(Morgan/Rover Engines) by Lorne Goldman
Orginal AFM was a Bosch 0280 202 046 though others will be vitually identical. Higher flowing capitable Bosch are also possible.

1. In any adjustment of the spring, you MUST make sure that;

a. the armature centre pointer (you can just see a tiny little dot at the end) is precisely pointed at the bottom left corner of the tiny shaded rectangle you see at the arrow "A"  If it is not, you can adjust the angle of the armature, by loosening the screw indicated at "B" You will notice that the screw does not enter a hole but rather an wide slot allowing for this adjustment.

b. You should place the idle air bypass screw (not shown) about 1/2 way down in adjustment. If the adjustment screw cannot be turned or has been not buy the unit.

2. Though it would seem that the large toothed wheel adjustment is simple, you must consider that there are 50 teeth in its 360 degrees and the wheel can turn completely about 4-5 times (by my bad memory) ..creating 200-250 possible air/fuel combinations. Each tooth, (within a range the car will start at all)  represents a 1% CO2 adjustment! You CANNOT adjust the AFM without a CO2 analyzer. (Gunsen makes the cheapest home version..about 100 GBP). You can get what seems a smooth idle without..and then find under load and normal speed that you have caused some prejudice to the engine by running far too lean..or, less seriously, far too rich).

The best procedure is to turn the adjustment wheel until the spring (with in the black wheel) looks pproximately like the picture below and try to start the car. If it doesn't start, loosen the spring a bit. (If your engine pulses...the spring is too loose).

Once started, turn the spring incrementally until your CO2 analyzer reads 2%. You can then refine the idle mixture later, after you close up, by using the idle air bypass valve.

3. The arrow "C" point to the fuel pump contact...a weak point on the L-Jetronic. In a eMog survey two years ago, we discovered that 8 of 12 of them here had failed and been bypassed. In my experience, it is the single most oft-asked thing that stumps the Agents on these flapper Morgan. The innards of the L-Jetronic are delicate.... use the wrong sealant and the fumes corrode the contacts and they fail. Clean with alcohol and air before resealing.

Additionally, the fuel pump contact is a tiny wire going to a red relay-like affair called the "steering module" and then on to the fuel pump relay with a more robust wire. Forget it. Have your fuel pump function with the ignition interrupted by an inertia switch..(I use one from a Jag). This is far more reliable, simplifies the standard system and acts as an ignition cut your insurance company will pay for it AND reduce your premiums. (smile)   


The key component in L Jetronic is undoubtedly the airflow meter. It is composed essentially of a graduated air passage containing a hinged flap which deflects against a spring according to the flow of air through the passage. The flap is mounted on a spindle and directly controls the position of a sliding contact along a resistive track.

Although the track itself incorporates a complex array of laser trimmed resistors the principle is very simple: just a potentiometer producing an output voltage according to the deflection of the flap (see diagram).  Like most things of course the satisfactory operation of the airflow meter involves some sophistication in its design features. For instance a simple flap pivoting in the air-stream would be overly-sensitive to any resonant pulses in the induction tract and any spit-back from the engine would be likely to blast it back violently against the incoming flow to the limit of its travel. To resolve these problems a second flap was added at 90 degrees to the first, pivoting within a damping chamber. The idea was that any pulse or spit-back striking the two flaps would be largely balanced either side of the pivot point and any sudden movements would be resisted by the damping chamber.

This worked quite well for pulse absorption but the much stronger shock wave generated by a spit-back could still blast the flap onto its closed stop with such severity that the spindle bearings could be knocked out of alignment causing the flap to jam. Originally a spring loaded relief valve was built into the flap to relieve such pressure waves but did not react quickly enough so was superseded by the simple expedient of a small rubber buffer at the entrance to the air passage.

The Air Flow Meter or AFM is one of the most expensive components of the L-Jetronic system. Fortunately they rarely wear out or fail and there are plenty of inexpensive used ones available. The AFM is simple in operation. Air entering from the air filter side pushes a little door open. As the volume of air increases it pushes the door open farther. The AFM measures how far the door opens to determine the volume of air. The AFM also measures the temperature of the air. These two bits of information are combined to determine the total number of air molecules entering the engine and that information is sent to the ECU. The ECU then uses this information to help decide how much fuel the engine needs and adjusts injector duration accordingly. Of course the ECU gets information from many sensors but at full throttle the AFM's signal is primary. That means if you want max power a properly operating AFM is critical.

 * A bad AFM can cause the following problems: Difficult or impossible hot or cold starting, the starts and stalls syndrome, lack of power, high emissions, and irregular idle.

I am afraid the official Bosch procedures for checking these things are not too good. 

by Lorne Goldman

The system on the Flapper Plus 8 is known for stalling. There are three reasons for this specific to L-Jetronics, though stalling can happen for any number of causes common to all other EFI systems. Two of the L-Jetronic stalls can be quickly cured but the last, the most common, has to be adjusted as best possible.

The first two are related.

The AFM Fuel Mixture Adjuster The owner or some misguided mechanic adjusts the fuel mixture at the Meter screw to the point where no idle air can feed the engine (unless the throttle is used). They don't notice this when they set off as the Bypass Air is opened at startup, feeding the engine fuel and air. When warm, they will come to a stop and stall.

The Idle Adjuster at the Plenum  The owner or some misguided mechanic adjusted the idle at the plenum screw when the engine was either not warm or too warm. Again, they will run the engine, come to a stop and the engine will exhibit an unwanted idle or stall.

