Hey guys, maybe this is a silly post, if so, wont be my first. I am an old motorhead, and like to work with engines to gain performance & often fuel economy.

I understand how the EGR valve works, and what it does. On older engines, you can block it off & go on. On the newer EFI engines, there are sensors to tell the EEC if it is working or not.
My questions follow. Can anybody offer me any light on this subject?

1. I have been told that disconnecting the EGR will cause idle problems. How can this be, since EGR only comes in at cruise speeds?

2. Is it the sensor on the EGR valve that tells the EEC that there is a problem, thus going into "limp" mode? Or is it the lack of exhaust gasses, sniffed by the O2 sensor?

3. How would blocking off the EGR valve cause fuel economy to suffer? I know by introducing exhaust gas into the air/fuel mixture cools the flame, but it also would help quench the fire, robbing the cylinder of power & efficiency, wouldnt it? Or, are we back to a confused O2 sensor, causing it to run rich?

4. If I remove/block off the EGR, will this mean less possible timing for the engine? More detonation & lose efficiency due to less timing?

5. My last thought is to just block it off, yet leave the valve connected, both electrically & through the vacum supply, if the above can be worked through.

Please dont give the "pollution" lecture. I know it helps control emissions. Thanks guys!

 

If you leave it all connected, the computer will think that the engine is recieving exhaust gases, when in actuality it is not. The computer leans out the mixture when EGR is active, since there is less oxygen available for combustion. The computer will still try to lean it out, which can cause problems. I really don't believe there is anything to be gained from blocking off or removing the EGR.

 

Ok I don’t know jack about EGR and all the pollution control crap on my truck. But… when I did my exhaust I did away with the cat. converter and this had a EGR pickup tube on it which I also cut and plugged with a plastic cap that happened to fit nicely. I don’t think this exhaust or the EGR tube plug did anything for my fuel economy either good or bad. It does have more power but then the converter was old and plugged up a bit, and I did away with the catback exhaust and stock muffler and went dual glasspacks and out the sides of the truck. This sounds really great BTW LOL. I also had a separate problem which came into being before the exhaust mods, this was that sometimes the truck would not idle well, sat up at about 2k rpm! This drove me nuts because it made it harder shifting and was terribly hard to drive smoothly and in my mind’s eye I could see the clutch getting worn out extra because of this. It didn’t do it very often until finally it just did it constantly. One day while poking around under the hood (after I did the exhaust, long after it) I noticed the air check valve tube was disconnected. While trying to hook it back up (I didn’t know what it was then and didn’t realize it was useless to me) the valve/filter assembly broke off of one of it’s screw on connectors. Great, now I couldn’t get to it to take out the old part or put in a new one. I did get a new one for $30 (then realized I couldn’t get back to it to put it on) then someone told me I don’t need it because I plugged my EGR pickup tube. So I took it back for my $30 back. It seems that this might have come disconnected in the time range of the idle problem getting much worse but I couldn’t say for sure. I was told the idle problem was probably a vacuum leak somewhere. I lubricated and cleaned the throttle body valves well and the throttle cable where I could get to it. Didn’t seem to do anything for it. I made sure the upper intake manifold bolts were tight, this also didn’t do anything for it. Oh, the 4 little colored vacuum tubes that go to a black box by the battery accidentally got broken one cold day when I accidentally touched them. This possibly had something to do with the idle also but it was doing that before they broke. So I finally just added a small helper spring to the throttle body (I can get pics and the stock number from Lowe’s if interested) and the problem is fixed! Idles great now all the time. The throttle doesn’t cut back quite as sharply when you shift and let off the throttle. I mean it goes right to idle but not real sharply (so it doesn’t cackle the pipes really). Not a problem though. Cost about $2 or so and was well worth it for the aggravation. Probably didn’t have anything to do with the real problem that caused the high idle but it did fix it so that’s all that I care about! LOL. The wiring on my truck is a mess but everything works like it should. I’d like to go through and gut all the EGR/vacuum related crap since I really don’t actually use it anymore, I’m sure the computer just needs adjusted somehow to account for these changes but it does run really great and sounds great. I was told my exhaust mods might mean the timing should be changed but I don’t see its necessary at all and the person who told me that never mentioned that it sounded off timing.

Oh, the missing EGR air check valve/filter whatever-its-called lets the air make an annoying clicking noise so I might try to plug that up if there would be no ill effects??? Anyone know about that?
Thanks, sorry this is long but maybe it would help someone in a small way. Just some of my escapades LOL.

 

Are you sure that you took off the EGR and not the air injection tube? The EGR is the valve on the intake manifold. The computer will throw a code and you will have a constant check engine light with the EGR system disabled. It possibly will run in open loop all the time killing fuel economy, and otherwise make the truck not run right.

 

If you unhooked the pipe that was attached to the cat, I'm pretty sure you just unhooked part of the smog system. It goes from the air pump along the passenger side of the engine, then to the crossover tube between the back of the heads and down to the cat. I removed all of this on my 90, 351, including the air pump and cats. Takes 2 short bolts to plug the ports in the back of the heads since they are threaded. 5/8 or 3/4, can't remember .

 

Here's an easy EGR block-off that I used for a while until I could replace my bad EGR valve--unbolt that stovepipe, slip a dime in there, and bolt it back up. It's invisible, and the truck was much more driveable. The old EGR valve must have had a weak spring because just tapping the gas made the valve open up fully and it leaned it out pretty badly. In fact, the junkyard valve I bought six months ago for $5 is starting to do the same thing...

 

Bigric, I love the idea! And it will only cost me 10 cents! It can be a trial & error, and will see firsthand how things run out. I am buying a fuel mixture meter to test the air/fuel mixture, and be sure I am not leaning out. It just seems like a neat tool, and can rest in the cabinet beside my vacum gage & timing light, when I am not doing repairs. $25 at Autozone.

Honestly, I dont know if it will affect driveability, power or economy by blocking it off. If there is nothing to be gained, I will leave it functional, unless it gives trouble. If I do notice an improvment, or find problems, I will give a post. I dont like driving by the glow of my "check engine" light, so I was looking for information & hopefully keep the EEC happy.

Since this engine seems to have quite a bit of blowby, and uses 1 quart of oil per fill up, I plan to freshen it up with a good rebuild. It will give me an excuse to work the heads over, and put in a towing/RV cam, that will be compatable with the computer. I am also looking into the Diablo chips & headers.

Thanks for the info guys!

 

I've seen recommendations to reduce the opening at the egr to about 1/8 in. and have been told that this greatly improves idle and low speed driveability and doesn't trigger any codes or adversely impact gas mileage , haven't tried it myself as mine runs fine.