Mercedes CDi help needed
Discussion
I am by no means a professional mechanic but would consider myself reasonably technically competent so will describe the problem to the best of my ability and hopefully somebody can shed some light on the situation and enable me to fix it.
The vehicle in question is a 2001 Mercedes Sprinter with the 2.2 CDi engine. Just about to push the 200k mark.
The problem: The van drives fine but at full throttle under load, the engine cuts out. It will restart when the key switch is turned off and on but will not restart by dumping the clutch with the ignition on unless it has been turned off and on again first.
What I've done so far: 2 of the injectors were heavily carbonised, copper washers were obviously blowing out so I took them out (nightmare of a job), reamed out the holes, fitted new washers and refitted the injectors. Seemed to have cured the carbonising problem but my original problem still exists.
It was still happening so I did a leak-off test on the injectors, found one to be faulty so replaced it.
Problem still exists. Tried swapping the ECU, key switch and the wee box behind the dash with one I knew was good and that didn't cure it either.
Hooked it up to the computer and there are no fault codes logged.
I've read on a few MB websites and seen that the wiring loom can rub through in a few places causing the ECU to short out and temporarily switch itself off to prevent damage. I have checked all these places and looked at the rest of the loom and there doesn't seem to be any obvious damage.
Was also told this could be caused by a faulty brake light switch (I didn't believe it but swapped it out anyway and inspected the wiring to it).
Totally stumped and would appreciate any help. Scary when you pull out to overtake something and your engine just dies.
The vehicle in question is a 2001 Mercedes Sprinter with the 2.2 CDi engine. Just about to push the 200k mark.
The problem: The van drives fine but at full throttle under load, the engine cuts out. It will restart when the key switch is turned off and on but will not restart by dumping the clutch with the ignition on unless it has been turned off and on again first.
What I've done so far: 2 of the injectors were heavily carbonised, copper washers were obviously blowing out so I took them out (nightmare of a job), reamed out the holes, fitted new washers and refitted the injectors. Seemed to have cured the carbonising problem but my original problem still exists.
It was still happening so I did a leak-off test on the injectors, found one to be faulty so replaced it.
Problem still exists. Tried swapping the ECU, key switch and the wee box behind the dash with one I knew was good and that didn't cure it either.
Hooked it up to the computer and there are no fault codes logged.
I've read on a few MB websites and seen that the wiring loom can rub through in a few places causing the ECU to short out and temporarily switch itself off to prevent damage. I have checked all these places and looked at the rest of the loom and there doesn't seem to be any obvious damage.
Was also told this could be caused by a faulty brake light switch (I didn't believe it but swapped it out anyway and inspected the wiring to it).
Totally stumped and would appreciate any help. Scary when you pull out to overtake something and your engine just dies.
OK, I do a fair bit of this kind of stuff, and while others will no doubt have other ideas, here's what I would do.
It's probably (possibly) cutting out die to excess fuel pressure on the rail. You need to check the rail pressure. You can do this easily by using an oscilloscope if you have one, or a multimeter if you don't. Insert the multi meter probe into the back of the centre of the 3 wires on the common rail pressure sensor, and measure to earth. KOEO (Key on engine off) reading should be 0.5v (If you have 5 or 0, that's the power supply and earth). Start the engine. At idle, you should have 1.1 -1.3v. Take it for a run, and hook up the meter so you can see it. (or a friend drive it is better). Try and get it to cut out. You (should / may /might) see the voltage go over 4.0 - 4.5v - in which case the engine will shut off, but you should see at least 3.5v.
It's also possible it's turbo overboost, but check the pressure rail first.
It's probably (possibly) cutting out die to excess fuel pressure on the rail. You need to check the rail pressure. You can do this easily by using an oscilloscope if you have one, or a multimeter if you don't. Insert the multi meter probe into the back of the centre of the 3 wires on the common rail pressure sensor, and measure to earth. KOEO (Key on engine off) reading should be 0.5v (If you have 5 or 0, that's the power supply and earth). Start the engine. At idle, you should have 1.1 -1.3v. Take it for a run, and hook up the meter so you can see it. (or a friend drive it is better). Try and get it to cut out. You (should / may /might) see the voltage go over 4.0 - 4.5v - in which case the engine will shut off, but you should see at least 3.5v.
It's also possible it's turbo overboost, but check the pressure rail first.
bearman68 said:
OK, I do a fair bit of this kind of stuff, and while others will no doubt have other ideas, here's what I would do.
It's probably (possibly) cutting out die to excess fuel pressure on the rail. You need to check the rail pressure. You can do this easily by using an oscilloscope if you have one, or a multimeter if you don't. Insert the multi meter probe into the back of the centre of the 3 wires on the common rail pressure sensor, and measure to earth. KOEO (Key on engine off) reading should be 0.5v (If you have 5 or 0, that's the power supply and earth). Start the engine. At idle, you should have 1.1 -1.3v. Take it for a run, and hook up the meter so you can see it. (or a friend drive it is better). Try and get it to cut out. You (should / may /might) see the voltage go over 4.0 - 4.5v - in which case the engine will shut off, but you should see at least 3.5v.
It's also possible it's turbo overboost, but check the pressure rail first.
Thanks for that It's probably (possibly) cutting out die to excess fuel pressure on the rail. You need to check the rail pressure. You can do this easily by using an oscilloscope if you have one, or a multimeter if you don't. Insert the multi meter probe into the back of the centre of the 3 wires on the common rail pressure sensor, and measure to earth. KOEO (Key on engine off) reading should be 0.5v (If you have 5 or 0, that's the power supply and earth). Start the engine. At idle, you should have 1.1 -1.3v. Take it for a run, and hook up the meter so you can see it. (or a friend drive it is better). Try and get it to cut out. You (should / may /might) see the voltage go over 4.0 - 4.5v - in which case the engine will shut off, but you should see at least 3.5v.
It's also possible it's turbo overboost, but check the pressure rail first.
I've had boost problems with this van before, turned out to be the boost valve. Replaced it about 6 months ago. It's reading 16.5 ohms across the terminals now, same as a perfectly healthy working one.
When you see hook the meter up so you can see it, do you mean using long leads so I can see it when its driving?
Yeah, trail it through the engine bay and back to the passenger seat. No need to mention not to get it tangled in the auxiliary belt is there? - then drive it with a mate.
Have a look at the picoscope website -you'll see what you are after, albeit with a multimeter rather than a scope.
Have a look at the picoscope website -you'll see what you are after, albeit with a multimeter rather than a scope.
Gassing Station | Engines & Drivetrain | Top of Page | What's New | My Stuff