642 fuel pump issue, relay? - PeachParts Mercedes-Benz Forum

MB140300SD · #1 10-23-2018, 06:45 PM

So I just got my 07 R320 back on the road after being down for a while. It kept throwing a code for high fuel rail pressure which ended up being fixed by replacing the left fuel rail. Before that the in tank fuel pump was replaced with a brand new one, as well as the fuel quantity valve. Anyway on to the new issue. Drove the car on a 1200 mile round trip last week. It did fine except on the way home went to fill it up, when I went to restart it, no start, just cranked. After several attempts if finally fired up and was fine after that.

Yesterday, wife called and it did it again while she was at the store. It finally started and she drove home but it died about a mile from the house. She got it restarted again then it died right after. I showed up and could not get it to start. I pulled it home with the truck. When I got it home it did not sound like the new in tank pump was running when the key was turned on. After cycling the key off and on a few times I could hear the pump kick it and it started.

I went out and messed with it a little bit and I suspect it could be the relay. I went thru several starts and it was fine but had the no start happen a couple of times. With the car running, I sort of moved the relay a little with my finger to see if I could get the pump to cut out and I think it may have, just a short amount of time but not enough to kill it (split second). So, I suspect the relay is flaky or something with the contacts in the fuse box. I see the relay is less than $5 so I guess I will order one up. Anybody BTDT with this issue? Does this sound like the relay going bad, or more likely something with the contacts in the box?