Fuel flow problem

1979-1991 280SE, 300SE, 300SEL, 380SE, 380SEL, 380SEC, 420SE, 420SEL, 420SEC, 500SE, 500SEL, 500SEC, 560SEL, 560SEC
Post Reply
Omar
S Class
Posts: 77
Joined: Wed 12 Nov, 2014 10:19 pm
Model you own: w126

Fuel flow problem

Post by Omar » Fri 22 Jun, 2018 12:39 pm

Hi all,

I’m having an issue with my ’86 420SEL that has me baffled.

In short, I would like to know what might prevent fuel from flowing through a fuel distributor, i.e. flowing out of the ports on the top of the fuel distributor, if the fuel flow to the distributor is adequate and the fuel distributor is in good condition. The fuel pressure regulator and EHA have been eliminated as possible causes.

Some time ago I refurbished the fuel distributor with a new diaphragm and O rings. I re-installed it, and, before connecting the pipes that go to the cylinders, I jumped the relevant terminals where the fuel pump relay sits, to get the fuel pumps running, and depressed the air flap to make fuel come out of the ports on the top of the fuel distributor. At first, fuel appeared in each port, but, before it reached the top of the ports, the fuel flow stopped for some reason.

I tried the refurbished fuel distributor on another car, to eliminate the possibility that I had reassembled the fuel distributor incorrectly, and it worked perfectly. The fuel pumps (Bosch) and fuel filter are new. I can’t actually check the fuel pressure but the flow is as good/fast as it is on another working car.

Any suggestions will be greatly appreciated.

Thanks in advance.

Omar
S Class
Posts: 77
Joined: Wed 12 Nov, 2014 10:19 pm
Model you own: w126

Re: Fuel flow problem

Post by Omar » Wed 04 Jul, 2018 5:23 pm

Hi all,

After reading the relevant sections of the informative book, at the following link, I conducted a test that allowed me to determine what’s causing the problem I described.

https://www.scribd.com/document/3215544 ... on-systems

As mentioned in my opening post, I wasn’t able to check the fuel pressure, but the fuel flow was good. So, acting on the possibility that there was too much pressure in the system, I removed the fuel return line from the fuel pressure regulator and connected a hose to it. And, I put the other end in a large jar to catch the fuel that would come out of it. After jumping the fuel pumps, and depressing the air flap, fuel started to flow out of the ports on the top of the fuel distributor, as it should.

I figure my return fuel line is blocked and the excess pressure in the system is preventing fuel from entering the upper chamber of the fuel distributor. Hopefully, after I clear the fuel line, it should work fine.

KimB
300 SLR
Posts: 1564
Joined: Thu 20 Dec, 2007 5:57 pm
Model you own: w126
Location: Sydney

Re: Fuel flow problem

Post by KimB » Wed 04 Jul, 2018 6:13 pm

Hi Omar,

Keep your fingers crossed!

Cheers,
Kim
W126 86 300SE Champagne
W126 84 380SEC Signal Red

Omar
S Class
Posts: 77
Joined: Wed 12 Nov, 2014 10:19 pm
Model you own: w126

Re: Fuel flow problem

Post by Omar » Mon 09 Jul, 2018 3:07 am

It's all good now.

Post Reply

Return to “W126”