84 300sd low fuel pressure? Gummed injection pump? - PeachParts Mercedes-Benz Forum

Knuckleballerr · #1 12-30-2013, 03:32 PM

I was opening my fuel lines, trying to purge it of air chasing a "crummy power" situation.. (40 mph up a hill tops with 50 mph start before the hill) when I noticed something quite odd.

Let me make clear the air was being purged while the car was on and running so nobody is confused (Yes, I was safe about diesel in the skin. I only did it that particular day because it was convenient). When I'd open lines 1-3 (left to right, from perspective of drivers side) there is almost zero change in idle power. In fact, its hard to tell the line is even open? I feel like I can take the line/s off and there would be no change. Line 4 only has a slight drop in power.. but when line 5 is cracked a significant amount of idle power is lost. This is on a MW-Pump.

Tinkering with it.. I've found what can best be described as a "rusty red goo" on just about everything post lift pump.. undoubtedly from the PO's veg oil use. I've purged this pump plenty of times in the past... seafoam.. diesel purge. But I have a strong feeling that's too weak for this (its quite tough!)

I've seen other's on this forum use a long acetone & gasoline soak. Should I do this? (Is it wise to do it during winter? I don't care about working in the cold but I'm not sure how much temps play into this). I've since fixed the lift pump leaking issue that I think is very much related.

Am I to disconnect the lines from the injectors and send acetone through the whole system and let it soak for a LONG time?

~

Also, I considered on cutting a mark on the injectors.. taking them out & opening them up for a super good clean. Sand the surfaces (except nozzles) with 2000 grit paper.. and put it back together and line up the marks. I might not have a pop tester to see pressures.. but would this be wise? Is it possible to use the injector pump to see the spray patterns?

ROLLGUY · #2 12-31-2013, 08:13 PM

A weak or bad return line check valve (on the side of the IP next to the block) can cause low fuel pressure, especially if WVO was used in the system. That is the first place I look when a low fuel pressure symptom occurs.

Diesel911 · #3 12-31-2013, 08:25 PM

Also remove the Fuel Supply/Lift Pump and take it apart and clean and inspect it. The Valve springs on the Lift Pump are not very strong. Gunk can easly mess with the Springs and get between the Valve Seats and the Valves.
The Pump Piston can also get stuck.

Conserning your Injector Cut out Test Right now the test you did could be either a bad cylinder/s or bad Injector/s or the Injection Pump.
If you swap the #5 Injector (the one that appears to be good) with one of the Bad Injectors and the problem follows the Bad Injector you will know if it is the Injector.

You can't back flush the Fuel Injection Pump by way of the Fuel Injection Hard Lines without remving the Delivery Valve Holders, Sopring and the center part of the Delivry Valve Assembly (each center part of the Delivery Valve is mated to the outer part and they cannot be swapped around so if you do that only do one a time.)

Even though the WVO had gone through the spin-on Fuel filter it is possible for gunk to build up inside of the Fuel Injection Pump; especially if the Vehicle had sat a long time and also if WVO was left inside when the Engine was cold allowing the WVO to solidify.

In the pic is one of the Elements and the Fuel Feed Hole in the Element that that has to be open to let Fuel in.
However if you remove the Element it can change the Fuel quantity that the Element puts out and with no Calibration Stand you will not now how much the Fuel quantity had changed.

jay_bob · #4 12-31-2013, 08:30 PM

If you need your injectors rebuilt and popped contact greazzer on the forum. He has a pop tester and all the right stuff to break them down, clean them, and properly set them back up.

ROLLGUY · #5 01-01-2014, 02:18 PM

Quote:

Originally Posted by jay_bob

If you need your injectors rebuilt and popped contact greazzer on the forum. He has a pop tester and all the right stuff to break them down, clean them, and properly set them back up.

And the quality is very good, and the price can't be beat!