Your gaskets might be shot, but also check the piece that joins up to the bottom of the manifold for cracks. If there is enough exhaust leaking, the oxygen sensor won't get enough flow over it and will tell the ecm to add fuel, decreasing your mileage.

 

read the secone post in this thread. Your jumping idle can either be from a poorly adjusted idle screw, or vaccum issues. In one case i had to tap on the Throttle Position Sensor and idle re-stabilized on my truck. good luck


http://www.toyotanation.com/forum/t158538.html



-Adam

 

actually....

If you have an exhaust leak upstream of the O2 sensor, it will allow air to enter the exhaust stream and the extra O2 is interperited as too lean by the ecm causing it to add more fuel.

It will definitely kill the fuel economy.

You should correct this before doing anything else.

 

With positive pressure in the exhaust and normal pressure in the air outside the exhaust I seriously doubt that any air will actually enter through an exhaust leak.

I don't doubt that it may alter the readings from the O2 sensor, but it won't be from air entering.

In my experience exhaust leaks are nothing more than an annoyance.

The bouncing idle is probably due to the idle being set wrong but can be influenced by bad sensors, vacuum leaks, and misadjustments. Start by turning the idle down. I find that I have a very narrow idle range I can be in where it doesn't bounce when I have the air on and the brake pressed. If I get too high it bounces, too low and it sputters. Hence yet another reason why I hate my 22re...

 

no ovrrdrive:slap:

hes right about the exhaust leak, when you let off the gas pedal and you hear a pop because of a backfire that is what actually happens , the compression in the engine causes the exhaust to suck in air from the exhaust because its easier than sucking in from the intake side when the throttle is closed. this it why you hear backfires on cars with exhausts that are too big or too short. dumbass!!!
:nutkick:

 

Howdy. I'm the new guy. Nice to meet, y'all.

Ok, my '89 4x4 22RE has a couple problems. The gaskets coming off of the bottom of the exhaust manifold are gone, and I'm replacing them tomorrow. Would that exhaust leak cause the following problems:

1) decrease in gas mileage (a 4cyl. getting 15mpg highway...*sigh*)
2) bouncing idle (it idles at about the right rpm, but it hops 500rpm every second or so)

I realize that these are probably basic questions, but I appreciate your input.

Thanks guys,
Jared

In my opinion, the exhaust leak could effect the performance and mileage of an already underpowered 22RE. I would suggest changing the exhaust gaskets before you do anything else. They obvioulsy need to be done anyway. At the very least, it will remove any suspicions you may have.

Be careful removing the nuts off of the exhaust studs. They tend to strip or break and if they do, you will have to remove the manifold, drill out the studs and retap the threads. A stipped stud could hace caused the leak in the 1st place. Be sure you have the tools and parts available before you start in case the worse case scenerio unfolds. It definately wouldn't hurt to have a torch handy.

Now go eat turkey insteady of posting on some forum. Oh.........wait a minute..........see ya.

 

Venturi effect

When air, or a fluid, flows through a pipe the static pressure drops. Once the flow is great enough the pressure drops below atmospheric pressure.

Air entering the exhaust upstream of the O2 sensor is not an uncommon cause of drivability problems. Usually it just causes increased fuel consumption, but if it is bad enough and/or goes on for a long enough time, the rich fuel mixture can cause the plugs to get carboned up and cause a misfire which then sends even more O2 down to the O2 sensor causing the ecm to fatten the mixture up even more.... in an ever increasing spiral of poor drivability.

On a later model vehicle, if the leak is after the main O2 sensor but before the post cat O2 sensor the air entering can trip a check engine light for catalyst inefficiency.

P.S. After thinking about it some more, it's dynamic pressure not static pressure

 

yea i forgot about the venturi effect , it simply starts sucking air in.. when your exhaust gasses are going fast enough to cause suction...

 

Yeah, that venturi effect really sucks.

 

You guys are funny... :lol:

There is indeed a "venturi effect" that does what you are implying an exhaust leak does, but there is no way in hell it would apply to this situation. I have a waterbed drainer that hooks up to a sink that uses this principle to suck water out of the mattress and it works great, exactly as it was engineered because it was just that: engineered. But an exhaust leak is just that, it's a leak.

Let me ask you this, if your dog chews a hole in the garden hose does the water come out the end of the hose looking carbonated because it's sucking so much air in the hole?

Of course it doesn't because a hose has positively pressurized water flowing through it and the hole your dog just chewed in the hole will spew that water out as fast as the water is flowing through the hole. However, if I put the waterbed drainer inline with the hose it all of a sudden will start sucking air through the hole and no water at all will escape.

