mikedamageinc

iTrader: (49)

I put the car on the dyno recently and it was breaking up around 4500 rpm as you can see on the sheet, and puts out grey smoke, see video link below. I was told it was valve float and the problem is valve springs, I replaced springs with LS6 version and spark plugs and still same problem, hasn't been on the dyno again but smokes and stops pulling around 5K will get back on the dyno soon just to compare results, but just trying to get some input).

Details...
Stock internal LS1 M6 with 216K miles, doesn't burn any oil, good compression (all ~160psi), used oil analysis shows no unusual wear. Pulls very strong and runs great, up unto the valve float.

Full bolt ons-filter, lid, p&p TB, LS6 intake and injectors, headers, hi flow cats, LM1, UDP, 160 thermo, and tuned to support all mods.

I know the easy answer is rebuild, but I dont have the cash to spend and it runs strong otherwise so I'd like to see how far she will run until a rebuild is unavoidable. I've done a ton of research and springs seem to be the only reason for a stock cam car to float valves. When the valve covers were off I didn't think to check rods or lifters but rockers looked okay.

Thanks for any input!

http://www.youtube.com/watch?v=sjcE_Xe3TOs

garygnu

check the push rods to make sure they are not bent..I would upgrade the stock rocker arm trunions to comps trunions.

HotSilverBird

pulling oil in from someplace fouling the plugs a little IMO

vettenuts

iTrader: (4)

Interesting that the fueling in the red curve had such an effect. What is the duty cycle of the injectors? The valve springs (assuming stock cam) should have corrected a float issue.

Darkman

iTrader: (2)

I would change the fuel filter unless it is known to be fresh.

Soul TKR

iTrader: (4)

how many miles do you have on that motor?

mikedamageinc

iTrader: (49)

216K on motor, and the fuel filter is about a year old and 20K miles. Not sure on the injector duty cycle but they are the LS6 (a couple pounds higher than stock) and the tuner didn't say there were any problems there.

Any chance the lifter could be sticking to cause this? I think I may replace the rods and rockers just because they don't cost too much and would be a slight upgrade.

Thanks for the suggestions, please keep em coming!

redz_02

iTrader: (4)

I would also look at the timing chain and lifters. That's alot of miles.

vettenuts

iTrader: (4)

You could also shim the valve springs, are these the yellow ones?

mikedamageinc

iTrader: (49)

Yep, yellow LS6 from Summit http://www.summitracing.com/parts/NAL-12499224/

G Engines

Sound like it's time for a valve job your guides and seals could be worn and leaking oil past them causing you break up at higher rpm's . you could do a leak down to check for this problem.

SUCK MY SS

iTrader: (14)

i would also check the connection for the crank position sensor.
a loose connector/faulty wiring here, could cause a loss of signal @ certain rpm/driving conditions...
if you have a scanner handy, i would watch the ckp sensor signal during the dyno, to see if it loses signal when the car breaks up...

mikedamageinc

iTrader: (49)

So I decided to throw it on the dyno to find out if it looks the same up top and on the first run a piece of the cat's honeycomb was found behind the cat. We did another run and about five horses were gained with a smoother graph, and on the third run a total of ten horses and seven ft/lbs were gained from the previous dyno day plus a stronger curve throughout the range, it pulled until around 5500 with a smooth decrease. (I havent had a chance to scan the new sheet yet)

So I went home to take out the rest of the cats (SLP cats) and when I got the Y pipe off, it was already clean! The cats were completely gutted already! I have a LM1 behind the cats with Spiral flow mufflers and I looked in and didnt see anything in the open part so hopefully there is nothing caught in the spiral parts. Anyways it is much better than before, I think the dyno run blew most of it out because the exhaust stinks now. I bought the cats used so I cant speak of the quality but I thought they were pretty new when I got them a little over a year ago.

The smoke appears to be oil burning, not sure where but the compression check was decent, around 160 psi per cylinder, and I replaced valve seals when I didnt the springs and no change so who knows. I wanted to see how many miles this engine will go but I dont want it to crap out at a bad time so I might just replace it soon with a LS6.