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  #1  
Old 06-04-2004, 08:23 PM
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Exclamation Mechanical Fuel Injection Pump not working properly

I need some immediate help with my 1970 280SEL 6cyl. I parked the car yesterday afternoon and went to start it up this morning as usual. As I attempted to start the car, the car seemed to fire like it normally would, but would only continue to run for a fraction of a second. I initially tested the ignition circuit and found it to be working properly as all the plugs are firing. However, the problem never seemed to be electrical in the first place since the engine seems to be firing properly. I then suspected fuel flow issues.

I disconnected the fuel line before it reaches the fuel filter since it was the most accessible line. I turned on the ignition to activate the fuel pump and it immediatly filled my sample cup. The fuel was transparent with a yellow tint, and it burned cleanly when I threw a sample on the ground and lit it. I then disconnected the fuel line to the cold start valve to take a sample there since the CSV supply T's off of the fuel filter output. The fuel pump was able to quickly fill a sample jar within the 1L/15sec published figure. However, what pressure is the fuel pump supposed to put out? I am wondering if the fuel has to be at high pressure like on modern EFI engines? Is it possible that my fuel pump could be weakened to the point that is delivers proper volume but not pressure?

I then disconnected an injection line from the number six cylinder since it was the most accessible, and then cranked the engine. The injection pump squirts out fuel to the timing of the engine. However, I need to know how much pressure should be feeding the injectors? I did not remove the injector, just the supply line.

Also, I disconnected the ignition coil wire and cranked the engine. I then removed a spark plug and found no fuel residure on it after a 5-7 second crank. I would have expected to find some fuel residue if fuel were being injected in the cylinder.

I am asking anyone who knows about these systems to please provide me with any suggestions on rectifying the problem. Otherwise, does anyone know where I could get a good price on a used injection pump?

Many Thanks in advance!!!!!
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  #2  
Old 06-04-2004, 08:55 PM
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Next step for me would be pulling an injector intact and fanning a piece of cardboard with the spray while wearing heavy gloves as somebody else cranks the engine or using a remote starter button with my other hand...... caution is danger of spraying your hand with 250 lbs. pressurized fuel. This is also a poorman's method for checking injector tips - examining the patern on the cardboard left by fuel spray.
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'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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  #3  
Old 06-04-2004, 09:17 PM
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If I remove an injector from the manifold, I am going to need a new seal, right? Or can I reuse the current seal for the mean time while I am troubleshooting?
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  #4  
Old 06-05-2004, 01:42 AM
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The fuel pump supplies low pressure fuel unlike the modern FI system that supplies it at 35 - 40 PSI. The injection pump supplies the high pressure fuel, 250 psi or so as previously mentioned. Be very careful, the high pressure spray can get into your skin or tear it. Gas is not good for people.

Do not adjust the throttle body stop or the injection pump stop to adjust the idle speed.


Will the engine run if you give it gas?
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Warren

Currently 1965 220Sb, 2002 FORD Crown Vic Police Interceptor

Had 1965 220SEb, 1967 230S, 280SE 4.5, 300SE (W126), 420SEL

ENTER > = (HP RPN)

Not part of the in-crowd since 1952.
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  #5  
Old 06-05-2004, 03:10 AM
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gimme a low-tech 240D
 
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Regarding new injector seals - purists say yes, cobblers say no..... but if they leak it will be really obvious. Gotta torque em too and allign the seals carefully.

Maybe somebody here who has seen an injection pump go bad can advize you better than me. I've honestly never seen or heard of an MB/Bosch IP that failed.

Another culprit could be the ignition coil causing feeble orange spark instead of blue. And another often ignored 2 bit item is the condenser...... yes a bad condenser can stop an engine from starting.
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  #6  
Old 06-05-2004, 08:49 AM
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Quote:
Will the engine run if you give it gas?
No, it will not run if I apply the accelerator at any setting.

Also, the idle stops on the injection pump have not been adjusted.

Quote:
Another culprit could be the ignition coil causing feeble orange spark instead of blue. And another often ignored 2 bit item is the condenser...... yes a bad condenser can stop an engine from starting.
Well, I already tried switching the ignition coil from my father's 1968 280S to my car (both have standard ignition) and starting it. There was no difference with the 280S's ignition coil. The condensor was replaced about 6 months ago when I installed a new set of points. I also checked the points and they were a little off, but the engine still would not start after resetting the point gap to the published value.

What it really seems like is that the engine starts, but immediatly exhausts its supply of gas and quits.
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  #7  
Old 06-05-2004, 09:39 AM
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A couple of questions...

> immediatly exhausts its supply of gas and quits.
The tests you did with the system open, did they last more than a few seconds?

