94 Lt1 C4 5.7-- Help – Big Problem With Bogging Ou

[greek53]

1994 CONV C4 LT1 AUTOMATIC ADMIRAL BLUE - WHITE RAG – RARE 1 OF 409 –

Hi, I’m currently experiencing a bogging problem with my vette. The car was put on a SNAP-ON diagnostic computer but didn’t throw any codes. It boggs and sputters along with the occasional mild backfire, it seems to do this more frequent when cold but even after running for a few hours it still has the same problem. I notice it most around 700 to 900 RPM (while turning a corner or accelerating slowly, I’ll try to describe the symptoms the best I can, but seeing is believing so please bear with me. When I first pull away after starting out, the vette will bogg heavily creating a jerking movement, it sounds really hollow and if I continue to press the gas pedal it will not increase in speed, it just seems to hover around the 3000 RPM (at about 20 MPH) mark while sputtering, after a few seconds of this I’ll let up on the gas and drive it at about 15 MPH for a few minuets and it normally shapes up and is driveable. It only has this glitch under load, never in neutral or park. If I hold my foot on the brake and increase the RPM to 1500 or 2000 and let the brake off entirely while mashing the gas there is no problem. As fun as this is, this is not how I want to drive all day and the car deserves better than to be bagged every time it hits the pavement. It also looks like the water pump was leaking at one point in time due to the visible mild rust stains, I went through some bills from work performed on the vette and the previous owner had a new opti installed along with this repair on the water pump leak at 62000 miles or in 2001 (I’m the third owner). Once I noticed this I scheduled the car for plug and wire changes as per dealer advice since there is 85,000 miles on the car, this happens in a few days, but crawling around the corvette pages on the net I found you, “THE EXPERTS” so I imagine you have had the same question posed to you or have heard of such problems, if so I would appreciate your advice. -Lately the car is driving me instead of being driven—

Please reply,
PAUL (stressed out)

I have since decided to do the plugs and wires myself, checked the ohms on the injectors they are all giving a reading of 13.2, changed the fuel filter, tested the EGR, Still the same problem, but the plugs, wires and filter made a noticeable difference in top end power and feel of the car.
Sorry for being naive, but I was just looking at the engine and see that the front driver side has a header bolt missing, I’ll obviously replace it but would that have any effect on the performance.

I'm thinking of taking the opti apart to have a look. I still plan to check out the cats and o2 sensor before doing this, any other ideas??

I need a little direction here, I’m not afraid to work on the vehicle with a little direction.
I may need a little more time to do the work first time round, but it will be carried out to a “T”. I just changed out the plugs and wires and it took me three hours or so to complete, but I’m very confident that it was done correctly, but the initial problem exists.

[vetteheadracer]

Hi Paul,

Good to see a Canadian on the forum! I had a 1996 and that went thru 2 opti-sparks in 2 years! Your symptoms sound exactly like the opti-spark is giving up. Does yours have the vacuum line coming off the bottom or is it a sealed one? It could be the vacuum line has dropped off and therefore it isn't clearing any condensation out. Most likely though is you need a new Opti-spark, which you can do yourself if you are mechanically competent, or you can bite the bullet and get your dealer to do it.

Good luck,

VHR

[Camaro SS]

We replace the optispark on our 94 almost every year, its a pain! Only other thing that might cause some of your symptoms are the 02 sensors although that would usually throw a code (just had them done on mine!). Good luck

[blackzr]

Change the water pump at the same time, disturbing the pump to change the opti spark is usually enough to start it leaking from the rear seal.