It's the exact same thing with the exhaust. There is no way in hell that a hole or leak in the system will suck air into a pressurized environment. The easiest way to prove it is to put your hand near the leak and feel the puffs of air coming out of the hole. Now just exactly how is that supposed to be sucking air in through those leaks when air is puffing out?

An engine is basically an air pump. It sucks air in and creates an explosion and forces the air out. The resulting pressurized system is not going to create a "venturi effect" though just any hole that forms in the pressurized exhaust. And no matter how you slice it sublim, even when you have the throttle closed and are coasting to a stop there is still plenty of pressure in the exhaust system. Evidence of this is when the truck idles and you walk behind it and feel the puffs coming out of the pipe. Why isn't it sucking in instead of blowing out?


Just because an entire forum believes in something doesn't mean its right and neither does one person arguing the opposite. Simple physics dictates that a leak is going to do just that, leak. In order to suck it will take an engineered product to be installed inline with the exhaust. I really don't think there's any way that you could convince me otherwise.

Subliminaltrips, remember when we put the egr tubes on my engine and had it leaking?

Was it puffing out when you put your hand behind it or sucking in?

Bottom line, the exhaust leak can affect the O2 reading simply because there is less CO and O2 in the mix at any given RPM's because some of it is leaking out the leak. But its in no way because it is sucking air in.

 

thats because the velocity of the gas wasnt enough to produce a suction.. unlike your waterbed water sucker outer thingie. it would also depend on the backpressure in your exhaust.... dumbass....

how often do you hear a backfire at idle? it usually occurs when the engine is turning faster than it normally would when throttle is in a closed position its trying to suck in air from anywhere it can . if the exhaust is too short it will not have enough backpresure to keep from sucking clean air into the exhaust and igniting inside the exhaust pipes and sometimes reaching all the way back through the throttle body. granted that is with an agressively advanced or retarded timing condition in most cases.

 

I think it is funny...

when someone makes very generalized assumptions based on very limited experience and tries to pass it off like they know what they are talking about.

If you drill a hole in a hose or pipe and have a steady stream of water running through it, It will indeed aereate the water stream. The device to drain your waterbed was engineered, To take advantage of this principle.

If you put a valve on the outlet of the hose and raise the static pressure too high then water will come out of the hole. But most of us do not have a valve on the outlet of our exhaust and the static pressure inside the exhaust system is not very high so it does not take very much flow for the pressure inside the exhaust to drop below atmospheric pressure.

At idle the exhaust flow is low and the pressure pulses cause exhaust to leak out between when air is being pushed (nothing is ever sucked) back in by the greater outside pressure. As the engine speed increases so does the exhaust velocity causing the pressure to steadily drop allowing even more air to be pushed in.

Your assumption of the operation of an O2 sensor is also incorrect. It has nothing at all to do with flow or any other component of your exhaust except oxygen. You can simply view it as a type of battery that gives out a voltage signal proportional to the difference of oxygen inside and outside of you exhaust pipe. The greater the difference the greater the voltage. a rich condition uses up all the oxygen so the voltage goes high (above.45V), the ecm reduces the injector pulse width until the voltage is below .45V. Then it increases the pulse width until it is above .45V If you introduce air into the exhaust stream The difference between the inside and outside is less so the ecm incorrectly adjusts the mixture to compensate resulting in an overly rich condition.

 

when someone makes very generalized assumptions based on very limited experience and tries to pass it off like they know what they are talking about.

Dude, you're doing the same goddamned thing...


You're wrong on this one... A hole is a hole. Exhaust has pressure inside of it, and pressure takes the path of least resistance. Period.

You seem intelligent enough, but severely misguided.

And subliminal, you'd agree with anyone that had something you wanted.

 

I've been wrong in the past

But not this time.

Certainly not mis-guided.

I have extensive experience diagnosing and repairing drivability issues on cars for over 20years. I've had factory and state emmisions training. and support several repair forums where I routinely help to guide others to find problems just like the author of this thread describes.

What is your experience in this field?

 

i dont agree with him cuz i want anything of his, althought he has a nice truck. i agree with the scientific part of it, it just plain makes sense. think about how it sounds vrooom pop pop pop....vrooom pop pop pop. who cares anyways? if you have a leak fix it....

 

Neither one of you have given any conclusive evidence to support your "theory" at all...

Oh wait, except for the blanket "I have been doing this for 20 years boy" statement from above which still doesn't amount to a hill of beans. Martha Stewart has been buying stocks for over 20 years and she still obviously can't give stock purchasing advice.

At least I gave a few examples...

I could also say I had been a mechanic and not offer any proof... Like proof would quantify my opinion anyway.

