1975 450SEL Request for Help to Get Running

[TwitchKitty]

I have volunteered to help a friend get a 1975 450SEL running after the car has been stored for awhile. I am not sure how long. I have not tried myself to make it run so I am after general systems information for now.

The data plate under the hood says it is a 276ci engine. By searching old threads and reading the scarce reference material I have on this car I think it is an M117.983 (4.5L). I think the body is a W116.033.

This is a V8. The injection is electronic and I think it is L-Jetronic. The distributor has ignition points.

Do you have any favorite threads you could point me to for this car? Searches came up pretty thin.

1) Is the ignition a straight points ignition with no interface to the controller?

2) Hydraulic lifters or solid? I think solid?

3) Electric fuel pump? Not in tank?

He told me that when he tried to start it the car would run for a few seconds and die. It may have run a few minutes one time. He says he thinks it has an ignition problem. We shall see.

Thanks if you can offer any insight or experience.

One thread that I read lamented the lack of these cars remaining on the road. I will be happy to help this one run again and document my experience here to possibly help the next person who tries.

[TwitchKitty]

Went to have a look at the car.

Decided the injection is D-Jetronic and the controller does not affect the ignition. There is an interface for the injection that ties into the distributor. It looks like it provides the pulse for the ignition and has an engine speed signal of sorts. Five? engine speed signals?

Pretty sure it has no hydraulic lifters, the tag under the hood has valve clearances on it.

Since the injection is regulated by vacuum I am guessing that this car will not run worth a hoot if the valves are not adjusted properly.

[psfred]

OK, here's the skinny:

Drain the tank. The fuel pump is underneath the rear seat, driver's side, I believe. Get as much of the old gas out as you can, it isn't going to burn by now.

Put in at least 5 gal of fresh fuel, then add a bottle of Techron or RedLine fuel injector cleaner and jumper the fuel pump. Someone else will have to help with fuel pump relay location, I don't know where it is on the W116s. Run pump at least half an hour, then try to start. Make sure the pump is actually running properly, too.

The ignition is transistorized, the points are just a signal to the switchbox to operate the coil. Start and then failure to run is often a bad connection on the ignition resistors, there are two. If the connection at the first one is bad, you only get spark while cranking. You may want to clean the points by dagn a slip of paper through them. Don't pull it all the way out, or you will leave shreds in there and the igition won't work.

You can check for operation of the EFI by listening for the injectors clicking while cranking (you may need to pull and ground the coil to distributor lead to do this). If they click, the EFI is working.

Once you get it running, you need to drive out all the fuel in the tank and refill with fresh premium before doing any more troubleshooting. I'd also plan on new plugs, the ones in there will probably foul from the rotten gas.

Once you get it running, we can give you more ideas.

Peter

[TwitchKitty]

Thanks, lots of good info. Sounds like I would have gotten nowhere with that ignition.

A search for ignition resistors is turning up much better info than my earlier searches.
My 1972 280SE 4.5 V8 still won't start
My 72 sl surges when the engine is cold
D-Jetronic

[wbain5280]

I would have to opine, fuel pressure regulator. If the internal diaphragm leaks, engine vacuum will pull the fuel right into the inatke manifold. Take the vacuum line off, turn on the key and wait for a leak.

Change your oil, get the gas out of the manifold and keep a fire extinguisher handy, preferably with an assistant.

[Tomguy]

Warren, I don't see how that's possible... maybe with mechanical injection but, with D-jet, the injectors cannot release fuel unless a pulse is sent to them. They're under constant pressure. If a vacuum of 14" would pull fuel out of them, then no 4.5 would ever run

It sounds more like a fuel problem than an ignition one to me. Specifically, trigger points. It sounds like it fires off the cold start valve, then dies out after it kicks off. Clean and inspect the trigger points:

1) Rotate engine to where the distributor rotor lines up with the notch (~TDC) or another spot you can remember.
2) Remove the set screw for the distributor, as well as the plugs for the trigger points and ignition points, and vac retard line, and pull the distributor out.
3) Remove the 2 screws holding the trigger point unit in.
4) CAREFULLY clean with an index card or similar stiff paper, or contact cleaner. Inspect wires to make sure all connections work. Put a SUPER light coating of grease on the rotor (I put the tiniest bit on the highest part of the two lobes, maybe about 1/2 of a mL at most) and reinstall everything

[TwitchKitty]

Mercedes Benz 4.5 Transistorized Ignition
Voltage test:

block points open with something non-conductive. Check voltage to ground at both coil connections and both resistors. Should have battery voltage at all points. If you have voltage on one side but not the other of any component, it's broken, replace. If you have something other than battery voltage, unplug the transistor unit and recheck -- if you now have battery voltage, switching unit is bad (in which case, a Crane or Pertronix system is both better and cheaper than fixing the factory unit!)

