Ljetronic rev limiter
03-10-2003, 05:03 PM
#1
Nordschleife Master
Thread Starter
Ljetronic rev limiter
Why did Porsche chose to make the l-jetronic rev limiter like it is?
In the service manaul, it says that hitting the euro style rev limiter would dump fuel in to the exaust, killing the cat, IIRC.
I don't see how thats so. The L-jet computer stops injecting fuel when the ignition stops fireing. If the Euro style distributer stoped fireing the spark plugs, the L-jet computer should kill the injectors. No fuel, no spark, engind hits the rev limit!
Conversly, as the l-jetronic is set up right now, it'll take a bie of time to let all the fuel pressureiszed up in the rails, and lines to be exausted, before the engine hits the rev limit. Seems to be a mush less precise sysem than the euro style "kill the spark" system.
In the service manaul, it says that hitting the euro style rev limiter would dump fuel in to the exaust, killing the cat, IIRC.
I don't see how thats so. The L-jet computer stops injecting fuel when the ignition stops fireing. If the Euro style distributer stoped fireing the spark plugs, the L-jet computer should kill the injectors. No fuel, no spark, engind hits the rev limit!
Conversly, as the l-jetronic is set up right now, it'll take a bie of time to let all the fuel pressureiszed up in the rails, and lines to be exausted, before the engine hits the rev limit. Seems to be a mush less precise sysem than the euro style "kill the spark" system.
03-10-2003, 06:25 PM
#2
The Euro rev limiter is no more than wieghted contact on the rotor that send the spark energy to a different plug in a "safe" part of it's cycle.
There is no electronic shutdown of the ignition or the fuel pump therefore the CIS injection continues to spray, metered at the airflow level of rev-limit (6300ish RPM).
I don't know how the twin dist. LH-jet Euro rev-limit but the one on the CIS is harly precise; just a spring and weighted contact.
Rather than a "kill" it's more of a controlled mis-fire which will force engine RPM to drop slightly and ignition energy to re-route to proper firing order.
There is no electronic shutdown of the ignition or the fuel pump therefore the CIS injection continues to spray, metered at the airflow level of rev-limit (6300ish RPM).
I don't know how the twin dist. LH-jet Euro rev-limit but the one on the CIS is harly precise; just a spring and weighted contact.
Rather than a "kill" it's more of a controlled mis-fire which will force engine RPM to drop slightly and ignition energy to re-route to proper firing order.
03-11-2003, 09:51 PM
#3
Instructor
According to the microfiche manual, the US/Japan K-jet engines were rpm limited by a fuel pump cutout also.
What could be simpler for an efi engine than the brain limiting rpm by simply not opening the injectors?
What could be simpler for an efi engine than the brain limiting rpm by simply not opening the injectors?
03-11-2003, 10:05 PM
#4
Nordschleife Master
Thread Starter
Thats the thing, it doesn't.
Ask me, I know!
The computer shuts the fuel pump off, but the injectors keep fireing.
Here's how I know. I've been running around with a digital external tach for the last few days. If you rember, I burnt the fuel pump realy, and am running around with it jumpered. A relay is on the way. Unforchantly, it's at home, and I'm not. :-(
Anyways, I've been testing to see just under what conditions I have the 4,000 rpm miss. Well, in the process, I hit a freeway entrance ramp, and ZOOM! I almost think I've got it fixed, but some more testing is in order. ;-)
I was horrifed when I hit 6450 or so, and no sign of the rev limiter.
Anyways, wanna get rid if the rev limiter on the US L-jet car, jumper the relay!
Ask me, I know!
The computer shuts the fuel pump off, but the injectors keep fireing.
Here's how I know. I've been running around with a digital external tach for the last few days. If you rember, I burnt the fuel pump realy, and am running around with it jumpered. A relay is on the way. Unforchantly, it's at home, and I'm not. :-(
Anyways, I've been testing to see just under what conditions I have the 4,000 rpm miss. Well, in the process, I hit a freeway entrance ramp, and ZOOM! I almost think I've got it fixed, but some more testing is in order. ;-)
I was horrifed when I hit 6450 or so, and no sign of the rev limiter.
Anyways, wanna get rid if the rev limiter on the US L-jet car, jumper the relay!
