67 250S firing order
 

I've been looking for the firing order for my 67 250s with the carbureted 2.5L straight six. All I'm finding is Ford engine orders. I've worded it many different ways and still only Fords pop up. Does anybody have a diagram of the firing order?

15, 36, 24

too young, too old, just right

Okay I have the firing order correct then. Is there a certain starting point on the distributor? I can smell it getting fuel, all the grounds are good, and all the wires, plugs, cap, rotor, and ignition coil are new.

Okay, so, the firing order is now correct, new plugs, new wires (fully secure), new cap, new rotor, new ignition coil, it's getting fuel, all the grounds are good, timing is dead on.

I noticed fuel is starting to pool around he carburetor next to the firewall. Not sure why.

It cranks over but it still seems to have no spark. All the fuses are good as are the relays.....I'm out of ideas....any help?

How has timing been determined to, in fact, be "dead on"?

If the coil wire is removed from the dist. and held ~1/4" from a ground, is there spark when the engine is cranked? If so, is there also spark at each of the plugs when cranking?

I had my neighbor come over and take a look at it when I first got it because he's been working on these for years and he said the timing is "dead on" so that's not the problem. He gave me a list of things to check before he left and I've gone over all of them.

I'll check the wires for spark again to be sure 100%. In the morning I'm going to rent a compression tester and see if that's the problem. The oil and coolant aren't mixed and I see no spots on the ground under the engine from leaks.

Okay so I just tested the ignition coil plug wire and it give off a very very very faint spark. I also tried one that I know for a fact is good from my 72 because it ran before I pulled the engine and it did the same. So it's something with the spark not being strong enough.

From what I can find, the 250S has points/condensor type ignition system. Points not adjusted correctly or a bad condensor can cause weak fire from the coil. I have worked on many old domestic cars and trucks, but not on old Mercedes. Maybe some of the older forum members can chime in about these old systems.

Paul

Lo-Key:

The questions about spark quality were the first steps; now that you know that the spark is very weak, the next question is why. pmc has started you down that path; point cleanliness, correct gap, and condenser quality are some of the factors. Also, what is the voltage at the hot side of the coil, both with key on, and when cranking? This is a step-by-step process; there will probably be a few iterations.

I remember my old 220 firing order was stamped on to the engine block. Look for "zündfolge".

RayH

It's generally on the valve cover.

yeah I found it on the valve cover after I asked then felt stupid for asking haha.

I'll swap the ignition components from my 72 over to this one to see It helps any. I'll check back in after I do so to let you guys know if it's working or not. Thank you guys for he help so far.

Alright.....so I swapped over the ignition coil, wires, and all the relays. Nothing changed. There's still only severely weak spark. I did notice though that the ignition coil is getting really hot. I accidentally put my arm on it and it burnt me.

Lo-Key:

Suggest you re-read post #9.

I checked the point this morning, it's burnt. I have to go back to the part store tomorrow and get another one again, they gave me the wrong one.

You know, that's how I used to remember it for years. At least, until about the first time I had a girlfriend turn 30... Then you didn't really want to go repeating that handy mnemonic real often.

MV

if your CB points burnt out then your condenser is shot, the condenser's job is to prevent arching on the CB points.

The other case in burnt points is using a coil whose impedance is too low, but you did mention weak spark- which is a bit backwards in this case.

does your coil also have a resistor in series on the positive side? and does this system also include a bypass for starting on full juice.

Pretty much everything has been replaced with brand new parts as of now. Plugs, Wires, distributor cap, rotor, ignition point and ignition coil. I'm installing he new point tonight and in the morning running down to get a new condenser. If the spark is sill weak after all of this I really have no idea what's left to replace.

I would get a new condenser (capacitor) anytime the CB points are changed, what is the impedance of the coil primary circuit?, if its a built in resistor type and you have an external one too, your ignition system will be pretty feeble.

