C4 issue
Thread Starter
5th Gear
Joined: Sep 2019
Posts: 5
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From: South Ga.
C4 issue
My name is Billy Grafius and I am a new member needing some advice solving a problem with my 1995 corvette coupe 5.7L. Car is in excellent shape with about 65,000 miles. Car runs great down the road but upon stopping, like at stop sign or light engine begins to shake and seems like it’s about to cut off but doesn’t. Then upon acceleration acts like it’s not getting gas and after a few seconds begins to perform as should. Have it in the shop now and diagnostic test showed no problems and fuel pressure test showed no problems. After speaking with one of my vette buddies and mechanic suggested changing out optispark and possibly water pump if original since it had to be pulled anyhow. Didn’t guarantee this may solve problem but since optispark is the weakest link on this model was a good start. If anyone has had similar problem and has any input it would be appreciated. Thanks in advance.
Zen Vet Master Level VII
Joined: Mar 2016
Posts: 5,214
Likes: 1,173
From: Southlake, TX
After speaking with one of my vette buddies and mechanic suggested changing out optispark and possibly water pump if original since it had to be pulled anyhow. Didn’t guarantee this may solve problem but since optispark is the weakest link on this model was a good start.
You said that the shop said "no problems" with fuel pressure.... what exactly does that mean? A reading will help. Did they check it at idle only, or did they check it under WOT? You may have adequate fuel pressure at idle and then not even close to enough under acceleration. The fact that the car wants to die after running tells me you need to really dive into the Fuel Pressure (filter is suspect).
40 PSI +,- is your friend
Le Mans Master
Joined: Oct 2004
Posts: 7,706
Likes: 485
From: Everett WA
C4 of Year Finalist (appearance mods) 2019
Welcome to the world of C4! These days changing out the opti is the last thing you want to do. There is not a reliable supply of replacement opti's (tons of threads on this) because the optical sensor that is the heart of the system is no longer manufactured by the original mfg (Mitsubishi). As suggested above, prove out the fuel pressure under the conditions where the car wants to stumble.
10 years ago at 70K I had the opti on my 95 changed out when I had work being done on the engine. It was running fine and the supply of replacements was good. I've put almost 70K on that replacement opti and the car runs just fine.
10 years ago at 70K I had the opti on my 95 changed out when I had work being done on the engine. It was running fine and the supply of replacements was good. I've put almost 70K on that replacement opti and the car runs just fine.
Melting Slicks
Joined: May 2013
Posts: 2,692
Likes: 349
From: Sacramento California
I agree, don't just start throwing parts at your car. Your distributor might be working just fine. The 1995-1996 distributors were upgraded and much more reliable than 1992-1994 models. Check for codes (very easy), check all the related components including TPS, ICM and coil, IAC, etc. Most of them have a standard voltage or OHM (resistance) factor that will tell you if they are working. I also agree that you should get some numbers after the fuel pressure is checked, not just "it's fine." An overall tune-up as suggested above (plus fresh fluids) is not a bad idea on any used car purchase.
Race Director
Joined: Sep 2001
Posts: 14,659
Likes: 749
From: NEwhere Ohio
My name is Billy Grafius and I am a new member needing some advice solving a problem with my 1995 corvette coupe 5.7L. Car is in excellent shape with about 65,000 miles. Car runs great down the road but upon stopping, like at stop sign or light engine begins to shake and seems like it’s about to cut off but doesn’t. Then upon acceleration acts like it’s not getting gas and after a few seconds begins to perform as should. Have it in the shop now and diagnostic test showed no problems and fuel pressure test showed no problems. After speaking with one of my vette buddies and mechanic suggested changing out optispark and possibly water pump if original since it had to be pulled anyhow. Didn’t guarantee this may solve problem but since optispark is the weakest link on this model was a good start. If anyone has had similar problem and has any input it would be appreciated. Thanks in advance.
or did you just buy the car?
we’ve seen scenarios where a newb buys a 95-96 corvette where the previous owner ‘replaced a working fine’ optispark (bc they heard they will fail) with a $50 chinese optispark (not knowing the difference).
Then they sell the car when it doesnt run right
