hello vaidlookman,

before you start throwing parts at your benz, if i were you , i would do some research on this forum. there's a ton of information, along with good people who are willing to help , just be patient, and i'm sure you'll resolve your problem.

for starters, your benz has the M104 engine with the 2.8L displacement. your engine(M104 2.8) and the M104 3.2L are essentially the same engines, i'm pretty sure the only difference between the two engines is that they have different displacements. So, any info that you find on here regarding the M104 3.2L pertains to your engine as well.

Check out the following link (it be smart to add this to your favorites): http://www.peachparts.com/shopforum/showthread.php?t=219192&highlight=m104

Although your benz is not suffering from a missfire, there are a series of tests provided by Mr. Dalton which can be of much use to you.

I would take a close look at page 1, post#6:

" But fuel pressure is a next step.
On the top of the fuel rail, you will see a test port cap..That is where you can hook up a gauge. That fitting is the same as an R12 fitting, in case you do not have one.
So, first check is to start the engine and let it idle..now, pull the vac line at the regulator and see if any gas is shooting out that port on the reg. There should be none and if there is, the diaphragm is leaking and you need a new regulator. [ raw, unmetered gas getting sucked intio intake.]. Also check for any evidense of fuel in that vac line..again, you want none.
If all is well, then hook up gauge and do this simple 3 part test.
1-Engine @ idle, Vac line ON-- FP should be 3.2-3.6 Bar
2- " " , Vac line OFF-FP should jump to 3.7-4.2 Bar


3-Engine OFF , wait 30 min. -FP should maintain at least 2.5 Bar
*** I believe if it fails this test, your check valve may be failing. The job of the check valve is to maintain the fuel pressure between the fuel rail and fuel pump*** NOTE: the red text, is info i have added, and i might be wrong, so do the research

*Bar = 14.5 PSI... [ you already know that, but this winds up in archieves]"

Sorry for the long post, but hope you find at least some of it useful.

good luck