Testing fuel pressure on M103.. Which ports? - PeachParts Mercedes-Benz Forum

Cap'n Carageous · #1 08-25-2003, 03:27 PM

Which ports do you use to check upper chamber and which tests lower chamber? System pressure too while we're at it.

1991300SEL · #2 08-25-2003, 05:48 PM

Not MB, but CIS. Might help

http://www.geocities.com/jonnyguru/vw/fpressure.html

stevebfl · #3 08-25-2003, 05:58 PM

A lot depends on what you want to measure. The two fitting in the picture are in and out. The "In" comes from a hose and the out goes straight to the fuel pressure regulator. We use a Bosch adapter and take our system reading at the inlet. Our fitting is a tee that is inserted between the hose and the fitting and the gauge.

The screw that is in the picture allows access to lower chamber pressure. With two gauges calibrated to each other (both used to measure the same pressure to gauge their relative accuracy) the system pressure minus the lower chamber pressure gives differential pressure.

Cap'n Carageous · #4 08-26-2003, 07:49 AM

I connected my gauge to the fitting on the right top seen in the picture on the left. I was assuming this was upper chamber. I get 5.5 bar there with the fuel pump on and the fuel distributor in the 'at rest' position. Is that right?

stevebfl · #5 08-26-2003, 08:17 AM

Yea, that sounds right. Use the similar screw on the right picture to do the lower chamber.

ps2cho · #6 07-15-2008, 11:10 PM

Nice thread! iwrock found it for me

Just to clarify as I'm not sure....I can attach my pressure gauge to the "in" port so I can test the fuel pressure to make sure its okay. Should I test both the upper and lower chambers to make sure my misfire is not fuel related? Correct me if I am wrong, but isn't the lower chamber for low speed and idle conditions? So I should check it for sure, correct?

Whats the correct pressure for an 88 300TE?

Also, anybody know where I can get one of these Bosch T adapters?

cc260E · #7 07-17-2008, 01:54 AM

Quote:

Originally Posted by Cap'n Carageous

Which ports do you use to check upper chamber and which tests lower chamber? System pressure too while we're at it.

I did a self made kit. See my post if it can help both for lower and upper pressure measurement simultaneously.

http://www.peachparts.com/shopforum/showthread.php?t=107290

ps2cho · #8 07-18-2008, 12:21 AM

Quote:

Originally Posted by cc260E

I did a self made kit. See my post if it can help both for lower and upper pressure measurement simultaneously.

http://www.peachparts.com/shopforum/showthread.php?t=107290

Ok I can see how you tested simultaneously. Perfect!

What did you use for the self made kit? The picture is a little small to see too well.

Hit Man X · #9 07-19-2008, 03:58 AM

Hrmmmmmm...

so to bring up or decrease the lower chamber pressure do I adjust the EHA valve?

ps2cho · #10 07-20-2008, 11:46 AM

Quote:

Originally Posted by Hit Man X

Hrmmmmmm...

so to bring up or decrease the lower chamber pressure do I adjust the EHA valve?

I don't know for sure, but I assume that's correct! After a few adjustments that I have made to it, I need to return it to factory settings now.

S-Class Guru · #11 07-20-2008, 03:23 PM

Hitman, yes, the EHA and the airvalve hex screw are the two ways to alter the pressure differential and richen/lean the mix.
But, of course, this only has an effect when the O2 sensor is not controlling the EHA, such as cold start and full throttle. When in normal closed loop, the O2 takes total control, if the initial settings are not too far off for it to alter.

Check the DIY articles herein for a better explanation - I think it was Steve who wrote a very comprehensive one.

DG

Hit Man X · #12 07-21-2008, 04:08 AM

I turned the EHA a 1/4 turn CW and it has appeared to help my warm start out. I may turn it 1/4 more and see what happens, certainly can't hurt. Cold start still exhibits longer cranking than I believe to be necessary, but could be perfectly normal for the M103 for all I know. My M117 fires right up with minimal cranking but also has half the miles. My 300SE fires up quicker and the mileage is around the same (maybe freeway miles vs city, being high RPM?)

Car runs fine after a cold start. No stalling, no surging, no anything really. Power is adequate for what the car is, moves along fine (it's no 400E, but gets the job done). I'm not wondering if my worn head is causing a drop in cold cranking compression to fire up.

Then once hot/warm the guides have expanded some against the valves

The fuel pump is very noisy and with the mileage/years I'm going to go ahead and replace it for piece of mind. Maybe if it's not putting out enough flow/pressure, pressure to the fuel distributor is off causing the differential pressures to be off.