Hi
I have a project 300 SDL and am trying to work out why it is such a difficult starter when cold. I have checked the glow plug black box with the six individual outputs and have also checked the individual glowplugs for zero resistance with a multimeter.

Can it still be the glowplugs? Are they easy to pull out and change on a 603 or are they prone to getting stuck and threads being stripped?

Or should i be looking elsewhere, like the hydraulic lifters, for example. I have noticed that there is a clicking/ticking sound both from cylinder one and six. Lazy bucket lifters?

thanks


MJ in Morocco

OM603 glow plug change

__________________
CC: NSA

All things are burning, know this and be released.

82 Benz 240 D, Kuan Yin
12 Ford Escape 4wd

You're four times

It's hard to

more likely to

concentrate on

have an accident

two things

when you're on

at the same time.

a cell phone.

www.kiva.org It's not like there's anything wrong with feeling good, is there?

Worn/collapsed hydraulic lifters are common on the 60x engines, but they won't cause hard starting issues. They're just noisy and irritating. Eventually after tens or hundreds of thousands of miles they can cause wear to the valve and seat, but that's really about it.

Impedance of the glow plugs are only part of the equation. Is the light coming on on the dash when you turn the key to preglow? The glow plug controllers can and do wear out. The points can fail inside, the capacitors can dry out and cause an excessively short glow cycle, the strip fuse inside the lid can develop a micro fracture and "look" ok but be open and cause no glow.

Set up a multimeter to your DC scale and measure from a glow plug stud to the block. Have a helper turn the key to preglow. You should read ~11V if the glow system is working. The glow plug relay should glow the plugs when the key is turned to the preglow position and stop the glow cycle when the key is turned to the start position. These early cars (pre-1990) do not have afterglow.

I assume it's still somewhat warm in Morocco? The 603's with decent compression tend to start reasonably well even without a preglow down to ~50˚F. Even my 300SDL with cylinder walls like glass would compression start down to ~55˚F. 5-6 compression hits and it would light off. Rough running for 3-5 seconds, but it would settle down pretty quickly.

Hard starting and rough running could be air ingress issues. If you still have the fuel preheater thermostat present, bypass it so that the fuel line goes straight into the lift pump. The preheater thermostat is a very common source of air ingress and is unnecessary. If the fuel lines look old, they need replacement. The correct size is 7.5mm. Using 5/16" or 8mm line will cause air ingress issues on these cars, the flare on the end of the metal lines is not large enough to get a reliable airtight seal on the suction side of the lift pump. How greasy/wet is the top of your injection pump? The 60x engines use a rubber O-ring seal on the injection pump delivery valve holders and are prone to leaking. A bad enough leak can cause an aired up fuel system when the car sits. The O-rings and internal copper crush washers are a DIY replacement job, look on this site for a very well written how-to article. Reassembly requires a torquing sequence that is very important.

The tapping/knocking noise can be injector noise or it can be lifter noise. Typically the lifter noise is a hollow "clanking" sort of sound. Injector nailing/knocking is typically a very sharp "metallic" noise, not unlike a hammer striking an anvil. Injector noise can be caused by worn injectors, worn delivery valves in the injection pump, air in the fuel system (especially at startup), injection timing, low compression, etc.

__________________
Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

HI
thanks for that. Its not too hot here at the moment. Like spring in Europe, with days from 17 to 21 degrees.
Yes, i do have the glow pre heat light on the dash and it goes out normally.
What i did finallly was find the block whcih sends the current and pulled off the six pin connecter and sent 12v down each line. Two gave the full 12.4v
One gave 11.9
And three wouldn't deliver anything.

So, can i assume its three injectors which have failed entirely? Or, could it be the cables?

I guess i have to remove the inlet manifold and have a proper look.

thanks for your time. much appreciated.

MJ

thanks for this. I'm sorry about confusing you or other members about what exactly the bloody car is. Let's assume it a 500 SEL gas.

What about injectors? Are they also not prone to failing?

OK I will "assume it is a 500SEL gas. You defiantly do not have a problem with your glow plugs, glow plug relay or glow plug wiring. And also no chance at all of breaking off a glow plug on that engine.

So, indeed your advice was very good. it seems on very close inspection i can see on the first injector that there is a tiny leak at the top. It's really tiny, but the diesel shines in the sun and also at the base of the black plastic housing, there is also a tiny leak.

Question. If the leak is a the top does that suggest that the injector is blocked somehow and this is the consequence?

Also the black plastic bases. Should i replace it with the injector.

Or should i replace all the injectors?

thanks