1967 250 se

[Anthony Cerami]

Hello All,
I have a 1967 250-se coupe. (F/I) The car runs very rich lots of black smoke.
There are two obvious problems. I think that they are related. First, in the trunk there is a black canister with three hoses. Two on one side, and one on the other. Two lines appear to connect to the fuel tank neck. The other????? There is no evidence where the third hose attaches. I have no idea how or where this canister mounts. Maybe near the taillight assembly. There must be a bracket missing.
Can someone please post some pictures? Where would the third line go? Is it a vent? Back to the engine?
Second, the engine appears to be a 1968 280. There is a switch on the throttle body passenger side that is not connected at all. Two maybe three wires seem to attach there. However they are cut off. Just a stub remains. There is no harness or wires near this switch. Since this not the original engine there may not be a connection at all. What does this switch do? What is the difference between the 250 and the 280 throttle bodies? Maybe the 250 did not have this switch. Pictures of this area may help.

[Anthony Cerami]

In the trunk there is a black canister with three hoses. Two on one side, and one on the other. Two lines appear to connect to the fuel tank neck. The other????? There is no evidence where the third hose attaches. I have no idea how or where this canister mounts. Maybe near the taillight assembly. There must be a bracket missing.

[300SDog]

Backing up to my fintail days..... can recollect the breather apparatus is meant to condense otherwise evaporated fuel, i think they call it a 'fuel evaporator' in the book, probably filled with internal baffles. It's possibly the only silly and ridiculous component of the fintail era where almost nothing superfluous found its way into MB automobile design.

The thing should attach to metal clip/cut out attached to trunk cardboard (111 sedan), but dangles free when cardboard warps as it always does.

On running rich with lotsa black smoke.....

First, I'd suspect injector pump timing is late and blowing alot of unburnt fuel (diesel logic) through the chambers. Next, I'd be thinkin sticky/worn injector tips are pissing fuel into the chambers with incomplete vaporization. Yep, IP timing would be my first guess but you should probably check valve clearances first by way of protocol to eliminate other variables. And how do the spark plugs look??

__________________
'80 300SD/ w116
'79 240D 4-spd
'71 750cc Guzzi

previously owned:

'83 240D 4-spd
'77 280SEL 4-spd
'74 280/8
'72 250/8
'65 220Sb 4-spd
'63 220Sb 4-spd
'63 190c 4-spd
'61 220Sb 4-spd
'60 190b 4-spd

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Last edited by 300SDog; 06-21-2004 at 11:36 PM.

[wbain5280]

The engine uses port injection, before the valves, not direct injection like a diesel so injection pump timing is not important.

The black smoke may be caused by a leaking cold start valve, or possibly always on cold start valve. There are realys on the firewall or a bracket that control it. You need the engine schematic, which is really simple btw. Use a voltmeter or test light to see if the CSV is always on.

It could also be mis-adjusted linkage.

As for the switch, it's an emissions related switch that does not apply to your 250SE.

Since it's a 280SE engine in a 250SE, things may be improperly connected.

[Anthony Cerami]

Thank you Waren and Diesel dog.
I actually found another 67. The switch in question in fact does not belong. I will however look into the CSV and the wiring, The relay for the CSV has scotch tape on it. Himmmmm. Looks like someone has repaired it with a hammer!
Is there an idle adjustment on the TB.? How do you set it? (800 RPM)
As for the 'fuel evaporator'. Does anyone have a drawing or a picture of how the lines are connected? Two lines connect to the fuel tank neck. The third is a mystery to me.
The cardboard is missing in the trunk. A photo of each side would certainly help. I could then make a template for the cardboard inserts and fasten the evaporator like DEP intended.

[wbain5280]

Setting the idle on a 220SE, 250SE, 280SE and 300SE/L requires adjusting the amount of idle bypass air and the amount of fuel at the injection pump. DO NOT ADJUST THE LINKAGE STOP SCREWS.

