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.

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.

I understand that this might be as simple as a temp sensor -- which one might that be and how to test it?

C.

Joel Adams  
My Link

    
(click for Texas-sized view!)             NCRS

"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"

Thanks Joel -- Is this the suggested procedure?:

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

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.

Also need to know where to find the temp sensors mentioned.

Thanks.

C.

After tests, scans, and head-scratching: it's running fine and no more "rich" .....  (no codes either)

I'm chasing a ghost.

C.

Thanks, 396 --

C.

connections seem fine but how do we know they're actually making contact.

Problem returned briefly for a trip of about 10 miles. (Blackened pipes and fan on unneeded) - so I'm guessing that it's a temp sensor problem that the CCM is reading and trying to compensate for.

  I parked and did a scan for codes and found:

Module 1:  C-12

Module 4: H-63, H-77, and H-78

Module 9: H-72

C12: I've read is current but indicates all ok.

The H codes are history codes and not current.

I recorded the codes and did a reset for the codes and CEL -- drove it the next day and seems fine again. No black pipes, no CEL, no roughness.

Can't find anything wrong.

C.

Yes it helps mucho, and thank you Dave. Still more or less groping in the dark with the '94 but coming along slowly (with a little help from you kind guys).

Yes the 77 and 78 codes will be because of the manual fan control. I was warned that there would be codes and a history. As you say: no worries.

Looks like we've found the cause of the issue: RF O2 sensor.  Will get my man to order one in for me. I understand they're not as expensive on the C4's. I'll probably do both sides if so.

BTW, you say " H2OS "    -- is that the O2 sensor you're referring to?

Again thanks for the help. Yes it's fun to get involved -- I love it.

Cheers

Colin.

Cheers brother -- My man will get me the O2's I need and all will be fine again.

C.

Filled car today and I'm thinking that I may be filling up the tank too far causing overflow into the recirculating system and subsequent CEL's.

Is this possible and is overfilling something to avoid?

CEL came on for a few minutes on a short journey (after filling) and I could fell the engine run a little roughly. Within a miles tho the light cleared and the engine smoothed out and seemed to run fine again.

Came home and did another scan and this time found both H63 and H64 codes had set.

DTC 63 -  Bank 2 (Right Front) Heated Oxygen Sensor (HO2S) #1 Circuit (Open Circuit)

DTC 64 -  Bank 2 (Right Front) Heated Oxygen Sensor (HO2S) #1 Circuit (Lean Exhaust Indicated)

I reset the codes again and will see what returns. I'll also let the fuel run down somewhat to see if the problem returns. I suspect that it won't.

O2's coming soon anyway.

Thanks for the continued help.

C.

So we've narrowed it down to O2's and the fault code has directed me to RF, which suggests that there are 4 sensors.

I have read thru the FSM's and can't find the exact section describing the O2's -- just various exhaust and header parts.

If someone can direct me to the right section in the FSM's I'd appreciate it and if anyone knows the number of O2's on my '94 LT1 I'd appreciate that too.

I do have a 7/8" (22mm) Crowfoot wrench and wondering if that's the right size for my '94 P2's.

I also understand that they O2's are plug and play once I change them out.

Thanks

Colin.

EDIT:

Found it: '94 FSM, 6E3-A-1 and there's a diagram on 6E3-A-5

Looks like there are 3 x O2's and there's some discussion that the rear one is unused until '96 (OBD-11).

Found the section in the FSM -- and ordered an 02 from Amazon (bosch).

FSM says there are 3 02's

Found the electrical connection at the RF 02 to be loose. Connected properly and all is well again (so far). Have 02 and tool JIC.

Thanks for help.

C.

Installed new Bosch 02 and all is well once again.

It took a while to maneuver the old one out and the new one in but overall a fairly straightforward fix.

Thanks for all your help guys.

C.