Hi All, I brought my car for a tune a few weeks ago and during WOT pulls the car kept breaking up and wasnt making power. After a few pulls of going wot and immediately getting out of it my tuner said i have a mechanical issue, he believes my passenger side head is floating a valve. His exact words were "Passenger bank O2 reading goes lean wot while driver side bank is sufficient and shows fuel. One common cause is valve float." He ruled out injectors not delivering fuel "as if it was an injector it would be constant all the time ". He kept adding more fuel and it wasnt making up for it so he ruled it as a physical mechanical issue. I have a 2009 Z06 with ECS 2200 blower Mamo msd cam and fixed heads, full catless exhaust. I bought the car as is, only change ive made was i installed the mamo msd right before the tune. I had an un-ported msd on it before that

I just did a leak down test today on my pass side and all were less than 10% leakage on a COLD motor. I used the trick of removing the rocker arms instead of bringing each piston to TDC. I had read that a cold motor could give worse readings but if all of them are 8% or lower leakage while cold, that would mean its the same or better when the motor is warm, correct? Cyl 2 was about 4%, cyl 4 7-8%, cyl 6 6% and cyl 8 2%. I had coincidentally done a compression test over the winter and all was good as well, highest was 200 and lowest was 190

Does this leak down test rule out the possibility of a valve issue, or is it possible for a valve to float/not seal only during wot? And if it does rule out a valve float issue, any idea what else could be the issue? Could it have been one cylinder had a bad plug/wire or was loose or something?
I pulled the plugs and attached a photo, theyre 2-4-6-8 from right to left. plug 2 looks a little light, no?

Now whats annoying me is I had an intake valve spring break over the winter in cyl 2. We replaced it with what was believed to be the same replacement dual spring thats good for 675 lift. My cam is 641/651 lift. I was under the assumption from advice I was given that there is no valve lash to check on ls7, that it should be good to just re-tighten and torque the rocker down and its good to go. Is that incorrect? This is the same cyl I had a valve spring break on. Any other ideas on what sort of mechanical issue could be happening?





and just in case someone is wondering, the tuner i chose is an independent tuner. He doesnt do mechanical work, he just rents dynos and tunes by appointment. Hes known to be a great tuner, my close friend used him for his c7 Z and all went well.

 

If you had a valve spring break in cyl 2: Check your Intake manifold! Maybe it melted and leaking. Air from outside comes in and lean out the mixture.

 

Definitely need a spring part number and installed height. Valve float is EASILY visible on the dyno. I trust your tuner in this case. For SURE, find out what springs are in it and what their installed height is. It makes a HUGE difference. Is this an LS2?

 

It's an LS7.
I don't think I'm gonna be able to find out what springs were in there, I already tried tracking down the last shop/owner and couldn't get the info. I might have to do all new springs in that case I guess

 

If you're willing to buy the tools, you can measure installed height and spring rates. But it may just be cheaper to buy new springs. But you MUST have a valve spring height gauge to know where you're installing them.
https://www.summitracing.com/search/...ht-micrometers

 

A few things:

1) Do you have a dyno graph? You can see valve float really easily on a graph. Or were you unable to make a full clean run?
2) Those plugs look awful and probably the cause of the breakup....but the question is why they look like that...Is there oil in your intake manifold? Do you have a catch can? Do they smell like fuel or oil? How many miles were on them?
3) The MSD intake manifolds are notorious for coming loose, double check and make sure all the bolts are torqued (like 5-6 passes minimum). Also, I'd recommend going back to stock or to an aluminum for a boosted setup, less likely to leak.
4) Was that one spring the same that was on all of the other valves? Why did it break? I'd recommend replacing all the springs with the same. If you had one break, you should have replaced all the others as a just-in-case measure.

 

Don't have a graph, he wasn't making full pulls.

There was a small amount of oil in my last intake manifold. I installed a catch can over the winter but have barely driven the car since. These plugs have less than 5k miles.

When I did the new msd I did 5 passes of torquing down, but I can always check them again.

As far as the spring, I'm not 100% sure if it's the same. We tried matching it up size wise, thickness of the spring coils and making sure it's good for the lift of my cam. I didn't change them all, just the one. It broke right after I gunned it and the tires spun and the rpm shot up to 6500-7k

 

Take some pics with the valve covers off. Post em up. Were these dual springs, or beehives? Normally a busted beehive spring lets the valve face and piston face kiss deeply and a rebuild is in order. If the engine is still good, I'm betting there's dual springs in there.