Before spending any money I would test spark at the spark plug boots, use a screwdriver and lay it across such that it has a 1/4 inch gap to shoot the spark to ground. You should see strong blue sparks making a loud clacking sound

I'm going to test the spark again tonight. I had the part store order a new condenser from the wear house. They said I can pick it up in the morning anytime after 7:30am. There is a cylinder type deal connected to the ignition coil, I'll get a picture of it, with it connected the car now back fires every now and then but wont start. It back fired out of the exhaust twice and once out of the carb.

I have a few different ballast resistors That I've tried and I know the others are good hat I have and it hasn't worked

Could the ignition timing be off? I'm running out of ideas on what to replace and check. Once I put in the condenser I'm not sure there is anything left to check.

Lo-Key:

Do you not recall these words? The situation would seem to be that the timing is not "dead on", but rather in the condition of Monty Python's parrot: Just plain dead.

I'm speaking of the distributor timing I should of been more clear on that. I'm not sure if it's retarded or advanced too much. I'm not really sure why else it would just back fire and not start. I noticed there's a fine adjustment piece on the distributor. I'm not sure if it's set properly or is off a bit.

you can get a tablet shaped largish 0.47U capacitor from radio shack to replace the condenser to test the low voltage system.

the cylinder type deal you mention on the coil maybe the resistor, most MB resistors I have seen are a ceramic piece like the one used in later models fan wirings.

If you are getting backfires then either your ignition sequence or timing is wrong (I had that once in a Honda, the distributor cap fit perfectly but was of some really odd ball model whose firing poles were offset - this caused the ignition timing to be completely out of sync)

I know the engine timing itself is set properly but I'm not sure about the distributor. The firing order is stamped right on the valve cover so I know that's correct as well. I'm not sure how to go about adjusting the distributor though.

Lo-Key:

From the outset this thread has been about the ignition system, and in that context the use of the word "timing" would be understood to refer to the timing of the spark. Are you using the term highlighted above to refer to the camshaft timing? If so, that is interesting, but not entirely germane to the attempts being made to solve an ignition timing problem.

In an earlier post you indicated that you were going to test the compression pressures. Did you do that? What were the results? Have you adjusted the valve clearances? Valve clearance will affect compression pressure.

You were also asked about the presence of external resistors in the primary circuit. Yes/No? Value of resistors? What is the internal resistance of the ignition coil?

From the accumulated posts I believe that the position of the spark plug wires in the dist cap is in error. Do you know how to position the crankshaft so that #1 & #6 pistons are at top dead center (TDC)? If you do know how to find TDC, do you know how to determine if #1 or #6 is in firing position?

If you will supply us with a few answers, it will help us help you.

Unless it has been verified with a timing light on a running engine, yes the ignition timing could be off. If you are getting a fairly strong spark and the engine still won't run, I suggest you start over on getting the ignition timing right.

If you don't have a timing light, or or too young to have ever seen one, then do an Ebay search for 'ignition timing lights' and see if you can buy a good one with a Xenon light since you need one that is brighter than daylight.

Setting the ignition timing is easy with the light, but you have to have the car running. Set the number one piston to top dead center and then position the distributor, with the cap off, so that the rotor is pointing at the plug wire tower for the number one piston. This is known as the initial setting and should get the car to running even if it is running poorly.

Do some research on setting ignition timing and you will find more info than I can give you here.

I think the first order would be to check the crank pulley for TDC for cyl 1 - Mercedes Benz usually mark their pulleys with a lot of markings and one being OT - the OT = top dead center for cyl 1.

the OT will coincide twice on the marker, once on compression (aka power) and once on exhaust, you need to make sure the cylinder is on compression (as if you wanted to set the valve clearances for cyl 1)

now remove the distributor cap and see where the rotor is pointing - that is cyl 1 for you. Install cables into the cap according to the "zundfolge" sequence.

And make sure you know which way the distributor rotor turns. This should be in the manual (next to the firing order), but if not or if you don't have the manual you can find out by cranking the engine over with the distributor cap off.

I had it towed to the garage I do bodywork at and asked two of the mechanics there if they could check it out for me over the weekend well we were closed. They said everything checks out but there's no power going to the ignition coil and they could smell burning wires but were unable to pin point where.