Hey there.




Young girl here who is learning to work on cars, bought a nice c3 vette two years ago with a 454 LS6 blueprinted except apparently compression ratio of 9:1 or 9:5

-It has a hydraulic roller from Comp Cams, Xtreme Energy.
-Forged pistons and what not.
-16 degree initial timing.
-Holley Projection 4Di TBI

During the summer i noticed a weird noise coming from cylinder 6 or 8 area. It was not that loud back then so i thought it was just me exaggerating. That weird noise turned into a slamming type of sound now when i started the car today. What do you think when listening to it? It has a very strange tone to the sound. All though 1500rpm cold start and choke? It sounds like someone secretly put a new cam in it, it sounds obnoxious and horrible.

Last time i drove was when driving on the freeway when it suddenly died. It was firing abit when i had no throttle like if i ran out of fuel. But when i gave alittle throttle it just freerolled, totally gave up. I could not hear the fuelpump when i tried to start it. I waited 15 minutes and had called a towtruck when the pump kicked in and started so i could continue driving. It was running like a turd though.

- Oily wet sparkplugs before changing them.
- Sootmarks on garage floor from downpipe
- When i started it as long as on video and shutting off, i exhale alot of visible smoke in the air.

It is running rich. But the last set of plugs made me worry of bad piston rings because they were wet of oil. Does the video implies for broken cam lobe? Or could the problem be an extremely bent pushrod or broken valve? It certainly sounds like something is slamming, and i would bet it would run like a turd when driving it. I dont know fuelpressure, had no time to check. Sounds like the piston is about to come through the valvecover any second.

Help guys?

Edit: Seems to have 45-55 oil pressure at all times. Had a pressure that went crazy and switched from low to high repeatedly earlier but i changed the oil pressure sensor and my pressure was back at 45-55 at both idle and cruising.

 

Sounds like an exhaust leak header or collector gaskets. Ck your fuel pump connections

 

It just hit me from a comment from youtube. How does this sound like? Judging from the enormous stench of gasoline from within the car and exhaling of smoke. I might have an exhaust leak somewhere that enrichens the sound of one particular cylinder. The leak must be at the cylinder head ports right? because if the leak would be at where collector meets 3" pipes, it would not draw attention to one specific cylinder? The slamming noise might be the piston detonation from a cylinder that leaks out making the illusion of a wrecked rod or something?

Too much gasolinevapor inside my lungs and too blonde to think straight haha. Still trying though.

3/8" -16 x 3/4" Is that the correct size for exhaust manifold bolts? I know the heads are rectangular, but i dont know if they are aftermarket or not. Ordering new bolts and gaskets for my 3" collector and manifold. The choice for 3" collector bolts went upon 3/8" x 1"

 

It will just make noise especially when giving it gas thats all. gaskets are cheap do those first, then double check your timing, then adust carb as needed. one thing at a time. Bigger cams will stink a little at idle
Like the old M/T valve covers

 

Okay i will order gaskets and bolts and check for the leak. It must be a leak that is causing this sound. I mean the engine SHOULD be fairly new, and with hydraulic rollers and lifters i should be somewhat safe. It has a rear end ratio of 2:79 so i really both believe and hope the valvetrain, the cam lobes and the roller lifters are okay. I might be able to retard my timing to 12-14. There is no carb though, i have a holley pro jection 4barrel tbi injection that is a BITCH to work with. I have to have a windows 95 laptop and it is extremely hard to understand as i am just beginning to learn cars and engines. Thank you for helping me out by the way.

The rocker arms are slightly loose in sideways. Should they be completely still or is that okay?

 

Probably an exhaust gasket, but also could be a head gasket. Have you looked at the coolant to see if it is down or has oil in it? Also check the dipstick to see if there is anything unusual like drops of water on it or a milky look.

 

Engine off yes you may be able to slide the rockers side/side a bit. Sounds like you need to work on the tune some. No need for new exh bolts just gaskets. If you are using an 02 sensor this is important to have NO exh leaks, this could be your problem the computer picks up on this and adjusts

 

Coolant is clean. I will check the oil. Yes there is a o2 sensor on both collectors. The leak is probably causing problems with the o2 sensor measurements. Thank you all for taking your time helping me.

 

Sounds like it to me too.

 

A motor has to have 3 things: fuel, air, and spark. If something dies going down a freeway it is not a good sign. But why did you say you could not hear the fuel pump? does it have an electric that you turn on before starting the car?

If I had major noise out of the motor I would pull the valve covers off and see if everything is fine. I have seen bent valves, broken springs, broken rocker arms, broken rocker studs, flattened cam lobes, and bent pushrods.

Another item is you don't set your timing by looking at initial timing. You set your total timing at say 3500 rpm with the vacuum advance plugged off to what ever your head type requires. Like 38 degrees. The initial timing can only be changed by the total mechanical advance curve.

In the it doesn't really matter, but the correct terminology is BBC for big block Chevy

 

I had been driving rough with the car prior to its death on the freeway, alot of launches and such. I think the fuel pump dies when it gets hot because when i had no throttle it was firing the cylinders abit and when i opened the throttle it just freerolled. I think this is due to the small amount of fuel that was left in the tbi versus the amount of air coming in when opening the throttle.

When turning to ignition mode, you can hear the fuelpump coming on really loud for 3-4 seconds like on race cars. The pump was dead silent so i think it is bad. The pump is an electrical one with "metal" body, it also sits locked on a metal plate and is located near the rear wheel. Perhaps the metal plate it sits on contributes to the heat.

I will be putting on a traditional carb or EZ-EFI 2.0 that seems easy to work with so the pump will be out the door soon enough. I just need to check for a good place to mount a pump on a c3 by searching here on the forum. The only thing that bothers me with EZ-EFI is having the need to mount a o2 sensor on those sidemount headers im planning on buying in the future.

 

Sorry I didn't look closely at your pictures and notice the TBI. I was listening.

The O2 sensor just needs a bung welded to the down tube near the motor.

It is hard to trouble shoot via posting. I would get someone over to look at it.

 

Are you using the proper guage wiring and a relay for the fuel pump? Regulator?

Metal plate mount wont make it go hot

 

i would pull that valve cover as well, i had a problem with my 427 like that, and it turns out that my intake rocker arm had broken on #6 Cyl, i thought i had hurt my engine.

 

You also might want to do a compression test, that will tell you if you have a head gasket or valve train problem. Testers are cheap here is an example of one. If you lose compression it will act very sluggish.