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95 C4 runs rough after 30 or so miles

MIKEM3401

Member
Joined
Dec 28, 2006
Messages
13
Location
Simi Valley
Corvette
1995 white coupe
Just bought a C4 with 46K on it.
of course I did'nt catch all the gotchas.
Today (my first lengthy ride) Drove great for 20-30 miles until I came to the first stop light after 20 miles, began running rough and smokes with a little acceleration. (Possibly oxygen semsors).
Mike
 

92ghost

Well-known member
Joined
Oct 23, 2002
Messages
120
Location
NY
Corvette
1992 White Coupe
Any lights come on the dash? Oxy sensor should throw a code if dirty or going bad. Also, I've had somewhat similar symptoms that was attributed to the Optispark in my 92. Ran great until coming to a stop then erratic idol etc. I think moisture in the opti had a hand in this but also the Throttle Body was dirty too. A little cleaning of the TBS and some "hot runs on the highway" to burn out the carbon as thay say - did the job. I think it just heated up the opti and got rid of the moisture. No problems since.
 

vee93

Well-known member
Joined
Nov 15, 2002
Messages
585
Location
Mississippi
Corvette
1993 Medium Quasar Blue Metallic Coupe
Let's see..., an 11 year old Vette with only 46k on the odom...
Check all of your hoses for leaks. Change all the fluids. When's the last time the Vette had a tune-up? Throttle body, O2 sensor, air filter, battery terminals, fuel filter, etc... Hope you find the problem. :w
 

John Robinson

Gone but not forgotten
Joined
May 3, 2005
Messages
1,555
Location
Muncie, Indiana
Corvette
1993 Polo Green Coupe
Put some injector cleaner in it and go for a 300 mile drive. When you get home it should have cleared up. Dont forget premuim gas.:)
 

MIKEM3401

Member
Joined
Dec 28, 2006
Messages
13
Location
Simi Valley
Corvette
1995 white coupe
yah I eventually get check engine soon light and then goes off.
Funny thing is it appears to clear up once the light comes on then rough again after going out.
 

onedef92

Well-known member
Joined
Jun 12, 2004
Messages
214
Location
Louisville, KY
Corvette
1992 Dark Red Coupe
Also, check your ICM (Ignition Control Module). It can cause your car to run rough if it gets too hot as its begins to weaken with age. You can take them to AutoZone or NAPA for free diagnostic/testing.
 

MIKEM3401

Member
Joined
Dec 28, 2006
Messages
13
Location
Simi Valley
Corvette
1995 white coupe
Thanks for the info. I have put it up on blocks and currently making my way to the opti spark. I'll have the ICM tested this weekend.
I did find moisture at the weep hole of the water pump, also looks like a small leak at the front oil seal, some vacuum lines look weak as well.

NOTE: I should note that when the car would start running rough after 20-30 miles it also smoked quite a bit.
 

vetteboy86

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Joined
May 26, 2003
Messages
2,760
Location
IN
Corvette
1986 Black "Indy 500 Pace car replica"
Your first stop would be to check which engine codes were set. This will give you a valuable clue into the problem. Did the 20 or so miles include alot of highway driving?
 

onedef92

Well-known member
Joined
Jun 12, 2004
Messages
214
Location
Louisville, KY
Corvette
1992 Dark Red Coupe
Thanks for the info. I have put it up on blocks and currently making my way to the opti spark. I'll have the ICM tested this weekend.
I did find moisture at the weep hole of the water pump, also looks like a small leak at the front oil seal, some vacuum lines look weak as well.

NOTE: I should note that when the car would start running rough after 20-30 miles it also smoked quite a bit.
If that's the case, your water pump could be leaking directly unto your Optispark. You have the revised, vented Opti, so that should buy you more time, but it sounds like a water pump, plug wire swap, new spark plugs and possible new Opti are in your near future.

Oil leaks are common on LT1 and LT4 engines, too, particularly around the intake. For leaks that are hard to detect, you can have your car leak-tested at a repair shop by having them use a special flourescent dye that's added to your engine oil. The shop techs then use UV light to detect the leaks.
 

MIKEM3401

Member
Joined
Dec 28, 2006
Messages
13
Location
Simi Valley
Corvette
1995 white coupe
Your first stop would be to check which engine codes were set. This will give you a valuable clue into the problem. Did the 20 or so miles include alot of highway driving?

Engine code was 0016.
Mostly highway. I have removed the opti spark and observed a yellow ish residue.
by the looks of the rotar and cap there has definately been some spark issues here.
 

MIKEM3401

Member
Joined
Dec 28, 2006
Messages
13
Location
Simi Valley
Corvette
1995 white coupe
black.
I have pulled the plugs and found that the pssenger side all look great, the drivers side all look powdery black (not oil).
Again I think this points to opti spark.
 

Galen

Well-known member
Joined
Oct 15, 2003
Messages
66
Location
Bay City MI
Corvette
1990 White/Black Interior 6sp Coupe
EGR can cause rough idle and doesnt throw codes very fast.
 

Florida Guy

Well-known member
Joined
Oct 16, 2003
Messages
166
Location
Florida
Corvette
'96 Torch Red LT4
If it was the Opti spark, why would it clear up when the Check Engine light comes on?
Someone list the componets that would affect the fuel mixture (or spark) on the 4 cylinders on the left side of the engine.
 

MIKEM3401

Member
Joined
Dec 28, 2006
Messages
13
Location
Simi Valley
Corvette
1995 white coupe
Good point.
could it possibly be something with the ECM trying to correct the opti error?
Just a wild guess?
 

jmccloud

Well-known member
Joined
Feb 1, 2003
Messages
694
Location
Maryland
Corvette
1995 White Coupe LT-1 Auto
Runs bad warm

Sounds more like a bad O2 sensor on the driver's side. The O2 sensor does nothing until the engine warms adequately to go into closed loop. At that point the O2 sensor signals whether the mixture is correct (low/high) and the computer corrects for it.
A bad O2 sensor lies and the computer will cause rich or lean depending on how the O2 sensor has failed.
 

MIKEM3401

Member
Joined
Dec 28, 2006
Messages
13
Location
Simi Valley
Corvette
1995 white coupe
O.K have now replaced Opti spark, Water pump, wires. hoses and done a little much needed detailing.
Took her for a spin and had the same scenario. After doing more reading it appears that the ECS runs in a open loop until the O2 sensor reaches about 600F, then goes into a closed loop mode were the O2 sensors have an impact in fuel/air mixture.
In summary I'm now going to look at the O2 sensor again.
ANY THOUGHTS?
 

MIKEM3401

Member
Joined
Dec 28, 2006
Messages
13
Location
Simi Valley
Corvette
1995 white coupe
Sorry made this post without reading you previous posts.
Looks like I', closing in on it, and we have concurrence.

Thanks All!!!
 

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