Postby Cologne [OP] » August 14th 2013, 1:01am


I’m posting this to help everyone here with this sneaky problem that baffles so many people. I screwed around with this slowly developing tricky problem for a long time. I searched the web until my eyes became googly. I now have a pretty good understanding of the smog system. I’m surprised how few people on the web could help me. Most help was the same answer, which was check EGR valve. The clue was correct but I couldn’t find enough information for the issues I was having. But then, One reply here on AstroSafari Forums, asked me to check the EGR valve exhaust tube. ?! That got me to thinking. That was the clue I needed that helped me figure out that my manifold intake EGR valve port was clogged. I thank that person and this forum for helping me. So this post is my way to return the favor and support this forum with some helpful info.

First, the issue I had. Will this sound like yours?

For a long time I had misfire probs/ codes. I kept changing the rotor, cap, wires & plugs. The misfire kept coming back. Drove me nuts. I finally noticed ONLY the # 1 spark plug would foul from carbon build up. I figured must be burning oil real bad in just that cylinder. I have an oil leak too so it was easy to believe. So I would just keep changing that #1 spark-plug out every time it started running rough/ misfiring about every 1000 miles or less. It was a quick fix for a bigger problem that was literally growing like a fungus. The source of all my problems then and to come was/ is carbon!

Then, a little at a time I started getting a mixture of misfire codes, EGR & bank 1 related codes. So I changed out the EGR and codes for it went away. Guess at the time the EGR valve was sticking open or closed do to carbon build up. So then after a short time, I got the dreaded LOWFLOW code, P0401. (duhnT!)

This code I’ve learned is for a CLOGGED or partially clogged EGR valve intake or exhaust port (Low Flow).

HERE'S HOW TO CHECK IT OUT without a scan tool :confused:

For this test I'm assyou&me-ing cap,rotor, spark plugs & wires/ Tuneup is OK. :whack:

*EGR valve stuck open will cause EGR codes & rough idle.
*EGR valve stuck closed will show EGR & low flow codes but engine will idle smooth.
*A clogged manifold EGR valve intake or exhaust port will cause code P0401 but the engine will idle smooth. This problem can be a very expensive fix...

If you don’t have EGR valve codes then the EGR valve is probably OK. If you do, then take it off and clean it with EGR cleaner or BBQ carbon cleaner. PAUSE! Before you put it back on, plug the connector back in for it and hang the EGR up somewhere out of the way.

Have someone else start your engine because you will need to be looking at the EGR valve and the holes where it mounts to.

*If the engine idles fine and doesn’t try to die, then you have a plugged intake passageway from EGR valve port/ hole on the manifold.

*If the engine runs really rough but doesn’t die then the manifolds EGR valve intake passageway is only partially constipated.

*If the engine flat out dies, then the manifold intake passageway for the EGR valve is clear. And that my friend is a very good thing. To have my manifold removed and cleaned cost me $1000! mostly labor because its a Van with a Vortec engine.

Rev up the engine. check the exhaust port/ passageway for the EGR valve by looking to see if exhaust is blasting out of the hole. If yes then its OK. If no exhaust blows out then you have a plugged EGR valve exhaust tube, manifold port/ passageway.

Rev up the engine and look to see if the EGR valve is opening and closing smoothly. If the valve isn’t moving at all then you might need a new EGR valve. A good name brand can be found for under $200.
**Buy a gasket for it that has a screen built in it. The screen will stop carbon from clogging up the EGR valve and intake port. Next time you have flow problems you can just clean the screen and blow out or clean out the exhaust tube/ manifold port. :thumbup:

In closing, some people will block off the EGR valve ports with a piece of sheet metal in with the EGR valve gasket. Then remove it just for smog checks. The EGR valve might be a good thing for pollution control but its really bad on the engine. The intake manifold, valves, spark-plugs and cylinders just get blasted with filthy carbon build up. And that makes an engine run rough. I believe Its really just a BIG money maker for the auto industry. They don’t care about pollution. If they did we would all be driving electric or steam engine cars.

98 GMC Safari/ Cargo van AWD (200k miles) With Big AssFat Wheels = P295/50R-15 Proxes
Image cutout back of front wells + 4" bump stops.

Original Poster [OP]
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Firing on 1 Cylinder (L1)
Firing on 1 Cylinder (L1)
Years of Membership: Cologne has been a member for 13 full yearsCologne has been a member for 13 full yearsCologne has been a member for 13 full yearsCologne has been a member for 13 full yearsCologne has been a member for 13 full yearsCologne has been a member for 13 full yearsCologne has been a member for 13 full yearsCologne has been a member for 13 full yearsCologne has been a member for 13 full yearsCologne has been a member for 13 full yearsCologne has been a member for 13 full yearsCologne has been a member for 13 full yearsCologne has been a member for 13 full years
Posts: 118
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Joined: January 2008
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Van Model Year: 1998
Van Make/Model: GMC Safari
Extra Info: AWD

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