No thread hijacking please, edited for your pleasure, reposted for cleanliness.
Make Suggestions of issues you want answered or site posts that should be included!
The Bosch LH Jetronic fuel system is managed using the following inputs:
MAS/AMM - Air Mass Meter - Which is used to determine the airflow entering the intake system. The volvo uses a Bosch Hot-wire type sensor. There are three wires in the housing, two heated "hot-wires" and one sensor wire. Resistance changes with temperature, so the AMM is measuring the temperature drop caused by the the airflow between the hot-wires and the sensor wire by measuring the resistance across the sensor wire. Most AMM/MAF scale between near-zero at idle to 5vdc maximum; but the volvo sensor at idle reads approximately 2.3-2.5 volts and rails out to a maximum of 5.05-5.10v. This has caused some confusion with piggy-back boxes and tuners alike. If you run an oiled cotton type air filter, I suggest using fast drying electronics cleaner on your AMM insides as the factory burn off (a built-in cleaning function) may not remove all the oil residue. Residue + sensor wire = lean. It is also important that there is no unmetered air entering the system, as this air has not been measured, these leaks cause fuel mixture trouble!
Coolant Temperature Sensor - Which is used to control the additional injection of fuel into the motor below operating temperature. Fuel will not ignitie as a droplet, only as a vapor, therefore at colder internal temperatures considerably more fuel is needed to ignite and run smoothly without misfires. I would ensure proper operation of this sensor if you're running extremely rich, and can't find an obvious reason why. In general don't meddle with this, it is a bad idea to attempt fuel enrichment with this sensor.
Thermo-time Switch - Switch used to drive the cold-start injector (if equipped). This is a simple electromechanical device which handles cold-start enrichment on all LH2.2 and most LH2.4 cars.
Lambda - 02 Sensor - Which is used by the ECU to maintain A/F ratio of 14.7 or stoich. The factory narrowband O2 sensor was intended to be used for tailpipe emissions, and therefore is only truly accurate at .5v which is 14.7:1 A/F ratio. Do NOT trust your "Mr. Blinky" or calibrated voltage gauge, the indicated voltage is not accurate enough to ensure safety! The O2 sensor can be used as a tuning aid, but attempting to modify its signal will not be profitable, as the ECU ignores the O2 sensor signal at WOT. In short, the narrowband sensor should be used as nothing more than an 'idiot' light for serious enthusiasts.
TPS - Throttle Position Switch - Which is used to inform the ECU as to whether the throttle is in the IDLE or WOT position. Due to the nature of the throttle switch, and lack of a 'scale' to determine engine load, most piggyback engine control systems will require some form of customization in order to work. Some members cut down the shaft to use a volvo 850 TPS for EMS, however this will leave your factory LH system without proper input. It is possible to put micro-switches on the throttle assembly(similar to nitrous WOT activation switches) to simulate the factory TPS while mounting the proportional TPS on the throttle butterfly. Some members, including myself, have noticed significantly better part-throttle response than at WOT. It has been determined that the LH2.4 ECU adds fuel MUCH more aggressively, this works okay for a totally stock car, but at the increased airflows of elevated boost...the injectors prematurely reach 100% duty cycle.
In order for you to fuel tune a B230FT (Engine Code) LH (Engine Management version...2.2, 2.4 etc.) car you have to address a few issues.
Your car can max out the factory fuel system on the stock turbo! This means that you have more power potential then you have fuel for at this very instant. The stock fuel system has enough fuel to support roughly 200 crank hp. Once you've upgraded your intake and exhaust, and increased your boost pressure (12-15psi), you should be at the limits of the factory fuel system.
You have a few choices to overcome this issue.
You can raise the fuel pressure with a rising rate fuel pressure regulator (also known as an RRFPR or FMU), in order to allow the factory fuel injectors to deliver more fuel by increasing the nozzle fuel pressure proportionally to boost pressure you are able to deliver considerably more fuel through the factory fuel injection. This is accomplished by increasing fuel pressure not at the factory rate (1psi boost:1psi fuel pressure), but by using an auxiliary fuel pressure regulator with an oversized diaphragm, some which are adjustable from factory (1:1) to in excess of (1:10).
