Just a few silly questions - comments. Some of you must have noticed a Blazer or Jimmy out there with this kind of EGR sytem. Leak in exhaust will cause EGR problems. Extra back pressure in exhaust will do the same. Going for a set of headders or less restriction of any sort is the same as a leak. A lower back pressure causes failure of the EGR system to operate properly. leading to a car that doesnt run right, of course. Now the simple solution is to "FOREVER" leave this car stock. Not my wishes of course. So give me some ideas.. My own involve ripping the trash off and throwing it away. Any better ideas out there?? Such as EGR's built for lower restriction exhaust systems and such. Any bright folks with easy answers????

 

I disagree with your assumption that headers will make an EGR system fail. Just look at the 3800 community with the L67 or L36 or the Camaro/Firebird or the Corvette. Many MANY people have put headers on and still remain 50 state legal. Less backpressure will have nothing to do with the performance of the EGR system unless you've got ZERO backpressure which is not even a possibility even with open headers. So long as the headers have provisions for the EGR and all other emissions equipment, you should be good to go.

 

http://www.tomco-inc.com/Tech_Tips/ttt26.pdf

Just one of the many helpful tech tips found at tomco. I guess the best explanation is that not all egr valves are alike???????

I too was completely surprised at the suggestion that an egr valve could actually work to sense the amount of exhaust back pressure. Yet I am finding out quite a bit about these things lately. This is not your average 35-80 dollar egr valve either. This is a heavy price item, running easily into 200 bucks for the part alone. Matter of fact, I priced one for a car and came up with a SAVINGS of over 112 dollars cause the 190 dollar price tag was SUCH A GOOD DEAL??????

No sense explaining how many cars can function beautifully that DO NOT have this type of egr valve. Try to come up with a way to convince me that a low restriction exhaust can be built by REPLACING this egr with some other kind cause when the exhaust on any car with this setup is opened up, it will cause the car to idle so erratically that it shouldnt be driven. An increase in rpm raises the vacuum and backpressure, resulting in the vehicle running better, but at idle, any exhaust "leak" will cause real problems. Matter of fact, the egr system can be "tested" by opening the pipe at the exhaust manifold just a little so as to cause the "leak".

No suggestion was made that "headers" would cause such DRASTIC a failure. A set of headers cannot, by themselves, lower REAL backpressure. Properly welded and hooked up, all bolts tight, that is. At least not to the extent that the low restriction mufflers behind them do. A real lowering of STATIC back pressure does not happen till the cat and muffler system are changed. Lowering restrictions to a lesser point has to have some effect on the egr system as a whole when this type of egr is used. EVEN if no noticable effect is found, there still has to be an IMPROPER effect happening. We must be careful here to keep things in perspective. With no egr system at all, the problem would also not exist.

A hole in the cat or muffler will certainly cause trouble codes and erratic idle. A set of dual glasspacts is the same thing.

 

Well, considering that the information in that *.pdf file is about 10 years old, use of it what you will. The vacuum assisted EGR valve hasn't been used by GM since the advent of OBD2 and electronic EGR valves, cerca 1995-6 on most GM vehicles (but may be earlier on some).

There is MUCH more of a vacuum in the intake at idle than there ever would be backpressure in the exhaust. So if you are worried about EGR performance at idle, your backpressure theory is a complete wash. Then another consideration is that when backpressure is at its highest and intake vacuum is at its lowest, WOT (wide open throttle), all EGR systems (electronic or mechanical) are closed, not allowing exhuast gasses into the intake for better performance.

But hey, its not my job to sell you on this information. If you don't think headers or exhaust work can be done, then don't mod. The simple fact is that S10s, Blazers, Grand Prixs, Bonnevilles, Camaros/Firebirds, Corvettes and just about any other GM vehicle with aftermarket exhaust options (inc. headers) have been being modded and that most have done so completely legal.

 

Thought I'd add in some more info. An exhaust leak before the O2 sensors would introduce oxygen into the exhaust causing an abnormally lean condition and result in the PCM increasing the IPWs to richen it back up. Because the lean condition was a result of an exhaust leak and not an actual lean condition in the cylinders, the result would be over fueling and very poor performance. An exhaust leak after the upstream O2 sensors would exibit NO concerns at idle or any other RPM other than possibly higher noise due to the exhaust leak. It may however trigger a code for the downstream O2 sensor which is for catalyst monitoring only (only on OBD2 vehicles).

 

Oh, I was just writing about my 11 year old car, produced at just about the time this set of pdf files were being typed. ( I have 3 mini blazer style vehicles) The site is up to date otherwise. Seemed really usefull for some of us working to upgrade our older exhausts. Being aware of what we are dealng with will prevent serious problems for many of us. There are very few of these. Trouble is, I have one.

 

Still, looking back at the performance market for EVERY other car that utilizes that same EGR system and no one has ever had any problems. Heck, the exhaust system on my dad's '94 K2500 4x4 is FAR from stock. It has been true dual with 2 cats (one per side) and flowmaster mufflers for 2 full exhaust systems now (5+ years). Still uses the stock manifolds, but it was cheaper to bend up and weld in our own system than it was to buy the factory replacement. No issues what-so-ever with idle or performance in any way. That engine (350 tbi) is very similar to the early 4.3L and has the same EGR valve setup.

