3.5 liter injection pump in a 3.0 liter engine - PeachParts Mercedes-Benz Forum

Maxbumpo · #1 01-22-2017, 08:58 AM

Dieselvolk,

I've got an injection pump from a '94 with 3.5 liter engine that I've installed in my '87 wagon with 3.0 liter engine.

Here's the situation: My 124.193, with 365k miles, isn't running well at all. Under anything more than gentle throttle, the engine pings and smokes. Mileage is bad, around 22 mpg in town, about 25 on the highway. I used to get about 26 in town, 28 on the highway. Starts fine, idles fine. A diesel-purge treatment will clear it right up, and it will run just fine (and get better mileage) for about a month, and then it declines back to poor running. Italian tune-ups will also help a bit (especially with the smoking).

What changed? I installed an injection pump from a 3.5 liter engine. One of the three hold-down tangs on the original IP broke (long story) so I had to replace it, and I had this 3.5 liter IP on the shelf.

When I installed this "new" IP, I overhauled the delivery valves, and adjusted the ALDA 1/2 turn richer. I have since moved the ALDA screw back to the original position, I think, I need to check the records. I may have only moved it back 1/4 turn.

What else is wrong? I have the wrong glow plugs installed. When I installed the "new" head a few years ago (with oblique injection) I swapped in the relatively new glow plugs from the original head. Oblique injection heads use a glow plug that is shorter.

Two weekends ago I adjusted the timing (it was a couple degrees advanced), and then went on a 900 mile highway trip for work. No change in performance. I think that this bigger pump is over-fueling the engine, resulting in lots of un-burned fuel and carbon build up.

Yesterday afternoon I installed a boost gauge and measured only 8 psi boost. I shortened the waste-gate rod 1.5 turns (which took about two hours, what a pain!) which only bumped up the boost to about 9.5 psi. That did seem to help, but after thinking about it overnight perhaps all the "Italian" tune-ups that I did to test the performance are what improved the rough running.

Options that I can think of:

1) Back off the ALDA screw a little more.

2) Install the correct glow plugs.

3) Fix the turbo output with external controller, bump it back up to 14 psi.

4) Remove the 3.5 liter injection pump, put a 3.0 liter IP back in (now I have a complete engine/tranny with pump that I can raid).

5) Pull the engine and tranny, swap in "new" engine / tranny that are much younger, only 143k miles. The downside is that engine still has the original #14 head, but that is minor (I think the head is sound).