RocketZ06

Hello all,

During a second gear pull at about 5k rpms my car started to miss. I got out of it and coasted back to work. Two hours later I tried to start it and then it had a really bad tick/ knocking sound. It only would idle at around 500 RPM.

Had it towed home, and did a compression test on it. It has compression, fuel, and spark. But for some reason it's only firing the front four cylinders(front of the car). The valve train looks fine. So I have no idea what it could be next. Any help would be appreciated.

Car is a 2003 Z06
Mods: Shorties, vararam, fast 90/90, Small cam, Msd wires, the guy that tuned it said it had ford red top injectors, stock heads. Light weight fly wheel, and a monster clutch. The car has 98000 miles on it. The mods done to it are from the 2nd owner at 85000 miles. The first owner used it for a work vehicle to travel. 4

Any help would be appreciated, thanks!

TooLateVTEC

iTrader: (2)

Could you tell where the knock was coming from? Top or bottom?

Could be a spun bearing.

Have you checked the valve springs yet?

bjamick

iTrader: (31)

How's oil pressure? Drain oil and check for metal, that's the first dead give-away.

RocketZ06

valve springs look fine. Oil pressure was at 45-50 while we had it on last night. Next thing where gonna do is drain the oil.

TooLateVTEC

iTrader: (2)

Was the pressure "jumpy" did you notice?

I would drain the oil next and look for metal.

RocketZ06

It wasn't jumpy at all. Yeah, next thing I do will be oil when I get home.

chasgiv3

iTrader: (1)

Are there any codes set on the computer? Knocking noise would indicate spun bearing however it should still idle. When you say you have spark but it's only firing the front four cylinders. What's drawn you to that conclusion? What do the spark plugs look like? When you have the valve covers off and spin the motor do you see all valves raise up and down like normal?

Checking the oil is key for sure.

427LS7HCI

bent pushrod? collapsed lifter? broken valve spring?

02*C5

iTrader: (1)

My vote is for collapsed lifter or bent pr. its not hard i'd pull the heads you'll know asap once you know this.

jman54002

iTrader: (11)

this is what my car did one month ago...It was a valve spring. The back four cylinders where not firing. I found one valve spring broken on #6 hole. I didn't see it right away but I pushed on each spring and could fell this one had play in it. Not much but enough to have me look at it much closer. And there I found it at the bottom of the coil. I had no codes. It would not idle and the back four were not firing. The header tubes stayed cool after I started it and ran it for 30 sec.

RocketZ06

Pulled the intake manifold and found out that #3 valve broke.

RocketZ06

I thought it was a spring. But after pulling the intake manifold. I saw that a valve was broke. Pulled the head to find out that it's all marred and there's a hole in the piston. Oh well, time to rebuild. Thanks everyone for your help.

dudeiwin86

iTrader: (1)

probably still a valve spring failure in that case.
good luck with the rebuild.

TooLateVTEC

iTrader: (2)

Yea I wouldnt be surprised if the spring was broken on that valve.

That sucks man, good luck on the rebuild !

RocketZ06

She's all fixed now! Found out it had cnc ported stock heads, Texas speed pushrods, springs, and cam.
What size are the stock valves? It has 2.02's in it. Had to replace the intake and exhaust valve, and all the guides. My machinest told me that whoever put it back together put the wrong guides in. He figures it got hot and shrunk and held the valve down, which smacked and piston and broke it. Oh well, everything breaks.

Ps thanks everyone for your help and suggestions.