But hey, you want to believe one document you turned up on the internet somewhere, go right ahead. I'm sure that you'll find plenty of other information that will contradict what that article has to say.

BTW, are you sure that GMs EGR valves (older designs) are positive backpressure EGRs anyway?

*EDIT* - I'm betting that the EGR valves used on the earlier engines were negative backpressure valves. The positive just sounds way to complicated for what is actually there. If that is the case, and I'm betting it is, then the article you quoted has nothing to do with your truck.

The article for Negative Backpressure EGR valves says nothing about exhaust system changes affecting the performance of the EGR system.

 

If I were a betting man I would look up the particular vehicle and try to find a "performance exhaust". One that was manufactured as a kit for the PARTICULAR vehicle I am referring to. I have done this. Since You do not yet know what kind of vehicle we are writing about, why all the fuss?

I am asking for REAL information. I dont have any idea who is right here, but your arguments seem so far off base and so far removed from anything factual that I cannot take them seriously. The examples cited are NOT this car.

I have a car that had an exhaust leak. To test a mechanics theory I simply made sure to find the leak and rather than replace the muffler, which is where the leak was, I simply placed some of that weld goo on its seam. I just know you are not going to believe it, but it solved the problem. Now I will need a new exhaust. Even if it is pure COINCEDENCE, I am stuck with the fact that I already lost the argument that you are proposing. It was very embarrasing, I might add. I build my own engines and rebuild my own stick shifts, rear ends and the like. I did not like losing this argument.

So proceeding on several theories, including yours, which is far more palatable, (and the same as mine) I might add; I went searching for a performance exhaust. Since I deal mostly with Summit I immediatly brought up their website and proceeded to punch in the particular car. I found a single exhaust replacement. Cat back to single muffler to single tail pipe. Only the sound was advertised as being improved. No mention of lower backpressure or any performance gains. Does this mean I have to settle for this or not?

I really still dont know because no second or third person has enterred the discussion here and your own opinions are just too full of emotion and bias to take much stock in. Guess I will proceed to check other places for a dual replacement and see what happens.

The question I inferred is this. Is it possible to do away with such a problem when it DOES exist by replacing this POSITIVE pressure sensing egr valve with one that is NOT? Would a simple non sensing egr valve solve the problem so I can add an exhaust system like others that seem the same but are simply NOT?

 

Geez man calm down. Call me a freakin' liar already and move on or something. This backhanded sarcasm is rediculous. You don't like what I have to say about things, move on somewhere else where everyone can agree with you so you can feel better. Either that or stick with anything pre mid 80's so you don't have to worry yourself about this new fangled technology.

So, if you are looking for "REAL" information, why not let us in on the vehicle you are working with? You have only stated that it is a pre-95 vehicle. NOTHING ELSE. You are working in generalities as well so don't criticize me for doing the same.
Are these things even a blazer/jimmy/bravada or for that matter even GM? Should this conversation be moved into the OFF TOPIC section? Also, are you even having a problem or are you just doing all this incase you have a problem?

I will say this, I have read on some fbody forums that some poeple have had weird experiences with the addition of an aftermarket exhaust that flowed too much. Their solution was the installation of a corvette EGR which uses a negative pressure valve.

With any exhaust installation, you need to maintain a certain amount of backpressure. You can't just go throwing a 3" dual setup on a street driven v6 cause it will run like crap, egr problems asside. Just adding a higher flowing cat and a higher flowing muffler to a stock sized exhaust system won't throw things off. So if you keep the overall pipe area the same, you shouldn't have any issues. If you have a 2.75" single exhaust and want to go dual, you should go with two 2" diameter pipes (frictional losses will make two 2" pipes which have a larger total flow area equivalent to a single 2.75" pipe). This is what we did on my dad's K2500 (stock 3" diameter pipe to two 2.25" pipes).

I'll have to ask a fellow firefighter in my department what he used on his K1500 shortbed with a 4.3L v6 seeing as how this is the EXACT application (motor/trans) although not the same year range... He has a high flow cat and a custom cat back through two flowmasters.

Other than that, take information for what it's worth. Don't go bitching about it. Just because you build engines doesn't mean that you know jack about today's engines. I have built and rebuilt my fair share of engines over the last 15 years, from 2 stroke single cylinder go-cart motors to v8 Detroits and a few computer controlled applications as well. I have also helped out with MANY exhaust system upgrades on a variety of newer and older GM vehicles and none of them have had issues after the install. But hey, I don't know a damn thing. Have a nice life.

*EDIT* - just had to add another thing.

 

Just another source, should any of us have a P on our EGR valve.

http://www.asashop.org/autoinc/dec97/egr.htm

Yes also an older article. But as you may notice it also states that a low backpressure condition can cause some real problems. ( Most of the article may have to be read to see the info though) Just takes the "right" coincedence?

I do happen to see often repeated signs of these very (EGR) problems in this and other Forums I participate in and am doing my best to pass on some info and get some back. It may be that its hard to get to and even look at, so it gets ignored.