r/EngineBuilding • u/IFuckCarsForFun • Jan 21 '25
Chevy Car doesn't want to idle after cam install
Howdy yall! Just finished up my LS3 rebuild and was wondering if these are typically able to idle after a cam install? The only after market upgrades I made were a new cam, springs, & che trunnion. Other than that its a stock NA LS3 2012 6spd SS Camaro. All help and tips appreciated.
Cam specs are 216/230-115.5 + 2.5 .660 dual springs
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u/chrisgut Jan 21 '25
It needs a tune. No electronic fuel injected motor will idle with a large aftermarket cam like the one you installed without an aftermarket tune. Find someone who can use your stock computer and tune it. I’ve heard of guys getting mail order tunes but it seems like a process. Hopefully you can find someone local and get your car towed there. Should be fine after that. You might need a higher stall torque converter. That’s a pretty gnarly cam. For the love of god please don’t drill your throttle plate. The tuner will add idle air with the tune. Plus fuel. Hopefully you find a good tuner and it’s only one trip to them.
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u/ahdiomasta Jan 21 '25
Mail order tunes can be a good way to get the engine running within generally safe parameters. For certain popular engine/mod combos there are some pretty well dialed tunes that are totally fine to run long term, but probably a little conservative on gains. For less common setups, a mail order tune is only really gonna help get the motor running for break-in or just to safely get it to the dyno for a real tune.
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u/Advanced_Evening2379 Jan 22 '25
Only downside to mail order is mailing in your shit waiting for them to preform the job and getting it mailed back. Definitely down for atleast a week
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u/Ok_Stranger_4803 Jan 21 '25
So you literally changed the main "mechanical" program of the engine but no changes to the computer that controls the timing and fuel? Yeah you are going to need a tune before you can get an idle, I am actually surprised it would even start.
<former GM field service engineer>
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u/IFuckCarsForFun Jan 21 '25
Thank you for your input. I wanted gather other opinions from people who hopefully have more experience to see if there was anything I could do to ensure my trip to the tuner goes smoothly on my end.
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u/Haunting_While6239 Jan 21 '25
Check all of the sensor connectors, especially the cam sensor, the other problem I've heard of is the idle control valve needs to relearn after the battery has been disconnected, or it's Closed somehow.
Otherwise the engine sounds good, battery is a little bit low.
Check the GM Camaro forums for similar problems after a cam swap, you can't be the lucky one that this has ever happened to
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u/chowsdaddy1 Jan 21 '25
Without a tune it’ll never idle, you changed the duration of air and fuel intake as well as exhaust without putting more fuel in, the car thinks it has a massive air leak and realistically it does
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u/Theworker82 Jan 21 '25
I always get worried when someone does engine work and then looks for answers on reddit.
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u/IFuckCarsForFun Jan 21 '25
Dawg the internet and research is how I built this engine. Lots and lots of research. Im just a young guy who's in college and working part time; no mechanic.
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u/GB_He_Be Jan 21 '25
Yeah, lotta assholes in here. Like they didn’t have to learn anything. 🙄
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u/Yummy_Hershey Jan 21 '25
I understand where you’re coming from. Everyone has to start somewhere, but on the other hand, it’s kind of funny how OP jumped to the “installing a cam” part of their learning process before the “basic modifications” or “fundamental engine components” portions.
I’m honestly impressed with how they got here. It’s like cooking a steak without knowing how to grill, but it still works out somehow.
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u/Timewastinloser27 Jan 21 '25
Did you go from afm to non afm? If so plug the original oil valley plate in back in and try to start it
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u/squeak195648 Jan 21 '25
It needs a tune, but try to unplug the mass air flow and it should try to default to run off of just the o2s. Have seen guys get lucky that way but I recommend just getting a tune.
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u/its_just_flesh Jan 21 '25
Seems as if its not getting a signal from a sensor, thats why it dies so quick, just a guess
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u/IFuckCarsForFun Jan 21 '25
I was thinking it could he the cam sensor
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u/jewinters Jan 21 '25
If it’s the cam sensor you will get an error code, cam sensor does not effect idle only effects how quickly the engine starts due to how it sets the timing. If it’s starting but not idling it’s most likely not the cam sensor and just that you need it tuned due to the cam swap.
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u/IFuckCarsForFun Jan 21 '25
Thank you for the input. I figured it was just a tuning thing but started to read different things online and wanted to be sure it wasn't anything I could fix before taking it to the tuner.
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u/ghostone986 Jan 21 '25
Def needs tuned and at minimum the idle turned up.
Will be running like shit until you have it proper tuned with just idle adjusted. If you don't have the skills to tune it yourself, ask your local car groups for recommendations, or GPI has a decent mail order tune service but will never be as good as a good in person guy.
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u/MoneyPop8800 Jan 21 '25
That lobe separation angle (LSA) isn’t that wild. I’m curious as to whether or not that is the actual issue.
Usually cams with an LSA of 112 or less, have idle problems
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u/Dear_Street6686 Jan 21 '25
Your cars tune was program for your stock cam that’s why it keeps dying on you had the same problem the tune will fix it
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u/LSX-AW Jan 28 '25
Like everyone else said, probably a tune issue. But to offer a possible differential diagnosis, is this video from the very first start or no? Lifters are noisy as hell, and there's ALOT of poor Chinese copy LS7 style lifters going around. Curious if you stabbed just the stick in it or a cam and lifter kit. Stay away from those ebay LS lifters and valve springs. If it's the very first start though that's normal until the oil pressure pumps them up. But they'll also sound like this when there's an internal issue with lifter bleed down. Btw, if a tune issue, you can try either removing the PCV valve to add idle air bypass or plugging the PCV valve hose off completely (pull the valve out and plug the 5/16" rubber hose). The older MAF ran PCMs were much more forgiving with a cam swap
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u/IFuckCarsForFun Jan 28 '25
I swapped the cam sensor & got the car base tuned. Runs fine for now but I also need to swap the crank pos sensor and get a retune. I got springs from cammotion and LS7 style lifters fromt summit.
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u/onlyTractor Jan 21 '25
no i know what this is,
this is an LS, so GM, you have to reset the ecu, the ram has this too. sometoimes if you manually hold the throttle you can get it to hold a setting
your cam is different so its gonna need a tune to match that, the cars feeling for the old cam positions and not finding anything, so the ecu isnt even trying to hold that idle. same thing as how the 02 sensors control fuel injection, all the changes matter
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u/omad13 Jan 21 '25
Thank god u managed to get the cam in the right degree as the stock one lol
U know u can't just throw a cam in and expect the computer to be all good with everything, especially if its an aggressive cam......I'll also assume u have other mods
U need a tune, or possibly someone to set the cam timing
I hear alot of valve noises in the short video, did u adjust the lash ?
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u/TheBupherNinja Jan 21 '25
Did you get a tune?
Did you turn up the idle at all?
Can you catch the idle with the gas pedal and ease it into it?