Does anyone have an idea what vacuum I should see on the 3vz at idle? I thought maybe 15" to 20" .... I'm getting about 8". This is a rebuilt I swapped in, so it's highly likely I switched or spaced-out a line somewhere. Symptoms are a really rough idle (but never dies) and the resonator growls angrily when the rpms fall to idle speed. Seems to run OK at higher rpms.

 

My excellent running 3vz pulls about 19" of vacuum at idle @ 4000' elevation.

If your gauge is accurate, you gotta problem, for sure.

 

Thanks. Just got the gauge from Harbor Fright, so 50-50 chance it's accurate. Of course, it's probably accurate enough to tell the difference between 19" and 8". I had noticed the brakes were soft when rolling slowly to a stop. A little research on vacuum assisted brakes, and now I know why.

 

Doesn't take much vacuum to operate the booster. You'd think so from the big hose and big fitting at the manifold/plenum. But take a look inside that fitting to find a teeny tiny orifice. Which is because of the whatchamadoohicky thingamabobber. I'll look it up again...

Yeah...I'm not finding what I read. Something about a check valve and residual pressure IIRC. But between the tiny hole observation and that, it made sense to me at the time.

 

Thanks guys. Millball, do you test warm, all plugs removed, throttle open? My test was cold, plugs in, throttle closed, 5000ft ... which I now realize is probably all wrong. I guess the only thing I learned is that all my cylinders are about the same, which is good.

If testing warm, how do you get all the plugs out without burning your hands? And was there any issue with galling when removing the steel plugs from the aluminum heads?

 

Engine vacuum is measured with the engine running.

You may be confusing this with compression testing, which is done with throttle open, all plugs out. Hot, or cold, should'nt make too much difference.

2 totally different tests, using totally different instruments and different testing regimes.

Best to use compressed air to blow any debris away from the plug area after loostening the plug a turn, and maybe then apply a little WD, or other penetrating oil before plug removal.

I always use a bit of Never-seize when installing plugs, to help with future removal.

 

Oops, got my threads crossed up. Yes, I was asking about compression. My vacuum is about 7" everywhere I check, but I can't find any major leaks. I thought maybe if my rings were terrible, the engine might not pull enough vacuum in the first place, so I measured them cold at 95psi. Seems like the engine wouldn't run at all well at 95psi, so I suspect my testing method or instrumentation is faulty. This is a rebuilt engine, but I now suspect the builder is a fraudulent operator out of Cali, and suspect he may not have replaced the rings / pistons on the rebuild job. My first clue was all the valve clearances were set too tight, but he said "they do that on purpose because they will get larger as the engine is run in". I think it's the opposite, and he sent me an old engine without bothering to measure or replace the shims (and maybe old rings too).

 

Sounds like you got the root on your engine, sorry.

Yes, valve clearances do mostly close up and seldom get larger.

95 psi compression is indeed very weak

Any hope of the seller making it right?? I suppose not.

I dread the day when I am no longer able to do my own work.