Injection Pump Replacement ?'s - w124 300D - PeachParts Mercedes-Benz Forum

Jmana · #1 10-21-2007, 10:34 AM

I am going to tackle replacing my crapped out injection pump on my 87 300D and have a few questions about it. First, I know that I am supposed to get the engine at TDC, and make sure the notch on the sight hole in the IP is visible, do the same on the donor vehicle, then replace. Well, I bought a pump that was already off the vehicle, so not sure how to get the notch lined up. It doesn't seem like I am able to rotate anything, any ideas?
Now, looking at the new pump, I see at the front of it there is a threaded rod that goes into where the timing chain is. What exactly is that threaded into? When I go to take the old one out, do I have to do anything to the chain? That seems to be the biggest gray area for me, is how this end of the pump fits into the timing chain system. Thanks for any help!

junqueyardjim · #2 10-21-2007, 07:02 PM

I guess it depends on how handy you are. Also, how badly you need to drive that car. "Necessity is the mother of invention" is the old line. And I think that if you screw with it long enough, it might or might not run again. If it runs right now I would seek out an Indy to do that in heartbeat. There are a lot of things I will do on and for my Benz. Messing with the IP is not one of them.

sixto · #3 10-21-2007, 08:46 PM

Don't set the engine to TDC. Set it to 13* ATDC #1 then look/feel for the timing lug in the IP. Center the timing lug in the view port as best you can or use an IP locking tool. With the IP off the car, put the locking tool in the replacement pump. Gus Pfister of Pacific FI said to wrap the IP driveshaft with a towel then turn CW with pliers or grips.

[EDIT] I mean set the engine to 13* ATDC then bump it slowly as you look/feel for the timing lug.

Sixto
87 300D

sixto · #4 10-21-2007, 08:54 PM

Sounds like you're attempting this without a manual. I don't think anyone would advice you to proceed without guidance unless you're a top notch DIY.

You have to remove the engine vacuum pump to get to the bolt on the IP timer (sprocket). This is a left hand threaded bolt as indicated by the arrows on the bolt head. Put a bar through the cam sprocket to hold the chain while you loosen/tighten the IP timer bolt. I've R&R'd the IP without removing the chain tensioner. Be sure to mark or zip tie the chain to the timer.

There are three 13mm head bolts from the front of the engine to the IP. These bolts are held by square nuts that slide into slots in the IP case. Keep a finger or magnet on these nuts as you remove the bolts. If a nut drops between the block and AC compressor, it won't be fun to retrieve. There's a bracket on the back end of the IP that should come off as well. The cruise control actuator has to come off so there's enough room to slide the IP back. As you pull the IP, keep track of the adjustment screw. It will likely stay with the IP but it's loose and will fall out of place if you tip the IP. It might not be obvious how it fits in the slot if you don't have a visual in memory.

Don't forget a new o-ring for the IP into the block.

Sixto
87 300D

Jmana · #5 10-21-2007, 11:49 PM

I am still confused as to how the threaded rod at the front of the IP fits into the timer sproket. It doesn't make sense that there is a bolt behind the vacuum pump, what does that bolt screw into? And what does the threaded rod screw into? I currently have everything apart ready to remove the pump. I got the intake, vac pump, injector lines, and all the wires and hoses removed. Got a good view of the damage with the intake off, I'll try to post pictures of it, but there was a big chunk of the casing that got blown out. I shined the flashlight in there, and there was a ball bearing sitting loose, so I would say something inside is really messed up. After seeing that it amazes me the thing still runs, I drove it a good 2 hours like that!

dieseldiehard · #6 10-22-2007, 12:01 AM

As I recall the bolt behind the vac pump screws into the timing device then to the center of the IP shaft and is left hand thread. The bearing you saw may have come from a disintegrating vac pump bearing, it rides up and down on that ramp on the timing device and if the surfaces on that ramp are scored at all you will be better off getting a new timing device before installing a new IP.
You should pursue borrowing renting or buying a timing indicator, a small box with LED's on it that attaches to the side of the IP and indicated precise timing. Are you more confused now? I hope not. As sixto said, you need the manual and if you can get it, and experienced helper else take it to an Indy to get the job done right.

Jmana · #7 10-22-2007, 12:25 AM

I have tried finding a manual for it, but have not seen any good ones. And I can't afford a mechanic, they all charge a minimum of $60 an hour around here, they told me labor only of $800 to change the pump. I'll do it myself....somehow! Anyway, the bearing isn't from the vac pump, that is only about a year old. I will post a pic soon, but the actual IP casing blew out on the backside, where the camshaft looking thing is. I knew there was a small hole blown out the bottom, right under where sight hole is for the IP timing notch, but I didn't realize the backside was blown out also.

sixto · #8 10-22-2007, 01:09 AM

The driven end of the main shaft of the IP has splines on the outside and left hand threads on the inside. The IP timer (sprocket) has chain cogs on the outside and splines on the inside to engage the IP. It's pretty much the same way the cam is driven.

Sixto
87 300D

sixto · #9 10-22-2007, 01:14 AM

Are you sure you have the right replacement IP?

Sixto
87 300D

Jmana · #10 10-22-2007, 08:01 AM

I hope it's the right one, it's off a 350sd, with basically the same engine. The pump looks identical, but this threaded rod is what throws me off. Maybe the guy screwed this in to protect the end during shipping. I have to check it out.