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Discussion Starter #1
Just a hypothetical question: Seville with the 4.9, if the catalytic converter has been replaced with a striate pipe (aka cat-delete) does the EGR valve have any use? Can it or should it be removed (aka EGR-delete) as well.
 

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1997 Cadillac STS (BOSE w/AUX In, Massage Seats, URPAS, "Z")
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I thought the EGR valves allow recirculateing some of the exhaust gas back into the cylinders to finish up the unburned traces of combustible. Theoretically should kind of help saving some gas and help getting a cleaner exhaust gas composition (like CO and other nasty stuff), catalytic converter is also part of the solution for the cleaning process. I guess you can say the EGR helps the cat but the cat does noting for the EGR.
 

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2002.5 F55 CORSA STS, 2014 Explorer XLT FWD
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Ignition, timing, and fuel mixture curves are calibrated for EGR. Remove it and you have real engine problems. EGR recirculates exhaust gas in metered amounts in order to cool the combustion cycle and prevent fuel knock/ping, thereby lowering NO. There's also no reason to remove the cat. Modern converters present no restriction problems, and if it is gone you may begin to set sensor and fuel mixture codes.
 

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69 Thunderbird | 90 Seville | 03 Corolla | 89 Marquis(scrapped) | 72 Torino(scrapped)
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Removing the cat will not set a code on these cars. But it WILL make it much louder. I have a flowmaster camaro style muffler... I got greedy and removed the cat. It sounded awful after that and there was no loss or gain in performance. Not worth it. I also had to rebuild the exhaust from the 3" merge collector back to the 90. Not cool...

I had my EGR deleted for a few thousand miles also.... No codes, no ping, no problems... Yet, no loss or gain in performance either. Also not worth the effort.
 

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Discussion Starter #5
Removing the cat will not set a code on these cars. But it WILL make it much louder. I have a flowmaster camaro style muffler... I got greedy and removed the cat. It sounded awful after that and there was no loss or gain in performance. Not worth it. I also had to rebuild the exhaust from the 3" merge collector back to the 90. Not cool...

I had my EGR deleted for a few thousand miles also.... No codes, no ping, no problems... Yet, no loss or gain in performance either. Also not worth the effort.
This is very interesting info. There seems to be a lot of different schools of thought on this. Sevillian273 what do you think about what submariner had to say "Ignition, timing, and fuel mixture curves are calibrated for EGR." I am asking all these questions because my cat rotted right off last weekend & I had to put in a strait pipe as a temp until I can get my new cat.....but what has happened since then is very odd. My KMs per Liter has gotten better by at least one third. I will know for sure by the end of the week as I am going to run this car dry.....that’s if I don’t get pulled over by the cops first.:shhh:
 

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69 Thunderbird | 90 Seville | 03 Corolla | 89 Marquis(scrapped) | 72 Torino(scrapped)
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This is very interesting info. There seems to be a lot of different schools of thought on this. Sevillian273 what do you think about what submariner had to say "Ignition, timing, and fuel mixture curves are calibrated for EGR." I am asking all these questions because my cat rotted right off last weekend & I had to put in a strait pipe as a temp until I can get my new cat.....but what has happened since then is very odd. My KMs per Liter has gotten better by at least one third. I will know for sure by the end of the week as I am going to run this car dry.....that’s if I don’t get pulled over by the cops first.:shhh:

Im only speaking from experience. I cant guarantee anything, all I can say is that on MY car, removing the cat and EGR has no effect. What sub says makes perfect sense. I did that to my own vehicle as an experiment and to diagnose some issues I was having. On OBD II cars, removing the cat WILL set a code because there is an O2 sensor downstream from the cat. On our cars there is not, so the computer doesnt know when the cat is removed.

Your increase in mileage is probably due to the condition you old cat was in at the end of its life. I suspect you will retain the good mileage after you get a new one.
 

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2002.5 F55 CORSA STS, 2014 Explorer XLT FWD
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:yeah: Right - no after cat sensor, no codes w/o cat. Senior moment.......

I don't think the 4.9 has a knock sensor, so removing the EGR might or might not mess with the fuel trim. A blocked or partially stuck EGR will cause ping on light to moderate acceleration, so therefore the caution on its removal. BUT, if you remove it the exhaust/intake manifold passages have to be blocked off. A 2-bolt oval plate/gasket ???
 

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69 Thunderbird | 90 Seville | 03 Corolla | 89 Marquis(scrapped) | 72 Torino(scrapped)
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:yeah: Right - no after cat sensor, no codes w/o cat. Senior moment.......

I don't think the 4.9 has a knock sensor, so removing the EGR might or might not mess with the fuel trim. A blocked or partially stuck EGR will cause ping on light to moderate acceleration, so therefore the caution on its removal. BUT, if you remove it the exhaust/intake manifold passages have to be blocked off. A 2-bolt oval plate/gasket ???
A 2 bolt plate with some RTV is what I used. I made it out of some sheet metal... I've always run shell 93 and the engine is in good health with low miles so maybe I was just lucky? Either way, it did nothing for performance so I wouldnt bother. Removing the valve is a PITA with the fuel rail in the way.

You would think that GM would have designed it to be within a certain degree of pinging so if the EGR were to fail on its own, it would not damage the engine....

FWIW: I did the block off on a 89 ford 5.0 for tens of thousands of miles with no issues on 87 octane... still no gain in performance. You can even get aftermarket billet block off plates for many popular engines online. They are categorised as 'off-road' :rolleyes:

No knock sensor in the 4.x engines btw. So no fail-safe if you screw around too much. This is why you cant put in 87 like our fellow Northstar owners. :thumbsup:
 

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Something not mentioned above. Some EGR valves work with a certain amount of back pressure to lift. Removing designed in back pressure by removing the cat can cause non operation or faulty operation of the EGR. Bottom line this aint the 60's anymore. Engines, and emmisions are all designed in, so removing any thing most times affects performance adversely.
 

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Madwacker1, if you are in a part of Canada that requires Emmission testing then all of the above is academic as you will fail for sure with both those items removed otherwise go for it.
 

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If I recall correctly, EGR helps cool the combustion temperatures as well as improve fuel mileage.
 

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69 Thunderbird | 90 Seville | 03 Corolla | 89 Marquis(scrapped) | 72 Torino(scrapped)
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Bottom line: The EGR is not worth messing with. You gain nothing and open yourself up to possible detonation. Once you see how much of a pain it is to remove you will change your mind.

As for the cat, you can get a universal from magnaflow for around 60-70 USD.

On a side note, Im curious how you replaced yours with the straight pipe. On mine the 3" collector is welded to a 2-bolt flange and bolts directly to the cat with no pipe in between. I had to cut the 3" before the flange and use a 3" x 2.5" adapter....

The pic was for a thread where I was trying to find a flange/pipe to attach in place of the cat... The 2 13/16 turned out to be 3" O.D. pipe.
 
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