Injector Pump Timing - PeachParts Mercedes-Benz Forum

#1 02-21-2003, 08:55 PM

I need some help with my logic please. I am trying to time the injector pump on my new 1976 240D. I need it to pass emmissions here in Denver so I'm putting a lot of time into the maintenance. I tried to follow the Richard Easley method on the Baylor.edu website which is straight forward but I never saw fuel coming out of the pump (pooling in the fitting). I was not sure the hand pump was pressurizing the pump enough so I tried to go one better and hook up my Heise gauge to the pump to check for pressure changes. The Heise is real sensitive--it will pick up a sneeze from 40 feet. I hooked up my air compressor line to the fuel line and pressurized it to about 30 pounds. The Heise was hooked to the pipe outlet to #1. I figured if I turned the engine I should be able to see some pressure when I reached the injection point. I never did. I had the linkage set to WOT but that made no difference either. Sorry to be so long-winded but according to my logic, this should work pretty slick and be real accurate. My poor brain is quite dizzy at this point so could someone enlighten me on why this isn't working?

Stevo · #2 02-22-2003, 01:15 AM

Why do you think the pump needs timing, its not usually a maintenance item unless someone has screwed it up. Did you remove the little spring and disconnect the vacuum line?

#3 02-22-2003, 11:38 AM

Stevo,
I am not sure if it needs timed but seeing the screwed-up repairs that was done on this car, I figured I better at least check it. Examples of screwed-up repairs: none of the intake valves had any clearance, engine had about zero compression-- I could turn the crank pulley by hand; only one bolt holding the power steering pump, the rest were broken off in the block. I did not remove the vac line. What/where is the little spring? While I have you here--how do you check for cam chain wear?
Thanks for your help! I live for this stuff.

Fisherman · #4 02-22-2003, 11:40 AM

I don't have a clue about your method here although in theory it should work. Fluid dynamics was not my strong suit..

I do know that the drip mehtod is not that hard to do once you have been able to perform it on a system...

That being said, I messed with my first one for a good 2 hours before I could get any fuel to come out the pipe I had made (picked up a line at a wrecking yard and hack sawed it off).
Now it seems too easy when I check it on a car...

Seems that if you start with the balancer at about 30 degrees BTC you can get fuel out of number 1 which is at least a little reassuring that fuel is flowing. Then you can advance the motor to the spec and check the pump again.

The spring that Stevo is referng to is the one that fits under the pressure fitting on the IP. You did remove the spring and valve under there correct? When I did this with a full tank in the 123 the tank wanted to empty itself through this fitting...
Also you should wire open the throttle to full and disconnect the shutoff vacuum line from the back of the IP.

#5 02-22-2003, 12:47 PM

Thanks Fisherman! I'm on my way to the garage to try it again. I did not disconnect the spring or vac line but I will. I am fuzzy on the valve but I will look for that. I did have it at WOT but never did see any fuel in the fitting. I've been collecting my bag of tricks for 20-25 years but none of them are Merecedes related. At least they helped me fix the broken studs that hold the power steering pump to the block. Ace Hardware sure has a great selection of hardened metric fasteners that helped me fix this better than factory original.

Fisherman · #6 02-22-2003, 12:49 PM

Gary,
Before you head out do you have the Haynes book?
I can walk through it a little slower/step by step if that would help...

Stevo · #7 02-22-2003, 01:12 PM

Gary

Sounds like you have multiple issues. I would suggest you go to the archives and check 'timing chain stretch" lots of info on that and timing. Do you have a Haynes manual. It covers most things fairly well. Most folks use the drip method for timing although I use the bubble method because thats how I was taught. I could not get the Easley method to work very well either. Anyway check out those archives and let us know as you can get the basic info down then if you get hung up someone will be able to help.

#8 02-22-2003, 07:23 PM

Thanks again. I have multiple issues with most things but my life is never dull. I think when I die I'll go straight to Heaven and not have to spend any time in Purgatory becaue I'm paying my dues as we speak. I don't have the Haynes manual but I bought a CD on eBay though it's hard to use. I still can't find the spring and valve previously mentioned. I turned my inspection mirror in every possible direction but don't see them. Theoretically, these procedures sound easy but I still can't get any pooling of fuel to show. I want to check the chain since I have the whole front of the engine apart. I think that would make it easy to replace if I have to. I'll check the archives for chain stretch. Fisherman, I would sure like more instruction if you don't mind.

Fisherman · #9 02-22-2003, 08:58 PM

After you remove the piping to the injector you are left with a 15 mm fitting sticking out of the Injector Pump (IP). Remove this fitting and just under it is where you will find the spring (be careful not to lose it). Under the center of the spring is the valve. You can reach into the IP with a pair of needlenose and withdraw this part from the center of the hole. Do not take out anything else...

Now put the 15 mm fitting back in and attach your test tube (old injector line bent over 180 degrees and cutoff) and you're ready to go. The pictures of the test line are on the CD. I made mine up long enough that I could get a jar under it easily...

if the motor is about 30 degress before TDC on the compressions stroke of #1 you should get some fuel flow out of the pump without any pumping. At least i did on mine.

