help with my 72 350sl starting
 

hello folks

note: this is a 72 so it has the electrical fuel injection no fuel distributor.

i got a problem with the 350sl. tried starting it up but nothing. it turns over just fine. ran just fine last time it was moved. plenty of battery. plugs are fine.

i've checked the voltage and resistance of the coil it was at the top limit of resistance so i replaced it. every thing from the cap to the plug is almost new and the plug wires are new bosch.

the fuel pressure is where i can not give an actual psi. i can say however there is no 50 psi. it flows but no where near 50 psi.

i've even sprayed starting fluid down the throat but not even a cough.

this is what i do know. the secondary voltage is way down. ground a plug and turn it over the color is yellow at best. now this is strange. the plug does not actually jump from the center electrode to the tang. it arcs sideways to the base of the tang. in fact you don't really see the arc very well because it is going sideways. i attached a bmp for you to see. i know that sounds crazy but that is exactly what is happening.

as for the trigger points i don't know yet. i had to come to work to get my longer metric allen keys so i could pull the distributor to address the points.

one last thing is for all the turning over i was doing there never was a wet plug pulled out.

i guess it boils down to the poor plug arc and maybe the trigger points are not releasing fuel. i'm sure the gas flow is sufficient to start and run the car. i only move the car in and out of the garage so i can get to other stuff and that's all it's run about 6 times in the last 2 years.

can anybody shed some light on the plug arc thing i've got going. i've never seen an arc so poor and going sideways.

help i'm stuck and i can't get it out of the garage.
tks
craig

well i hope this takes

Your car was equipped with a transistor box under the fender. It is part of your ignition system. Maybe that is the problem?

Mine went bad many years ago and the cost to replace it is rediculous even by third party outfits. Two options around this that I know about:
1. convert over your system to standard breaker point ignition. This is the lowest cost approach as you will be bypassing the defective transistor box and ballast resistors. You will have to replace your coil with another model coil (if you need the Bosch model number I can look it up) and you will have to use a condensor like the one that originaly came with your car's distributor but was later eliminated by MB mechanics. The condensor can be special ordered at Pep boys for your car for about 3 dollars instead of about $60 at MB. Don't worry about the performance of the condensor from Pep Boys it works fine. The job of the transistor box is to add longevity to youir points by minimizing the point damage (arcing?) during car starting. Points are so cheap and don't need replacing that often anyway (I do it every 12K) that I consider it a very small price to pay. My 1972 350/450SL runs fine at all speeds with this "fix".

2. The other solution which I would do if money didn't matter is to change over to an electronic ignition system. Check out this website: http://www.durranceeng.com/
He really seems to know his stuff and the site is packed with info and he can sell you what you need.

Regarding the trigger points at the base of the distributoir:
They have nothing to do with the ignition system. They control the fuel injection. Take them out and clean the points with an ignition file. Since they operate at low voltage (unlike ign points) they last a real long time. They are very expensive to replace (unlike ign points). I don't recall but there are either 2 or 4 points. Some of the points you can get to but one or two are covered in a small plastic box. To get to that point you need to cut a slot into the transparent plastic box to allow you to slip in a small ignition file. I don't recal if I used a mini solder tip or my dremell to make the slot.

Good luck

erubin


tks much for the reply. my 350 does have the std point system with an external resistor coil. i will get the distributor out tonite i made a taper hex socket wrench to drive into the socket head. the shop for the po kinda rounded this puppy out.

do you have any idea why the plug spark is so weak and weird? i attached a hand sketch of how the spark is arcing or not.

i figure i'll see some dirt etc: on the trigger points. the plugs were not wet at all even after cranking it a number of times

tks much for any help
craig

You've only started the car 6 times in the last 2 years? I wonder how the gas is. I learned back in my lawn mowing days to empty the gas tank over winter else a varnish would set up making it hard to start in the spring. I wonder what that old fuel is doing to your injectors.

You said <<every thing from the cap to the plug is almost new>>. But what about between the distributor and the cap. How are the ignition points, condensor and ign rotor. It seems you have a weak spark. If you've not changed the points then check if they need cleaning with an ignition file.

You said <<my 350 does have the std point system with an external resistor coil.>> I already know this. You have a Breaker-Controlled Transistorized Ignition. I know it has points but it also has some other ignition parts you may be overlooking. Are the two resistors (1-2 inches long one is white and the other I recal is blue) on the left inner fender in the engine compartment and the Transistor Switching unit found in the wheel well bypassed? If the system was not bypassed have you tested it to be certain that is not what is causing your poor spark?

If it was bypassed then you may have the wrong replacement coil in addition to your other problem(s). In a bypassed system a different coil is needed then originally called for in your car.

erubin

you know now that you mention it after i saw the points and the condensor i quit looking farther up the line. you're right on the 2 resistors and all i have are 2 old chilton and some other type books. naturally my home computer is down so i don't have my cd's available.

ok as soon as i get home i'll look for add'l components.
tks
craig