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1974 450SL 1965 Thunderbird 1927 Oldsmobile 1950 Buick 1977 Jeep CJ7J7
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Discussion Starter #1
If you followed previous threads, you know I am trying to get a '74 450SL that has been stored for twenty years running again. I started the engine last night after a lot of hard work replacing various components. This morning I awoke to discover the car would not start. I was a bit depressed. I cranked on that starter so long, the battery voltage had dropped to 11.7. I put it on the charger. I was sitting in the car wondering what to do next, and decoded to dump some fuel down the air intake and try starting it one more time. It started and then died (I had flooded the engine trying to start it). I finally got it running, albeit a bit rough. I let the engine run for about twenty minutes, and decided to pull the charger. The second I disconnected the clamp on the positive terminal, the engine died. I put it back on, and the engine started. To be brief, I discovered, quite by accident, that if I disconnected the positive clamp, the engine would die, even if the battery charger was unplugged. Being a bit slow, it took a few minutes before I noticed the clamp was grounded a big black wire that was attached to the battery terminal clamp by the clamp bolt. Close inspection revealed the bolt was so corroded in its hole, that the wire was not making contact with the positive terminal. When I put the battery charger clamp onto the terminal, it covered both wire eye and the terminal, grounding the big black wire to the terminal. I disassembled everything, cleaned it all up, and reassembled it all. The engine cranks freely now. The corrosion on the bolt was hidden from view. I wonder how long it would have taken me to discover the reason the car wouldn't start if I hadn't been charging the battery with the engine running. I feel like that blind hog that was looking for an acorn.

If you acquire an old car that has been sitting up for years, count on having to clean pipes, hoses, and electrical terminals. Tomorrow I rebuild the injectors and replace the sparkplugs and wires. There is no rest for the weary, unless the dreaded virus gets 'um.
 

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R/C107 Moderator
1986 560SL: '84 500SL: '84 280SL 5 speed: other 107s
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How are you going to rebuild the injectors?
 

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'72 350SL, '85 300D, '98 E320, '19 Subaru Outback (sold '14 GLK250)
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10,338 Posts
I was wondering that too :)
You can remove them and replace the rubber clamp bung, the top hat seals, pintle caps and the internal screens. Other than that, you can flush to clean with some type of injector cleaner. Then set up a test rig and compare flows at 30 psi. You can't dismantle the injectors themselves.
 

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1974 450SL 1965 Thunderbird 1927 Oldsmobile 1950 Buick 1977 Jeep CJ7J7
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98 Posts
Discussion Starter #5
How are you going to rebuild the injectors?
Mayhaps "rebuild" was too strong a word. "Recondition" may be a better word. I am going to clean and replace those parts that can be replaced, as well as replace the electrical connections from the wiring harness. I will rig each injector downstream of the opposite fuel rail (30 psi flow stream) and activate the injector with a momentary strike against two little 1.5 volt batteries in series. It is my understanding that the injector activation voltage is 3 volts - if I am mistaken, please correct me. Visual observation of the injector flow stream is not perfection, but it is the limit of what I can do in a timely manner.
 

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1974 450SL (US), 2005 SLK200 (UK)
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I was wondering that too :)
You can remove them and replace the rubber clamp bung, the top hat seals, pintle caps and the internal screens. Other than that, you can flush to clean with some type of injector cleaner. Then set up a test rig and compare flows at 30 psi. You can't dismantle the injectors themselves.
I put mine in a ziploc with Techron then into an ultrasonic cleaner. I don't know if it really made a difference but the Techron was black afterwards and I felt like I had accomplished something - turning Techron black. :D Andy
 

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'79 450SL, '04 CLK200 convertible; former A124, W210, A209.
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Good progress, a lot of times it's the "one step forward, two steps back" approach but you will arrive at your destination. (y) 🚗
 

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'72 350SL, '85 300D, '98 E320, '19 Subaru Outback (sold '14 GLK250)
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I put mine in a ziploc with Techron then into an ultrasonic cleaner. I don't know if it really made a difference but the Techron was black afterwards and I felt like I had accomplished something - turning Techron black. :D Andy
I at first did that too except I used Seafoam followed by Simple Green. Also did the injector filter/screens on their own. (you can extract them using a coarse thread screw)

Wanting feedback, I set up the crude test rig that I think may still be in the Djet Comprehensive Guide in EGv107. Used it to flush with Seafoam, then flow test using mineral spirits.