Do the symptoms change if you remove the gas cap?

What happens with a little bit of ether?

The test you did for cylinder 6, that was at the injector end of the line, not the pump end, right?

Have you checked your oil recently? Do you suddenly have a lot more of it?

-CTH
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  #8  
Old 06-05-2004, 10:04 AM
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I assunme you have the shop manual for your FI system so you can check circuits. My next check, since you say you're getting fuel there, would be to check for power at the cold start valve. you can also check for power at the cold-start solenoid on the injection unit. There's also a coolant regulated thermostat on the injection unit that controls fuel mixture according to engine temperature that could be stuck.
My '59-67 Mercedes shop manual came with a couple of supplemental pages covering later model injection units. They mention a fuel cut-off solenoid for stopping fuel delivery during coasting but there's no picture.
Hope this helps.

Happy Motoring, Mark
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  #9  
Old 06-05-2004, 12:01 PM
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>The tests you did with the system open, did they last more than a few seconds?

Yes, I attempted to pump fuel out of the injection line for about 5 to 7 seconds. I did not remove an injector, so I cannot yet say how much fuel pressure the system is delivering to the manifolds.

>Do the symptoms change if you remove the gas cap?

No, I already suspected a clogged vent and removed the cap. The fuel pump seems to be delivering plenty of volume.

>What happens with a little bit of ether?

I did not try ether. I don't have any, and I'm hesitant to try. I'm assuming ether in the intake manifold would suplement the need for gasoline temporarily.

>The test you did for cylinder 6, that was at the injector end of the line, not the pump end, right?

It was the end of the injection line, but disconnected from the injector itself.

>Have you checked your oil recently? Do you suddenly have a lot more of it?

Actually, oil was down about a quart. I burn 1 quart per 1K miles. I added oil accordingly and the oil on the stick has the viscosity of SAE30, no gasoline dillution.

Quote:
My next check, since you say you're getting fuel there, would be to check for power at the cold start valve. you can also check for power at the cold-start solenoid on the injection unit.
I don't think it has a solenoid on the injection pump for cold starting. The CS valve has the solenoid on the intake manifold itself as the fuel supply T's off to the valve before it enters the intake on the injection pump.

Quote:
They mention a fuel cut-off solenoid for stopping fuel delivery during coasting but there's no picture.
I may look for that one. I do not have a shop manual specifically for the injection pump, just the Mercedes shop manual.

Thanks for the suggestions!
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  #10  
Old 06-05-2004, 01:28 PM
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There are a lot of pump types out there. A quick look at the 1972 TDM shows 4 possible pumps from 1968-1972. Look for an ID plate that says something like "PES 6KL 70B 120 R??Y". Those last 4 characters are the unique pump type. R20Y, R22Y, R24Y, R28Y.

On the back of the pump is one or two solenoids. One is a fuel cut-off. Armed with a pump number, I can probably dig up the correct schematic diagram for the wiring.

-CTH
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  #11  
Old 06-06-2004, 11:31 AM
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It was ELECTRICAL!!!!!!

The problem turned out not to be the fuel system at all. Rather, it was an ignition ballast resistor. I thought that I would be absolutely sure about the ignition system before I pulled an injector, so I started to check the path of power from the battery. It seems that the starter applied power directly to the ignition coil while I was cranking, and then as soon as the starter disengaged the engine quit. It turned out that my .4 ohm resistor was reading in the Mega-Ohm range. I replaced the resistor with a .6 ohm that had been connected to the transistorized ignition system (long since disabled by the PO). As it turns out, .6 was the correct value for the system anyway.

I promise I'll never say anything bad about the injection system ever again. Mechanical injection must be nearly fool proof.

Thanks again to everyone that responded.
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  #12  
Old 06-06-2004, 11:59 AM
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Always check the basics first. Thanks for letting us know.
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Regards

Warren

Currently 1965 220Sb, 2002 FORD Crown Vic Police Interceptor

Had 1965 220SEb, 1967 230S, 280SE 4.5, 300SE (W126), 420SEL

ENTER > = (HP RPN)

Not part of the in-crowd since 1952.
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  #13  
Old 06-06-2004, 12:40 PM
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There are a small number of combinations of ignition parts that work well together. The balast resistors are coded by the color of the metal band. The Coils are also color coded.

Balasts: blue, silver, gold, red
Coils: blue, black, red

Use BOTH the blue and silver balasts with the blue coil.
Use the gold balast with the black coil.
Use the red balast with the red coil.

The blue coil is ONLY used with a transistorized switching unit. There are something like 4 possible units for points systems. Two are interchangable without rewiring. The details on which one is which are published in the archives someplace.

-CTH
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