E55 Hard starting when warm but it starts!
05-22-2011, 09:52 PM
#1
Senior Member
Thread Starter
E55 Hard starting when warm but it starts!
Hey guys it’s been awhile since I’ve been on here. My E55 just hit 96,000 just did plugs and wires. Just in the past few weeks my engine when warm (not cold and not hot) turns over about 5-8 times then starts up and runs great. This is not CPS just installed a year ago. I read another W210 E55 with same problem he said his fuel pressure regulator was bad with fuel in the vacuum line. The fuel loses pressure when warm. This only happens one to three times a week in the last few weeks and when it does happen my car was sitting not running for a few hours when the problem comes up.
He replaced it and everything was good after that. When I replaced my plugs and wires yesterday I did not look for this due to me thinking it was the wires and plugs. I have read that our E55’s don’t have a fuel pressure regulator on the engine, is this true? He said his was in the back of engine on the fuel rail. I will look this week.
What do you guys think has anyone had this problem before?
Here is link to his problem and fix http://forum.mercedes-benz-clubs.com...3c272c4fbb73c4
I had an existing warm hard start problem that was gradually getting worse. The car would start perfectly with the engine cold, but had difficulty when it was already warmed up and left for awhile, i.e., leaving the mall after movies and groceries. Did some research and realized that among the probable culprits were leaking fuel injectors or the fuel pressure regulator unable to hold pressure.
Having learned my lesson to start on the easiest/cheapest jobs first when troubleshooting a vehicle, I looked at the FPR. The moment I pulled the vacuum hose connecting the FPR to the intake manifold, fuel gushed out. So luckily, I found the culprit without moving to the harder stuff. The R&R:
Depressurize Fuel System
1. Locate the fuel pump fuse in your fuse box and remove this.
2. Crank your vehicle and let it run until it shuts down.
3. Disconnect battery terminal. Some may feel this is unnecessary but since I was working with the fuel system I did not want to take any chances.
Locating and Removing FPR
The FPR is located on the left side fuel rail near the firewall, easily identifiable by it's round shape and a vacuum hose connecting it to the intake manifold. Disconnect the vacuum hose. Have a piece of towel ready to soak up any fuel spillage.
The operating principle of the FPR as I know it is that the vacuum line controls a rubber diaphragm that keeps the fuel pressure at a specified rate, or increases it depending on engine load, the signal of which it determined by the amount of vacuum present in the line. If fuel can be found in the vacuum line (like in my case), then the rubber diaphragm has likely been perforated or torn, and is sucking fuel into the intake manifold, and leading to an over rich situation.
Shut off the engine while performing this test, because pressurized fuel might squirt out. Keep a towel handy to soak up whatever fuel might come out. Remove the battery terminals even to be on the safe side. Even with the engine cold, if the FPR is sucking fuel into the vacuum line, there will be fuel present once you remove the vacuum line.
My symptoms were:
-Warm hard starting (more than 5 seconds)
-Found fuel in the vacuum hose leading from the FPR to the intake manifold
-Engine rpm dives to 0 mark when slowing down from high rpm (my rationale is the injectors are likely flooded with extra fuel from the intake manifold at high rpm which became unburned during stopping...I could be wrong).
After FPR replacement:
-Quick starts with engine warm or cold
-No more rpm dives
-Engine runs a couple of degrees cooler (two needle widths away from the 100C mark where it previously stays pegged on the 100C mark)
Thanks I look forward to your feed back.
Dawson
He replaced it and everything was good after that. When I replaced my plugs and wires yesterday I did not look for this due to me thinking it was the wires and plugs. I have read that our E55’s don’t have a fuel pressure regulator on the engine, is this true? He said his was in the back of engine on the fuel rail. I will look this week.
What do you guys think has anyone had this problem before?
Here is link to his problem and fix http://forum.mercedes-benz-clubs.com...3c272c4fbb73c4
I had an existing warm hard start problem that was gradually getting worse. The car would start perfectly with the engine cold, but had difficulty when it was already warmed up and left for awhile, i.e., leaving the mall after movies and groceries. Did some research and realized that among the probable culprits were leaking fuel injectors or the fuel pressure regulator unable to hold pressure.
Having learned my lesson to start on the easiest/cheapest jobs first when troubleshooting a vehicle, I looked at the FPR. The moment I pulled the vacuum hose connecting the FPR to the intake manifold, fuel gushed out. So luckily, I found the culprit without moving to the harder stuff. The R&R:
Depressurize Fuel System
1. Locate the fuel pump fuse in your fuse box and remove this.
2. Crank your vehicle and let it run until it shuts down.
3. Disconnect battery terminal. Some may feel this is unnecessary but since I was working with the fuel system I did not want to take any chances.
Locating and Removing FPR
The FPR is located on the left side fuel rail near the firewall, easily identifiable by it's round shape and a vacuum hose connecting it to the intake manifold. Disconnect the vacuum hose. Have a piece of towel ready to soak up any fuel spillage.
The operating principle of the FPR as I know it is that the vacuum line controls a rubber diaphragm that keeps the fuel pressure at a specified rate, or increases it depending on engine load, the signal of which it determined by the amount of vacuum present in the line. If fuel can be found in the vacuum line (like in my case), then the rubber diaphragm has likely been perforated or torn, and is sucking fuel into the intake manifold, and leading to an over rich situation.
Shut off the engine while performing this test, because pressurized fuel might squirt out. Keep a towel handy to soak up whatever fuel might come out. Remove the battery terminals even to be on the safe side. Even with the engine cold, if the FPR is sucking fuel into the vacuum line, there will be fuel present once you remove the vacuum line.
My symptoms were:
-Warm hard starting (more than 5 seconds)
-Found fuel in the vacuum hose leading from the FPR to the intake manifold
-Engine rpm dives to 0 mark when slowing down from high rpm (my rationale is the injectors are likely flooded with extra fuel from the intake manifold at high rpm which became unburned during stopping...I could be wrong).
After FPR replacement:
-Quick starts with engine warm or cold
-No more rpm dives
-Engine runs a couple of degrees cooler (two needle widths away from the 100C mark where it previously stays pegged on the 100C mark)
Thanks I look forward to your feed back.
Dawson
05-23-2011, 08:43 PM
#2
Fuel pressure regulator in our cars comes in the fuel filter. Replace it. comes in the driver side in front of the left/ rea tire. under a black cover with 3 x 10mm plastic nuts
Is common in this models a faulty fuel pressure regulator
Hope that help bro
Fabio Daniel
Is common in this models a faulty fuel pressure regulator
Hope that help bro
Fabio Daniel
