CDI Glow Plugs - PeachParts Mercedes-Benz Forum

DieselPaul · #1 12-10-2015, 09:27 AM

Well the CDI failed the start the first couple of tries on a cold morning, and when it does start it clearly is starting on somewhere between 3 and 5 cylinders. No CELs but this sounds like glow plugs to me as it's entirely temp dependent. Car will start fine the rest of the day.

So, CDI glow plugs! Someone line vendors say cars were either Beru, or Bosch. I admittedly have not pulled a plug out to look. Pelican however does not make a brand distinction.

I called the dealer with my VIN and they told me to get 001 159 7401 which according to online vendors is the Beru number.

However the Bosch *looks* the same and is half the price.

So are all glow plugs the same, or are there Beru cars and Bosch cars?

This pelican review of the Bosch plugs on Pelican is interesting

Quote:

DO NOT BUY THE BOSCH for W211 USA e320 CDI
The Bosch glow plugs are 11.5v, not the correct 5v for your USA spec 05'-06' e320 cdi! They have worked fine for me but do not heat near as quickly and will be replaced shortly with the correct Beru/OEM Plugs. They carry same part number BUT ARE NOT THE SAME AS STOCK!

shertex · #2 12-10-2015, 10:57 AM

Sounds like the Beru is the one you want.

FWIW after years of using Bosch, I'm done...they burn out too early. On my cars that can take either I will spend the extra money and get Beru.

DieselPaul · #3 12-10-2015, 11:04 AM

I'll pull the engine cover after work and see if I can't easily do a quick multi-meter test to see if any of the plugs come up bad that way, then I'll call the dealer back and get some coming.

ILUVMILS · #4 12-10-2015, 11:55 AM

I'd check the low pressure fuel circuit before you replace the glow plugs. FWIW, I've never seen a faulty CDI glow plug or relay that didn't turn the CEL on......

GregMN · #5 12-10-2015, 12:05 PM

Quote:

Originally Posted by ILUVMILS

I've never seen a faulty CDI glow plug or relay that didn't turn the CEL on......

X2

Check your fuel system.

How old is your fuel filter?
Check your injectors for an open return fuel circuit.

A $69.99 UltraGauge will let you see the fuel pressure in the fuel rail. You can see what the pressure is during the start sequence. It has to be about 3500psi for the injectors to fire.
One injector with an open or weak return fuel valve can bleed off enough pressure to prevent a cold start, but work find the rest of the day.

DieselPaul · #6 12-10-2015, 12:26 PM

No CELs. I assumed I would get a glow plug CEL, aren't even 606 cars capable of throwing a GP code?

I did the fuel filter about 5,000 miles ago with a unit from the dealer.

I have an eBay Mercedes Carsoft scan tool like this:

Mercedes Benz Sprinter Diagnostic Scanner Tool SRS ABS Engine Icarsoft Mbii I980 | eBay

I'll see if I can get a look at rail pressure with it.

Glad I posted, I'll see what data I can come up with and post back. I appreciate your insights Greg and Iluvmils. Not as much good info out there on the CDIs yet, looking forward to learning more and more about them.

GregMN · #7 12-10-2015, 01:11 PM

The way to check for a leaking return circuit on an injector, or to find which one(s) is the bad one :
You will need a 6" piece of clear tubing that fits on the return fuel nipple for each injector.
Remove the return fuel connectors and replace each with a clear tube standing straight up.

During the start cycle, there should be no fuel returned, so all the tubes should be empty. If you have a leaker, that one is the problem.

When the engine is running, all the return tubes should fill at the same rate. If any are returning fuel faster then the others, those are candidates for replacement.

This test is so easy to do, but so many bad things can go seriously wrong. The parts are so fragile that if you are not careful you can make the problem you are looking for seem trivial compared to having to replace parts that were perfectly good before you started messing around with them. Find out how all the connectors you will try to disconnect work before you get started. Many times they are "clear only if known", like the fuel connector locks on the 606.

DieselPaul · #8 12-10-2015, 01:45 PM

Cool, sounds like a straightforward enough test, I'll try first to see if I can get a reading on the rail pressure with my scan tool.

Anyone rebuilding injectors yet for the CDI or am I stuck dropping like $390/injector or whatever I saw online if one turns up bad.

GregMN · #9 12-10-2015, 02:22 PM

Quote:

Originally Posted by DieselPaul

I'll try first to see if I can get a reading on the rail pressure with my scan tool.

Do that first.

It looks like that tool will everything except put away the dishes once they are clean.

If the problem is fuel rail pressure, then test to find the leaking injector.

GregMN · #10 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 · #11 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 · #12 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 · #13 12-14-2015, 12:58 PM

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

DieselPaul · #14 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 · #15 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.