M103 fuel distributor or fuel pump? - PeachParts Mercedes-Benz Forum

lsmalley · #1 01-18-2022, 12:09 AM

My car 190E 2.6 has developed a rough idle and I have narrowed it down to a fuel problem. To be precise, a fuel problem at cylinder #1. I let the car idle at operating temp and starting from cylinder #6 I pulled the plug wires one by one. Each time a pulled a plug wire, the car idling would get much worse until I put it back. Finally got to cylinder one and pulled the wire and noticed no change at all, however there was definite spark at the wire. I moved the plug from cylinder #1 to cylinder #2 and the problem was still at cylinder #1. I then disconnected the fuel line from the injector and put the end into a bottle and cranked the engine and I got maybe a less than an ounce of fuel that dribbled into the bottle. I pulled the entire line off to check for blockage and it's clear. I'm wondering if a faulty fuel distributor would only affect the one cylinder or if a fuel pump failing would cause this. I last replaced the fuel pumps in 2016 with Walbro pumps. Other than the rough idle the car runs fine. Thoughts, suggestions, or advice is much appreciated.

Sugar Bear · #2 01-18-2022, 10:58 AM

The fuel pumps feed the entire fuel distributor not any individual injector. IF, the pumps are supplying sufficient volume and pressure then any individual injector problem would be in the injector or distributor.

The perfect diagnosis would be a pressure test of the fuel pumps to rule out insufficient fuel to the distributor. If the other injectors/lines are working ok it is a quite safe assumption it's the distributor. Compare #1 to others.

In these circumstances I'd also do a compression test especially on #1.

Good luck!!!

Frank Reiner · #3 01-18-2022, 11:49 AM

As noted, begin with a compression test.
Pump(s) are a rather low probability; all cylinders would be affected equally.
There is a very low possibility of a single cylinder fault in the fuel distributor.
The injection nozzle/valve for #1 is a fairly high possibility.

lsmalley · #4 01-18-2022, 11:50 AM

Correction: car 'was' running fine. I now find myself sitting on the side of the road because the car stalled. Started back up, but as soon as I move it to D and depress the gas pedal it stalls out. So I can have it idling, but when I depress the gas pedal in D it stalls. In P or N it will rev up if I depress the gas pedal. I was actually able to adjust the small nylon nut on the gas pedal to have the idle increase to 1500 and I shifted to D and was able to let the car roll using the high idle momentum to get to a gas station. So now I'm guessing fuel pump maybe?

Sugar Bear · #5 01-18-2022, 02:12 PM

Unfortunately without testing all we can do is guess...How old is the fuel filter? Can you feel both pumps running? If both pumps are running and the car hasn't sat for a long time the fuel pumps are unlikely the problem source, if the car has been sitting for loooooong extended periods then they are prone to gumming/seizing. Is there a reasonable chance the fuel is bad, can you sample the fuel?

Has the boot been replaced under the fuel distributor or the large IAC hose(s) been replaced? I'm thinking toward a large vacuum leak brewing.

Good luck!!!

lsmalley · #6 01-18-2022, 02:35 PM

The car hasn't sat, it's my daily driver. I had everything off yesterday trying to diagnose the problem. The large boot is sealed up and pliable. Vacuum is pulling at about 15 with no leaks. I'm in tow now on my way home. I'll get the car up and test the fuel pumps for function like I should've done in the first place and report back.

Zulfiqar · #7 01-18-2022, 03:38 PM

You have an unmetered air leak that is causing the fuel starvation, the cis system requires the manifold to have a nice solid vacuum so the air sensing plate can react properly.

Otherwise you are going to have to test the distributor for supply issues, what you can do is to check the fuel inlet screen if its dirty.

lsmalley · #8 01-24-2022, 10:13 PM

Ok guys, here's where I'm at:
1)Fuel pumps and filter have been replaced and still nothing.
2)Spark plugs and wires are new as well.
3)Distributor and rotor are also new.
I'm not sure what's going on. It's definitely getting fuel. Does anyone have any other suggestions that I may try?

Sugar Bear · #9 01-24-2022, 10:50 PM

Have you been able to confirm spark at the plugs? Did this occur after a recent refuel?
Can you give a description of how/when the symptoms came about?
If spark is good I’m leaning toward zulfigar’s unmetered air leak theory.
Good luck!!!

lsmalley · #10 01-25-2022, 12:03 AM

Car already had sort of a stumbling issue, but always fired right up. On the day it happened I was driving to work on the highway and came to a stop at one of about 3 lights on a 20+ mile stretch. Car was idling rough, but when light changed green I went to accelerate and car died. I tried to start it up, which it did, but then died when I gave it gas. I adjusted the nylon nut by the gas pedal to bring the RPMs up to about 1500 + then put the car in D and let it drive off the highway to a gas station and got towed back home. Since its my DD and my only car, I've been able to keep mostly everything in good order. I swapped out the FD. No change. Swapped out the MAS relay, no change. However, I did just install 2 new pumps and a new fuel filter since it happened and still nothing, but I can't get it to start now. One thing which may help is that it seems like it want's to start if I spray a bit of gasoline on the throttle plate. So gas related maybe? If so, which part would cause this issue? I pulled the plugs today even though I just changed them earlier this month and I did notice that cylinder #6 was darker than the others, which is interesting, because I thought cylinder # 1 was giving me the issue. I am at a complete loss.

Dave Kost · #11 01-25-2022, 06:55 AM

You need to test your fuel pressures. System and differential as well as fuel volume.

The KE Jetronic principles is based on fuel pressures being within specifications.

Also, 15 vacuum seems low, so unless you did a smoke test to confirm, you still may have a vacuum leak.

Sugar Bear · #12 01-25-2022, 10:31 AM

EGR valve could be hanging open creating a large vacuum leak or a leak in the tube to the bottom of the intake from the EGR.

Dave Kost's idea of a smoke test is in order...now how to do that at home???

Keep at it, you'll win.

lsmalley · #13 01-25-2022, 11:36 PM

Since I can't start the car to create vacuum, I'm wondering if connecting my vacuum pump to the intake to create vacuum would still work to test for leaks.

Sugar Bear · #14 01-26-2022, 09:58 AM

Any way you could pressurize the intake? Perhaps a small electric leaf blower or shop vac exhaust would work and inject smoke at the same time to see where it exits. Search on YouTube, it's very likely been figured out for us.

IMO the vacuum pump won't create sufficient volume for a test.

Good luck!!!

lsmalley · #15 01-26-2022, 06:37 PM

So no vacuum leak detected. I used my 5.3 amp shop vac connected to intake with key on and tested for leaks and got nothing. Just out of curiosity, does anyone know what pressure or force the actual fuel pumps are supposed to be putting out at? Also, what should the fuel pressure be at? I ran 12v to cold start valve and cranked it and it turned on, but ran rough.