Vac gauge readings extremely fast needle shake

[urdrwho]

Vacuum gauge reads 20>21 but needle has needle shake and it is why I say 20 or 21. It has needle shake like scenario #3 on the link below except that the numbers are 20>21. Shakes so fast it is very blurry.

http://www.secondchancegarage.com/public/186.cfm

The explanation of such rapid needle shake as that on scenario #3 is valve overlap, intake and exhaust momentarily open at the same time. A car with such needle shake would be a high performance engine with high lift, long duration and large over lap. I don't think that is a description of a stock 2.5.

None of the 15 scenarios come close to my results -- except #3.

Err I can't remember but acceleration drops the needle to zero or close proximity and up to @25 on deceleration.

 

[Falken]

Looks like it is from my automotive textbook someone scanned in:

http://www.google.ca/imgres?imgurl=http://i275.photobucket.com/albums/jj287/naskeet/Vacumm-Gauge.jpg&imgrefurl=http://www.thesamba.com/vw/forum/viewtopic.php?t%3D286854&h=712&w=1023&sz=155&tbnid=ASB9QRVIqbHBmM:&tbnh=90&tbnw=129&zoom=1&usg=__a9Ibv04B9DMmhgNQ9P7mfFeH5EI=&docid=SubBSmAV0805dM&sa=X&ei=TlbEUfaBD8Wj4AOds4HICg&ved=0CDQQ9QEwAQ&dur=0

Number 8 may be your problem.

http://www.youtube.com/watch?v=dVIGpUW2g7E

 

[urdrwho]

Thanks for the link. I've looked at other charts but none show the needle shake of only 1 or 2 on the scale. Worn guides are rapid needle shake but the swing is like 4 or 5.

I'll do the test again, I was sipping a beer while doing the test. It was a nice summer like evening....what can I say.

 

[ARCOgraphite]

Street engine have modest overlap, intakes open ~10 deg BTDC while exhaust is about to seat. You need to damp the vac gauge with a small oriface or needle vale or use an oil damped gauge.
But - How's the valve lash look? You MIGHT have a tight valve, I suspect tight valve on my honda as i have very shakey idle and a loss of available low end torque over performance as-new. Unfortunatley honda makes it VERY hard to adjust the valves compared to imports ive worked on in the 80s and 90s. The Sin of Poor Design and no maintenance consideration for such a simple SOHC engine with archaic jam-nut adjusters.

 

[urdrwho]

Well the car throws an intermittent code P304 (cyl 4 misfire). To check the valves on that side of the engine is difficult because on a Subbie 2.5 engine it is the side with least amount of room to work. Installing plugs in that side is a PITA.

I have shaky idle but on the highway cruising at highway speed, you would never notice a problem.

 

[urdrwho]

Well now this is odd. Using the PCV hose to plug in my vac gauge I thought I noticed less shake on the gauge. Still shakes a half point either way of 20. So I took the car out with the PCV hose off the crankcase and I am quite sure idle is a bit better and low speed acceleration is smoother.

What's up with that?

I can't run with the thing constantly disconnected but I am tempted.

I wonder how many cycles it would take before the OBDII finds out the PCV isn't working?

 

[SteveSRT8]

Originally Posted By: ARCOgraphite
Unfortunatley honda makes it VERY hard to adjust the valves compared to imports ive worked on in the 80s and 90s. The Sin of Poor Design and no maintenance consideration for such a simple SOHC engine with archaic jam-nut adjusters.


I would agree it is ludicrous to have to adjust a valvetrain in this day and age.

All design engineers should be required to work on the piece they produced, this might help a bit.