LH 2.2 injector selection question [Archive] - SaabCentral Forums

: LH 2.2 injector selection question

4th August 2002, 12:33 AM
As far as I can tell, the LH 2.2 computer has only one output pin (#13) to drive the injectors.

I can count four injectors under my hood.

How the hell does that work?

4th August 2002, 11:30 AM
They all fire together.

Never actualy met a car where the injector firing is 'timed' (sequential?) but I'm told they exist.


4th August 2002, 11:51 AM
Are you serious? That's insane.

Does the gas just pool up on top of the valve waiting it's chance then?

4th August 2002, 01:36 PM
Ok. I also don't see anything like a crank position sensor.

Please, please tell me that it uses the signal from the ignition to fire one injector at some semblance of the right time (and, of course, the other three simultaneously while their valves are closed)

4th August 2002, 11:32 PM
Neither my LH 2.4 or my Lucas cars use sequential injection.


5th August 2002, 03:31 AM
Dear God, this is terrible. I feel like my technological heritage has been stolen.

We develop the technology to inject fuel (more or less) directly into each cylinder as the valve opens, and what do we do with it? We hook it up in parallel!

It's like 95% of the rockets we launch are hauling gravel into orbit...

A friend and I are just about ready to start from scratch (almost) and build our own integrated ECU. Is this forum a likely place to look for technical information on sensors and actuators (at least the ones used in Saabs)?

21st August 2002, 04:29 AM
I've got a fiar knowledge of the c900 sensors and how things work on both the LH2.4 systems and the Lucas systems. Let me know if I can help you out.


Johann F
21st August 2002, 05:05 AM
Sequential injection is pointless on anything but a very, very slow turning engine. at normal engine speeds the fuel will never have time too 'pool' around the intake to any significant degree what with all the turbulence in the intake etc - a single pulse at one revolution of the engine for all practical purposes is a totaly adaquate way of fueling an engine. There are other areas of the management of a Saab engine which are much more primative and if you want to put some work into improving it try these;
No provision for ignition advance against RPM, No provision for inlet air temperature measurement, no O2 sensor (on UK 2.2 models anyway) no throttle position sensor (until LH 2.4)- well thats enough to start with :D The LH 2.2 FI system is very, very primative - it was never adopted by other manufacturers who quickly moved on to mototronic systems with multiple sensor inputs - even these dont fire injectors sequentialy though!

21st August 2002, 08:28 AM
Bosch Motronic M2.5 used sequential injector firing.
Found on the early 150bhp GM 2.0 16v C20XE/J engines.

GSI Cavalier, GTE astra, etc.


21st August 2002, 08:37 AM

What's happening with your car?

21st August 2002, 09:46 AM
Still in bits :(

I was going to go silly and spend a couple of grand on go faster bits, but I'm finding it hard to justify throwing that amount of money at it when I really should be concentrating on buying a flat.

I might just put it back to standard and move it on.

I do miss driving it, but I can't believe how much it was costing me!

21st August 2002, 03:05 PM
On the Vauxhal cars its possible to get the management system to drop into a 'limp home' batch fire mode. CCC magazine tried this as an experiment and found virtually no change in emissions, economy or performance between sequential and batch fired modes.

Once an engine is turning fast enough and running with enough load the injectors are almost permantly open anyway.