C4 1995 Corvette Runs Rough/Check Engine Light


#1

85,000 miles and no problem until now. Here’s the series of events:



1. Changed leaky valve cover gaskets

2. Engine began to run rough, poor gas mileage, check engine light comes on, black smoke coming out of exhaust

3. 02 sensors replaced

4. Ran okay for about one week

5. Rough running and check engine light returned

6. Then car did not want to turnover

7. Had fuel pump and fuel filter replaced…worked for one day but still ran rough.

8. Car couldn’t turn over at all

7. Water pump, optispark, spark plugs, spark plug wires replaced, fuel injectors cleaned, new computer

8. Car starts, but still runs rough, black smoke from exhaust, check engine light on and off, poor gas mileage

9. When check engine light comes on, the car seems to idle better but gas mileage is still terrible



Any ideas? I need help! Thanks.


#2

That CEL (check engine light) is just a kid in class waving her hand trying to get you attention because she has the answer. You need to have the codes read. Some places will read them for FREE. Try Autozone or Advanced Auto Parts. Get the exact code (like P0123) not just their translation into English and post it back here.

Regarding warning lights:

  1. if the coolant temp light comes on, shut off the engine ASAP

  2. if the oil warning light comes on, shut off the engine ASAP

  3. if a FLASHING MIL/CEL comes on, shut off the engine ASAP

    ASAP means driving to the berm of the highway right now and not waiting for the next exit.

But if the MIL/CEL is not flashing, then it’s not an urgent indicator.


#3

Sounds like a lot of guesswork has been going on. Pull the codes and test the fuel pressure regulator.


#4

Had the codes read and it pointed to the oxygen sensors. All of which were replaced and rechecked. Now what?


#5

You’re assuming because you have an O2 code that the O2s are bad and it does not work this way. Any O2 code, whatever they are, only means there is a problem in the O2 circuitry (or the O2 themselves) or something is affecting the O2s.


#6

or that they are staying out of range one way or the other for too long, in this case black smoke would indicate a rich condition meaning they are staying above the 450 mv range and if they are and not switching above and below the 450 mark like they are supposed to they may be working just as intended and this is a insufficient switching code. and i would look at the map snesor , coolant sensor (if it is telling the computer that the engine is still cold when it isnt the computer will be dumping in too much fuel), and check the fuel pressure regulator . the key here is black smoke= too much fuel. i believe you have one temp sensor for the gauge and one for the computer


#7

have the mechanic who changed the o2 sensors and check to see if he plugged in the right plug for the o2. pre and post they are all the same plug in type if they are swapped will cause this same condtion. running rough black smoke. if they are correct check for a vacum leak at the intake manifold ie: loose vacuum tube or leaking intake gaskets.


#8

wires arent long enough for this to be the case


#9

You’re not sticking with that shop which did all of those unnecessary parts changes, are you?
The best mechanic isn’t the one who changes the most parts; it’s the one who changes the least.


#10

Changed leaky valve cover gaskets

  1. Engine began to run rough, poor gas mileage, check engine light comes on, black smoke coming out of exhaust

Did it really start all of the rough running right after the valve cover work? If so, go back to the scene of the crime. Double check all of the electrical and vacuum hoses to make sure they are connected properly. I had a '91 that ran like this and it was a leak right at the brake booster. Vacuum leak after the MAF messes up the ECM fuel injection calculation big time.


#11

What were the specific code(s)?

Remember the codes DO NOT mean this or that part is defective. It means “I am seeing something unusual with the reading from this part.” It could mean a wiring problem a sensor problem or something triggering the sensor.