Now tie off the throttle at full throttle, disconnect the vacuum shutoff hose from the back of the IP. and then set your crank at whatever vaule is given for you motor. I think is probably 24 degrees before TDC on #1. You can check TDC on #1 by pulling the oil filler cap and making sure that neither of the front cams are engaging the rockers. They won't both point up but side to side as I remember indicating that they are not pressing down on the rocker thereby indicating that #1 is on the compression stroke.

One thing, before advancing to 24 degrees or whatever value is give try pumping the hand pump a few times and see if fuel spurts out of your tube.

Now loosen the IP mount bolts a little (3 on the front and one on a bracket in the rear) the rear one was designed by a sadist bye the way... The front ones can be reached with a universal on your 13 mm extension. The rear one by the grace of GOD...

Now while pumping hand pump on the IP you should be able to get fuel flowing in a steady stream by rotating the IP away from the engine. If this happens GREAT! Then while still pumping with the hand pump slowly rotate the IP towards the motor until you get down to only a drop per second dripping out of the tube.

That's the setting at begin of delivery.

Tighten the IP mount bolts and then just because, check it again... This time you can check by rotating the motor around two turns to the compression stroke on #1 again and then stop short of your setting of 24 at say 30. You should have a steady stream. Rotate the engine to your mark and it should slow or stop very near to your mark on the crank.

One other little thing. DO NOT rotate the engine backwards (CCW) in order to get on the mark. If you miss it go around two times again to the mark. Kind of important since the engine rotates CW and your timing will be off if you go backwards.

Somebody check me here to make sure I covered everything okay?

Good luck and let us know if you need more help...

Beagle · #10 02-22-2003, 11:00 PM

There is just one small point I would add to Fisherman's comprehensive instructions:

After you remove the piping to the injector you are left with a 15 mm fitting sticking out of the Injector Pump (IP). Remove this fitting and just under it is where you will find the spring (be careful not to lose it). Under the center of the spring is the valve. You can reach into the IP with a pair of needlenose and withdraw this part from the center of the hole. Do not take out anything else...

Before you withdraw the valve thoroughly clean out the cavity. Dirt and grit in the thread will have fallen on top of the valve seating and will be sucked onto the metering piston as you lift it out. I find the best way to do this is to hold the valve firmly closed with a thin screwdriver and blow out with compressed air.

#11 02-23-2003, 11:32 AM

Thanks guys for the help. I think Mercedes has an entry on their engineers employment app that rates sadism, the higher you rate, the more likely you are hired. I am headed out to the garage as we speak to try this. I have the valve cover and oil pan off to clean them so finding TDC will be easy.

#12 02-23-2003, 03:08 PM

Once I removed the spring and valve, I got fuel to flow. Boy am I relieved about that! I'm still trying to invent my own procedure using my Heise digital pressure equipment though. There are definite pressure decreases and increases noted as I rotated the crank. Pressure was high until I reached about 40 degrees BTDC then it dropped to zero. As I approached injection point, I noticed just a few mm pressure increase until 24 degrees then it was full pressure. This was way cool to see-- now I have to figure how that correlates to the precise timing point. I definitely appreciate npnye's advice and I am considering having a trained tech time it until I learn more about the injection process. I am curious about what damage is seen when the timing is not correct. Once I get this thing put back together, running, and passing the emmission test, I will be happy. Thanks again for everyone's help. I'm sure I'll have many more questions to ask. My goal is to be a respected senior member like the others on this site.

psfred · #13 02-23-2003, 03:26 PM

No need to invent anything, alas. The drip method is fast, easy, effective, and accurate.

What you are measuring is the point at which the piston covers the intake slot and starts raising the injection pressure. The only better way is to use the Hall effect pickup on later pumps.

Check the stretch on the timing chain before changing the injection timing, though -- if the valves were too tight, chances are maintenance was sloppy, and the chain is worn. This will make both valve timing and injection timing late, both cured by a new chain. Procedure is covered extensively in other posts, and isn't too hard. If you change the timing, then find out you need a new chain, you will have to repeat it, and that paper gasket under the IP will eventually tear and start to leak.....

Peter

leathermang · #14 02-23-2003, 03:45 PM

Have you looked at the shop manual for that engine? You may not have to invent anything due to explicit instructions being in there.... I think everyone uses the drip method because they do not have the high pressure gear to do it the other way... like a Dealer would normally do... I may be dreaming... but you should check it out....

#15 02-23-2003, 04:01 PM

MY manual is a CD I bought off eBay and it's hard to use. I'll buy a better one I guess. I believe the previous owner was neglectful and that is why I only paid $450 for the car-- no rust and a fairly straight body. I used the cam tower procedure to check for chain stretch but I understand that may not be very accurate. I have dial indicators but I can't follow the instructions for this method on the site. Anyway, using the cam tower, the chain is stretched 3-4 degrees. I guess I just want to get some use out of my pressure unit that I've had for a few years; it is the most precise instrument on the market. I think it's good to keep the brain stimulated. I will get the fitting and try the drip method though. If someone can better explain the proper way to measure chain stretch, I would appreciate it.