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Running rich

Forum: C4 Engines, Driveline and Handling

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Running rich

Posted: 5/18/14 10:08amMessage 1 of 20
c
cco
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Car runs fine with decent mileage but blackens the exhaust pipes after only a few miles.

 No smoke, no CEL -- why the black pipes so quickly? 

Gas is from my regular station and runs fine in my other cars.

'94 LT1 Auto with only Corsa exhaust.

Any input would be appreciated.

C.

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Re: Running rich

Posted: 5/19/14 10:55amMessage 2 of 20
c
cco
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Now it's running rough and my mileage is down.

Starts ok, just runs rough like it's misfiring. Blackens up the pipes quickly too.

Not sure if it's Optispark, wires, or plugs so I'm guessing that's a good place to start.

24k miles and has had best of care from original owner.


Any help would be appreciated.

C.

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Re: Running rich

Posted: 5/20/14 1:52pmMessage 3 of 20
c
cco
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I understand that this might be as simple as a temp sensor -- which one might that be and how to test it?


C.

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Re: Running rich

Posted: 5/20/14 7:45pmMessage 4 of 20
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Adams' Apple
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Duncanville, TX - USA
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Vette(s): #1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/ Am-Fm/map light National/Regional/Chapter NCRS "Top Flight" #2-1985 Bright Red/Carmine Cp.L-98/auto Member: NCRS, NCRS Texas, Corvette Legends of Texas
I would suggest pulling codes. Just because the CEL is not on doesn't mean it doesn't have codes. Might also pull some plugs and have a look-see.
If it starts and runs fine when cold, it may be a temp sensor, but it could also be leaking injectors. So many possibilities...codes would be the place to start.

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Re: Running rich

Posted: 5/21/14 9:22amMessage 5 of 20
c
cco
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Adams' Apple said: I would suggest pulling codes. Just because the CEL is not on doesn't mean it doesn't have codes. Might also pull some plugs and have a look-see.
If it starts and runs fine when cold, it may be a temp sensor, but it could also be leaking injectors. So many possibilities...codes would be the place to start.



Thanks Joel -- Is this the suggested procedure?:


 http://www.corvettebuyers.com/c4vettes/codes.htm

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Re: Running rich

Posted: 5/21/14 10:39amMessage 6 of 20
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396c4
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Temperature sensor will mess it up if it thinks it's really cold when it isn't (and scan tool or Autotap would be best to tell you what the ECM is seeing). I've even heard bad or corroded contact is common but if that's OK , check the vacuum line to the fuel pressure regulator. If the regulator is not getting vacuum or the regulator is faulty, it will keep the pressure too high which will leads to rich condition because it's not compensating for manifold vacuum.
Or, if the EGR is not working properly, that will cause rough idle and other issues.

You can test both with hand held vacuum pump although you also need pressure gauge on the fuel line.


|UPDATED|5/21/2014 10:39:04 AM (AZT)|/UPDATED|
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Re: Running rich

Posted: 5/21/14 5:22pmMessage 7 of 20
c
cco
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396c4 said:
Temperature sensor will mess it up if it thinks it's really cold when it isn't (and scan tool or Autotap would be best to tell you what the ECM is seeing). I've even heard bad or corroded contact is common but if that's OK , check the vacuum line to the fuel pressure regulator. If the regulator is not getting vacuum or the regulator is faulty, it will keep the pressure too high which will leads to rich condition because it's not compensating for manifold vacuum.
Or, if the EGR is not working properly, that will cause rough idle and other issues.

You can test both with hand held vacuum pump although you also need pressure gauge on the fuel line.





Thanks 396...no scan tool for my '94 system AFAIK -- have to read the ECM another way.

Bad or corroded contact at the ECM? and exactly where is the EGR -- as you know room and accessibility is at a premium around the engine..


Took one plug out and as expected it was black as Toby's A$$.

C.

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Re: Running rich

Posted: 5/22/14 3:21pmMessage 8 of 20
c
cco
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Also need to know where to find the temp sensors mentioned.

Thanks.

C.

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Re: Running rich

Posted: 6/1/14 3:01pmMessage 9 of 20
c
cco
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After tests, scans, and head-scratching: it's running fine and no more "rich" .....  (no codes either)


I'm chasing a ghost.

C.

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Re: Running rich

Posted: 6/5/14 5:34amMessage 10 of 20
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396c4
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Could be connection problem on the temperature sensor. Bad contact  or sensor could make it think the engine is really cold and so make the mixture rich. Look on the head on the passenger side. The EGR is at the very back of the intake manifold roughly where the distributor used to be.
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