sk8rax350

iTrader: (2)

I'm in dire need of some help, as my car has me thoroughly confused in what is going on! It's a 99 Camaro SS with 93k miles. Stock heads. Mac mid-length headers, off-road Y-pipe, Flowmaster catback. Just did a cam swap with the El Toro cam (230/230 .613"/.591" 111 LSA 109 ICL), 7.425" pushrods, PSI LS1511ML springs, LS6 oil pump, and LS2 timing chain. I did the springs prior to the cam swap due to valve float from one of the stock springs. Car ran perfectly fine before the cam swap.
Now it has a really bad misfire according to Torque Pro on cylinder 6 and a some on cylinder 7 as well. Got the P0300 code immediately, and once got P0306 also for cylinder 6. If I try to drive the car, SES light flashes. The misfire isn't a false, you can watch the engine stutter and occasionally backfire. However, when I hold the throttle just out of idle, at a consistent RPM like 1,000 or 1,700, the misfires all go away and it sounds to be running flawlessly. I try to drive it with varying RPM and that's when I get the flashing SES light. Tried swapping injectors, coils, wires, and plugs for cylinder 6 and the problem remained there. Did a compression test that indicates a dead cylinder #6, but have no idea how it runs fine when at a consistent RPM above idle, especially when the car ran perfect before the cam swap. When you place your finger by the spark plug hole, without anything in it, the air coming out feels the same as a cylinder that doesn't indicate as dead. Swapped 7.425" pushrods with stock ones and still the same thing. My tuner took away some of the fuel at idle that was causing it to run really rich, and he is also as clueless as I am as to what the underlying problem is. He advised a cylinder leakdown test, so I suppose that will be next.
I am stumped and could use any help or advice I can get, please.

ls1 1990 VN

Get a new tuner!

vettenuts

iTrader: (4)

The PSI 1511 valve springs are excellent springs, however they set up light on the seat. You cam lift is pretty high. Have you measured the seat height of the valve springs to ensure you don't have coil bind or are not near it at full open?

Decadence75

iTrader: (17)

I encountered frequent P0300 shortly after my cam swap as well. Swapping out the O2s cleared it up. I would check on those to see if they are fouled.

gagliano7

Also make sure none of your coils are weak.

sk8rax350

iTrader: (2)

I haven't had much time to work on the car in the last 2 weeks, but I just took the rockers off, aired up cylinder 6 from the spark plug hole, and air is exiting through the exhaust. Going to rent a boroscope in a bit. My guess thus far is either a bent valve, somewhow, or a jacked up valve seat. Any other suggestions?

NHRAFORMULA00

iTrader: (2)

Sound like a bent valve.

sk8rax350

iTrader: (2)

That's what I'm afraid of. No one had a boroscope to lend. -_- Was hoping I wouldn't have to pull my head off.

sk8rax350

iTrader: (2)

Ok, so it was a bent exhaust valve. Found a good price on a good used set of 241s that I will be installing after I take the 853s off. My question being, what do I need to do to prevent bending another valve? Cam was installed dot to dot on the cam gear and crank gear, so it should be timed properly. Maybe I was ignorant in making the mistake of not checking pushrod length and went with the 7.425" others have used? This is my first cam swap, so please don't bash on me too hard...

ls1 1990 VN

My feeling would be 7.400 pushrods, 'BUT' you need to measure or get someone that knows how to to do it for you.

JakeFusion

iTrader: (7)

Bent valve would indicate your piston and valve said hello to each other. Measure your PTV clearance and cut if necessary.

sk8rax350

iTrader: (2)

241s get here tomorrow. Going to do a ptv clearance check and pushrod check. Before I do everything, I'm just trying to get an understanding of why this only happened on one single valve. Any input? Want to take all precautions to avoid this happening again. Pushrod length didn't seem to be an issue on any of the rest of the 15 valves. Going with GM MLS gaskets for the "new" 241s.

sk8rax350

iTrader: (2)

7.425" pushrods worked fine on every valve other than exhaust for #6. Thinking something other than pushrod length caused my issue. Anyone?

twinturbo496

iTrader: (2)

You changed springs because of valve float

Perhaps the valve has been bent slightly for a while already and finally burnt bad enough to misfire at idle

NHRAFORMULA00

iTrader: (2)

That cam when we installed it on my sons car was real tight on the intake valve. We retarded it 2 degrees with an adjustable timing gear for more clearance. You need to check piston to valve clearance with a light spring on 1 intake valve and 1 exhaust valve. Get 2 used lifters and take them apart and shim them up with washers until the are solid, then put them back together. Get a dial indicator and a stand and put it on the top of the rocker arm. Cycle the motor around and check clearance by moving the rocker by hand up and down. If its too close on either the intake or exhaust( less than .060 ) usually the other valve is a lot more like .120 or more. The adjustable timing set will alow you to move that clearance around so that you have more on one valve and less on the other.

NHRAFORMULA00

iTrader: (2)

The valves are usually the closest at 8-12 degrees before or after top dead center.