More Vacuum Stuff... Search already done (2 Viewers)

[srplus]

I read an excellent article on Vacuum readings and symptoms and diagnosis... what all of the Vacuum readings mean and what they are supposed to be. I thought this was a sticky but could not find it... I can not find the link to this excellent article and information.

I have searched the forum and the individual threads and can not find the link... Can somebody recall the article and what the URL was for the link?

Really appreciate it.

thanx

 

[srplus]

I found a cut and paste I had to a text file on my HD

Here is what I found and can not credit it... if anyone has the source I would appreciate it... I think this is somewhere on mud or maybe even (shudder) Pirate or the Aussie Crusier site... If you know the source, please post it up - the author is Jack Conrad. This needs to be in the sticky (if it is not already and in my old age I just could not find it):


Vacuum 101 (or...Your Engine Sucks)
Tech information furnished by Jack Conrad


Your Engine Sucks…

…or at least it is supposed to. As the pistons descend during the intake strokes a vacuum is created in the cylinders and throughout the intake manifold. This is good. Vacuum is our friend. It literally sucks the air/ fuel mixture into the cylinders.

Additionally, Vacuum tapped off of the intake manifold is used to power or operate a wide variety of automotive systems. The most common use of vacuum on today's vehicles is for brake boosters and to actuate the advance mechanism on distributors. On older Cruisers it is used to shift the transfer case from two to four wheel drive. In days gone by most vehicles had vacuum operated windshield wipers. It is also used to activate most of the heating and ventilation in many cars and trucks. I almost forgot, vacuum is also used to power the many thousands of devices scattered around your engine compartment by the ever popular smog nazis. ( Remember now, a gun is not inherently bad just because it is used by a criminal.) Vacuum is our friend!!

Vacuum is measured in inches of mercury. It is expressed as the number of inches of mercury pulled up a tube at sea level. Fortunately for us, some rocket scientist figured out how to make an accurate vacuum gauge with a diaphragm and a spring. You will find two basic gauges on the market.

The first usually has three colored sections on the face of the gauge. It may or may not have any numerals. This one is marketed as a fuel economy or gas mileage gauge. The color bands are most often red, yellow, and green. A reading in the green indicates your best fuel economy. A red reading means you are sucking the gas really fast. Several automobile manufacturers, BMW for instance, have put these gauges into the dash as part of their stock configuration.

The second type of gauge is the one we will focus on. This one has graduations around the dial with numerals from zero to 30 thrown in so you can get an actual numerical reading. This gauge will also tell you about your relative fuel economy. The higher the reading, the better your gas mileage. With a careful eye on the vacuum gauge you can modify your driving style/habits and realize a significant increase in gas mileage. Keep that needle at 15 inches or higher and you'll be surprised at how many miles that Cruiser can squeeze out of a gallon of gasoline. I guess I should mention that a driving style that will yield a steady vacuum reading of 15 inches or higher is usually associated with little old ladies. It would make for a very long and boring trip to anywhere. You obviously aren't into "boring" or you wouldn't be driving a Cruiser. So, let's get on to the main course.

The vacuum gauge is one of the most versatile diagnostic tools you can own. I have had one on the dash of my 84 FJ60, Big Toy, since it was one week old. I prefer an in-cab gauge. An occasional glance at the vacuum gauge let's me know everything is fine, or that things are heading south. With it in the cab you can get used to your trucks normal readings under varying conditions. A gauge used strictly in-the-shop is great for diagnoses, but doesn't give you the long term knowledge that an in-cab unit provides.

The vacuum gauge will usually give the first indication of problems. Long before they become apparent to the ear, or by feel, the vacuum gauge will indicate impending trouble. It can reveal a wealth of information about the internal functioning of your engine. It is also one of the least expensive troubleshooting tools. For the price, around $15.00 to $25.00, it definitely gives you the biggest bang for the buck. The vacuum gauge is also the biggest mystery to the average "Shade-tree" ( typical Cruiser) mechanic. Stick with me gentle reader and we'll explore some of the more common readings and what they are telling you about your engine.

Let's start by defining the engines we are going to be talking about. These will be your typical grocery getter or four-wheeler gasoline engine. High performance, radical camshaft, nitro burning horse power monsters have a whole different set of rules. You won't find many of these in our Cruisers so they won't be discussed here. We're talking generalities here, YMMV! If you are running a hot cam check with the manufacturer. They should be able to tell you what to expect from a specific application.

Any year F or 2F engine with all systems "go" is going to show a steady reading at idle between 15 and 20 inches. With a perfect engine, like the one we all maintain in our Cruisers, the needle will appear to be glued in place. The farther that engine is away from perfect the more the needle will jump or float around.

I could go on, describing each reading and what it means, but I thought the table below would do even better. There may be other engine problems that can be diagnosed with a vacuum gauge. If you know of any please write, call, or e-mail so we can pass the information on to all readers.

