Motronic rev limiters??? - Alfa Romeo Bulletin Board & Forums
 
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post #1 of 5 (permalink) Old 03-30-2013, 11:17 AM Thread Starter
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Motronic rev limiters???

To the best of my knowledge, my twin spark 164 2 litre is equipped with Motronic. I was romping on it today in 3d and looked down at my tach and it read 6500. Not a problem and I got to thinking. Does this engine management system limit the revs in any way??? TIA,, ciao, chris

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89 164 2l Twin Spark, 2011 Tonka Dump

Recently added: an 89 75 (Milano) 1.6 litre w/44K on the klok.

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79 Scirroco, ex plowed into an illegally parked house with it...
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post #2 of 5 (permalink) Old 03-30-2013, 10:30 PM
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Yep, there's two different rev limiters in your ECU. There's a detailed description of them in Biba69's big motronic thread.
edit - here's the link

Last edited by festy; 03-30-2013 at 10:33 PM.
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post #3 of 5 (permalink) Old 03-31-2013, 01:45 AM Thread Starter
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Wow, interesting read. You "smart" guys amaze me with some of the ***** you know. My experience runs along the lines of you rev too much and bump into the limiter and the engine kinda misses until you are back below the precribed value. in my case yesterday, I was enjoying the sound of the "air in air out" my little 2 litre makes and looked down and said "oopps" and let off the pedal. I'm guessing I mighta been close to the soft limit as the car just wanted to pull more. I assume from my reading, that the limiter kills the ignition to some extent until things slow down as it were. Thanx for taking the time to enlighten me Mr Festy and Biba. Not that I wanna explore it but the 6K limit shown on the tach (accurate as it might not be) is just a ball park figure no? ciao, chris

Maintaining my tenuous strain on reality.
89 164 2l Twin Spark, 2011 Tonka Dump

Recently added: an 89 75 (Milano) 1.6 litre w/44K on the klok.

Past loves:
79 Alfetta GTV w/Spica, my 1st Alfa

An 88 Graduate. Not really love but interesting nonetheless.

A 68 BMW 1602 - man do I regret letting that one go!

79 Scirroco, ex plowed into an illegally parked house with it...
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post #4 of 5 (permalink) Old 04-08-2013, 12:39 AM
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Sorry - I just noticed you asked a couple of questions in your last post that went unanswered....
Quote:
I'm guessing I mighta been close to the soft limit as the car just wanted to pull more
Rev limiter 101:
The soft limiter gives you 1.5 seconds grace, but if you stay above the soft limit for that long then the injectors are turned off until the revs drop below the soft limit.
The hard limiter is instant - if you go past the hard limit, the injectors are immediately switched off until the revs drop back down below.

It's pretty common to raise the rev limiters to ~7000 rpm on these engines.
As you noted, at 6k it still wants to keep going.

Quote:
Not that I wanna explore it but the 6K limit shown on the tach (accurate as it might not be) is just a ball park figure no?
The unmodified twinspark ECU I just checked had the following settings:
soft limiter: 6320 rpm
hard limiter: 6592 rpm
I would expect your tacho to be a few hundred rpm out, they're not precision instruments.

The soft limit is the one you'll most likely hit while accellerating through the gears, but you'll hit the hard limiter if you rev it out in neutral.
That's because the engine speeds up from 6300 to 6600 in less than 1.5 seconds standing still, but accellerating in say 4th gear takes more than 1.5s to get from 6300 to 6600 so the soft limiter time is hit before you reach the hard limiter.
They're a pretty advanced for a 25 year old ECU
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post #5 of 5 (permalink) Old 04-08-2013, 10:34 AM Thread Starter
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Pretty cool. I have no intent but just cause I'm curious. How does one modify the ECU to increase the rev limit? This tech is pretty neat for a car that's almost 25 years old and was at the beginning of the electronic age. Thanx for taking the time to reply. ciao, chris

Maintaining my tenuous strain on reality.
89 164 2l Twin Spark, 2011 Tonka Dump

Recently added: an 89 75 (Milano) 1.6 litre w/44K on the klok.

Past loves:
79 Alfetta GTV w/Spica, my 1st Alfa

An 88 Graduate. Not really love but interesting nonetheless.

A 68 BMW 1602 - man do I regret letting that one go!

79 Scirroco, ex plowed into an illegally parked house with it...
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