LS3/525 high idle

This post is information on a situation I ran into installing an LS3/525hp motor in my 56.

Upon installation and driving 10 to 15 miles, the engine MIL fault light came on. Reading the code (needing a Tech 2 compatible reader), it turned out to be a ‘high idle’ fault code. It turned out that the idle checked out to be at the specified 975 rpm (high for most motors, but I was told this motor with the ASA cam was programmed to that rpm).

The tuner indicated he’d run into this before, and the problem was it took too long to return to the idle rpm with no throttle. He changed a parameter to reset the idle time constant (more critically damped rather than over damped, for the engineer types). The engine does return to idle noticeably quicker.

i also had this code blocked from being able to set the engine MIL light, so it doesn’t potentially mask a problem I’d care about.

Are you using the GM "crate engine" controller or something from a production car?

To me it seems like 975 is a really high hot idle with that cam with 226/236 duration and 110 LCA. I would think it could idle at 850 or lower. Did you try to set it lower?

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Originally Posted by Rick_L

Are you using the GM "crate engine" controller or something from a production car?

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Yes Rick, it’s the GM controller that comes with the crate motor

Quote:

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Originally Posted by chevynut

To me it seems like 975 is a really high hot idle with that cam with 226/236 duration and 110 LCA. I would think it could idle at 850 or lower. Did you try to set it lower?

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No, left the factory number in. The idle rpm doesn’t really bother me, I was concerned that I might have a problem. The motor runs well and pulls strong, I’m a happy camper, Laszlo!

Glad to hear it was relatively minor.

I know you haven't driven it much, but what's your impression of the driveability with the 525hp engine and its controller? I know there's a guy over on the other forum with some horrible driveability problems, but others are satisfied.

So far, so good, Rick. I currently have about 160 miles on the car. Last week we drove it to the interior shop and back, about 140 miles round trip. It ran well: idle quality, part throttle acceleration, and an occasional sprint. It lugs under part throttle at 1500 rpm without bucking, also. It consistently ran about 195-200 degrees, in about 90 degree temperature. It appears to be a well engineered performance motor.

Sounds like it's working well for you. I think the guy on the other forum had a wiring or ecm problem, and he gave up, it was never made right, but not without some trying. Don't have a clue about the competence of those who worked on it. I've heard other reports that the tune isn't what it could be - but also many reports that everything works fine. I'm tending to think that those who aren't satisfied are making installation errors, or expect it to idle like an unmodified stock engine.

I have the 495hp version, not running yet. High expectations for it.

I did talk with an individual with a 430hp version with an automatic. He had a problem where the trans would not shift into high gear. After many hours and discussions with Chevy performance, it turned out the the factory miswired two pins in a connector. He had to do a signal pin trace to find it, Chevy apparently was not much help.

let us know how the 495 behaves. We’re thinking about putting that version in the 59 corvette we’re working on now - either that one or a gen v LT1...