QuestionQUESTION: I am asking this question for my Dad....he is restoring a '76 450sl....it starts.....runs well for about a block (2000 rpm's or so), then drops the rpm's and stalls....it can be restated immediately with no problems....only to do the same thing again....any help would be great...I am tired of googling!
ANSWER: fuel delivery needs constant pressure from the fuel pump and then the regulator delivers it to the injectors. Need to ensure fuel pump spins up and continues output, then if that is ok check fuel delivery at the fuel rails.
DOes this happen if it just sits and idles?
What about if it is sitting and you raise rpms, same result?
Could be pressure plate on intake sticking and not allowing air flow
Check by pushing down on plate , should go sown easy and feather back up. Lots of other reasons, just need to eliminate the basics first
Let me know and I can help some more
Ron
---------- FOLLOW-UP ----------
QUESTION: Thanks for your super quick response.
-The fuel pump is new
-The regulator is new.
-The fuel rails have been checked.
-The fuel pressure on the high (@80 lbs) and low (@45 lbs), check correct.
-It idles very rough....but does not die...or at least hasn't yet.
-While sitting idle and raising rpm's it DOES do the same thing.
-however...the pressure plate goes down easy, but does not "feather up".....it pops back up without resistance.
-Their is a plunger in the fuel distributor and he is not sure exactly how it works? thought it may be sticking....so he cleaned it....no change.
The car did sit for around 10 years without being started.
Dad did clean the fuel tank, and found no rust.
Answerhere is some (lengthy) information that may help. Sound like fuel deivery, have the injectors been checked?? What color are the plug tips? I have a nice PDF on the Kjet, that explains all the parts and functions, if you send me your email I will send it to you
Idle Bad with Cold Engine
1. Leaks in air intake system:
Check all air intake and vacuum connections. Any old hoses must be replaced.
Be sure to check the intake boots around the intake runners. Check all hose clamps.
Replace any collapsed hoses.
2. Auxiliary Air Valve does not open:
Check the hose connections to the valve. If these check good remove the valve and
check for leaks by closing off one end and applying a small amount of suction to the
other end, if air can be drawn through the valve, with the other end capped off,
replace the valve.
3. Cold Start Valve leaking:
Remove the cold start valve, located in front of the intake. Leave the fuel line connected,
place the valve over a container, disconnect the electrical connection, apply 12 volts
to one of the connections, apply a ground to the other side, look for an even conical
spray pattern, turn the power off, wait a few seconds, there should be no leaks. If
the pattern is not correct or the valve leaks, replace the valve.
4. Cold control pressure not correct:
Check the warm up regulator. I would look for a pressure of at least 1.25 -1.50 bar
(18-22 PSI) at freezing temperatures. Be sure to check the pressure coming from the
mixture control unit.
If the pressure is not correct, do a complete check of the warm up regulator.
5. Injector Leaking:
The opening pressure could be to low, opening pressure should be around 2.5-3.6 bar
(36-52 PSI). Check all the injectors for evidence of leakage. Test for opening pressure.
When you reinstall the injectors be sure to replace the o-rings.
6. Injected Quantities low:
Compare the fuel quantities of each injector. Place each injector over a container and
record the amount of fuel each produces at a given amount of time. They should be equal.
7. Basic Idle incorrect:
Check and rest the idle per the specifications. It is best to set it when the engine is warm.
Check the co output, also.
8. Fuel Leaks:
Inspect all fuel connections.
9. Fuel injector Clogged:
Pull the injectors and inspect for correct operation. Apply power to the fuel pump,
jump the wire terminal numbers 30 and 87a. Caution fuel will flow from the injectors
when the air flow plate is moved in an upward direction. Check for correct operation.
10. Control Plunger in the fuel distributor binding:
Remove the air cleaner and carefully move the plate up and down, do not force the plate.
If it binds investigate. If it is not simple to repair replace the unit.
11. Idle speed, Ignition Timing, and mixture out of tolerance:
Check and adjust all of the above.
12. Faulty Ignition System:
Check the ignition system. 1973-1977 check point gap .016, correct plugs see chart,
Condition of cap and rotor, 1978-1983 check for a distinctive hum in the CDI with ignition
on in engine compartment, (if no hum the CDI may be defective) CDI is the ignition
module located on the relay panel in the engine compartment left side.
Misses and Hesitates under a load
1. Fuel pressure incorrect:
Test fuel pressure.
2. Fuel injector clogged:
Same as above #9
3. Control Plunger Binding:
Same as above #10
4. Incorrect ignition timing or faulty ignition system:
Same as above #12
5. Clogged Fuel Filter:
Check the fuel filter. Replace if necessary.
6. Faulty injector:
Test all injectors for quantity and leaks.
7. Vacuum leaks:
Inspect all hose connections and clamps. Replace all old and loose fitting hoses.
8. Fuel Pump not working:
Check for voltage at the pump. If no power check the fuse and the relay.
Replace if necessary.
If there is voltage at the pump and it is not running replace the pump.
9. Warm Control Pressure too high:
Check for at least 40 PSI with out vacuum on the warm up regulator and 46 PSI
with vacuum on the warm up regulator.
10. Warm Control Pressure to low:
Check for at least 40 PSI with out vacuum on the warm up regulator and 46 PSI
with vacuum on the warm up regulator.
Hesitation on Acceleration
1. Air flow sensor plate not positioned correctly:
Check the plate. Remove the air cleaner and air intake. Check for at least a .020 clearance
between the plate and the bottom of the barrow. 1973-1976 adjust the clip. 1977-1983
adjust with a screw driver.
2. Fuel pressure not correct:
Check for pressure to be at least 66 PSI.
3. Fuel injector clogged:
Test the fuel injectors for quantities at a given time.
Jump terminal 30 and 87a to run pump.