NOTE 1: The information in the table below has been gathered over many years of reading, talking to other mechanics, and working with vacuum gauges. In many cases the exact numerical reading is not as important as what the needle is doing and how. Number 1 below lists the "normal" reading at idle. Your reading should be somewhere within this range. The exact idle reading isn't quite as important as the fact that the needle should be glued in place. There are many variables in the equation. Things like compression ratio, intake and exhaust manifolds, camshaft and ignition system all have an affect on your engine's normal readings. Only time and a close eye on the gauge will tell you what "normal" is for your rig.

NOTE 2: Notice number 4. The Vacuum gauge can help you set your idle mixture. As a general rule of thumb, and or fore-finger, the higher the vacuum reading at idle, the higher the low-end torque. Be careful with this. If the idle vacuum is too high your gas mileage can really suffer. I recommend tuning for an absolute max reading of 21 to 22 inches at idle.

NOTE 3: The readings listed in numbers six and seven below can be caused by a stretched timing chain. I know, they can't be in a Cruiser because it uses gears. Since these rules apply to vehicles other than Cruisers I wanted to let you know. These readings may also be caused by leaking piston rings.




CONDITION INDICATION
readings are at idle unless otherwise stated. Gauge readings are in inches
1. Normal Steady at 15 to 21
........................
Drops to 2, then rises to 25 when throttle pedal is rapidly depressed then released.
2. Intake leak Low steady reading less than 10
3. Head gasket leak Gauge floats between 5 and 19
4. Improper idle mixture floats slowly plus or minus 1 ½ to 2 ½ inches
5. Small spark gap or defective points slight float plus or minus 1 to 1½ inches
6. Late ignition timing Approx 2 inches below normal idle
7. Late valve timing 4 to 8 inches below normal idle
8. Worn valve guides Oscillates plus or minus 2
9. Weak valve springs Violent oscillation (plus or minus 5 inches) as rpm increases. Often steady at idle.
10. Sticking valves Normally steady, will intermittently flick downward about 4 inches
11. Leaky valve Regular drop about 2 inches
12. Burned or warped valve Regular, evenly spaced down-scale flick approx 4 inches
13. Worn rings/ diluted oil Drops to 0, then rises to approx 18 when throttle is rapidly depressed then released
14. Restricted exhaust system Normal when first started. Drops to 0 as rpm increases. May eventually rise to approx 18




Some poster’s ideas of best place to check vacuum:

best source for constant vacuum is the intake manifold....feeds vacuum directly to your brake booster...pull the line off the booster, plug in your gauge.

If you have AC, there's a second smaller tap in the same fitting as the brake booster hose. Its a little easier to pull the hose off and its the same diameter hose as most of the vac guage fittings.

Right under the carb on the driver's side there is a right angle hard tube that has a hose connected to it from the manifold. This is a easy place to measure your vacuum.


Spray carb cleaner around the joints between the carb & manifold & head with the engine running. If the RPMs increase you have an(other) intake leak at the point you are spraying.



another poster:
As a precursor to what I'm about to say, I figured I'd do a write up of the repairs that I did to my truck, from the diagnosis process through final button-up. I couldn't find too much info on my specific problem, so I figured I'd make it. Well, here it goes.

When I took ownership of my 1987 Land Cruiser in late April of this year, it didn't idle. I had no idea why it didn't, but It would not run under 1750 rpm's. Because this was my first car, I was kinda nervous tearing into my engine, because I didn't want to take it apart and then not be able to put it back together. I searched around on the net and found this site, but I did not realize how much info that I had accidentially stumbled onto. After posting a couple of n00b threads, like we all do, I decided that I should by an engine manual, so I bought the 2F engine manual that is supposedly the bible for all 2F engines.

I was still nervous. I wanted to have a starting point before I took anything apart. I asked the PO (past owner) what he thought was wrong, and he said that his mechanic thought that there was a cracked intake manifold, which produced a vacuum leak that would not allow the engine to idle. After more drilling, the PO told me that the truck had vastly overheated at least twice due to a plugged radiator. After that, I decided that the only way I was going to get the LC on the road before the end of the summer was i I actually worked on it.

Armed with some white tape, a sharpie, some wrenches and my 2F manual, I took piece after piece off, bagging, labeling and documenting everything. The only reason why my truck started after reassembly was because I labeled every vacuum line, bagged every bolt and drew diagrams of every step. MAKE SURE YOU DO THIS WITH EVERYTHING THAT YOU TAKE OFF YOUR TRUCK!!!

BTW, take off the hood when doing this much work under the truck, because it is a PITA (pain in the ass) to work under. Also make sure to get someone to help you with this, because it is the only part that you can't do by yourself.

After fighting with the bolts and things that were attached in the driver's side of th engine compartment, and splitting some sockets, I got the manifolds off. After close inspection, I found out that the intake manifold was not cracked, but heinously warped. MAKE SURE YOU CHECK FOR WARPAGE!!!

I bought a used set of manifolds from a dude on this forum, which is highly recommended, which were in good condition, and true. I went this route because SOR's manifolds are too expensive, and the guys on this forum are great!! Sorry I can't remember your name whoever you are!!

