1969 280se 3 Cylinder Injection Pump
 

I’m probably going to say a Hail Mary and go out to the driveway and hope the front three ports (for the back three cylinders) will miraculously start flowing the next time I crank the motor.

I don’t know WTF I’m doing.

I’ve never touched a mechanical injection Mercedes before.

This is a totally rotted, no title, purchase that’s cost me far more in time than money. The fact that I got the motor AND fuel pump spinning and am considering using it to build pressure in the pump is money in the bank IMO.

With injector lines off, I got spurts from the back port (for front cylinder) first, and then a bit from the next one forward, and then I pinned the throttle thingee to full throttle and got flor from the third.

Later I put the lines on those three and got flow. Then to plug the lines I added injectors. Low and behold Techron is flowing into the water bottles for those three. And that was just a few minutes after pouring Techron into a funnel to feed into the injection pump via gravity.

But as of yesterday morning, about 12-16 hours after putting the Techron in, I got no new action from the other three ports. The last thing I did was shoot some PB Blaster into the pools of Techron I’d poured into the top of those three ports. It displaced a bunch of Techron leaving the orangey bubbles and I shut the hood.

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The fuel filter was surprisingly clean. The inspection sticker on this parts car expired in 1986. That’s too many years for me you count on my fingers and toes, and my kids won’t sit still long enough for me to use theirs.

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So I’m wondering what to do next.

Remove injection pump from the car?

Supply pressure to the injection pump?

But first I will say that Hail Mary. Better yet I will call my lucky friend Bob. And if it doesn’t spurt Techron out those ports, I will blame it on lack of fuel pressures.

Opinions?

1969 280se 3 Cylinder Injection Pump
 

No luck tonight, but I’m guilty of not performing my voodoo rituals either. I started making a pressure IV bottle and realized my fuel pump hose connected to the Injection pump is too cracked to use for pressure, and I will need to make a new one, or do a stock hookup with the stock filter and pray. As I proved tonight, I guess I’m not much for praying.

Yeah, it sounds like a fuel feed problem. be sure to keep the injection outlets covered as any debris there could cause real trouble in the injectors.

So then rather than removing the pump or getting excited about the Injection pump not working, I should probably just put the filter assembly back on and push some fuel into it under pressure. Does that sound like the right thing to do? I guess this will be the time to test those pumps I recently took apart, cleaned and put back together. Sound about right?

No. The injection elements are probably stuck. Those little pistons can get stuck in their bores and it's only spring pressure that makes them move back down. You will need to remove the injection line fittings and the check valve then soak the stuck pistons with a penetrant. I use a golf tee and gently try to move the pistons down. If they're not too seized they might move. Torque the line fittings to only 19 ft - lbs or you can crack the main housing.

Not to be argumentative but did the op determine he had fuel coming to the injection pump? I have zero experience with mechanical injection for gasoline, but the diesel pumps seem to stay decent inside since there is no air present to cause trouble.

Here’s the sequence of events:

1) removed crusty pump from rear of the car.
2) determine the engine wasn’t seized by turning the key and the motor cranked briefly. (I thought it was seized.)
3) I removed all injector lines and the fuel filter in the engine bay.
4) I connected I fuel hose to the inlet of the IP and put a small funnel on it. On the return line I connected it and put the other end into a Gatorade bottle.
5) I poured Techron into the small funnel and in short order Techron started dripping into the return container.
6) I cranked the motor and got spurting from the #1 cylinder port at the back of the IP. Then the #2, the next one back. I didn’t get the front four ports flowing. So I then pinned the throttle linkage against the brake booster and got the #3 port flowing, all in a matter of minutes after pouring Techron in.
7) I put the injector lines on to capture the Techron. I put bags on the injector ends of the lines.
8) when I noticed the bags were filling up, I put injectors on the three injector lines assuming that would plug them up for a while.
9) the injectors all three were dumping Techron on the intake side of the motor, so I put them into water bottles.

That’s basically where I am now, just a few days later, and am wondering if fuel pressure would help the IP. But it sounds like maybe knocking the pistons around with a golf tee would make sense. They’ve been soaking in Techron and I’ve squirted PB Blaster into the three injector line holes too. No action yet.

So can I just try to wiggle a golf tee into the injector line ports and not damage anything too much? If so, that’s my next step I guess. I guess the pistons would be stuck up now that I see there’s a cam in the bottom of the IP that pushes the pistons up.


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Tonight I made an airtight connection to the pump feed with an IV-style Gatorade bottle and squeezed pressure into the system. The next injector port back (cyl 4) would flow gas when I squeezed. I also tried blowing air into the ports in hopes of pushing the pistons down in the pump, and this would inflate my IV bottle when I put air to the cyl 4 port most times. I cranked the engine several times, and assume cyl 4 piston / plunger must be moving at least a little because sometimes it would not inflate the bottle.

Since I wasn’t having any success, I decided to remove the injection pump, assuming I put enough pressure to the injection pump.

Also, understanding that the plungers are probably stuck in the up position (because the cam will push them there) I am thinking that I need to open the side of the injection pump to get a view of what’s going on.

So the injection pump is now out of the parts car.

I'm just throwing out an idea...warm the pump with a heat gun and try the golf tee method while it's warm. By warming the pump it may expand enough to free the plunger.

1 2 3 moved as expected.
5 and 6 also moved fine. Weird.
4 didn’t move at all.
I noticed the plunger could be pushed down and rotation would push it back up. The spring wasn’t pushing it down. Somehow the spring was bound up. I freed the spring and it’s working now. Weird. I think the pump has been off the car before bc the back side was only mounted with one bolt and I see there are two mounting points RS for the back of the IP. The side plate screws were very easy to open, virtually no force required at all.

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I can’t believe it still looks so dirty after so much cleaning.


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1969 280se 3 Cylinder Injection Pump
 

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https://youtu.be/VlMq9RTUulQ

1969 280se 3 Cylinder Injection Pump
 

Maybe it’s got more issues:

https://youtu.be/dW-GJz8ZSiE


Edit:
I’m trying to find a video like this for a Mercedes 250 or 280 injection pump.
https://m.youtube.com/watch?v=1B1jyxqF86Q

There are all sorts of carb cleaners out there but the one I find works the best on old gunky oil and grease, like in the photos of the springs, is Easy Off Oven Cleaner, BBQ Grille formula.

Once that gunk is cleaned out it will be easier for any oil to get into the smaller parts and help to free them up.

I have used this stuff on a lot of alloy parts and it has never damaged anything yet.

I’ve cleaned most of the outside and decided not to remove all the oil from the Injection pump yet. But I guess it’s about time to do that.

I’ve considered giving the whole IP a gasoline or parts washer cleaning inside and out, but don’t yet know enough about these things to assume it’s ok to wash out the insides with gasoline. I’d think it would be ok, but don’t want to assume anything.

I learned that the brittle plastic cap that started cracking and chipping when I tried to remove it is an access to test the rack movement. I removed the cap, and here are my measurements with my bolt:
- resting: 32 mm from housing
- pull out: 34 mm from housing
- move throttle linkage to max: 34 mm from housing.
- push in: 15 mm from housing.

So it moves 2 mm out from resting, and in 17 mm from resting.