Read part 1 first !
https://www.sl113.org/forums/index.php?topic=38391.0WARNING! : DO NOT START WORKING ON YOUR FIP BEFORE YOU ACHIEVE THE BASIC SETUP FOR YOUR ENGINE : CORRECT VALVE CLEARANCE
AND IGNITION TIMING
AND LINKAGE SETUP !!
THIS CANNOT BE STRESSED ENOUGH , OTHERWISE YOU ARE TRYING TO SOLVE ONE PROBLEM BY CREATING ANOTHER ,WHICH WILL DRIVE YOU CRAZY IN THE END ! !.
STEP 4 : AIRThe amount of air needed for a good running engine is controlled at 3 positions : the main air regulator is the venturi via the accelerator(linkage), the airscrew is used for idle adjustment and supplemental air is supplied via the WRD,but only for cold starts .(The WRD will be further discussed in part to be issued later.)
Venturi and distributor should be a matching combination as mentioned under step 2 ignition
Check the main airfilter, its housing and connected hoses for an unobstructed airflow,damage or leaks. The same applies for the airscrew unit ,the little airfilter on the FIP and its connected hoses and tubing .
Don 't forget to check for air- or vacuumleaks at other hoses ,venturi housing ,manifolds and brakebooster . If necessary use a smoke generator. A nice lowcost hack is mentioned in this topic by Pawel66 :
https://www.sl113.org/forums/index.php?topic=38307.0Check operation and adjustment of the venturi throttle plate as mentioned in the linkage tour. See also that the throttle plate lever does not slip on the plate axle. Check the tiny opening (the bore for ignition vacuum) in the venturi housing for clogging or being covered by the throttleplate .
STEP 5 : FUELRemember the earlier mentioned WARNING about first achieving a basic setup of your engine? If not, return to step 1
Before even thinking of working on the FIP first get the basics right. For this discussion lets's split the fuelsystem in 3 parts.
1 .a relative low pressure fuel supply side feeding the FIP ( from fuel tank,electric fuel pump ,main fuel filter to FIP and CSV as well )
2. the circulation or return side of the fuel system ( from FIP via pressure regulator,damper back to the fuel tank)
3. the high pressure side ( FIP to injectors) Will be discussed in a later issued part
* fuel supply (low pressure)
Your FIP can only fuction properly when fuel is supplied with sufficient pressure AND volume and should be your first quick check.
Fuel pressure is measured at the CSV .Simply loosen the fuelline and hook up a pressure gauge with a piece of tubing. Pressure should be 0,8-1,1 bar
Fuel volume is measured at the returnline where it enters the tank. Volume should be close to 1 litre per 15 seconds which indicates adequate circulation all the way up to the tank entry .
The fuel tank :
The fuel tank may be a simple container in most cars, but in our SL's it is almost a piece of German (over)engineering and is a frequent troublesource.
Think of misfiring, stalling engine with a partly filled tank,vapour lock or starvation..
Take a look at the fuel tank tour first (
https://www.sl113.org/forums/index.php?topic=1712) for how it is designed and you know what I am talking about next.
Starting at the top rear end of the tank there are 2 pieces of metal tubing connected to the fuel expansion or overflow reservoir, but they also function as a fuel tank vent. Easy access by removing the
fillerneck cover in the trunk.
If clogged and fuel is used when driving it may after time create a vacuum in your tank and reducing the fuel supply and cause stalling.Open your fuelcap and when you hear a "whoosh", you found your problem
Fuel to the engine is taken ONLY from the "flowerpot" , so it should contain fuel all the time. Fuel flows towards the electric fuel pump via the large filter/strainer/drainplug in its center . Clean or replace it if necessary .Check the metal fuel supplyline going out of the tank for contamination/clogging as well.
The flowerpot is (re)filled in 3 different ways:
a. by returned excess fuel from the FIP via the metal returnline to the bottom of the flowerpot . An obstructed returnline prevents returned warmed up fuel from the FIP,causing the FIP to heat up and cause vapour lock. More to this later.
b. if your tank is more than about half full it fills mainly over the upper rim ,.
c. via the port/opening next or under the returnline entrance of the flowerpot. Clogging of this opening by rust or particles may cause stalling in a lower fuel quantity situation due starvation .
