apparent that the EGR valve and the EGR vacuum control solenoid had been replaced previously, so the mechanic ruled this out.

I measured the vacuum using a cheap guage and it showed -700mbar with a cold engine, but only -500mbar with the engine hot. Clearly the vacuum pump is weak but I couldn't afford to replace it at the time.

Through experimentation I found the vacuum was better if I disconnected and plugged the pipe to any one of the vacuum control solenoids - these solenoids all seem to leak a small amount of air through a vent pipe when in their open state.

I eventually elected to disconnect the solenoid valve which operates a diapragm which opens/closes some butterfly valves in the intake manifold. This solenoid is located nearest to the left headlight, next to the EGR control solenoid. The electrical plug must be left connected else the warning light will be illuminated.

Doing this increased the vacuum to -700mbar at hot idle, and I've not seen the warning light since. FWIW, the system that I disconnected simply blocks off the ports to 4 of the 8 intake valves at low revs. This is supposed to improve torque at low revs, but I can't feel any difference whatsoever. The default state of the butterfly valves is open, so the air intake is not restricted.

Try this if you don't feel like shelling out on a new vaccuum pump.

James of Sunderland.

Reply to
James

I have just read the three replies from Anthony, James and Moray and there is really good food for thought there. I will do my best to check it out over the week-end. It is very difficult to get a Tech2 readout from the dealer here or I would have started with that. It is not a recognised 'job' with a price on it to them so I have to beg one when they are not busy.

In particular I did not realise the use of vacuum to the recirculation valve on the heater box. I did check the EGR diaphragm in the past few months and it seemed OK.

Anyway, you have alerted me to the need to check each of the many items on the vacuum line individually and I should be able to improvise something in each case.

I will happily buy a new pump if it is required but I'd like to be sure it is first. Is there any way of improving the pump internals by good fitting? I am a time served engineer but not on 'Motors'.

Thanks again. They were very fruitful postings indeed.

Tony.

Reply to
Tony

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