94 Lt1 C4 5.7-- Help – Big Problem With Bogging Out – Sputtering – Jerking-

[greek53]

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 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.

 

[redc4corvette]

Check fuel pressure,should read 43.5 psi or 40.0 psi,
check exaust to see if it Blows your hand out of the way when engine reved.
Check to see if vacuum 3 way has hole in it on pass side of engine under fuel rail black cover.
check air cleaner and throttle body screen to see if bugs clogging screen.
check EGR valve at back of engine you did not say if engine is lt1 or lt4.
this is only a start is trans shifting ok?

 

[redc4corvette]

Check fuel pressure,should read 43.5 psi or 40.0 psi,
check exaust to see if it Blows your hand out of the way when engine reved.
Check to see if vacuum 3 way has hole in it on pass side of engine under fuel rail black cover.
check air cleaner and throttle body screen to see if bugs clogging screen.
check EGR valve at back of engine you did not say if engine is lt1 or lt4.
this is only a start is trans shifting ok?

Disconect the battery the pos cable for 90 seconds to clear all info in the computer.
When started in am does the engine idle at 1200 rpm or so .could be cold start valve?
throttle posession sensor?

 

[SSTibet]

Hello Greek53. I assume you are from Greece and hey congradulations for the Europe Soccer Cup; I am glad our neighbours made it (I am from Turkey).

I had a similar problem with my 95 LT1 Manual Corvette and finally got it resolved. Last thing that we did was replacement of all 3 oxygen sensors in the car (in 95 models there are two sensors on the passanger side and 1 on the driver side). We had also cleaned the EGR and IAC valves some time ago but these did not remove the problems I was having.

I was always getting the SES warning after driving the car from a cold start for about 10 miles or sooner. I was also getting (not always) engine stumbling and fuel odor inside the car. For some reason the SES and stumbling + odor thing did not happen at the same time. My car has its catalytics gutted by the previous owner.

I also added some injector cleaner and filled up from a "reputable gas station" (not all stations sell clean fuel here...). Last thing that we did was the O2 sensor change. I have been driving the car in all types of traffic since then and neither SES nor the stumbling is happening. Running so smoooooth now.

I hope this may help you. Hey also try to find the CAC member "FX GS" here in the forums; he is a wealth of information on these topics.

See ya soon neighbour...

 

[bnhynum]

Check to see if vacuum 3 way has hole in it on pass side of engine under fuel rail black cover.

Is it a good thing or a bad thing that there is a hole in this vaccum 3 way valve?
Mine has one and I can hear a constant hiss coming from it. When I cover the hole the hiss stops. If I remove the hose going into the manifold right by the valve the engine idle goes up. Normal?

 

[Daryllawman]

Mine did that and it was the fuel pump and sending unit.....sending unit was a dealer Item that sold for 630.00 here in Tennessee......replaced both and no more problems

 

[UB2 SLOW]

Also check the IAC, TPS and MAF sensor. Your Optispark might also be going out.

 

[Muttley95]

Greek53

I am currently having the same problems you are. Have you found out what is doing it yet?

 

[Idaho Slim]

Greek53

A question, You didnt by chance power wash off your engine compartment right before these problems popped up did you??? If you did, your problem is in your optispark.:cry

 

[Muttley95]

Update


I broke down and took my car to the dealer today. They are saying that my problem is caused by my spark plugs and wires. They are the original set that came with the car and I just went over the 98k mark not too long ago. I hope they are right and this is the only problem I have.

 

[onedef92]

Hope it's only plugs and wires and not the dreaded "Optispark Blues."

 

[582Boat]

Transmission shifting

Check fuel pressure,should read 43.5 psi or 40.0 psi,
check exaust to see if it Blows your hand out of the way when engine reved.
Check to see if vacuum 3 way has hole in it on pass side of engine under fuel rail black cover.
check air cleaner and throttle body screen to see if bugs clogging screen.
check EGR valve at back of engine you did not say if engine is lt1 or lt4.
this is only a start is trans shifting ok?

With reference to my 1985 Vette with surging at the 1000 RPM could there be a problem with the transmission shifting at the wrong RPM causing the surging, jerking motion at the 1000 RPM, can you explain the transmission shifting VS, RPM,s . Doc

 

[Itshakes]

Vacuum 3-way valve

Is it a good thing or a bad thing that there is a hole in this vaccum 3 way valve?
Mine has one and I can hear a constant hiss coming from it. When I cover the hole the hiss stops. If I remove the hose going into the manifold right by the valve the engine idle goes up. Normal?

I just replaced mine-GM part #14056648 Group 3.885 Valve $6.61

Just for your information - one side provides vacuum to the cruise control - the other port goes to the HVAC module under the dash.