The Throttle Potentiometer (aka the Throttle Pot)

This is a little device that tells the ECU the position of the butterfly flap the plenum nose that controls air inflow.  There are two versions, one for the Hotwire 3.9 and and an earlier, adjustable one for the Flapper, easily done with a multimeter and swiveling the device as needed on its two slotted screw holes. Sadly, they fail and the Flapper version is now hard to find. The smaller, later type, cannot swivel. However, and adapter plate can be made.  Scroll down on THIS PAGE to find out how to adjust it.

This last one I call the The Curse of the Flapper EFI  The Flapper was in use as a stock fueling system longer than any other EFI in history. It began in 1973 and continued until it last instllation in 1990. Remarkable! A testiment to analogue technology! However, it is a simple system, with a lack of bells and whistles. It was designed by carburettor thinkers and has many of the limitations (and joys) of carbs.

In this instance, it does not compensate for the fuel becoming gaseous (turning to a vapor state) in the fuel rail once it becomes hot. As the car stops or is turned off for few moments at a filling station, the fuel flow stops and what is in the rail won't seem to re-start the engine. To a degree, this sad effect can be largely tuned out. Firstly, please ignore your manuals, they were written by people trying to meet government standards, not reality.

A. I set my idle at 1050-1100 rpm, the 650-850 indicated by Rover is silly.

B. I simultaneously fiddle with my ignition timing

C. I use a Mallory Unilite Distributor.

D. I adjust my fuel pressure with a FSE Adjustable Rising Rate Fuel Pressure Gauge.

This keeps my L-Jetronic Morgan largely behaving...though on hot days even I will need to feed the thing more throttle to get it going smoothly after brief stop. It has become an automatic habit.

As an interesting side note, most do not know there was a solution created to resolve the issue. There was a time when separate Rover factories had more autonomy. None was more inventive and successful than the division in Australia. They had V8 variations that made them a legend. In this case, they attached a heat operated solenoid valve to the fuel line. If the fuel became too hot, it increased the fuel pressure. That eliminated the stalling problem.  Sadly, the part is no longer available. But it is on my list to investigate and attempt.


There can be no doubt that many L Jetronic problems involve the airflow meter, not that it is particularly troublesome but it does have several key functions and a fault in any of them is equally inconvenient. One of the most common is for the fuel pump relay switch ceasing to close properly. The cure is usually just to remove the black plastic cover (which involves some patient work with a sharp knife to gradually break the glue joint) and gently bend the switch contact arms until they close as the flap opens. However, if the switch is broken then the airflow meter will usually have to be replaced. Franky I do not trust the switch. On eMog, we found that 50% of them fail over time and that is a silly reason to go searching for a AFM that has not been produced in 20 years, espcially when you are a 1000 miles from home. I wire the fuel pump into the ignition with a modern impact inertia switch inline.

The wiper arm is secured to the flap spindle by a clamping screw and the wiper itself is adjustable on the arm, being locked in place by a small screw and washer. There is a slender possibility of either clamp screw slipping, perhaps after some sort of shock or backfire. If this should happen it does not take much movement to upset the fueling considerably and if this symptom is observed, and no other fault is apparent, it can be worth experimenting carefully with the slider alignment.

The resistance track sometimes wears through, usually around the much used first third of the wiper travel. This will obviously cause erratic fueling and whilst a track from an airflow meter which has failed for other reasons, from a similar car, could be substituted, some trial and error might be needed to set the slider position satisfactorily.

Resistance measurements do not provide an accurate means of assessing the serviceability of an airflow meter - it is a potential divider and the system depends on voltages not resistance. There should be smooth transition of voltage on terminal 7 as the flap is moved. Typical airflow meter terminal voltages are:-

Pin 6 0v
Pin 7 2.25v - flap fully closed
Pin 7 7.5v - flap fully open
Pin 8 7.6v
Pin 9 12v - nominally 2v below battery

A quite common occurrence is that slight wear in the spindle bearings allows the flap to rub on the housing. This can appear serious but in the majority of cases the flap functions quite normally when the engine is running. Occasionally one finds an airflow meter, or its connector, with a large (100 Mf) capacitor soldered across terminals 6 & 8. This was supposed to be a cure for a drivability problem during warm-up but how effective it was is a matter for conjecture.

If a new meter is needed, or you wish to refurbish your own, contact Fuel Injection Corp.  


Running engines is a24491975 tricky business. They are made to run their best when they are doing their job (2000+rpm and warm) yet we ask them to start up when cold and idle at a level way below their optimum running range! Carb'ed engine dealt with the second issue by altering the startup fueling with a manual choke that vastly enrichened the fuel mixture when used. Later EFI adjusts fuel feed by detecting coolant temperatres and using a stepper motor to adjust airflow. Early EFIs are moresophisticted than carbs and less so than later EFI systems.

The Flapper uses a second system of air/fueling that piggy-backs on the primary system. A 9th injector was added to the right side of the plenum for more fuel and an extra air feed (the Cold Air Bypass) was added (in the front of the plenum). They are both coolant temperature activated. If the coolant is cold enough, three things happen. 1. The ECU leaves all injectors open for a longer duration (through pin 4) and 2/3 both these addon devices bypass the ECU/AFM and add extra fuel/air. As the coolant warms, these temperorary feeds decreases and shut off. If either is not functioning perfectly, starting the car is a chore.