Low vacuum reading
My vacuum is reading 10 at idle on my autometer boost gauge.I was searching and looked on blue's website under vacuum ect.10 indicates that my valve timing is off.I did check for vacuum leaks ignition timing is set at 20 deg btdc.The car seems to have less power and torque.The car sat for about 3 years before i purchased it.
The previous owner really didn't know anything about the car only because it was his brothers car and he had lost interest in it.Does the valve timing seem to be the problem? 1983 280zxt
Mn_Z_Man Wrote:
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> It could be lot of things, but that is a good
> place to start. It will also lower your
> compression readings. Easy to check, and you can
> adjsut the valve lash while you're at it (if you
> have adjustable rockers, turbo of that year may
> not). Blues tech tips is a good place o start. If
> you do adjust the valve timing, please heed the
> warnings about using a block to keep your chain
> tensioner from popping out, which is a whole lot
> more work to fix.
>
> Eric
Thanks I forgot to mention that i did do a compression check.The readings were at 115 across.
No question, you are in need, will feel like a new car when you are done. Have a new valve cover gasket handy when you dig into it. Buy Felpro, they are very good.
I looked at the valve timing section on blues site.I'm a little confused about how to adjust it.I understand tdc ect.Do i have to take off the timing cover?Is there an easier way to explain the rest.Sorry but i'm very new to all of this.
Ok, reading a bit more.I understnad i need to take the valve cover off,jack the rear of the car up,turn the rear wheels ccw to get to tdc.After i know i'm at tdc.What do i need to do after that?It only shows how to check valve timing.I'm just confused.
check to make sure the balancer TDC mark is accurate by checking piston position thru spark plug hole. Sounds like the ign timing is retarded to me..
10 inches of vacuum is very low for that engine. I am assumingit is stock, and if not then you have one hell of a cam in the engine. Stock vacuum is right around 18-20 inches of vacuum.
Valve lash I dont know about that one, since the compression is all the same, but an adjustment would clarify things for you. If you have the hydrolic head there is no adjustment possible. Check the timing with the piston @ TDC like suggested and make sure the damper is not out to lunch, it should be indicating TDC as well.
That being said, if the valve lash is good, and the timing is good, there is only one last test to do.
This is a FI car? remove the hose going to the top of the valve cover. Plug the hose up and start the car. Remove the oil filler cap and see what you get. If you don't get any smoke puffing that is a good thing, if however you get smoke being puffed out the filler hole then that would indicate you have excessive blowby past the piston rings, now that is bad.
Puffing from the valve cover filler indicates that you just may have bad rings/pistons. That is the quickest way to check the pistons and rings. Also a good indicator is that the car will not idle very smoothly.
"My vacuum is reading 10 at idle on my autometer boost gauge"
You don't measure vacuum with a boost gauge. You measure it with a vacuum gauge and only at certain places on the engine. There are tutorials all over the net about this. Are you sure you did it right?
Do NOT base your engine troubleshooting diagnostics off a cheap boost gauge on your DASHBOARD!
Get a PROPER vacuum gauge with resolution and proper dampening, and check for vacuum (warm) at idle with the correct ignition timing.
If it is STILL LOW, then you can go to checking damper for proper TDC and verify ignition timing, and operation of the distributor. Most of the time lack of power is csaused by a malfunctioning vacuum advance cannister, and or stuck weights in the distributor. If you have the wrong ignition timing at idle, your vacuum will suffer, as will performance.
THEN, if all is well you should adjust your valves (can't do that without warming it up anyway, and verifiying that TDC mark on the crankshaft damper is really TDC ,s owhy not nail down the ignition timing BEFORE while you're doing those prep steps anyway?
Adjust those valves properly and then check again. I seriously doubt "Valve Timing" is an issue. 115 all across the board is an irrelevant number--you didn't tell us what kind of gauge you used to check it, and they are notoriously wrong if you got a cheap push-it-in-the-hole type, or if you gave us the 'first pump' reading.
All these other guys drew conclusions on the compression test ASSuMEd you did the test CORRECTLY. I don't. If that is the 'first pump' of the compresison test, you have a damn strong engine, and no rings or valve work is needed.
ALWAYS need to know the methodology of the testing before drawing conclusions.
Chances are you may need nothing more than distributor and valve adjustment. I would NOT start pulling heads, adjusting timing of the valvetrain, OR ANYTHING ELSE until PROPER instrumentation and methodology is followed.
That is the FIRST step. If the testing is wrong, the conclusions drawn are wrong...and damned expensive in terms of time, effort, and parts wasted that were fine to begin with!
115 is pretty low-ish as compresions go. I'd like to see 145-180 psi. Norm K.
What if he's using a K-Mart Surplus Gauge that only reads 150psi on a NEW DIESEL?
NEVER diagnose from readings when test instrumentation veracity can not be confirmed. The important thing was THEY WERE ALL EVEN. That is FAR more important than the READING.
And like I stated before, if that is a 'first pump' reading commonly used when el-cheapo hand-held in the plug hole style testers are used...that is DAMN good!
A 115psi first pump will return between 175 and 185 on the third pump (industry standard for checking)...
For all we know he's in Colorado at 8000 feet which would be a good THIRD PUMP number.
Or he checked with the throttle closed.
TOO MANY VARIABLES TO BE PULLING ANY SOLUTION OUT OF THIN AIR!
Thanks for the helpful advice everybody.I'll check the timing again.I think my problem is setting the timing correctly.Tdc instead of btdc.I'll also get a proper vacuum gauge as mentioned.I'll post back when i'm finished with the tests.
It could be lot of things, but that is a good place to start. It will also lower your compression readings. Easy to check, and you can adjsut the valve lash while you're at it (if you have adjustable rockers, turbo of that year may not). Blues tech tips is a good place o start. If you do adjust the valve timing, please heed the warnings about using a block to keep your chain tensioner from popping out, which is a whole lot more work to fix.
Eric
Eric
mostly stock and original and rust free '73 240Z, SU's, Pertronix ignition, Tokico HP kit