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Engine & DrivetrainDiscussions about the engine and drivetrain of your vehicle.
This is a discussion thread titled "Vacuum gauge readings?", within the Engine & Drivetrain forum, part of the Technical & Vehicle Assistance Forums category.
Does anyone have a vacuum gauge hooked up to a 4.7L Tundra? If so, what line did you tap into for vacuum and what are the readings at idle; and also when it is in Drive but at a stop? Just curious as to what normal readings are. Thanks for the help. Also any install pics of the line would help.
Originally posted by bkoneski47 Does anyone have a vacuum gauge hooked up to a 4.7L Tundra? If so, what line did you tap into for vacuum and what are the readings at idle; and also when it is in Drive but at a stop? Just curious as to what normal readings are. Thanks for the help. Also any install pics of the line would help.
As it happens, I installed a vacuum gauge a couple of days ago.
There is a spare vacuum tap under the throttle body cover. Once you take the cover off you can't miss it. It sticks up out of the intake manifold, turns 90 degrees and has a rubber boot over the end. The boot fits nicely on top of one of the bolts that holds the oil filler tube in place, as a means of storage.
I'm getting 19.5 inches of Hg at an idle in neutral with the engine at normal operating temperature. I intend to Tee into the vacuum line that leads to the valve in the power steering pump to see if both taps give me the same reading. I suspect they will.
If you'd like any further details, send me a PM and I'll tell you where and how I installed the gauge.
Originally posted by bkoneski47 Hey thanks. I'm getting about 18, but I'll look under that cover to see the fitting your talking about. I tee'd into a line going to the airbox.
It looks like we may be on our own, huh? Suggestion: Connect your gauge to the vacuum tap I mentioned that's under the throttle body cover.
I'm still getting 19.5 inches at idle which is normal. 18 inches is also normal. The normal range is 18 to 22 inches with the pointer remaining quite steady. But, I've had new engines that pulled only 17 inches of vacuum.
What brand of gauge did you install and where did you install it?
I have an AutoMeter Phantom gauge. I installed the gauge in a pod on the driver's side pillar, and the line tee'd into a vacuum line on the air intake tube. I still haven't had a chance to try the one by the throttle body. Its only 20 degrees out here in Massachusetts. I'll probably try it in a couple more weeks.
Originally posted by Agent WD-40 What would vacuum tell you? Does it corolate to engine load or MPG or anything else like that? Just trying to learn some stuff. Thanks.
That's a pretty astute guess. These things are mainly diagnostic tools that can be used to increase gas mileage a bit when taken seriously. Gauge reading give you a fairly good idea of what the throttle body is up to in terms of butterfly position.
A vacuum gauge indicates general engine condition and can be used to spot leaking valves, broken or weak valve springs, worn valve guides, piston ring defects, a blown head gasket, incorrect fuel to air ratios, intake manifold leaks, exhaust system restrictions, late ignition timing, late valve timing, and a sticking valve. You can also detect a leak in the brake system vacuum booster or a defective check valve.
For example, the top blew off the check valve at the vacuum booster on my Chevy truck. The engine started running poorly for no apparent reason. The onboard vacuum gauge was holding steady at 10 inches of mercury which pointed to a massive vacuum leak and that's what I started looking for and found.
They aren't really necessary but they do come in handy at times.
Originally posted by bkoneski47 I have an AutoMeter Phantom gauge. I installed the gauge in a pod on the driver's side pillar, and the line tee'd into a vacuum line on the air intake tube. I still haven't had a chance to try the one by the throttle body. Its only 20 degrees out here in Massachusetts. I'll probably try it in a couple more weeks.
Where did you buy the gauge? I like your choice of locations. Could you post a photo of the installation. I would sure like to see it.
I installed mine on a single gauge panel bolted to the front sloping surface of the ashtray. It's not the best location for frequent monitoring but it is out of the way yet readible.
Originally posted by bkoneski47 I posted the pic. Look under my photos.
I see that. That is a nice installation. Guess I'm going to have to move mine for sure. I can't tell from the photo, but how did you attach the gauge to the pillar. I see something that looks like a strap but I can't tell exactly what you did.
The gauge pod is made of molded black plastic just the way you see it in the picture. Hold it where you want, and drill a small hole (I forget what size but it tells you in the instructions) through the pod and through the stock pillar arm. Do this for the four corners of the pod. Before you mount it, I suggest to drill a 1/2" hole just in the pillar arm to snake the wires for the backlighting and the vacuum line through. After you have the line and wires through, the pod comes with 4 little black plastic push plugs for the holes. They hold it on neatly, and you barely even notice them. Mine is an Autometer brand, and if you decide to get one, the directions are very good with a detailed step-by-step guide. Some people have also found some spray paints to match their interior dash trim and painted the pod to give it a more blended in look. I didn't do it just because there's already black trim in the truck, so it doesn't look out of place anyway. Hope this helps.
You should be able to get one at any local speed shop or visit Autometer website for a list of distributors. This is used with or without a supercharger. Without one, the needle moves to the left of 0 from 20 in/Hg to 0 in/Hg depending on the throttle opening and the vacuum in the intake manifold. If you have a supercharger, it will do the same except when the supercharger gets into boost, the needle will go to the right from 0 lbs. to however many pounds of boost. The TRD SC runs at about 7 lbs. of boost. Cost is dependant on where you get it, but if I remember correctly the Phantom gauge and pod was about $80 together. It comes with everything you need and is very easy to install in about an hour.
Vacuum gauge readings?
