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[Webby the Bear]

Evening guys.

As I've mentioned before I'm not doing a mechanic school blog this year. Main reason being is we're covering a lot we did before and it's pointless repeating myself. However I did promise I would do some updates on things that are interesting and I today have found something that I think is very interesting... and you can probably tell by the title what it is 

Anyway, I remember when hunting down a vacuum leak on the Omega I was advised to hook up a vacuum gauge and see what the IM vacuum was like. I never did buy a gauge in the end as I found the source of the leak with throttle cleaner iirc. ANYWAY...

I was amazed at what you could find by hooking this gauge up to the IM assuming you can interpret what the gauge is telling you. It includes finding...

Burned/leaking valves
Sticking valves
Weak/broken valve spring
Worn valve guides
Leaking piston rings
Blown HG
Exhaust restriction
Incorrect air/fuel mixture
Intake manifold air leak
Late ignition or valve timing

So basically, for a lot less money and effort you can use this and it will do more than a leak down test and you don't need an air compressor!

However, if it can do all this why have i very rarely heard people mention they've used it? Have YOU used it with/without success?

Discuss.

Ps, i have the document here with all the correct parameters and how to interpret the gauge readings. if anyone wants i can upload it on here. The beauty is the parameters apply to all cars and are not manufacturer specific (hence the parameters  )

 

[blackviper90210]

If they are easy to instal and they give you reliable info and you have the parameters, that sounds like a good combination! 

[Marks DTM Calib]

I have promoted them for many years, very useful bits of kit, my take on your list is:

Burned/leaking valves - yep
Sticking valves - yep
Weak/broken valve spring - possibly, it would need to be a VERY weak spring
Worn valve guides - Nope
Leaking piston rings - Only if very bad
Blown HG - Again, only if combustion cahmber related and very bad
Exhaust restriction - Possibly
Incorrect air/fuel mixture - Yep
Intake manifold air leak - yep
Late ignition or valve timing - Good luck

[Kevin Wood]

It won't tell you which of the above it is, of course, so you will need other diagnostic aids. As a quick check to see if something's amiss, and to resolve issues with the Omega's vacuum powered heater and multiram systems, though, they are a very useful device to have in the toolbox.

[zirk]

Where also sold as Economy Gauges years ago 

[conalnugent]

Music to my ears. My gauge fitting kit just landed this morning. Had bought it to detect and fix boost leaks. Can I have the information about the other things you can check pleaseeeeeeee 

[Marks DTM Calib]

Where also sold as Economy Gauges years ago 

I seem to recall Scirocos having them

[Webby the Bear]

Conalnugent... here you go

ENGINE STATE VACUUM GAUGE READING INDICATION
Steady idle (800-1200rpm) Gauge steady, 17-22 Normal & healthy
Steady idle (800-1200 rpm) Intermittently drops several needle divisions Sticking valve or broken valve spring
Steady idle (800-1200 rpm) Steady, low reading, 8-14 Small vacuum leak or valve timing off; could have low compression/worn rings (verify with a compression or leakdown test).
Steady idle (800-1200 rpm) Steady, low reading, under 8 Vacuum leak (check brake booster, vacuum lines, etc.)
Idle (800-1200 rpm) Needle drops sharply on a regular rhythm Burnt valve, or a valve with clearance too tight
Idle (800-1200 rpm) Needle drifts up & down, along with rpm drift Mixture off or small vacuum leak
Idle (800-1200rpm) Vacuum gradually drops Excessive exhaust back pressure (plugged muffler or catalytic converter)
Idle (800-1200rpm) Intermittent fluctuation Ignition miss; sticking valve
Idle (800-1200rpm) Steady, above 22 Ignition timing may be too advanced
Open & close throttle quickly Drops to about 2, jumps to about 25 Healthy engine
Open & close throttle quickly Drops to 0, jumps to about 20 May confirm worn rings (especially if idle shows only about 15-20) Verify with a compression or leakdown test.

in addition when looking for HG leaks you're looking for a steady idle reading then a repetitive drop by up to 10inHG as the cylinder where the HG is blown is coming up on its' compression stroke 

DISCLAIMER - as mentioned these are the figures provided from school and i'm still learning 

[Webby the Bear]

In addition to those figures.....

Idle - 12-15 - Fair result but wearing/worn.

Which brings me neatly on to the fact I actually used this on the omega today and got some interesting results which I pondered for a long time, couldn't understand, then had a brainwave which i'd like to share (and hopefully Mark/Kevin will tell me if i'm right )

Ok, firstly on my V6 there appears to be just one place that you can hook your gauge up to and that's the vac pipe coming in to the rear multiram. I hooked it up as per this pic (note this is not a pic of my engine):


Now the reading I got was as follows:

Idle: 15'' of mercury but nice 'n' steady.
Snap throttle: goes up to 18'' of mercury whilst revs increasing but then drops down to 14'' of mercury when I shut the throttle.

Now being retarded this had me confused cos I was under the impression that when the throttle opens the vacuum should drop as you're lowering the pressure so therefore I was thinking WTF  as it went up!!!!

THEN my brainwave.....

The multiram system works off vacuum at higher RPM therefore the reason my gauge increased was because I was seeing the vacuum being sent to the multiram to make it work.... if there was another place in the manifold i'd have seen the usual drop when throttle opened. am I right?

[TheBoy]

That point in the vac on your car will be behind a vac tank, so no good.

Use one of the outlets off the T pieces on the manifold to servo pipe.

[Webby the Bear]

That point in the vac on your car will be behind a vac tank, so no good.

Use one of the outlets off the T pieces on the manifold to servo pipe.

oh  ok fair enough.

strggling to think where you mean Jaime. ill have a look in the morning and get the vac gauge out at school again next week 

[Webby the Bear]

...oh and was I right about the reason the gauge went up when I put revs on?

[conalnugent]

Where is the right place to connect the boost gauge into my 2.5td??? Currently I plumbex it into the small pipe thst comes off the bottom of the inlet manifold.  Is this alright? The gauge is in bar. Reads 0 on idleand just below 2000rpm boost kicks in and goes swiftly up to 15psi / 1 bar of boost then at the top of the rev range drops off.

Must upload a video before the day is out.

[Webby the Bear]

a vacuum gauge measures in inches of mercury (or ''inHG'')

Your gauge is for pressure. does it also have inHG?

[conalnugent]

Unfortunately not