Vacuum Gauge Install; Engine Line Tap Location

[Cobb]

Is that all the same piece of vacuum hose or are you redoing your plumbing under the hood?

[dlb]

that is a sharp looking mounting job. very nice.

what is your vacuum at idle after fixing the kink in the vac line? on an engine in good condition, it should be 18-21".

here's a great reference on how to use a vacuum gauge to diagnose a variety of engine issues. scroll down to the bottom for a great little graphic.

How to Use and Interpret a Vacuum Gauge

by t-ing into the vac line for the brake booster, do you find applying the brakes has much effect on the readings? for future reference, you can splice into any vac hose coming off the intake plenum but i prefer not to use the hoses associated with the brake booster, fuel return diaphragm, or PCV systems. that leaves hoses going to stuff like sensors, EGR, etc. alternatively and ideally, some engines have unused ports on the intake plenum or manifold that are capped at the factory. pull the plastic or rubber cap off and attach the hose to that port.

i've been driving with a vac gauge for a few months now and have managed to increase my mileage by an average of 10% so i'm a big believer in them.

[user removed]

I would suspect the vacuum would be slightly lower on a VX since the idle speed is a good bit lower than the average, around 550 RPM. The length of hose was enough to make sure it would cover the distance and routing involved.

My 37 Ford idled at 350 RPM. You checked it by letting it idle in top gear and it was supposed to be 7 MPH!

regards
Mech

[DOFZO]

Originally Posted by Cobb

Is that all the same piece of vacuum hose or are you redoing your plumbing under the hood?

I'll eventually get it cut to length. For now I'm going to need every inch if I keep crimping the hose installing the gauge!

Originally Posted by dlb

that is a sharp looking mounting job. very nice.

what is your vacuum at idle after fixing the kink in the vac line? on an engine in good condition, it should be 18-21".

here's a great reference on how to use a vacuum gauge to diagnose a variety of engine issues. scroll down to the bottom for a great little graphic.

How to Use and Interpret a Vacuum Gauge

by t-ing into the vac line for the brake booster, do you find applying the brakes has much effect on the readings? for future reference, you can splice into any vac hose coming off the intake plenum but i prefer not to use the hoses associated with the brake booster, fuel return diaphragm, or PCV systems. that leaves hoses going to stuff like sensors, EGR, etc. alternatively and ideally, some engines have unused ports on the intake plenum or manifold that are capped at the factory. pull the plastic or rubber cap off and attach the hose to that port.

i've been driving with a vac gauge for a few months now and have managed to increase my mileage by an average of 10% so i'm a big believer in them.

I'm located in Denver, so 16 in. hg. is pretty good negative pressure. Although the car is in great condition for it age, the suspension and brakes need work. I've pressed all new bushings into every suspension component* and I'm going to convert to rear disc at the same time. I will then do new rotors and pads, springs and struts all the way around.

So to answer your question, no, I haven't felt a difference with braking, but my brakes are VERY well worn. I just took her around the block and maybe up to 30 mph.

Without a vacuum leak within the booster line or my tap I don't understand why anything would change anyway. I'll monitor it though.


*I've sourced front lower control arms from a GS-R, rear lower control arms from a LS, front anti-sway bar from the LS and rear anti-sway from a Type-R , and Del Sol Si rear trailing arms for the rear disc conversion. New upper front control arms, rotors and pads. Koni STR.T struts with H&R springs. This is my plan for the suspension rebuild/conversion. Hopefully I find the time to start the project, I have all the parts.





ZO.

[Cobb]

Thats ok, helps add to your vacuum reserve. Gauge looks professional.

[dlb]

i don't think you would feel a difference in braking due to the gauge being run off the brake booster hose. what i wonder is if applying the brakes will cause the gauge to read slightly lower at those moments due to the brake booster diaphragm using most of the vacuum supplied to it. i'm not sure if it would show up or not, just curious.

[DOFZO]

Originally Posted by Cobb

Thats ok, helps add to your vacuum reserve. Gauge looks professional.

Thanks!

Originally Posted by dlb

i don't think you would feel a difference in braking due to the gauge being run off the brake booster hose. what i wonder is if applying the brakes will cause the gauge to read slightly lower at those moments due to the brake booster diaphragm using most of the vacuum supplied to it. i'm not sure if it would show up or not, just curious.

Interesting! I hadn't even thought of that. Once I get to driving the car regularly I'll report the results back.





ZO.

[DOFZO]

Originally Posted by dlb

i don't think you would feel a difference in braking due to the gauge being run off the brake booster hose. what i wonder is if applying the brakes will cause the gauge to read slightly lower at those moments due to the brake booster diaphragm using most of the vacuum supplied to it. i'm not sure if it would show up or not, just curious.

The vacuum drops (rises, moves towards zero) as I apply the brakes.



I'm getting 19 in. Hg. at idle. That reading doesn't make any sense to me. I personally haven't checked the ignition timing, but I asked and paid to have it done at a dealership just after I completed the install.






ZO.

[D.O.G.]

Originally Posted by DOFZO

The vacuum drops (rises, moves towards zero) as I apply the brakes.



I'm getting 19 in. Hg. at idle.
ZO.

I tried a couple of different locations before finding a "stable" one. The first ones I tried gave a big jump as whatever was being supplied vacuum by that line turned on or off.
I tap into the fuel regulator vacuum line now.

I get around 18 in.Hg at idle in my 1.8 litre Mazda.
Every car I've used a vacuum gauge on has given different readings.

[Stacygifford]

You could tap into hose 18, or 19 on the earlier diagram to get rid of the pressure fluctuations.
I used 18 on my 91 civic and 19 on my 94

looks awesome btw