There is a knurled nob on the end of the injection pump which is adjusted withh the ENGINE OFF. One click either way and then adjust the amount of idle air. The screw should be at the front of the intake manifold by the thermostat housing.

Additionally, there is a small injection pump oil dipstick. Do not overfill the injection pump. You may also want to remove the oil and add new oil.

You must keep the internals clean. There is a fine mesh fuel filter on the engine mount. There are also two fuel dampers, one for the fuel inlet, the other for the outlet.

To start a hot engine, turn the key on for 5 seconds and then start the car. You will hear the fuel pump pitch change as fresh fuel flows and expells the vapor.

[Anthony Cerami]

I had a chance to work on the car.
How do I set the stop on the throttle body? How does the linkage correlate to the I/P. I don’t think this is set up properly. I noticed I do not have full throttle. I did turn in the adjustment on the back of the I/P one click lean. No noticeable difference.
Car is still running very rich. When you drive it …It runs for 2 blocks and cuts out. It will start back up.
If you let it run at fast idle it will die out…..?? Restart and run fine …rich of course lots of black smoke………Not enough fuel pressure???
So far I have replaced the following. Oil change / Fuel filter.
Plugs, cap, rotor, wires, condenser, coil. Waiting for points ….Filed and cleaned for now.
Compression reading is 140 across all cylinders.
Fuel pump pressure is 10 – 12 PSI. Is this correct???
Dwell is 30.
Timing is 8 degrees w/ vacuum line pluged.
Idle set to 800 rpm.
The old coil was in bad shape. The center conductor was rusted away.
So I replaced it. What type of ballast resistor should I use???
I have a 1.0 Ohm ballast resistor.
The old coil operates at 10.7 volts. It measures 1.4 ohms between + and – terminals. 10.8 ohms between the secondary and +/- terminals.
The new coil operates at 7.9 volts. It measures 0.6 ohms between + and – terminals. 11.56 ohms between the secondary and +/- terminals.
If I use a 0.6 ohm ballast the new coil operates at 8.7 volts.
What ballast resistor is correct??
Still trying to figure out the cold start circuit…..
Nothing is connected ………………Grrrrrrrrrrrrr!!
The sensor at the throttle body is disconnected. I opened the harness and there are no wires available that would connect here. Again on the top of the intake manifold the electric dash pot is just sitting there. There are no wires attached or nearby. Connected to the Cold start valve are two wires Black / wht / pink and a brown wire that is ground. These wires are part of the harness they follow along the rear fire wall and end at the brake booster with two terminal rings attached. They are just hanging there not connected.
In addition, on the back of the firewall passenger side is a red / grn wire that is cut off and hanging.
I tested the CSV by connecting 12 volts and it works the engine stalled out with the extra fuel.
It appears as though I am missing a harness, or the wires that connect all of this mess.
Had a chance to look at another car. 1967 250 se. This car has all the same components and is wired correctly…… I think??? This car is a show car so I was only able to take some pictures. The harness looks different than my car.
Does anyone have a diagram of how all this stuff connects? Is there an under hood harness available? Can someone buzz out a harness to see how the harness is wired?? Any help would be greatly appreciated.
-Anthony
South Jersey

[M_Anker]

I'll try to help you out a little bit.

As far as the throttle linkage goes, I was told that the idle stops were not to be adjusted, but I guess that the linkages are fair game. I found on my car that the injection pump linkage was adjusted so that the injection pump was not against the idle stop at idle. Basically, the injection was putting out more fuel for the amount of intake opening, and loosening the injector pump linkage leaned my car up a bit. From 13 to 15 MPG! To adjust these, you need to pull the pushrod off of the ball joints and screw the ends in or out. It is very intuitive once you try it. The linkages should be set so that both the air intake and injector pump are resting on their idle stops. You then need to set the idle by the adjustment screw on the intake manifold toward the front of the engine.

