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2001 Chevy Express EGR

Tiny
SMETZ
  • MEMBER
  • 2001 CHEVROLET EXPRESS
  • V8
  • 2WD
  • AUTOMATIC
  • 330,000 MILES
My van all of a sudden started stumbling and showing a loss of power (only at mid-upper rpms). Check engine light came on, so I took it to autozone and they gave me p0401. I have researched this and researched this, changed out the egr valve. I have read about vacuum lines being clogged-I believe mine does not run on vacuum. I read about carbon build-up--I saw some, but only around outside edges, didn't seem bad to me. I am guessing that it might be the sensor for the egr valve, but don't wanna play change this, change that. I have a fluke voltmeter, if it can be used to check the sensor, but don't know how to check it. This van has 330k on it, and I want it to see 1000k because I am a poor floorman that cannot afford a new van; so I do my very best at fixing/maintaining it. I have some training from UTI also, but like I said I am a floorman now. Your input is greatly appreciated.
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Monday, October 18th, 2010 AT 1:06 PM

31 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,874 POSTS
The code is for insufficient air flow. Even though it wasn't plugged, are you sure the valve is working properly?
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Monday, October 18th, 2010 AT 1:45 PM
Tiny
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I am "pretty sure" that the Egr valve is working because I bought and installed a new one with the same results.
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Monday, October 18th, 2010 AT 1:50 PM
Tiny
WRENCHTECH
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That code is insufficient EGR flow but I doubt it has anything to do with your symptoms. This EGR system is self contained within the EGR valve so there are no other components. The most likely problem is the passage between the EGR valve and the throttle body is plugged up with carbon. You should be able to clean it with some carb cleaner and a coathanger.
As I said though, it's doubtful that will make it run any better.
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Monday, October 18th, 2010 AT 1:51 PM
Tiny
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So what you are implying is that I need to disregard the problem code and use the basic engine troubleshooting techniques to identify my problem? Ie:checking for proper spark, compression, fuel flow etc?
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Monday, October 18th, 2010 AT 2:04 PM
Tiny
WRENCHTECH
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No, not exactly. You still need to resolve that code but you will likely have other issues to resolve after that.
A scan tool would be helpful to analyze all the sensor data during the failure.
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Monday, October 18th, 2010 AT 2:14 PM
Tiny
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I am going to try and return the new egr that wasn't the problem and trade it for a scanner. Hopefully this won't kill me, but make me stronger.
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Monday, October 18th, 2010 AT 2:17 PM
Tiny
SMETZ
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Ok, so I got a scanner. First I cleared the prior code, which never came back. I recorded live data during idle, cruising at 55, acceleration, and deceleration. I am clueless at this point. I could not record the full acceleration at 3/4 throttle because it started pinging severely, which worried me, so I let off of it. I did get a 1/2 throttle acceleration though.
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Monday, October 18th, 2010 AT 6:23 PM
Tiny
WRENCHTECH
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That's the EGR problem causing the pinging. Fix that first.
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Monday, October 18th, 2010 AT 6:26 PM
Tiny
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So then, since the new egr valve did not correct that problem, what am to do? And thank you for all of your advice so far.
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Monday, October 18th, 2010 AT 6:30 PM
Tiny
WRENCHTECH
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I already covered that.
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Monday, October 18th, 2010 AT 6:33 PM
Tiny
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So since I am mostly sure it is not the egr valve itself, then I need to simply spray a bunch of carb cleaner into the passageways involved in the egr process and scratch it out with a coat hanger? What about the residual particles that will break off during this process? Will they simply evaporate with the cleaner? I don't want to get stuff in my chambers. I only want to understand the process.
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Monday, October 18th, 2010 AT 6:48 PM
Tiny
WRENCHTECH
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Blow them out with compressed air. They won't hurt anything. Just make sure you get all the way through the passage to both ends.
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Monday, October 18th, 2010 AT 6:54 PM
Tiny
WRENCHTECH
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You might have to remove the throttle body to access the small hole o that end.
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Monday, October 18th, 2010 AT 7:04 PM
Tiny
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Ok. I will do that tomorrow morning. Good thing I have no work to do currently. Will it be ok for me to clean the valve in the same manner?
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Monday, October 18th, 2010 AT 7:31 PM
Tiny
WRENCHTECH
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No need to do anything to the valve as long as the pintle is fully seated.
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Monday, October 18th, 2010 AT 7:39 PM
Tiny
JACOBANDNICKOLAS
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I started with you and have been watching the progress since. I agree with him that where the EGR mounts can be clogged. That was going to be one of my suggestions, but.

As far as the noise you get at full throttle, is it valve ping?
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Monday, October 18th, 2010 AT 8:00 PM
Tiny
WRENCHTECH
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Ignition "ping" would be an expected symptom of not having EGR flow. Get the EGR working and that will go away.
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Monday, October 18th, 2010 AT 8:05 PM
Tiny
JACOBANDNICKOLAS
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Would you please PM me.
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Monday, October 18th, 2010 AT 8:17 PM
Tiny
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I believe it is ignition ping, but at 3/4 throttle it did sound like there was some kind of noise from the valves or rockers also. Not completely sure about that though. I am certain about the ignition ping. I am wondering if this whole situation is just bad gas. I cannot PM until I post a couple more.
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Tuesday, October 19th, 2010 AT 9:28 AM
Tiny
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Here is a snapshot from the scan tool during the pinging:
DTC_CNT 0
FUELSYS1 CL
FUELSYS2 CL
LOAD_PCT(%) 40.0
ETC( °F) 199
SHRTFT1(%) -21.9
LONGFT1(%) -0.8
SHRTFT2(%) 16.4
LONGFT2(%) 12.5
MAP(inHg) 26.9
RPM(/min) 2890
VSS(mph) 42
SPARKADV( °) 20
IAT( °F) 97
MAF(lb/min) 12.146
TP(%) 44.7
O2S B1S12--B2S12--
O2B1S1(V) 0.095
SHRTFTB1S1(%)-19.5
O2B1S2(V) 0.045
O2B2S1(V) 0.705
SHRTFTB2S1(%) 8.6
O2B2S2(V) 0.745
OBD OBD1
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Tuesday, October 19th, 2010 AT 9:46 AM

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