If you haven’t started at the beginning, then you are missing some things in your education. Please go to Post 1 and start there NOW to be sure you get a thorough understanding.
Within the normal engine, there are, as we have already seen, many areas where leaks can occur that will have a negative effect on your engine’s efficiency. In this post, we will cover two locations that are generally difficult to identify as problem zones for your engine efficiency. Two are inside your engine, another two in your exhaust.
Let us consider first the one that is least considered. That is the intake manifold gasket. This gasket, when it goes bad, is virtually unnoticed. Unlike the head gasket, when this one goes bad, there is no symptomology beyond perhaps a gradual decline in mileage and performance. This is generally dismissed as simply age.
Nothing could be farther from the truth. Age causes decay, no doubt. This is something I am reminded of every day! In the engine, the same is true. When the intake gasket goes, the leaks can be quite problematic for the average garage-level tinkerer.
We will take for example the most notorious (from my experience), the GM V-8 engine of all sizes.
In the V-8’s, GM has designed yet another flaw into the engines, this one affecting the longevity of their gaskets. In these engines, they decided (in their infinite wisdom) to route the exhaust gases through the intake manifold.
Think about this for a moment. One port has cold air going into the head, the next two 800 degree exhaust gases are ducted up into the intake manifold, and the next cold air into the head. No matter WHAT you do, this area is going to experience a tremendous amount of stress. As a result, the gasket begins to decay rather quickly.
Sample Intake Manifold Gasket Set
This is a standard gasket set for this series of engine. You can easily see the problem areas would be the seal BETWEEN the exhaust and the intake ports.
All right, then how do you detect when this gasket is bad? This is really terribly simple and (in most cases) easy to check. As the gasket ages, it decays. As it decays, the seal is compromised, leaving a gap between the intake and the head. Fortunately, this leaves the formerly tight seal somewhat loose. This, in turn, leaves the bolts below torque standards.
So, all you need do to check them is to put a socket or a wrench on the bolts and give them a turn. Should you find the most central bolts looser than the others, then it is a certainty the intake manifold gasket has lost its integrity. If you have the time, then you should replace the gasket. As an intermediate measure, you can simply re-torque all the bolts.
This will NOT cure the problem, but it WILL reduce the leaks. Any reduction in the vacuum leaks is a REAL good thing as you well know by now! If you opt to replace your intake gaskets on your GM V-8, I recommend you use the new Fel-Pro gasket sets. These are made from heavy gasket material with a neoprene type seal around the ports and will last MUCH longer than the standard (and cheaper!) sets.
This is a good test, no matter what your engine, as ALL gaskets decay. So, if you find all your other efforts to get the mileage up failing, check this one! I recommend checking it while you’re under the hood the FIRST time if they’re easy enough to get to.
There is yet another area that is not considered for vacuum leaks, and that is the injector seals. If you notice dry, cracked hoses-or oil-soaked lines, then you would do very well to take a can of Carburetor Spray and spray a little bit on the base of each injector while it’s idling. ANY change in engine speed indicates a leak. This is a really good way to check all areas of the intake manifold, and is an excellent tool for you to use.
Cheap, fast, and accurate, the spray will uncover many leaks that would go otherwise unnoticed. Take your time. Spray a short burst and wait a second or two. Then, move to another area and spray a short burst. You’ll be very pleased with just how well this technique serves to locate hidden leaks in the system.
There is one other area that also remains ignored or dismissed by both mechanics and vehicle owners as well, thinking it to be unimportant, and that is in the seal between the exhaust manifold and the exhaust pipe, the exhaust flange or “donut” gasket. It is a round seal, and it, being exposed to extreme temperatures, also decays as in the case of the intake manifold.
If the exhaust gasket is leaking, the same thing happens.
Wait a minute here. How can an EXHAUST leak cause problems with the engine? Isn’t it PAST relevant systems? Well, consider the Oxygen sensor and its placement. In many, MANY systems, the O2 sensor is located just past this seal. When the exhaust leaks out, it takes with it the heavier portions of the exhaust which is your unburned fuel. This increases the relative oxygen content of the exhaust, and the ECU sees this increase in oxygen content and does what it is PROGRAMMED to do: keep the Air-Fuel Ratio at a predetermined level.
So, it adds fuel to adjust the exhaust AT THE SENSOR to the programmed level.
The modern vehicle is a complete system, and it is ALL tied together through the ECU. Many many maintenance issues will be revealed in the process of Grooving a vehicle. The more of these deficiencies you can identify and CORRECT the first time you’re under the hood, the more pleased you or your customer will be with the results.
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Next up: Post 7-Diagnosing Error Codes
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