2 words of caution: first ,on internal recoated tanks,if not done properly, openings and fuel/vent lines often end up obstructed .Second ,microscopic rustparticles from your tank entering the fuel system may cause
erratic running behavior which can drive you crazy.Tank cleaning is often only a temporary solution ,if at all.
Clog help topic :
https://www.sl113.org/forums/index.php?topic=11754.msg79061#msg79061The fuelpump (short or second version only)
Fuel from your tank is gravity feed to the electric fuel pump,so your pump should always be lower than the tank.Fuel enters the pump via the hose union with a built-in filter/strainer. This filter is often overlooked and may get clogged and hamper fuel supply.
On the exit side there is a springloaded checkvalve to prevent backflow of fuel.Check if it is functioning. These pumps are "wet running",meaning the motor compartment is filled with fuel. The pump must be able to produce pressure AND volume at the same time as mentioned above. If not , first check fuse nr.4 and see if you have at least 11V at your pump with ignition switch in "run".You should observe a steady humming of the motor within a few seconds.If no sound,either the motor has failed (windings,brushes or rotor) or you may have a stuck impeller due contamination.If the motor and impeller are still OK cleaning an rebuilding is not extremely difficult.If the bottom cover has scores polish it to a flat(!) and even surface. To prevent cavitation install the impeller with the sharpest side of the teeth UP, so to the motor side. Use new NBR O-rings These are fuel/oilresistant Buy them for just peanuts in a good hardware/machine shop .Complete or partial rebuilt kits seem to be available as well. Check for leaks after assembly and repeat the pressure and volume check.
https://www.sl113.org/forums/index.php?topic=3659.0 https://www.youtube.com/watch?v=PkC8WQd3_H4 Fuel filtering
The most important filter of the fuel system is the main fuel filter.Remember the two other fuel filters/strainers ? ( in the tank and in the electric fuelpump)
There are fine mesh filters in the CSV inletcoupling and inside the 6 injectors. They may get clogged by varnished fuel over time. All 10 (!) must be clean ! Need I say more ?
* Fuel circulation /return fuel and pressure regulation
A very important element of the fuel system. Your electric fuel pump provides a ( basic) fuel pressure and a relative high volume of fuel to the FIP.
Why the high volume ? The engine doesn't need so much ! Short answer is : cooling . Only a small part of the fuel supplied by the el. fuel pump is used in the FIP to actually run the engine, even at high rpm.
The remaining largest part is used for circulation via the FIP pressure regulated outlet and return line in order to keep your FIP running at a moderate temperature. Imagine driving on a hot day and/or in stop and go traffic. The engine compartment gets very hot and without fuel circulation the FIP really heats up . At a certain temperature or low pressure the fuel tends to boil , airbubbles form and block the fuel supply ,a phenomenon called "vapour lock " causing poor running /stalling/hot starting problems. Note : modern ethanol fuels have a lower boiling point ,so cooling thus circulation is nowadays even more important !.
2 simple checks :
1.remove the fuel cap,loosen the return fuelline from the pressure regulator at the FIP outlet. Blow air through it. If you hear bubbles in your tank your return lines are open.
2.Fuel volume is measured at the returnline where it enters the tank. Volume should be close to 1 litre per 15 seconds with el. fuelpump running.
The correct supply fuel pressure (0,8-1,1 bar) for the FIP is achieved by the adjustable springloaded regulator valve,maybe strangely enough, on the FIP outlet. Check it for sticking or leaking (you may try lapping the tiny valve) and adjust if required. I bench tested it using compressor air ,some hoses and my fuel pressure gauge.Install it when done and recheck pressure at CSV inlet.
By now you should have a better understanding about the most common problems. Hope this will have helped you !
If you observe anything incorrect in my text please PM me so I can adjust it.
TO BE CONTINUED AT A LATER DATE : CSV ,FUEL INJECTION PUMP (FIP) AND INJECTORS
Happy motoring
Rob "rosch"
Halle ,Netherlands