The fact remains that an exhaust pipe is a pressurized container with one little outlet 10 feet away from the manifold. If at any point in that pipe a leak develops the gasses will take the path of least resistance and spew out that leak. There's no way you can even say with a straight face that the exhaust sucks back in if there is a hole...

Please, I'm waiting for proof from either one of you on this...

 

Actually, exhaust can suck back in. I was sitting in votech a while ago, reading a book on testing valves without ever popping the head. The tutorial said you could put a piece of thin paper, or a dollar, or something back at the tail pipe. I don't remember all of the procedures, but I do remember one, because it was sort of odd. If the dollar was sucked back towards the tail-pipe every once in a while, you had either (a) a burnt exhaust valve, or (b) a leak in the exhaust. So I wouldn't doubt that it can actually produce a suction back into the engine from the exhaust side.

 

When the exhaust valve opens, the charge of gases that travels down the exhaust pipe is a like a "pulse". Now this happens every time the exhaust valves open, so of course there's a lot of these "pulses" passing through the pipe, not just a continuous smooth flow of exhaust, unless your cat is really plugged solid.

You can try the priciple this way. Take a straw and fill it with water, holding it straight up with your finger over the end to prevent the water from running out the bottom. Momentarily lift your finger off the straw and then put it back on. Did you feel the little bit of suction on your finger? That's the same as what happens in the exhaust pipe. When there's a hole (other than the one at the end of the pipe) in the exhaust system, the pulse of exhaust creates a lower pressure situation behind it. If there's a hole, the exhaust loses some of it's velocity through the hole but also draws in air behind it because of the low pressure behind the pulse of exhaust.

Now if there was a hole in the straw, the weight of the water (which represents the moving "pulse" of exhaust in the first paragraph) draws air in though the hole. That brings us to our next point, which is exhaust scavenging. (If you have a more highly testicle explanation, please post it)

If the exhaust system is designed correctly, the pulse of exhaust actually helps to draw in the fresh charge of air/fuel, which means more efficiency. If the exhaust is too big, the velocity of the exhaust pulse dissipates too quickly and cannot scavenge properly. If the exhaust is too small, the pulses of exhaust pile up in the pipe and cannot draw the fresh air/fuel charge into the combustion chamber as efficiently because of the exhaust pressure in the pipe.

 

Sorry to start a little feud here, but I fixed the leak, and it seems to have fixed the problem. Hmmmm.... :thumbup:

Jared

 

Have you ever measured the pressure inside the exhaust?

Well I have, I can tell you that unless there is an exhaust restriction it pulses between less than .5 psi and a vacuum with a mechanical guage. The large hole at the end of the exhaust pipe is what prevents pressure from building up.

I guess it could be dimissed that I'm just some jerk-off that gets on a forum to spout a bunch of un-substantiated garbage, But I guess there could be others that fit this category as well.

Oh by the way, if anyone would like to make an experiment and post the results on this forum about the "un-proven theory" of air leaking into the exhaust. I'm sure that all expreienced automotive technicians would be interested to find out that what they have been using for diagnostics is a bunch of crap.

 

At least DCM was able to give an example and put in to words what this theory is based upon rather than just to say that he had been doing this for 20 years and had a big cock so I had to believe him...

I can see that there is a possibility that on paper this phenomenom could exsist, but to say that when you let off the gas pedal the exhaust turns into a vacuum hose I'd still have to say is hogwash.

Honestly, I could care less about what qualifications you claim to have, what experience, training or even handy man status either. I can show you a hundred mechanics with a piece of paper on the wall around here that will destroy your engine if you let them do something as simple as an oil change to it. Truth is, until you impress me you're just another greasy glove waiting to try to swoon me with his ultimate knowledge of my truck and have me dump transmission oil in my gas to lubricate my exhaust bearings to make my truck run better. I judge people on what they say and do and not what they tell me they are.

Everyone on the internet is an expert...

 

Overdrive,

I think you have clearly wooed everyone on this forum with your supreme logic.

I yield to "Da man"

 

ovrrdrive, i think you guys should kiss and make up... besides nobody mentioned penis size... if they did id be the winner and youd be the weiner :wiggle:

 

I think you have clearly wooed everyone on this forum with your supreme logic.

I yield to "Da man"

Well ok then...

Btw, it's ovrrdrive not Overdrive...

ovrrdrive, i think you guys should kiss and make up... besides nobody mentioned penis size... if they did id be the winner and youd be the weiner :wiggle:

I really hate to go here but I will...

That's not what I heard boy... Not at all. :lol:

 

WOW! That was an awful lot of scientific garbly goop for "change the gaskets."

Glad to here you got it fixed easily.