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[Tick Tock]

Hi Guys, I'm looking for suggestions as to where to look next regarding sluggish take-up on my 2.5V6 engine (manual transmission).

Today I've taken the plenum off, checked all the vacuum hoses and connections and I've still got the same problem. It's purring like a kitten on tickover, but pulling away it's sluggish and the engine vibrates. Over 3000 revs and it runs sweetly and accelerates well, but anything under that it isn't happy.

I've ruled out plug leads, spark plugs, dis pack, oil leaks or water in the plug wells and breather system. I've tried to understand more about the multirams and have an identical car for which I can compare with. I've read that blipping the revs to over 4000 should actuate the rear multiram, but neither of the engines do that.

So I'm now stumped.... hoping someone may have a suggestion or know the root cause.

[TheBoy]

After you turn car off, if you disconnect vac hose from multiram actuator, can you here the vacuum?

If not, check one way valve in reservoir

[Tick Tock]

Both front and rear multirams operate when a vacuum pipe is connected. When you say 'actuator', do you mean the electrically operated valve?

Vacuum present at front T piece after vacuum tank, but rear looks to be fed from the nearside air intake which doesn't seem to have vacuum.

[TheBoy]

Pretty certain both multirams fed from tank near alternator.  Check Marks DTM's diagrams in the Guides section for how they should be routed.

[Tick Tock]

There's been no recent work on the car so it's piped up correctly (was running fine until yesterday).

So for clarity, should I be looking at front or rear multiram for this low RPM problem?

[Tick Tock]

In the Omega maintenance guide - vac pipes setup, it shows both multirams piped from the vacuum tank (near the altenator), whereas on both my cars the rear multiram is piped from the nearside air intake  - according to other sources this should connect to the fuel pressure regulator which isn't shown for clarity on the maintenance guide.

They've both been working fine with this arrangement.

Should that nearside air intake pipe go to the fuel rail? It doesn't appear to produce vacuum when engine is running.
 

[sjc]

If both vac reservoirs are working then it won't really matter which one the rear multi-ram is connected to, but it sounds like the one beside the cabin filter is not holding vacuum.

Would be worth temporarily plumbing it to the front vac reservoir to see if things improve.

As mentioned in the guide... The fuel regulator has a pipe that goes to the throttle body and doesn't connect to the other vacuum pipes.

[sjc]

Also, the rear vac reservoir supplies the infamous heater bypass valve... if the diaphragm in that has ruptured then it will create an air intake leak... easy to test by removing the vac hose from the HBV and plugging the end.

[Tick Tock]

I'm beginning to think that some re-plumbing might be in order, although both cars have been piped this way and working well for over 10 years (as acquired). I've also seen other images on this forum of cars piped this way. Even if it is incorrect, this problem only started yesterday.

So what we're saying is, this pipe should go to the fuel regulator?

[sjc]

I'm beginning to think that some re-plumbing might be in order, although both cars have been piped this way and working well for over 10 years (as acquired). I've also seen other images on this forum of cars piped this way. Even if it is incorrect, this problem only started yesterday.

So what we're saying is, this pipe should go to the fuel regulator?

Correct - the hose from the IAC pipe should go to the FPR.

The one for the rear multi-ram will be the typical thin rigid plastic hose with a 180deg rubber elbow on the end

[Tick Tock]

Thanks so far for the assistance.

IAC pipe now on FPR -  rear multiram now connected to front multiram pipe - problem remains.

Disconnected and sealed all cabin & HBV vacuum pipes to eliminate - problem remains.

No vacuum being held after switching off engine.

Could it be the vacuum tank?

[sjc]

You could try switching a tank from your other car.

Presume there's no fault codes showing?

[Nick W]

Thanks so far for the assistance.

IAC pipe now on FPR -  rear multiram now connected to front multiram pipe - problem remains.

Disconnected and sealed all cabin & HBV vacuum pipes to eliminate - problem remains.

No vacuum being held after switching off engine.

Could it be the vacuum tank?

Of course it could.


But it's much more likely to be one of the vacuum pipes or connections that litter the engine bay.


I would suggest a cheap handheld vacuum pump and careful inspection to track down the leak.

[Tick Tock]

Every day's a school day!!

No fault codes showing (apart from 21 earlier [paperclip] when I forgot to plug the ICV plug back in) doh.

I'll make a start on swapping the tanks - handy having more than 1 car.

I've been through all the pipes in the engine bay with a fine tooth comb, nothing chaffing or likely to cause a leak.

[Tick Tock]

Tanks swapped and no change  :'(  I've had enough for today.

[sjc]

It's possibly the actuator on the rear multi-ram, you could try switching the plenum between the cars.  Just remember, everything you eliminate gets you closer to the fault

Found this thread with some relevant info on how the system works - rear valve open at idle and over 3000rpm, actuator operates to close it between those 2 points.

https://www.vauxhallownersnetwork.co.uk/threads/multi-ram-problem.86442/

[Tick Tock]

Quote "Its not connected right.....in fact its connected very badly....!"

8 hours faffing about and no further forward. Swapping the pipes to the correct position didn't make any difference, but thanks to TB earlier I suspect there should still be vacuum held in the system after turning the engine off.....  which I haven't got and need to investigate further.

