An easy way to be rid of those annoying 3Ltr limp mode issues forever.

[Turtle_au]

A zener diode has a breakover voltage. You pick a size thats just under limp mode.
So if you picked 3.9 volts, the MAF volts will rise as normal until you get to 3.9 volts then anything over that is diverted to earth. The ECU will only see upto 3.9 volts.
Yes above that the ECU could do a couple of things, keep injjecting the amount of fuel for that air volume and try to increase the airflow by increasing boost ( which is already over what the MAF volts are telling it )
I would not add the diode without firstly having some form of boost limiter fitted and maybe even a BIG warning light to let me know I have hit the limit so I would know to back off before overboost and under fuelling killed the engine.

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[mudski]

A zener diode has a breakover voltage. You pick a size thats just under limp mode.
So if you picked 3.9 volts, the MAF volts will rise as normal until you get to 3.9 volts then anything over that is diverted to earth. The ECU will only see upto 3.9 volts.
Yes above that the ECU could do a couple of things, keep injjecting the amount of fuel for that air volume and try to increase the airflow by increasing boost ( which is already over what the MAF volts are telling it )
I would not add the diode without firstly having some form of boost limiter fitted and maybe even a BIG warning light to let me know I have hit the limit so I would know to back off before overboost and under fuelling killed the engine.

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Yeah right! That makes sense. Thanks. Over boosting isn't the killer of these motors too. Its the under boost at certain levels which creates massive cylinder temps and then the pistons give up in the end. My old Di happily spent its life at 25psi, went bloody good for what it was too.
I kind of wish I still had a 3Ltr so I could experiment more on this. Maybe I'll buy a shitter of one. Hmm....
Off topic, I did speak to a guy last week who had used the intake side of a BMW turbo, I can't remember which motor it was, on the stock turbo and he's getting over 300nm by 1800rpm. Seems pretty impressive.

Its good to see more people thinking outside the square with the motors now.

[nissannewby]

A zener diode has a breakover voltage. You pick a size thats just under limp mode.
So if you picked 3.9 volts, the MAF volts will rise as normal until you get to 3.9 volts then anything over that is diverted to earth. The ECU will only see upto 3.9 volts.
Yes above that the ECU could do a couple of things, keep injjecting the amount of fuel for that air volume and try to increase the airflow by increasing boost ( which is already over what the MAF volts are telling it )
I would not add the diode without firstly having some form of boost limiter fitted and maybe even a BIG warning light to let me know I have hit the limit so I would know to back off before overboost and under fuelling killed the engine.

Sent from my SM-T355Y using Tapatalk

Doesnt quite work like this. The ecu has a map so if it sees a abnormally high maf voltage for a given parameter it will go into limp. For example if the maf voltage goes over 2.5v at 2000rpm with a tps under 60% and the map sensor is only seeing 5 psi it will go into limp.

The good thing about what mudski has linked is it can be tabled like an ecu so you can program for a setpoint so maf voltages between certain rpm say in 100rpm increments. So this allows you to control the output maf voltage to the ecu and basically tune limp out.

Also diesels work the other way to petrol. The leaner the afr the better. Rich afrs can and will kill a diesel engine. Only thing high boost will do to the standard turbo is kill it.
@mudski

[mudski]

Also diesels work the other way to petrol. The leaner the afr the better. Rich afrs can and will kill a diesel engine. Only thing high boost will do to the standard turbo is kill it.
@mudski

Never killed my old turbo.Haha It was still like new when we pulled the motor out. Just the rest was failing around it. This makes me wanna get a 3ltr now and do some mucking around.

[Hodge]

Never killed my old turbo.Haha It was still like new when we pulled the motor out. Just the rest was failing around it. This makes me wanna get a 3ltr now and do some mucking around.

Now now ...

[mudski]

Now now ...

Thanks Eric. I need to be brought back to reality... Haha!

[Turtle_au]

Doesnt quite work like this. The ecu has a map so if it sees a abnormally high maf voltage for a given parameter it will go into limp. For example if the maf voltage goes over 2.5v at 2000rpm with a tps under 60% and the map sensor is only seeing 5 psi it will go into limp.

The good thing about what mudski has linked is it can be tabled like an ecu so you can program for a setpoint so maf voltages between certain rpm say in 100rpm increments. So this allows you to control the output maf voltage to the ecu and basically tune limp out.

Also diesels work the other way to petrol. The leaner the afr the better. Rich afrs can and will kill a diesel engine. Only thing high boost will do to the standard turbo is kill it.
@mudski

Ok I follow that.
What about early non-crds that only have MAF sensor and no MAP sensor.
Also that unit uses the low side of ignition coil for rpm sensing.

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[mudski]

Ok I follow that.
What about early non-crds that only have MAF sensor and no MAP sensor.
Also that unit uses the low side of ignition coil for rpm sensing.

Sent from my SM-T355Y using Tapatalk

The Direct injection motors, pre CRD, also used a map sensor. Its found mounted on the intercooler....

[nissannewby]

Ok I follow that.
What about early non-crds that only have MAF sensor and no MAP sensor.
Also that unit uses the low side of ignition coil for rpm sensing.

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You can use the tachometer or the low side of an ignition coil. The rpm for the module is as simple as splicing into the correct wire that goes to the ecu in a zd 30. You dont have to use the rpm either but it gives you only 16 setpoints rather than a nice table when using the rpm.

And there is a map sensor on the earlier di motors.

[nissannewby]

Never killed my old turbo.Haha It was still like new when we pulled the motor out. Just the rest was failing around it. This makes me wanna get a 3ltr now and do some mucking around.

Push it beyond 25 and you may find its limit pretty quick.