bridfi

my 2007 LS is starting to have a lot of spark knock around 1800-2200 range and 5200+ after the stage 2 cams.

i have been putting 91 octane in it, and that helped, but its still knocking. i had solid motor mounts and i thought that was causing the sensor to go off, but i took them off and its still knocking.

i have the factory spark plugs in it right now, but soon, ill have NGK iridiums in it. would this help?

i dont know what else to do?

drivernoverdrive

one you really don't need to be running 89 or 91 unless you are runnin over 200 horse or so....kind of a waste of money really...I have an 07 LS and it runs great on 87. I recommend you take your car into the shop, let them plug in and run a system check and see if one or more of you cylinders is missfireing...if thats the case then get you a new plug(s).

bridfi

i think it might be over 200 horsepower at the crank. but not much over.

why would horsepower alone tell you what kind of octane gas you run?

i have alot of heat and high cylinder pressures, and was told by many people to run 91 with the stage 2 cams. they make the car completely different than your 2007 LS.

the plugs are good, they were swapped over from another 2007 LS. the tuner (vince) told me it wasnt a misfire at all, but it is knocking.

anyone else?

YSUsteven

Did it start just after you installed the cams? Maybe its an issue with your tune?

bridfi

yeah, vince said he got 27 degrees of timing out of the other cobalts with the same cams, and he said mine knocks at 14 degrees of timing, he thinks its something wrong with the cams or timing or something...

but he said my IATs were at around 145 degrees because of my short ram, i need to get a cold air intake to get colder air, thats why it could be knocking......

any other ideas? anyone?

Spanky's Monkey

iTrader: (6)

i know this sounds dumb but try removing your hood in a remote location and checking it for knocks then. it could definitely be the short ram intake pulling hot air in. if the hoodless deal works you then to either get a ram air hood or swap out for cai. i thank god the injen intake switchs to either one in 10 mins or less.

HackAbuse

Go with the Ebay intake, I love mine

Red07SSNA

Are you sure you got the cams timed correctly (timing chain)?

Do you have any DTCs that indicate a lean condition?

Compression, heat, timing, and a lean condition -- it's one of those. Can you try a higher octane - 100LL maybe (aviation fuel just as a test) to insure it's not bad gas -- or not really 91 octane?

If this started right after cam install I would suspect the timing chain is off.

bridfi

well the thing is i timed it myself, i lined up the marks perfectly, and rotated it over and over until they were all lined up again... if it is off, then it had to of jumped a tooth after the rebuild, which im almost positive it cant because of the chain tensioner thats in there - it adds alot of tension on the chain, more than stock...

i dont know where to get 100 octane. it could be a lean condition but vince, the tuner, says the fuel curve is spot on. really dont think its timing, compression is stock, 10:1.

heat is what we're unsure on. and the 145 degree IAT is worrying me...

no Trouble Codes either. but alot of them were tuned out...

actually that sounds like the smartest idea i have heard all day. thanks!

Red07SSNA

This is just poking in the dark for ideas -- did you erase the ECM of any codes (even if there weren't any) to reset the learn values?

The way the Cobalt's timing chain is it takes like 33 turns (not sure of the number) to get the marks to line up again so the initial line-up is extremely critical. I hope it isn't the timing chain -- I had a similar problem when I changed out a timing belt on a Honda. The darned thing would "ping" all the time under acceleration and the timing was on the mark -- turned out I had the exhaust cam off by one tooth.

bridfi

well i actually turned it by hand the 33 or whatever times to see if they lined up again and they did. the only way it could be off if somehow on the initial start up, it jumped teeth.

but i highly doubt it. but its not EXTREMELY hard to check so i can check that maybe tomorrow.

vince was also telling me that it could be just the grind of the cams. theyre not all perfect....

im gonna try and do a datalog under WOT with the hood off, ill send it to him and he can check the IATs and the knocking also.

copson20

maybe the cam senor is not on right. cause mine is running beautifully. last night ran against a 2.4 and bet em. im sure that the timing is right the only thing that i would be concerned about is the cam sensor on your 2007

copson20

IAT's 145 this is insane. have you checked your compression in the cylinders when you put the motor back together?

et00

Your right horsepower doesn't tell you what Octane to run. Octane is plain and simple... Resistance to detination (resistance to spontaneously combust before the spark plug ignites the fuel). Thats why you hear knocking. Your cylendar is firing off before the compression stroke is complete. So in short higher compression needs higher octane. 91 is fairly high enough so that the engine shouldn't be doing that imo. I am not a professional mechanic tho. Might want to run a diag like the others suggest.

exiged

some good info. . . saving

et00

If you really get into the theory of octane ratings you will find that it is heptane (not octane) that specifically causes engine knocking and is the "zero factor" of todays system. Think back to chemisty class...

http://en.wikipedia.org/wiki/Heptane

Acidangel_5.0

this is not a fuel issue... dont worry about the IATs temps your reading either.. ive seen much worse...this is not your problem

ill put money on timing.. or fucked up cam profile.. i noticed you said your the first cammed model..

spec sheet? my hunch is saying cam profile is off

copson20

i bet the compression is to high also. or you didn't line up the cams right .

for the ls 2007.

bridfi

cams are ligned up right (around 11 oclock and 1 oclock at cyl #1 TDC, and gears only go one one way, teeth match up to colored links), compression test is right around 185 psi.

i have yet to find a laptop that i can use to datalog my car with the hood off...


EDIT: could it be the exhaust not getting the hell out of my engine because of the stock catback????? (im throwing ideas out there, im really not sure whats causing this knocking)

Acidangel_5.0

dude,what is the cam specs

Red07SSNA

When changing the cams did you pull the engine front cover off? You are correct about the color markings on the cam gears -- there is also a color marking for the crankshaft gear -- is that one "spot-on" when the cam gears are aligned?

bridfi

yes the whole engine was taken apart, and all the links were lined up right (all 3)

Street & Strip (Stage 2) Applications power from 3000-7500rpm .440 intake and .436 exhaust valve lift, 258 intake and 262 exhaust duration advertized (216 intake and 218 exhaust @ .050" duration)

it only knocks around 1800-2200 rpms and 5200+ it gets pretty bad

same in every gear

IonNinja

maybe I missed something here but isn't there supposed to be a cam sensor on the 07's that prevent using these cams?

bridfi

we pressed on the cam sensor ring onto the cam. it has an extension on the end to go into a bearing, then a housing turning the power steering pump, well we cut it short and pressed on the cam sensor

because the 07s dont have power steering they have an electronic assist

Red07SSNA

That changes everything -- if the cam sensor ring isn't properly placed it would cause your problem and checking the ECM wouldn't detect a problem because it would provide advance without knowing the ignition was off to begin with.

The second statment makes no sense -- No Cobalt has a power steering pump -- all are electronic assist.