I got the best gaskets I could find, which are Fel-Pro gaskets by the way, as well as a valve cover gasket because it was leaking like crazy and it was easier to take the carb off with the Air Rail and Valve cover off. After cleaning all the surfaces with a de-greaser, I slid the gasket on the head, the exhaust doughnut on the downpipe and EGR pipe gasket on the pipe, and finally the manifolds. One piece of advice to anyone doing this, make sure you slide the heat shield that goes on the exhaust manifold on before you put the manifolds on , because doing it after sucks! Also, make sure that you thread all of the bolts before you mate the head and the manifold, because it is impossible to thread the end bolts after they are mated.

After torquing the manifold bolts to 38 ft/lbs in this order: 2F Manifold Torquing Sequence - 5 1 2 6 8 7 4 3 - which is straight from the 2F manual, I toqued the exhaust nuts and then worked my way north, following my diagrams. Note to wrenchers, put the air rail on after the carb, because it gets in the way, and the valve cover after that.

On top of the intake manifold, I installed a new Carb insulator, which is the only thing inbetween the manifold and the carb, because I broke mine taking it out. After I installed my carb, I tested my fuel cut off solenoid buy turning the ignition to the ON position, taking the little green plug out of the top of the carb, and plugging it in while listening for a clicking noise to come out of the carb as I plugged it back in. If you don't hear a click, then it is broken and your truck will not idle until you get a new one.

I jumped the truck and it ran, yet smoky, very smoky. While it was running, I put the air cleaner assembly back on, as well as all of the vacuum lines associated with it. After all the lines were attached, I took a flat-head screwdriver to the adjustment screws on the driver's side of the carb and calibrated it to idle at 650 rpm's as per the manual.

BTW, it runs perfectly. The PO said that it hasn't run this good in the past 5 years, so I guess that I did a good job. I love to drive it, although it is a little bouncy. Idles smoothly @ 650 rpm and has smooth acceleration.

Tools: Big metric wrench set ranging from 10mm to 19mm, Torque wrench, Open ended wrench set, same sizes, shop light, de-greaser

Good to hear. I just went through all the systems on my carb a little while ago and everything tested ok. Checked PCV and EGR, both move as supposed to. Then I pulle doff the four vac hoses at the carb base valve cover side and blew carb cleaner through the ports. One seemed clogged at first and then the cleaner went right through. After burning all of the carb cleaner out, it idled perfect again. Took it for a test ride and all good.



What should my compression be on an F?

By the manual: 150 psi is nominal, & limit is 128 psi. Difference in pressure between the cylinders should be less than 14.2 psi.

You should wet test them (add a few drops of oil to the cylinder before testing). If it brings the pressure up to normal, you probably have worn rings in those cylinders. If the pressure doesn't change, you are likely to have problems with valve seating.

 

[srplus]

It was on ih8mud - http://www.ih8mud.com/tech/vacuum.php

thank goodness for google search and good indexing.

so nevermind.

 

[60wag]

It was originally published in Toyota Trails.

I was was able to diagnose a clogged cat on a friends 4Runner with infor from that article. Good stuff.

 

[eastendmedic]

Another neat vac page

http://www.users.bigpond.com/ergoff/vac1.htm

kinda cool

 

[RenegadeQ]

If you hook up the vacuum gage to the brake booster/AC tap, you will see the vacuum drop to about 3 or 5 inches when you step on the brakes if the diaphram in the booster is bad. I used this to diagnose a bad booster once.

 

[hank14]

Has anyone really watched their vacuum while driving?

The numbers above refer to at idle, except for where he talks about the best fuel economy around 15 while driving like an old grandma.

I ran a temporary line from the A/C idle up vacuum hose that comes off the intake with the brake booster line near the DS firewall, into the cab, and hooked up my diagnostic vacuum gauge. The vacuum is usually 18 at idle, sometimes down to 17 or so. When I accelerate, the vacuum drops to 5 or so, and when I let off the gas, it jumps to above 20-25.

Is this typical? Without common readings while driving, I don't see the point in having it in the cab.

 

[RenegadeQ]

Those numbers sound about right for the conditions described.

 

[Yspen]

Has anyone really watched their vacuum while driving?

Yep , I watch it all the time . Sometimes I drop a gear and find the vacuum is lower thus better fuel consumption . By lifting foot from gaspedal slighty I find sometime that the car runs with the same power but vacuum guage drops thus it helps me to apply the right amount of pressure on the gas to get the best fuel consumption .

 

[octongue]

srplus - i am about to take the head off of my 2F and found the disassembly pointers under the intake manifold repair section really helpful. this will be my first foray into major engine work as well. Thanks for digging this up!

 

[hank14]

Maybe slightly off topic, but I hooked the temporary vacuum gauge line into a T on the EGR modulator line that goes to the EGR- the one that is normally bypassed to help with the common bucking and surging problem.

Driving with the vacuum gauge in the line and everything hooked up properly, the most vacuum I get is less than 5 inches. Can anyone with a working, non bypassed EGR check to see if this is normal?

I am wondering if the EGR valve or the EGR modulator is non functional.

 

[CREWZER]

I love having mine in-cab,worth the money and takes about 5 minutes to install.

 

[DocuDude]

I love having mine in-cab,worth the money and takes about 5 minutes to install.

Can you post how to install in 5 minutes?

Thanks