Gunnar Heinrich, editor of AutomobilesDeluxe, recently mistakenly filled a press fleet Cadillac SRX Turbo with regular unleaded fuel. The result? A catastrophic "mega knock event." His semi-harrowing tale of sudden unintended highway deceleration below. — Ed.


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IT'S nighttime and I'm rather unnerved.

I'm on the 101 halfway up some mountain outside Ventura, California in a 2010 Cadillac SRX Turbo that has just died in the narrow meridian.


I'm barking at some nonplussed 9-1-1 dispatcher on the cell, OnStar's on hold, and I'm ready to jump the jersey barrier if some dazed motorist drifts my way.

They all seem to brush by at light's speed.

This broken press car is one of Cadillac's latest midsize crossovers – a plush, Lexus RX fighter – that had just lapped its two thousandth mile before the car's engine bought the farm.

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In no time at all I had dropped from a comfy 65 mph cruise into a sputtering stop with black smoke billowing from beneath the silver hood and a long oily trail in my wake.

And now I'm awaiting rescue.

Minutes tick by endlessly. But the state police do arrive. The officer spies my precarious position and proceeds to snake his patrol car back and forth across the freeway- side-winder style.


Only then, does traffic slow to a grudging halt.

"If you can start your car, move it across to the right side." The officer coolly broadcasts over the loudspeaker.


Now, all of Ventura seems to be waiting behind him. The cars are like greyhounds at the gate and I feel like the rabbit as – rattled and frozen – I climb behind the Caddy's helm and press the start button.

Thunk-Thunk-Thunk-Thunk-Thunk-Thunk goes the mortally wounded motor.



Into drive.

We're on borrowed seconds!

The SRX c-r-a-w-l-s across the freeway to the far side. The go pedal's level with the carpet.


I reach the right side and the Caddy quits.

Traffic resumes its F1 pace, a discussion with the officer ensues, and ten minutes later the tow truck shows.


The driver shakes his head and says that only days prior some poor guy had similar trouble with his bike. When he tried crossing to the breakdown lane he got hit in roughly the same spot where I'd landed. He died.

So, what caused this fresh new Caddy to breakdown?

The answer arrived yesterday afternoon in a conference call with GM. Their findings are triggering a model-wide update to go into effect directly.


DAMAGE REPORT

On the phone is Tom Sutter.

Mr. Sutter is GM's chief engineer for the automaker's V6 engines. Also on the line is David Caldwell, Cadillac's press manager.


Mr. Sutter leads headlong into a thorough explanation of the wheels that were set in motion following the incident.

"We took this very seriously," he says. His tone is direct and earnest.

"As soon as it happened, we expedited the vehicle's shipment back to our test center in Warren, Michigan. We've been at this 24 hours a day, 7 days a week."


He and his team "tore down" the motor, analyzed the car's black box data, and sent a fuel sample to a third party lab for analysis. Additional tests on a dyno replicated the failure, but they've yet to duplicate the incident in real life testing.

The SRX Turbo uses a 2.8 liter, 300 hp V6. This same engine has served for five years in Saabs including the upcoming 9-4X. The engine also powers Germany's Opel Insignia.


THE BREAKDOWN

Mr. Sutter is describing my incident as a "Mega knock event."

"We have a high degree of confidence that we've sourced the problem," he tells me, getting down into the gory details.


What happened is as follows and was, apparently, a fluke:

The V6 in the Cadillac requires a minimum 91 Octane.

Lab tests had shown that the SRX was running on regular which meant that yours had inadvertently fed the car 88 Octane gas and not the factory mandated premium.


At some point during travel, between 2000-2500 rpm – or normal highway cruising speed – the engine's management system had adjusted the air fuel mixture to work too lean causing a retarded spark – but crucially – it allowed for a simultaneous turbo boost which led to a catastrophic pressure build up in the cylinder chambers.

This caused cylinder six to fail quickly -leaving yours stranded.

Mr. Sutter's team concluded that the resulting pressure in the chamber was four times greater than the stress during full throttle acceleration.


"We've been working on a new calibration which should be implemented in coming days," he says, indicating that this will ensure proper engine management going forward during what we might describe as "lean times" during the fuel consumption of a given SRX Turbo.

Mr. Caldwell stresses that what happened was an extremely rare event and that they've had only a couple of incidents that resemble what happened to me in California.


He suggests that the low Octane gas could be considered a contributing factor and not the primary cause of the engine's failure. But not everyone is careful with their choice of gas (as evidenced by this writer) and high Octane gas isn't always available in some rural areas.

Surely the car must be engineered to compensate?

Both acknowledge this aspect and say that the SRX's management system should have adjusted to accommodate for the lesser grade petrol and their system fix will ensure that it does going forward.


Nevertheless, Mr. Sutter maintains that the low Octane gas was the primary trigger in my car's failure.

"Ever since we've switched to low displacement, turbocharged engines, we've noticed a sensitivity [to Octane levels]."


The 2.8 liter, turbocharged V6 was created at GM's Pontiac, Michigan center in tandem with Saab staff in Sweden who engineered the turbo.

While most Saabs require only regular unleaded, the Cadillac SRX Turbo's V6 represents the highest output version of this particular powerplant, hence the requirement for higher grade fuel.


NEXT STEPS

As this article posts, GM is conducting field tests on six SRX Turbos in Death Valley to ensure that the recalibration they've devised will prevent a repeat of the failure when the vehicle runs on regular unleaded.


Once finalized, Cadillac will implement the engine management adjustments to the SRX assembly line so that new SRX Turbo units rolling off the line going forward will benefit from the update.

Current SRX Turbo customers will receive the update at their Cadillac dealer during service, though the company has not yet decided how it will inform customers on the need to getting their car updated.


We should receive word on their customer plan within the week. Also, GM will provide Automobiles De Luxe with another press car to complete our review. Expect our full take on the 2010 Cadillac SRX Turbo next month.

Here's hoping for a smoother road test.

—

Ed. Note: Special thanks to OnStar, Chris at Page One, and California Highway Patrol for their greatly appreciated help.


This item originally appeared on AutomobilesDeluxe on March 24, 2010.