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Marty, Mercedes Technician
Category: Mercedes
Satisfied Customers: 53904
Experience:  Bosch Certified Master Tech. Over 35 years experience.
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1976 450sl crank. No start,if I crank and feather gas pedal

Customer Question

1976 450sl crank. No start,if I crank and feather gas pedal it might start and run a few seconds then pops big fireball thru intake
Submitted: 1 year ago.
Category: Mercedes
Expert:  Marty replied 1 year ago.
Hi, it sounds like your control pressure may be incorrect. Control pressure is determined by the warm up regulator. If the regulator fails the control pressure will be too high and the car will be hard to start and will not accelerate. You need to get a fuel pressure gauge connected inline between the top line of the fuel distributor and the warm up regulator. The pressure on that line when the car is cold should be around 30 psi. If the pressure is up around 60 - 75 psi you will need to replace the warm up regulator.
I'm assuming that the car has been running regularly before this happened. Other common problems on the old SL's are a plugged fuel tank and low overall fuel pressure. A simple test is to pour a little fuel into the intake and see if it will fire momentarily. You can also use a starting spray to see if you can get the car running for awhile when using the spray. If it runs on the extra fuel or the spray your problem is with the fuel delivery through the fuel distributor. The fuel pressure test is the first step in determining the problem.
Let me know if you have any questions.
Customer: replied 1 year ago.
no car hasnt run since i got it i thought timing , i replaced fuel dist because motor oil was full of fuel and plugs n oil, the flooding issue is gone. but wont run n pops fire thru intake if i pump the gas
Expert:  Marty replied 1 year ago.
Ok, the warm up regulator would be the next thing to replace. I'd get myself a CIS fuel pressure gauge so you can check your pressures but if this car has sat for a long time you can pretty much count on having to replace the warm up regulator and the fuel distributor and usually the fuel tank. If the car will run on fuel that you pour directly into the intake it tells you that the ignition system is okay and your problem is with the fuel system. I'd disconnect the fuel pump when trickling fuel into the intake so the only fuel that goes into the motor is the fuel that you are trickling into the intake. I would not pour fuel while you are cranking in case of a backfire. Just pour a little into the intake and see if it will fire for a few seconds.
Customer: replied 1 year ago.
ok did that already and it don't run
Expert:  Marty replied 1 year ago.
If you have disconnected the fuel pump and tried running it solely on fuel that you trickle into the intake or by spraying ether then you need to go through the ignition system. Make sure the plugs, cap, rotor and wires are all good and that the firing order is correct. Put the motor on TDC and make sure that the distributor rotor is pointing at #1 cylinder in the cap. If it's backfiring it sounds like your firing order or timing may be incorrect or the cap and rotor is bad.
Customer: replied 1 year ago.
ok is there a mark on crank n where
Expert:  Marty replied 1 year ago.
there is an O|T mark on the pulley for TDC and the pointer is at the top right as you are looking down at the pulley.
Customer: replied 1 year ago.
marty, put at 0 degrees and dist at number 1,even with jumper on it cranks slow and neg term get hot,sprayed ether in and no change,did start months ago while cranking and feathering gas pedal ,ran for seconds than pop thru intake fire ball
Customer: replied 1 year ago.
can it be 180 out,the dist I mean
Customer: replied 1 year ago.
do you have any info on dist where number 1 is and number one plug ,I cant find it
Expert:  Marty replied 1 year ago.
There is a line on the body of the distributor under the distributor cap for #1 cylinder. Number 1 cylinder on the motor is the front right (passenger side) cylinder.