Points closed testing:

Attach red lead of voltmeter to terminal 7 of junction block (green wire). Attach black lead to distributor housing. Ignition on. Less than 0.1V, points good. More than 0.1V, clean or replace points.

Attach black lead to ground, check voltate at terminals 15 (resistor side) and 1 (switching unit side) on coil. Voltage must be 8.2 to 9.0 on termnial 15, 4.8 to 6.3 on terminal 1. If not as specified, check resistance of coil and both resistors. Coil should be .38 to .43 ohm, 0.4 ohm resistor .35 to .43 ohm, 0.6 ohm resistor .55 to .65 ohm.

Voltage drop of switching unit:

Attach black lead to ground, red lead to 0.6 ohm resistor connection going to swtiching unit. Voltage must be less than 2.5 V. If higher, switching unit bad.

It is possible to wire the points directly to the coil for troubleshooting. unplug the swtiching unit, then connect a wire from terminal 7 to the side of the 0.6 ohm resistor that goes to the coil with a 1 ohm resistor in series. This replaces both resistors with a single 1 ohm resistance and uses the points to switch the coil.

If it runs with the points connected directly, you must either replace the switching unint (if you can find one), repair it -- it's usually the big switching transistor that's gone, or get a breakerless unit (Crane and Pertronix both sell one that fits).

I extracted the above from this post
http://www.peachparts.com/shopforum/showpost.php?p=500215&postcount=11
by psfred and gave it to my buddy for testing. He says that the transistor unit is bad by these tests. Later in the same thread psfred said that it is possible to replace the transistor. The part number (0011 2/30) on the transistor cannot be cross referenced. I need a part number for this transistor.

http://www.peachparts.com/shopforum/showpost.php?p=515880&postcount=18

This is the link to the post where psfred says the transistor can be replaced. Anyone done this? Any chance I can get a part number for the transistor? There are several electronics supply stores in town I don't think it will be a problem to get a transistor when I know what I need.

Psfred, you out there? Thanks for your help on this.

Thanks for the rest of the posts in this thread also. There is a good chance we will get to these other tests before this is over.

[psfred]

You will have to do a search, I didn't write down the Radio Shack number.

Fat chance anyone at Radio Shack would know beans about electronic parts these days, but what you want is a high voltage high current switching transistor.

I believe someone posted the part number.

Peter

[TwitchKitty]

Thanks, I have run many searches with no part number. What would you use for search terms? I tried the obvious like: 4.5 transistor, 450 transistor, etc. There probably is more information out there, most of the posts that mention it are posted by psfred. Did you possibly get this from another web site?

We can crack open a few of these boxes and try to find a number that way.

RadioShack is not what they used to be. They had one transistor with that packaging in their catalog and it had two terminals instead of three. I don't think they will be of any help.

Do you know of anyone that rebuilds/refurbishes these things? They would know the number.

Here is a link to a thread where someone else was looking for the number.

http://www.peachparts.com/shopforum/showthread.php?t=45456&highlight=ignition+transistor+part+number

[MunichTaxi]

I believe what you are calling the Transistor unit is actually named an Ignition Module. It is silver colored and approx 3 inches square.

[TwitchKitty]

Yes, I posted a couple pictures of the ignition module above. I am calling it by several names, sorry for the incoherence.

The following is a post I clipped from another thread:

erubin said:

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.

[wbain5280]

I must have been thinking about another post where the intake manifold was filling up with gas.

[psfred]

I ran a bunch of searches my self later and couldn't find the thread, either.

It is an NPN switching transistor, TI and NEC both make them in a TO3 case. I've not had one of these apart, is it a silver can with two "ears" on it, or a squarish thing with a heat sink tab? Only difference is the case, I think.

There's not much in there, three resistors, a diode, and two transistors making up a Darlington pair. I'd bet a 40W NPN switching transistor will work, this ain't rocket science!

If it doesn't, try a lower wattage rated one.

Peter

[TwitchKitty]

Thanks again for the replies, I posted a picture of the ignition module and the transistor in one of the replies above.

I got a suggestion for a replacement part number in this thread:
http://www.peachparts.com/shopforum/showthread.php?t=45456

I will post here after I give this a try.

[arkie]

Mercedesshop has the remanufactured units (kind of pricy, but if you want to keep it original this is what you need). You can match it up by Bosch part number.

http://catalog.eautopartscatalog.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=1A417YEBZ&year=1975&make=MB&model=450-SEL-001&category=F&part=Ignition+Control+Unit&appChassis=_any