The ignition ballast resistor is supposed to be 0.6 Ohms. If it runs, then it's not too much of a problem going from 1 to .6 ohms. My car was running on a .4 ohm resistor that was a relic from the transistorized switchbox. I replaced it with the correct .6 ohm when the ballast resistor failed and left me searching for A.T.

I wouldn't worry so much about the cold start circuit as getting the mixture set correctly. If you need additional fuel for a cold start, pump the accelerator a few times.

I hope this helps a bit. My best advice for you, however, is to buy the blue service manual for the car off of eBay. It's one of the best $50 investments I made!

[cth350]

choice of balast is tied to choice of coil. If the coil is black, use a .9 balast (gold band). If the coil is blue, use two (.4 and .6; silver & blue bands). If it's red, use a 1.8 balast (red band).

For aftermarket coils, throw away the coil and buy bosch. -CTH

[wbain5280]

Anthony, I still owe you some info.

As for the stops, look on the top of the injection pump by the linkage stop. There should be a number stamped or cast on it. That's the stop setting.

Adjust the linkage rod ball joint sockets so they easily snap on to the little balls.

You need to take a pic of your injection pump and also post the oump type. There should be two solonoids at the rear of the pump.

Pics, we need pics.

IMHO, for the engine to run properly, you may need to add additional relays and wires since you have a 280SE engine in a 250SE.

[Gregg Bambo Jr.]

I had a similar problem with sooty plugs and missing. The problem was corrected by removing a high pressure aftermarket fuel pump and replacing it with an original manufacturers low pressure hi volume pump designed for my particular engine. The aftermarket pump put out too much pressure for my injection system.

[Anthony Cerami]

Thank you Greg .......
I dropped the fuel tank and flushed it out....
Cleaned out the check valves and the regulator valve. The fuel filter was really bad. Also replaced all the lines. I get 10-12 psi at the I/P inlet. The little filter on the I/P was clogged to the point where it was sucked into the port. I removed the thermal valve assembly and cleaned it out. Replaced the filter with a small breather filter I found at pep boys Looks great! Adjusted the mixture setting 2 clicks lean. Also installed a Pertronix system.
I’m getting plenty of spark! Ask me how I know!!
Compression Average is 145 psi
I still runs rich………?????????/

What else can i check??

[wbain5280]

Is the cold start valve dripping?

I owe you some info. You sent me some pics and I'll reply shortly. Sorry for the delay.

[Anthony Cerami]

Hi Warren ....
I disconected the fuel line to the valve.
After a good soaking ...The injectors look like brand new.
I cant figure it out???

[Mark DiSilvestro]

My Haynes manual gives a pressure of 18 for the '68 fuel pump but 10 -12 at the injection unit sounds OK as you're checking it after the pressure regulator. In any case, low fuel pressure shouldn't cause a rich condition.
The external mixture screw on the injection unit ONLY adjusts the IDLE mixture. If you're getting black smoke at other than idle speed you need to look elsewhere.

There are other mixture adjustments inside the injection unit but they shouldn't be messed with unless you have a FI service manual, a CO meter and are certain that ALL other components and systems are correct. You already said that some of the wiring is wrong or disconnected and were unsure about the throttle linkage adjustment.

On the FI unit, there's a cold start solenoid and coolant temperature sensor. The cold start solenoid fully enriches the mixture while starting and it's remotely possible that it could be sticking.

The most likely suspect is the FI coolant temperature sensor, which is located above that little filter you replaced. The sensor should have two coolant hoses connected.
First, it's important that the engine is
fully warming up. If it runs too cool, it will 'fool' the sensor into making the FI run rich. Or the sensor itself could be bad and simply not be leaning out the FI as the engine warms up. According to my Haynes manual, the FI coolant temp sensor should 'switch off' at 149F to 158F, or at 122F to 131F on later USA versions. While the engine is running, unscrew that little air filter and put your finger on the open port. If the car is fully warmed up and the sensor is working, there should be little or no suction. Hope this helps.

Happy Motoring, Mark