I later modified that rig using an old fuel rail so I could do 4 at a time. And not worry about using my 12v lawn tractor battery (at time I did one at a time it was probably at about 5V, having sat all winter). 3V is apparently the safe voltage to use.

Shop manual outlines a method using troughs or individual bottles while injectors are still attached to rails. Haven't tried that. Don't like the idea of uncontained gasoline spraying in engine bay.
 

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1974 450SL 1965 Thunderbird 1927 Oldsmobile 1950 Buick 1977 Jeep CJ7J7
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Discussion Starter #9
I at first did that too except I used Seafoam followed by Simple Green. Also did the injector filter/screens on their own. (you can extract them using a coarse thread screw)

Wanting feedback, I set up the crude test rig that I think may still be in the Djet Comprehensive Guide in EGv107. Used it to flush with Seafoam, then flow test using mineral spirits.

I later modified that rig using an old fuel rail so I could do 4 at a time. And not worry about using my 12v lawn tractor battery (at time I did one at a time it was probably at about 5V, having sat all winter). 3V is apparently the safe voltage to use.

Shop manual outlines a method using troughs or individual bottles while injectors are still attached to rails. Haven't tried that. Don't like the idea of uncontained gasoline spraying in engine bay.
I haven't decided how I am going to actually clean the injectors yet. As for testing, I intend to use a long 3 ft high pressure line from the rails into a 2-liter diet Coke bottle from a tee placed in the line to the fuel regulator. I block off the removed injector line with a 5/16 bolt clamped in place. Since I am re-conditioning them one at a time, it is a simple procedure. Turn on the ignition key, trip the injector, observe the spray, then turn off the key - simple and fast. I already have replacement screens, and I use a hook to pull the old ones out.
 

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'72 350SL, '85 300D, '98 E320, '19 Subaru Outback (sold '14 GLK250)
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I haven't decided how I am going to actually clean the injectors yet. As for testing, I intend to use a long 3 ft high pressure line from the rails into a 2-liter diet Coke bottle from a tee placed in the line to the fuel regulator. I block off the removed injector line with a 5/16 bolt clamped in place. Since I am re-conditioning them one at a time, it is a simple procedure. Turn on the ignition key, trip the injector, observe the spray, then turn off the key - simple and fast. I already have replacement screens, and I use a hook to pull the old ones out.
Just a couple of comments:
  • Turning on ignition will start the fuel pump, but it will turn off after a few seconds if engine is not running. You would have to jumper the relay to keep rails pressurized.
  • Taking one injector out at a time is not easy unless you cut and remove the hose. Maybe you will lift the complete rail first?
  • spray pattern is not too important on these cars. Injectors just squirt fuel into the intake manifold/head where it waits for valve to open. Getting equal injection from each is desirable although not as much so as with direct injection.
Good luck and let us know how you make out.
 

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1974 450SL 1965 Thunderbird 1927 Oldsmobile 1950 Buick 1977 Jeep CJ7J7
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Discussion Starter #11
Just a couple of comments:
  • Turning on ignition will start the fuel pump, but it will turn off after a few seconds if engine is not running. You would have to jumper the relay to keep rails pressurized.
  • Taking one injector out at a time is not easy unless you cut and remove the hose. Maybe you will lift the complete rail first?
  • spray pattern is not too important on these cars. Injectors just squirt fuel into the intake manifold/head where it waits for valve to open. Getting equal injection from each is desirable although not as much so as with direct injection.
Good luck and let us know how you make out.
My fuel pump does not shut off. My kit came with all new pre-cut hoses, so I will cut the old ones. I need to see the flow pattern. If an injector is plugged, it will be obvious.
 

