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6.5L Turbo Diesel 1992-00 6.5TD - Discussion forum for the 6.5L engine.

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Old 11-16-2017, 07:58 PM
gardentractorworld gardentractorworld is offline
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Default 6.5 diesel egr flow insufficient codes

I'm new here to the forum and I have a question about my 98 YMCA sierra 2500 2wd with a 6.5 diesel. Every time I drive the truck I get a P0400 and P0501 code for Egr flow and Egr flow insufficient. The truck is all stock other than I cut the muffler and converter off and put flex pipe on instead. I have done a few tests and I have vacuum to the first two black solenoids on the drivers side while the truck is ideling but I'm not getting any vacuum coming out of the middle solenoid. I checked all the vacuum lines and none of them are collapsed and they all look good. Does anyone know why I keep getting these codes. They come on after 20 or 30 minutes of driving and is it possible the codes are on because I removed the converter and muffler? Any help would be greatly appreciated.
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Old 11-17-2017, 11:26 AM
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Cutting the converter off probably reduced the back pressure and hence flow through the EGR system, enough to cause the code. The code might not affect performance, so, unless you have an inspection problem, it could be ignored. (Check the service manual to confirm this.)
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Old 11-17-2017, 08:44 PM
gardentractorworld gardentractorworld is offline
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Is there a back pressure sensor? If so is there a way to trick the computer into thinking it's fine. There is a noticeable loss in performance when the codes come on.
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Old 11-18-2017, 01:10 PM
Warren96 Warren96 is offline
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Have these codes been there before the modification, or have they always come up? The solenoids are not very expensive and the EGR valve is easy to clean. I have had to replace a couple of them that held vacuum. I had the muffler and catylast off mine for a short time, and the computer didn't care. The reason I put them back was because there was no increase in mileage or performance, and I preferd a quieter engine sound.
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Old 11-18-2017, 02:09 PM
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There's a mass airflow sensor on the intake. I'm not up on the particulars of the ODB II but I suspect if the airflow is not within certain parameters in assumes the EGR flow is responsible.
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Old 11-18-2017, 03:01 PM
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The codes have been coming up before muffler and cat removal but they seem to come on sooner since removal. Does anyone know if I should have vacuum coming out of the middle solenoid while the truck is ideling. I have plenty of vacuum going into the middle solenoid or at the right fitting but no vacuum coming out or at the left fitting
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Old 11-19-2017, 11:19 AM
Yukon6.2 Yukon6.2 is offline
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Hi
Seeing you are already "testing" without the cat and muffler...
I would "test" with the EGR system removed...

My.05 cents,i'm from Canada and we don't have penny's
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Old 11-19-2017, 08:13 PM
gardentractorworld gardentractorworld is offline
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So you would suggest taking off all the vacuum lines and electrical connectors and sensors? Wouldn't this throw even more codes
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Old 11-19-2017, 08:54 PM
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Quote:
Originally Posted by gardentractorworld View Post
So you would suggest taking off all the vacuum lines and electrical connectors and sensors? Wouldn't this throw even more codes
Yep. Just find another ECM of the same year/model as your truck, only from a 2500HD (8600 GVWR, F code) or 3500, or purchase a reprogram. The computer is already complaining. Save yourself a lot of headache and eliminate the problem.*

*This advice is for off-highway and diagnostic testing purpose only. It is unlawful to modify the emission system of any vehicle.
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Old 11-20-2017, 09:25 AM
Warren96 Warren96 is offline
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Have you had the egr valve off for cleaning? They fill up with a huge amount of carbon on mine. Besides, who is to say that the Canadian govt might change the law and now all your smog parts are missing.
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