Engine over-rev - Alfa Romeo Forum
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  • 1 Post By Cuore_Sportivo_155
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(Post Link) post #1 of 6 Old 03-07-16 Thread Starter
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Engine over-rev

Hi All,

Mine's a 159 sw 2.4 qtronic for reference.

The other day I set off from a set of lights in an enthusiastic and spirited manner. the road was wet from where it had been raining and the traction control stepped in a bit....but during the heated struggle for supremacy between traction control and torque, and I think actually after traction had returned ish and the revs climbed, the revs went over the red line and shot almost to 5000 rpm.....I backed out of it because it certainly didn't feel as if the car was going to upshift.....

I've experienced something similar before on my previous car, an merc ml270 auto.....

any body had this or got any ideas?

I don't know if maybe the computer just wasn't quick enough to up change with the wheels spinning much more freely than had I had good traction on the road or if this is an ecu glitch under certain circumstances?
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First gear and high revs isn't liked by my qtronic in manual mode. There is a large delay from pulling the upshift until it slots into 2nd which can cause the revs to shoot as high as 5 thou. The rev limiter should still be in place though so shouldn't be any harm.

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I would expect there to be a hard stop in the ECU mapping that will prevent damage if the load is suddenly removed with the accelerator on the floor. The needle on the dashboard rev. counter is probably not an accurate reflection of what actually happens under these circumstances.

What the ECU rev. limiter can't do is protect against over-revs caused by gear changes with a manual gearbox. Years ago somewhere on the internet I saw a set of pictures from the aftermath of a gear change mistake: I think the driver had accelerated up to the red line in 4th gear and then changed down to 1st instead of up to 5th. It was not a pretty sight.
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(Post Link) post #4 of 6 Old 03-07-16 Thread Starter
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I was in full auto mode, not using the shifter otherwise I could maybe understand why it would do it (maybe just about)

but yes, as you say stoxda big problemo if you make a cockup like that on a manual.

As you say the rev needle may not be 100% accurate, but from the engine tone it was definitely revving in that region judging from how it sounds at normal top revs.
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5000 rpm won't harm the engine. that used to be the redline on the older versions anyway. the fuel injection is lessened from 4500ish rpm towards 5000, so you can't go over.
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Dont worry about it. If you have the multiscan software it will tell you the maximum revs the engine has ever done. Mine was 5000rpm. Its a 2.4 diesel.
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