Robert Williams

This particular 2000 model ML55 cut out on me twice before leaving from work the other day. On the way home, 55 miles, she seemed to have no power, would hesitate when I tried to accelerate, and was very difficult to get above 45 mph. I made it home, but she was running rough except at idle. I searched the forums and decided it was time to replace th MAF. I was also showing codes P0400, EGR flow malfunction, and P0100, MAF circuit malfunction. After replacing the MAF, she would not start. I put the old one in and still would not start. Disconnected the MAF and still did not start. After letting her sit for two days, she starts, but if I am in R or D, she starts behaving badly at 1200 rpm or more. In N or P she runs perfectly and I have taken her up to 3500 with no issues at all. So I am thinking that this is computer related. Any ideas would be greatly appreciated.

Maj. Dundee

You must remove your EGR tube to see if it is clogged.

Robert Williams

I finally got a fuel pressure tester and found some interesting results. Number one, the needle oscillated about 10-15 psi rapidly while the engine was running. This indicates to me a problem with the fuel pump. Once the engine was running the readings fluctuated from about 13 to 30 psi. When my wife held the accelerator to 2500 rpm. the fuel pressure dropped to about 10-12 psi. Do you guys concur that I need a new fuel pump? How difficult is this to do? Do you have to drop the fuel tank? Thank you.

Robert Williams

Would the EGR tube blockage effect the fuel pressure?

Maj. Dundee

No it will not.