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'72 350SL, '85 300D, '98 E320, '19 Subaru Outback (sold '14 GLK250)
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If your pump keeps running when you turn the key and engine is not running, then your fuel pump relay must be already jumped or perhaps faulty. That function is built into these cars.
 

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1974 450SL 1965 Thunderbird 1927 Oldsmobile 1950 Buick 1977 Jeep CJ7J7
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Discussion Starter #13
I will check my relay. I was wondering about that situation. Thanks for the heads up.
 

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1974 450SL 1965 Thunderbird 1927 Oldsmobile 1950 Buick 1977 Jeep CJ7J7
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Discussion Starter #14
OK, I found one of the reasons for a very rough idle. I had removed the cold start sensor for cleaning, and I forgot to put it back on. Noticed it on my desk today and installed it. Low and behold, the idle went from a very rough 1800 rpm idle to a smooth 800 rpm idle. Sometimes I forget things, like my kid's names. It took me many years to perfect the art. Now I am an expert.
 

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450slc5.0cab 280sl5sp 280se4.5 500se+500slAMG +250seStkW108 350sl4spdX3 500secEuro
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I think it’s about once a month on average I tell d-jet owners who’s pump isn’t running that they should check to make sure the smaller wire on the positive battery terminal is tightly connected.
 

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1987 560SL, 2000 Kawasaki W650
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If you acquire an old car that has been sitting up for years, count on having to clean pipes, hoses, and electrical terminals. Tomorrow I rebuild the injectors and replace the sparkplugs and wires. There is no rest for the weary, unless the dreaded virus gets 'um.
Having spent many an hour slaving over a hot soldering iron replacing dead components in the belly of a 1960s-era tube amplifier, any electrical connection I run across either in an amp or a car that I haven’t cleaned and looks like it’s not been clean since 1963 or 1987, I hit it with some contact cleaner and/or fiberglass pen for really grimy contacts, daub it lightly with anti-oxidant. As I’ve read in the MB shop manual, “on principle.” Preventive maintenance is a lot easier than waiting somewhere for AAA, especially with electrical problems that can be hard to find. I had an intermittent starting problem, drove me bonkers for awhile until I traced it down to just enough rust between the ignition coil and the sheet metal to which it was attached, causing the coil to occasionally lose its connection to ground.
 

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1974 450SL 1965 Thunderbird 1927 Oldsmobile 1950 Buick 1977 Jeep CJ7J7
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98 Posts
Discussion Starter #17
Having spent many an hour slaving over a hot soldering iron replacing dead components in the belly of a 1960s-era tube amplifier, any electrical connection I run across either in an amp or a car that I haven’t cleaned and looks like it’s not been clean since 1963 or 1987, I hit it with some contact cleaner and/or fiberglass pen for really grimy contacts, daub it lightly with anti-oxidant. As I’ve read in the MB shop manual, “on principle.” Preventive maintenance is a lot easier than waiting somewhere for AAA, especially with electrical problems that can be hard to find. I had an intermittent starting problem, drove me bonkers for awhile until I traced it down to just enough rust between the ignition coil and the sheet metal to which it was attached, causing the coil to occasionally lose its connection to ground.
What contact cleaner do you use? I've never found one that worked very well.
 

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'72 350SL, '85 300D, '98 E320, '19 Subaru Outback (sold '14 GLK250)
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OK, I found one of the reasons for a very rough idle. I had removed the cold start sensor for cleaning, and I forgot to put it back on.
Which sensor is the cold start sensor?
Would that be the thermo-time switch that is mounted close to the idle screw. Or was it one of temperature sensors?
 

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1974 450SL 1965 Thunderbird 1927 Oldsmobile 1950 Buick 1977 Jeep CJ7J7
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98 Posts
Discussion Starter #19
I think it is actually the injector part of the cold start system, but bear in mind that I don't know didly about Mercedes's. This has all been a great learning experience for me. This sensor is located just aft of what appears to be the thermostat housing, but I could be wrong about that too.
 
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