CDI Glow Plugs - Page 2 - PeachParts Mercedes-Benz Forum

GregMN · #16 12-11-2015, 11:08 AM

How long does it turn over before it starts ?

Make sure you have power to the rail pressure relief valve. That valve is normally open, so no power - no pressure.

JimFreeh · #17 12-11-2015, 11:32 AM

Paul,

If a glow plug is bad, the tell tale glow plug squiggle light will remain illuminated after the start cycle.

Jim

DieselPaul · #18 12-11-2015, 02:20 PM

Quote:

Originally Posted by GregMN

How long does it turn over before it starts ?

Make sure you have power to the rail pressure relief valve. That valve is normally open, so no power - no pressure.

It will start almost instantly, pressure comes up 5,500+, then die, pressure plummets.

Starts instantly and dies, pressure plummets.

If you put your foot on pedal it will stay running and idle rough for 15 seconds then smooth out and run fine.

GregMN · #19 12-11-2015, 04:41 PM

If it starts instantly, then I don't think it is the glow plugs.
If it starts instantly, then it is probably not an injector leaking return fuel.

You are losing pressure in the rail.
It could be the pressure is being released from the rail via the pressure relief valve. This valve is normally "open" so it closes when powered.
It could be fuel starvation to the high pressure pump. With a new filter, and the fact that it runs fine once going, I might suspect air in the fuel line after sitting for a long time.

If you turn the key to the "run" position, but do not start it, the electric lift pump will be running. If there is air in the lines, you should be able to hear it rushing though the lines and purging back to the tank via the high pressure pump's return fuel line.

DieselPaul · #20 12-14-2015, 09:22 AM

New set of observations!

It was 74* in Columbus over the weekend, car started on all 6 gloriously all weekend.

However I made an observation, last night in the evening when it was cool out I went to my warehouse to wrench on another car. The CDI sat for 2+ hours. Got in it, started up fairly well, but noticed the temp gauge was at temp.

Thinking about it, I think I've noticed it not cooling down lately. i.e. when I get in the car to head home from work, the car shows as at 90*C on the gauge, not dropping in temp in 4-5 hours.

This morning its in the 50s. Try to start the car, same crap, doesn't want to start, have to hold my foot on the gas, keep the revs around 1,000rpms and it runs smooth. Look at the temp gauge. Reading at or above temp, high speed cooling fan is on.

Hook up my scan tool, 112*C it says... its been running for a minute or so. Shut it down, pop the hood, open the radiator cap. Zero pressure, motor is cool to the touch.

Data streamed on the ride to work, engine temp randomly fluctuated between 87* and 117*C. But once the car was actually warmed up, heat blowing warm etc, the car ran beautifully.

Current theory. Bad coolant temp sensor. If it always thought it was hot, the glow plugs wouldn't stay on very long (light doesn't stay on long) and the car would do none of its cold start/warm up protocols.

Edit: Sensor from the dealer was $13 my cost, he can have it tomorrow and I've got other parts coming in tomorrow so I'll just pick it up. The parts manager is a friend, he said admittedly they don't work on many CDIs, but they've had similar issues on gas cars and the sensor P/N has been superseeded several times. So we will see.

DieselPaul · #21 12-14-2015, 11:18 AM

Went outside and keyed the car on, been sitting for 3+ hours. Temp gauge shoots up to 120* and the fans come on. Pop the hood, engine is cold. Start the car and the temp came down to more like 100-110 on the gauge. I don't think its necessarily a short issue with the wiring because the value changes and isn't pegged high or low, but I'm definitely remaining suspect of the temp sensor.

Additional thoughts or insights are appreciated.

GregMN · #22 12-14-2015, 12:58 PM

I pretty much think you have nailed the problem. $13 and a pair of pliers.

DieselPaul · #23 12-14-2015, 03:47 PM

Is the W211/OM648 FSM online anywhere? I'm trying to figure out where the sensor is on the motor, maybe find a writeup for it but there is very little info out there.

It seems like its in the thermostat housing on the passenger side of the block. Can't really see it in the work parking lot with the airbox and engine covers on.

Replaced the serpentine belt last night with a genuine belt, that was actually surprisingly easy, the electric fan unit was a lot easier to remove than I expected.

GregMN · #24 12-14-2015, 04:52 PM

It is on the upper coolant outlet / thermostat housing. There is an o-ring. Might as well get a new one when you pick up the sending unit if it doesn't come with one.

DieselPaul · #25 12-18-2015, 04:49 PM

So I didn't take a picture of the P/N, it is on my invoice. I will edit later to add the relevant part numbers. BUY THE CLIP!

Install is simple, remove the 3 torx bolts and remove the intake manifold "CDI" engine cover.

Unclip the electrical connector.

Using a flat screw driver slide the retaining clip towards the firewall. Now, when it let go it rocketed into the bowels of the engine bay never to be seen again. For $1 or 2, buy a new clip with the sensor.

Pop in the new sensor, slide the new clip in, and plug the connector back in. 5 minute job and the car is fixed.

The new sensor DOES include the o-ring so that is nice. Mine appeared to be weeping a little on the old sensor and the o-ring looked pretty past it. So the o-ring definitely should be replaced, but you get one with the new sensor.