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1993 Saturn SL1 EGR valve

Tiny
777FTM
  • MEMBER
  • 1993 SATURN SL1
Engine Performance problem
1993 Saturn SL1 4 cyl Front Wheel Drive Manual

I have a misfire or hesitation at small throttle openings, the problem goes away if I disconnect the vacuum line to the EGR valve. I have replaced the valve, the solenoid and substituted the PCM all to no effect. There are no codes. I can read the output from the PCM but I do not know the exact conditions under which the valve is supposed to open. If the valve is opened manually the engine stalls. The valve I have and a replacement valve (from Saturn) are both negative back pressure valves, that is, vacuum on the pintle opens the internal valve preventing the solenoid vacuum from opening the valve. But the pintle is exposed to exhaust gas so I am wondering if the valve should be a positive back pressure valve. The valve part # is 21008566 and it is marked with the GM number 21000122 which is identical to the part number of the valve fitted to the car.
Any ideas?
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Tuesday, March 10th, 2009 AT 4:52 PM

8 Replies

Tiny
DAVE H
  • MECHANIC
  • 13,383 POSTS
Hello .. thanks for the donation .. much appreciated

Hope this helps .. let me know

Backpressure EGR System (2.0L, 2.2L, 4.3L, 5.0L & 5.7L TBI)
EGR uses positive and negative backpressure EGR valves. These valves may be identified by the letter in the last position of part number; "P" designates a positive backpressure valve and "N" a negative backpressure valve. Backpressure EGR may also use an ECM-controlled solenoid to regulate vacuum signal to EGR valve.
Negative Backpressure EGR Valve Vacuum is applied to upper EGR diaphragm via a hose connected to intake manifold vacuum. Manifold vacuum is also applied to lower EGR diaphragm (through intake port at base of EGR valve). When manifold vacuum in lower chamber is insufficient to overcome spring tension on lower diaphragm, bleed valve will be closed, allowing vacuum in upper chamber to open EGR valve. With engine at idle or under light load, high manifold vacuum applied to lower chamber opens air bleed valve in lower diaphragm. This bleeds off vacuum in upper chamber, keeping the EGR valve closed.
Positive Backpressure EGR Valve A control valve, located in EGR valve, acts as a vacuum regulator valve. Control valve regulates amount of vacuum to EGR diaphragm chamber by bleeding vacuum to atmosphere during certain operating conditions. When control valve receives backpressure signal through hollow shaft of EGR valve, pressure on bottom of control valve closes control valve. When control valve closes, maximum vacuum signal is applied directly to EGR valve allowing exhaust gas recirculation.


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Tuesday, March 10th, 2009 AT 8:08 PM
Tiny
777FTM
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Thank you Dave, my question is, which is the correct valve for my 1.9L SOHC (Vin 9)?
The valve I have is a negative back pressure valve.
Nick
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Tuesday, March 10th, 2009 AT 10:10 PM
Tiny
DAVE H
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The original valve should be marked with a N or P after the part number .. let me know !!


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Friday, March 13th, 2009 AT 12:16 PM
Tiny
777FTM
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Dave
The valve has a N at the end of the part number
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Saturday, March 14th, 2009 AT 7:49 AM
Tiny
DAVE H
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Hey.

if the ORIGINAL valve ON the car has an "N" .. then the valve you need is a Negative backpressure valve .. hope this helps


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Saturday, March 14th, 2009 AT 9:30 AM
Tiny
777FTM
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Dave
A negative back pressure valve is correct for this car, so no help, I'm afraid.

I have removed the exhaust, but that didn't make any difference (I thought the cat might be blocked).

I am fairly certain the command from the PCM is correct although it seems to be different when the car is stationary when it seems to use MAP as well rather than just TPS as per the manual which is what it does when it is moving.

I am going to download some more data with EGR vacuum on then off to see if I can detect any change.

Is the exhaust feed to the EGR valve from one cylinder or all four do you know? If more than one cylinder, then if one was blocked would that cause these symptoms?

I will donate more if you can solve this one, it's driving me crazy!

Nick
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Monday, March 16th, 2009 AT 11:51 AM
Tiny
777FTM
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Hi Dave
Problem solved!
Two of the new plugs leads that I replaced six months ago were open circuit, the shop replaced the lead set and the misfire disappeared. I can only guess that the misfire affected the pressure balance of the EGR valve and that is why disconnecting it seemed to fix the problem?
Nick
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Monday, March 16th, 2009 AT 7:36 PM
Tiny
DAVE H
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Well Done

Happy to be of a slight assistance .. remember we are here, should you need our help in the future and spread the word of our site to friends and family should they ever need us !!

Thanks for telling us of your final fix .. this may help others in the future ..

Happy Motoring.


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Monday, March 16th, 2009 AT 7:43 PM

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