 

A busted dual lets them kiss too - don't be fooling yourself.

Misfires will read full lean.

 

Touche. I'm my experience, this is more of a unicorn to witness than beehives letting go.

 

They were dual springs. The outer spring broke in two spots and I found one side of the rocker bushing was out and needle bearings everywhere including the oil pan.

 

That sucks bro.

 

Yup - that is true. Historically because beehives used to be crap and people would abuse them. Different animals now a day.

As for the broken dual spring - you probably have some wild harmonics going on. I'd suggest figuring out your setup over again as it sounds unstable.

 

Valve float will have the dyno power just flatlining and feel "soft" up top more than a "breaking up" feel. I would double check plug gap, wires, and coil performance first to make sure it's not misfiring or blowing out the spark. Although there's some variation in the color of the plugs, I don't trust that unless you shut the engine off right at the end of the WOT run and didn't let it come down to idle (which would change the deposits on the plugs during DFCO and stoichiometric operation).

 

Agree with this. I had my Grand Sport dynoed and when it got to about 6000 rpm it would break up/mis-fire. You could see it on the dyno graph and could hear it. Turned out to be a weak coil that only misfired when it got to higher RPM's. My tuner was able to tell which cylinder the misfire was happening in also. We swapped the coil to another cylinder and the misfire moved with it. Swapped out the coil with a new one and no misfires.

I would put in a fresh set of spark plugs, maybe even go 1 range colder from stock. Fresh set of plug wires. Check intake manifold tightness. See if your tuner can tell you exactly which cylinders are misfiring and try swapping coils.

As for valve springs, if you don't know how many miles are on them, its probably not a bad idea to put a fresh set in. Aftermarket springs should be considered a wear item and changed every 20 to 30K miles.

 

so borrowing a scan tool i found a p0103 MAF code. it wasnt throwing a cel but the tool picked it up. Also it came back after having cleared it twice, came back twice. If the maf is bad in any way and not reading accurately how much boosted air is flying in at wot than thats a problem.

Also something noteworthy about the maf, i mentioned i bought the car as is... Well whoever installed the Alky system put the meth nozzle BEFORE the maf, and my tuner let me know thats not how it should be done when i brought it for a tune a few weeks ago so we changed it to after the maf. So for the past 2+ years its been spraying meth onto the maf sensor. I never realized it and trusted the work that was done (supposedly by a well known reputable shop that even contributes on here, but i wont mention who in case it wasnt them). So im thinking its def a possibility the hesitation only at wot is due to the maf. Hoping anyway. the car runs great at pretty much anything but wot.

 

Anyway you could post some scan data? I agree new springs should be on the list, especially considering the history. The few times I have seen valve float was at the higher end of operating RPM for the engine.

Maybe I missed it in a post but did you mention when this problem first surfaced? Was it noticed only during dyno/tune?

 

So i ended up bringing the car to ECS where its current setup was originally done. Chris there told me the heads look like theyve never been done!! (besides aftermarket springs). I was told they were done when i bought the car in 2018. If its true its scary i was beating the car for almost two years with the stock heads. He said the 2 cylinders they checked had excessive valve play and the seals were shot, and there were no bronze upgraded parts that head fix/new heads usually have. I definitely agree with the seals being worn bc the car blows smoke sometimes on WOT.

So im going with LME ported LS7 heads instead of just stock head fix. I kinda wanted their heads for a long time anyway and this finally pushed me to get them.

As to black00ta's question, I felt the problem on WOT during cold temps but thought it was a tuning issue bc it was only during cold 45ish degrees and colder. This past spring I felt the issue even on 65 degree day. Now its possible there was just a tune issue and then a mechanical issue also surfaced.. Its possible my tune was not speed-density and being it was tuned in 90+ degree day in August 2018 and the shop i went to rushed me out, maybe they didnt leave room for the 50 degree swing in temp? But without a doubt there was more than a tuning issue when i went for a re-tune in April to the new tuner i went to, there was definitely a mechanical issue. I dont have the scan data unfortunately.

 

So my issue is fixed however unfortunately I dont have a specific answer as to 100% what it was.

They replaced my heads and also my meth pump being it was about 4 years old. Car runs fine now, I drove it the 2hrs home from NJ to LI and was fine the whole way.