what is turbo lag and limp mode..

[seekers282]

hello,..can someone explain to me what is turbo lag and limp mode..how can this turbo lag and limp mode happen?what can cause it?
zd30 nissan patrol

[Family4x4]

Watch this video on turbo's. Turbo lag is the time it take for the engine exhaust gases to build up enough pressure for the turbo to become effective.


http://www.youtube.com/watch?v=p_rzAXx6p_E

Limp mode is when the vehicles computer limits power to protect the cars components, it still allows you to drive but not to the full capacity of the car. It is usually associated with Toyota's and Fords.

[seekers282]

great video..thanks mate..gonna watch it and learn from it..

[mudski]

Limp mode is when your turbo charger exceeds the boost limit set by the ECU, usually around 16psi. When it does the car will simply not go, and you have to take your foot off the go pedal and back on again for limp mode to disappear. Turbo lag is, in a nutshell, the time between your turbo basically sitting there at its lowest rpm, (saying when your idle at the lights) and its maximum rpm (when you put the foot down and take off from the lights). If this time is too great, you experience sluggishness then you will feel the turbo start to kick in and get the car going. If you have a boost gauge you can see it. The needle will rise really slow to reach the maximum boost level.

[the evil twin]

ZD30's use a variable nozzle Turbo so turbo lag is significantly reduced in those engines.
VNT lets the Turbo stay spinning at much higher revs and adjust vane angle for boost which is heaps faster response than waiting for a fixed Turbo to spin up.
Turbo lag is there but no where near as noticeably as non-vnt jobbies.
The other way they reduce Turbo lag is compound turbos, common in light trucks etc.

Turbo surge is another issue in the ZD30's and is one of the reasons the oily goo gets "upstream" in the airflow and coats your MAF etc

[Hodge]

Turbo surge is another issue in the ZD30's and is one of the reasons the oily goo gets "upstream" in the airflow and coats your MAF etc

What exactly is turbo surge ?

[the evil twin]

Turbo surge or compressor surge is the "back flow" when you are on boost and then rapidly close the throttle so the engine cannot use the air being supplied.
For a few moments the high boost pressure can cause air to flow backwards in the induction plumbing until the flow masses equalise or you go wide open throttle (WOT) again and demand more air.
Pre compressor is hi flow low pressure air, post compressor is low flow hi pressure air so if you are working hard up thru the gears each time you change and got from WOT to closed to WOT again you get some surge back into the low pressure side.
Because the engine ventilates into the low pressure side the MAF and the air filters slowly get covered in the goo from the engine ventilation gasses.
A catch can helps reduce the contamination but does not affect the surge