Diesel Injection Pump Timing


Diesel Injection Pump Timing

I am probably not the best person to go to regarding engine and injection timing, but since I have had so much difficulty with the matter, I have had to educate myself a little more than I ever wanted to. Please read this entire write-up before you get started in case you have any questions, and so that you know what you are getting into. CAUTION: The Bosch 5-cylinder pumps can be somewhat sensitive. Dropping the pump or jolting it too harshly can cause the rack to become misplaced inside the pump, and you will have to have it serviced to fix this... IT IS NOT CHEAP! That being said...

First thing's first: Pull the valve cover. I find that unscrewing the three 10 mm bolts that hold in the cruise control actuator and moving it over allows for easy replacement of the valve cover, for what it's worth. Then remove the fan blad and shroud from the bay by means of the four 10mm nuts that hold the fan in place. This will give you enough "swinging" room for turning the engine over by hand. Use a 27mm socket (a 1-1/8" works, also) on a small extension, 1/2" drive for turning the crank over by hand, and never go backwards. OK, this is all familiar from the valve adjustment routine.

To pull the pump, remove all lines attached. There is one fuel line banjo bolt on the block-side of the pump, one fuel line banjo bolt on the fender-side, and oil-feed line on the fender-side, and the fuel suply that goes to the priming pump and then from the pump to the main filter. I usually leave the two that run from the filter attached to the pump, and just removing them from the filter block. Remove the oil-feed from the pump, and this will allow easy access to the first nut you will remove. It is a 13mm, and there are three of them. The bottom is the easiest, I think. Just lay barely under the front of the car, reach your hand up there with a gear wrench, and feel for it. It's easy. To get to the top one, I use a 13mm deep-wall on a 6-inch extension on a U-joint on a 3/8" drive socket wrench. It's not to tough. And the middle one (blocked earlier by the oil-feed) can only be had by an open-ended wrench.

The final attachment is held in the back. It is a royal PITA to get to, and I have made a mock-up replacement. You will almost HAVE to use a gear wrench for it (it makes life a LOT easier). Once that is off, go under the car, and remove the support bracket that mounts to the block at the rear of the pump (held on by two 13mm bolts). Once all of this stuff is disconnected, you can remove the pump with the filter housing in place by sliding it straight back and upwards at the same time. I have heard it is sometimes necessary to remove the rack dampener pin, but I have never had to do so, and I have done this job probably around 11 or 12 times.

Once the pump is out, you will need to put your new one in. Crank the engine over many times by hand to get everything "settled". I doubt this does anything at all, but it's a mental thing for me (OK, so I'm crazy ;-). Look on the cam shaft near the front of the engine where it slides through the first bearing mount. You will see a tick mark. Turn the engine over until the stationary tick mark and the mobile tick mark are lined up. Your harmonic balancer should read at 0* TDC. Crank the engine around again, passing TDC once (that will be the exhaust stroke), and stop at 24* BEFORE TDC the second time. The tick mark on the cam should be just shy of reaching the TDC marker.

With the engine at this time setting, you will shoot the pump in. Take a 3/4" wrench for socket wrench, and as you look upon the nut on the front of the injection pump, turn it clockwise, making several resolutions. Then crank it, and again, only clockwise, until the spot with a missing tooth lines up with the dash mark that is set about 15* behind 12:00. It is easy for it to move out of time, so you must be gentle with the reinstallation.

Slide the collar that came off out of the engine with the pump over the sprocket on the pump. There is no special way to do this... just slide it on without turning anything. Piece of cake. Then, gently lower the pump into the engine, frontside going down first at an angle, and let it slide into place. Tighten it down at a random position with the nuts (NOT the rear bolt) and connect the feed lines. Pump the hand-priming pump to hell, and vent off your fuel filter so that there is NO more air in the system. Crank the engine over by hand, and see if fuel comes out of the feed lines. If it does, great. If not, reconnect your fuel injection lines, and pull the socket wrench of the engine. Then, disconnect your glow plug relay, go in your car, and hit the starter a few times to build some pressure in the lines without starting the engine. Go remove the line #1 injection line, and soak up the diesel in the port with the corner of a shop rag, being careful not to leave lint or anything behind. Then crank the engine over by hand, monitoring that first port. When you just BARELY start to see fuel well up in it, stop. Look at your degree marker. If it is at 24* BTDC, then your perfect, though I hear running at 26* can offer a little more low-end power. To advance, loosen the three nuts, and tilt the pump AWAY from the block with a cheater bar of some sort. Two people help this to be done a little more easily, as one can hold the cheater bar in place while the other tightens the pump. The lines will act as a memory-spring that can be a pain to deal with. If you want, remove all the lines (which is what I prefer).

Once in time, tighten the three nuts down nice a snug, and reinstall the bracket that supports the rear of the pump. Instead of using the original 13mm bolt that goes throught the mount and holds the pump, I epoxied some washers to a 1/4"x1" bolt and slide it throught the hole. Then just tighten down a lock-nut on the front side of the hole. It will take you about 15 minutes of dropping the bolt to do it right, but I have yet to figure out how to put the original 13mm back in hole. Connect the spring from the support bracket to the small hole in the arm on the block-side rear of the pump (mechanic's fingers make it a piece of cake... without them it is nearly impossible, I think), and then reconnect your linkage. Check your timing again, and if it is spot on, put everything back in place, including your cruise control actuator, tighten the injection lines tight so they don't leak, but not so tight that they strip (that would suck!) and reinstall the fan blade and shroud. Jam the manual kill switch, and crank the start until oil pressure reads (the pump will then have oil circulating in it). Un-jam the kill (I just wedge the handle of a screw driver in it), and start her up.

First time I did this job, it took me about three hours. It now averages about an hour. Having a very clean engine always makes things much easier, less time-consuming, and overall more enjoyable.

Trace Cody







Ref: Frank Mallory's database and https://mercedes-benz-publicarchive.com