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26 Aug, 2009

Underperforming L99 engine Camaros : problem, diagnosis, and cure

Posted by: admin In: Main ()

A not insignificant number of V8 L99 engined Camaro owners have reported sluggish acceleration and seemingly underperforming power from their cars. These owners’ experiences not only relied on the old “butt dyno” but were borne out in timed acceleration runs showing slower-than-official estimated acceleration times.

Recently, member Scott@Bjorn3d’s L99 based Camaro was examined by GM engineers for the possible cause of the car’s underperformance. Officially, the reason provided was that the engine was operating at a reduced performance level due to the car’s first tank of gas being 87 octane gas (GM recommends high octane gas for the L99 engine). In effect, the car’s computer (ECM) had reduced the L99 to running from low octane tables (a safer and slower mode) appropriate for 87 octane gas. The problem was that, despite Scott fueling his Camaro with high octane gas after the first tank of 87 octane gas put in by his dealership, the ECM on his car did not re-learn and bump up its performance to match that of the higher octane gas even after hundreds of miles.

The official fix by GM was to reset Scott’s Camaro’s ECM thereby forcing the car’s computer to try running the L99 engine on the higher octane tables again, if it detected premium octane gas in the car. Evidently, the resetting of the computer worked as is apparent in THESE timed run comparison videos which show a clear improvement in the car’s acceleration. Many other L99 Camaro owners have also reported positive results from this process.

So, if you suspect that your L99 based Camaro may be underperforming due to past low octane gas, what can you do? You can try to pull certain fuses from the fuse panel which will result in a reset of the computer’s memory, thereby allowing it to attempt to re-adapt to running at a higher octane level. Instructions and photos of the process can be found HERE. Please note however, that neither Camaro5 nor GM officially endorse this DIY fix and taking such actions and its consequences will be at the owner’s own risk.

Computer reset instructions and L99 issue background information can be found HERE.

Read more on this story at the following LINK

1 Response to "Underperforming L99 engine Camaros : problem, diagnosis, and cure"

1 | JOHN

July 17th, 2012 at 6:09 pm


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