I suspect it's something stupidly simple - we'll get there.

[TheBoy]

If no leaks in the vac tubes and elbows, its common for the one way valves fail. You can get inline one way valves if this is the issue, but prove/investigate vac system first...  ...before spending more time swapping stuff

[Tick Tock]

Not going to get a chance to work on the car today.

Next session I'll start from scratch and remove and check all vacuum piping, refit as per maintenance guide, and report back.

[Nick W]

Not going to get a chance to work on the car today.

Next session I'll start from scratch and remove and check all vacuum piping, refit as per maintenance guide, and report back.

As TB said, you should check all the components too.
Which is where the vacuum pump comes in handy.

[Tick Tock]

Armed with a vacuum pump, pieces of pipe and soft plugs.......  Disconnected manifold pipe at plenum and sealed - system holds vacuum for at least 5 minutes. I can confirm the multiram vacuum tank non-return valve is fubared, and that's the same on the other car which runs well. A new inline non return valve will keep vacuum in the multiram pipework (on the shopping list), but I really don't think this is the cause of the rough running at low revs. When I unplug manifold pipe from brake servo, it hisses, so obviously that non-return valve is working.

Operating the multirams by hand when increasing revs makes no difference, so I'm back to square 1.

Fuel? No problem at high revs and the car goes like a scalded cat.

Ignition? Runs sweet on tickover.

Any other suggestions appreciated - and thanks for the assistance so far.

[sjc]

Is it still sluggish under 3000rpm with your foot to the floor?  Wondering if it’s MAF related, pretty sure you can test that by unplugging it - will bring on EML but should still run just not at 100% efficiency. Same with O2 sensors.

[Tick Tock]

That's a good 16 hours in so far....  I'm no further forward and the swear jar is overflowing.

I've learnt a lot about the vacuum system and multirams, but as much as it pains me to say, I'm going to have to start swapping parts from the good car to this one just to try to get to the bottom of the problem.

[cam.in.head]

yes .when you have another identical car part swapping is a good idea. one at a time until the fault swaps too !
some frown on this idea but nothing wrong with it providing you dont end up with 2 faulty cars !
and you keep tabs on what you are swapping and doing it methodically.
fault finding the other(technically correct way ) is fine normally until you have one of these 'strange issues'.
in the end you usually find its something simple or obvious and the signs were there !

[Tick Tock]

Update - as I didn't seem to be getting very far at the weekend. Took the car out for a fast drive to see how it performed at high speed and when I got back it seemed to be running worse than before. This is after all the engine bay pipes have all been connected up as per the diagram.

Removing all the spark plugs, number 2 & 5 are much darker than the other 4. Now suspecting coil pack maybe breaking down, so spent time removing it. I really don't like the idea of trying the one from the good car, as it's a nightmare to get to, so have a new coilpack on its way. No cracks or bulges or any visual indication it's faulty.

When it's all back together with some new plugs, I'll report back.

[sjc]

Yep, sounds like coil 3 in the dispack is on the way out or you have a shorting plug lead to either of those 2 cylinders.

[TheBoy]

Before swapping parts, fix the know problems if you haven't already (ie, the vac), else you could be chasing phantoms for ages and making things worse.

[Tick Tock]

After waiting several days for coil pack to arrive, fitted it this afternoon and reassembled plenum, intake, scuttle, etc, and now it runs just sweet again - job jobbed.

Vacuum non return valve ordered for multiram system, still hasn't arrived yet, but at least engine is responsive once again and under bonnet plumbing is in order. 

[sjc]

Happy days!!!!

[grifter]

After waiting several days for coil pack to arrive, fitted it this afternoon and reassembled plenum, intake, scuttle, etc, and now it runs just sweet again - job jobbed.

Vacuum non return valve ordered for multiram system, still hasn't arrived yet, but at least engine is responsive once again and under bonnet plumbing is in order.

Just out of interest, where is that located in the bay? you said it's fubared but does it give any obvious symptoms of failure other than not holding vac?

[Tick Tock]

The non return valve is inside the vacuum tank (a black plastic box located down below the air intake), with a supply pipe from the vacuum manifold, and another pipe providing vacuum to the multiram actuators. A replacement non return valve is now fitted where the supply pipe connects to the manifold, holding vacuum in the system after engine shut down.

As for symptoms of non return valve failure, this would only affect the torque curve of the engine so I'm lead to believe, so if you pootle around you probably wouldn't know it's failed. Or would you? I've learnt a lot about the vacuum system in the last couple of weeks (even though it was the coil pack breaking down that was the main culprit) and I've been driving around for nearly 20 years with the FPR plumbed incorrectly into the vac system without any problems, when it should have been fed from the nearside air intake pipe.

[grifter]

Is that the vac box you are talking about the item 20 in this diagram?

https://opel.catalogs-parts.com/#{client:1;page:part;lang:en;category:car;catalog:v94;group:g;groupsub:0;subgroup:58-1}

The non-return is inside this so you replaced the whole vac box effectively?

[Tick Tock]

I've retained the vac box/tank (item 20 on that drawing), just fitted a new inline non return valve on the vacuum supply pipe.