engine shake/rattle on startup normal?
Thread Starter
Heel & Toe
Joined: Sep 2012
Posts: 17
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engine shake/rattle on startup normal?
I just went test drove a 2007 vert manual and upon pressing the start button, the engine shakes/rattles for an instant. I was told by the salesman that is normal for vettes. Is this true?
Race Director
Joined: Dec 2010
Posts: 18,098
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Not sure about the rattle part but yes you can feel the cam lope when you start it up.
Melting Slicks
Joined: Jun 2012
Posts: 2,226
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From: Thomas Texas
On cold start up, the PCM uses references the start-up air flow table to calculate the amount of fuel to inject. If that table has too much air, then too much fuel is injected until the O2 sensors come on line at trim that back. They take about 10 seconds for the O2 sensors to heat up which is why there is the start up air flow table.
The solution may be as simple as a subtracting or adding values from the start up air flow table in the tune. I tuned my own car and once I subtracted 2.25 g/cyl of air from the start up table it started with the minimum amount of shaking. If it smooths out after 10 seconds, then most likely this is the issue.
In anycase its pure guessing until somebody with the right knowledge checks it out.
Thread Starter
Heel & Toe
Joined: Sep 2012
Posts: 17
Likes: 0
Depending on the mods, some of that may be fixed in the tune.
On cold start up, the PCM uses references the start-up air flow table to calculate the amount of fuel to inject. If that table has too much air, then too much fuel is injected until the O2 sensors come on line at trim that back. They take about 10 seconds for the O2 sensors to heat up which is why there is the start up air flow table.
The solution may be as simple as a subtracting or adding values from the start up air flow table in the tune. I tuned my own car and once I subtracted 2.25 g/cyl of air from the start up table it started with the minimum amount of shaking. If it smooths out after 10 seconds, then most likely this is the issue.
In anycase its pure guessing until somebody with the right knowledge checks it out.
On cold start up, the PCM uses references the start-up air flow table to calculate the amount of fuel to inject. If that table has too much air, then too much fuel is injected until the O2 sensors come on line at trim that back. They take about 10 seconds for the O2 sensors to heat up which is why there is the start up air flow table.
The solution may be as simple as a subtracting or adding values from the start up air flow table in the tune. I tuned my own car and once I subtracted 2.25 g/cyl of air from the start up table it started with the minimum amount of shaking. If it smooths out after 10 seconds, then most likely this is the issue.
In anycase its pure guessing until somebody with the right knowledge checks it out.
Melting Slicks
Joined: Oct 1999
Posts: 2,181
Likes: 421
From: Ponte Vedra Beach FL
My brand new 2013 GS does the "shake" for about 10-12 seconds, as does a friend's new ZL1 Camaro. This surprised me, because my 2003 Z-06 was as smooth as silk at start-up in any weather, as was my 2000 FRC.
I was wondering (smirking) if Chevvvvvvy put that shake in the PCM so we would think these engines were "racy" because they're not, witnessed by the fact that they go soooooo smooth once the cold-start has taken place. But I can believe the O2 sensor warm-up theory.
So, I guess I accept the shake as normal. Sorta.
I was wondering (smirking) if Chevvvvvvy put that shake in the PCM so we would think these engines were "racy" because they're not, witnessed by the fact that they go soooooo smooth once the cold-start has taken place. But I can believe the O2 sensor warm-up theory.
So, I guess I accept the shake as normal. Sorta.
Last edited by Tracy; Sep 24, 2012 at 10:02 PM.
Le Mans Master
Joined: Apr 2012
Posts: 6,956
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From: Camden SC
Mine even shakes a bit idling at a traffic light. I traded a Jaguar XK that idled smooth as a baby's behind so I was at first concerned, but now I am used to it.... I have been told this is normal...