The factory injectors are low impedence (peak and hold) rated at 300-320cc/min. A good start would be to source some 'Ford Brown Tops' from thelostartof, which have proven themselves as drop in replacements over and over, especially on LH2.4. I had excellent results with these injectors, as did bitjockey (personally witnessed). Another workable variant of this approach is to increase the base pressure of the fuel system (approximately 3bar or ~44psi) with an adjustable fuel pressure regulator, making sure that you use a boost referencing unit that will maintain the fuel pressure differential under boost (1:1).
You can also use larger injectors by lowering the base pressure and using an RRFPR to make the car idle properly. This is not optimal, as the lower pressure (especially during idle conditions) makes for less atomized fuel exiting the injectors. This is however a very workable option. There is also a FPR/FMU hybrid on the market that allows you to set base fuel pressure, rising rate onset, and rising rate ratio!
Quite a few people have utilized cold start injectors as an additional source of fuel. As a low buck option, this works fine. A couple of members simply flip a switch to control their cold start injectors. I, however suggest buying an MSD RPM switch P/N 8960 and a Hobbs Switch (Adjustable from 0-20psi), so instead of running the cold start all the time, or only based on boost pressure, you can set it up to activate when you'd really need it, say 14psi @ 4500rpm.
Another option is to correct for larger injectors with an airflow modifying piggyback. Most piggybacks will allow airflow corrections up to 50%, which would limit upgraded injectors to roughly 450cc/min. Keep in mind that LH2.4 has a built-in compensation function that can compensate for up to 30% larger injectors FROM THE FACTORY. The airflow correction is accomplished by fooling the engine computer into 'thinking' there is more or less air entering the motor. This is done by intercepting the 0-5v signal from the AMM and feeding a modified signal to the ECU. If the computer thinks there is less airflow than there is, it will adjust the injector duty cycle (the duration which the injectors are open during a combustion cycle) accordingly; therefore reducing the amount of fuel entering the engine. This is useful in the way that 300cc/min injectors deliver less fuel at the same duty cycles as 400cc/min injectors, so by correcting this, the larger injectors will deliver a nearly identical amount of fuel. These corrections are modified based on RPM and engine load (usually throttle posistion sensor (TPS) based on a +3v or +5v variable sensor ). This means that you have a set number of variables which affect the airflow correction that takes place. This collection of variables and user entered values is known as a 'map.' This would be an easily workable solution, except that our cars do not have a variable throttle positioning sensor, but rather a two position switch, not enough load points to properly adjust the airflow, since your car doesn't spend most of its time at idle and wide-open throtte (WOT), you would have no correction in between. I solved this problem by using a GM 3bar manifold absolute pressure (MAP) sensor (from a Grand National) fed it a ground and a +5vdc regulated power supply. MAP is a better indication of load than throttle position, especially in boosted applications. So I fuel tune using boost/vacuum pressure and RPM. This is also important, since I can control my fuel system past the maximum point the AMM can read.
You can also remove your AMM electrics from the housing it resides in, and place it in a larger housing, thus changing the amount of air that it samples proportionally to the increase in the diameter in the new housing. A fair guideline is to increase the area by the same percentage as the increase in size of your new fuel injectors.
The last (reasonable) option if you insist on retaining your factory engine computer, is auxilary injector control. Most auxilary injector controllers simply require an RPM signal, boost signal, and auxilary injectors mounted in the intake pipes and/or intake manifold. You are basically creating an entire fuel system totally isolated from the factory system, except for the common pressure feed it would share with the factory fuel rail. So you set a threshold (turn-on point) and gain (amount of fuel added per pound of boost) and that's about it. Some of the more sophisticated auxilary injector controllers also use maps much like a piggyback/standalone engine management system (EMS).
There are more options, which I have yet discuss here.
"Fuel Cut:" Many people running 15Gs and larger turbos have started reaching a stumble in their WOT adventures. This is caused by maxing out the AMMs sensing abilities and thereby 'jumping' off the fuel map. The ECU responds to this by cutting the fuel injectors off completely. This point is around 5.1vdc. I am currently working on a solution to this problem using a 'magic black box' but I'm having trouble keeping the voltage drop across the box from interfering with the normal AMM operation. More on this soon. 
***Cautions***
The factory fuel system comprises of a low pressure, high volume in tank feeder pump and a high pressure inline pump rated at 250hp to 275hp. If you are nearing or attempting to exceed this power level, a fuel pump upgrade is highly reccomended!
