OM606 fires less than 1 Revolution Cold. Takes 5 or 6 Warm. Normal? - PeachParts Mercedes-Benz Forum

777funk · #1 07-20-2021, 07:57 PM

This is something I've never seen before but my son's om606 needs to have the glowplugs cycled even in warm weather to start this quickly (1 rev).

The weird part though... when it's warmed up, it takes about 5 or 6 revolutions before it starts. It starts fine and no sputtering etc, but it's like it doesn't allow a warm start until this many revolutions.

Is this normal? Is there anything that can be checked if not? I would not think it's fuel bleed down since the first cold start of the next day (or even a week later) takes only 1 revolution. Also the o-rings are fresh and I see (or smell) no diesel mess.

jay_bob · #2 07-21-2021, 07:31 AM

I would start looking at the crank position sensor. That is what mine started doing before it failed totally.

Fairly easy to change and when it finally dies it will leave you totally stranded. Car will die while running and driving if it fails completely.

W210 CAN bus issues the fun starts at post 19

Get the actual MB branded sensor from the dealer, I tried aftermarket and it did not work.

engatwork · #3 07-21-2021, 07:15 PM

How many miles are on it? Mine does it at 250k miles. The items that are new are the spin on fuel filter, crank position sensor (MB part) and all the glow plugs work. I don't worry too much about it.

It has something to do with the fuel injection pump and the temp. Anyway my friend who has about 380k miles on his 98 E300 ended up finding a new, old stock fuel injection pump from the internet for $1500. Once we installed that it was easy starting again. His has car has run on a bunch of homemade fuel. Before the inject pump you would go through a couple of crank cycles without any success when engine was hot.

777funk · #4 07-21-2021, 10:54 PM

It's got about 350k on the clock and runs great. This is just a little bit odd. I'd guess it's controls in the pump vs actual fuel issue since it starts cold near instantly. But I don't know much about the electrically controlled pump.

engatwork · #5 07-22-2021, 06:12 AM

Very little electrically controlled in this pump. When it gets to the point where it either will not start or takes a couple tries will be the time to have someone go through it.

777funk · #6 07-22-2021, 09:42 AM

Quote:

Originally Posted by engatwork

Very little electrically controlled in this pump. When it gets to the point where it either will not start or takes a couple tries will be the time to have someone go through it.

Isn't the rack electrically controlled (i.e no fuel until it receives signal)? I know the shutoff is definitely electric solenoid controlled. I think that's an audible click. Maybe next time we hot start I'll listen. Likely that's in the on position as it should be as soon as the key is turned. The rack control will be a little more difficult to monitor. Maybe a scope and a volt meter. Jay Bob's mention of the crank sensor sounds like at least in his case, it was an electronics issue.

t walgamuth · #7 07-22-2021, 01:28 PM

Not to contradict Jim, but have you run a compression test? If it is low the oil on the walls may be thicker and give more compression when cold.

777funk · #8 07-22-2021, 10:46 PM

Quote:

Originally Posted by t walgamuth

Not to contradict Jim, but have you run a compression test? If it is low the oil on the walls may be thicker and give more compression when cold.

I wonder about this because it doesn't seem to start quickly when the weather is hot without glow plugging it. I'd think the engine should start easy without giving a second for the glow cycle when ambient temps are high (80F plus). I may have my son unplug the glow plug controller and try starting the engine the next 90F day we have.

It's not easy access to compression test these as far as I know (not looking at the engine right now). Aren't the glow plugs buried under the intake manifold? I suppose I could pull an injector but I hate messing with that if not required. It's running and driving great. Plenty of power. No smoke. No blow-by.

Oh... and in the winter (say 10 degrees F), it starts just as easy as if it were 90F outside. You'd never know it was cold outside. We'd do no YouTube 'cold start' videos with this car because no clouds of white smoke, no sputtering, no wearing batteries down, just immediately smooth and it even cranks fast. This is what's odd about this car. I've NEVER had any diesel start this easy cold and I've had probably 14 or 15 MB diesels and many others (GM 6.2, couple of 7.3s, 5.9 cummins, tractors, skid steer, backhoe, etc)

t walgamuth · #9 07-22-2021, 10:58 PM

With good compression you should not need glow plugs when starting a hot engine. The glow plugs are not too hard to change or remove. A lot like spark plugs but the metal pipes are fairly rigid. I always take off the metal pipes. When cranking the pulses on compression should be pretty obvious.

777funk · #10 07-22-2021, 11:42 PM

Quote:

Originally Posted by t walgamuth

With good compression you should not need glow plugs when starting a hot engine. The glow plugs are not too hard to change or remove. A lot like spark plugs but the metal pipes are fairly rigid. I always take off the metal pipes. When cranking the pulses on compression should be pretty obvious.

I've done a compression test on some of my previous older MBs (for sure OM617), but it seems like the glow plugs are under the intake and none are reachable without removing the intake on a 606. I will need to go look at it. I could pull the injectors and test there but I just hate to mess with buying new copper crush washers and to have to bleed the fuel system etc. Probably just leave it be for now and check the compression when the glow plugs need a change. I will likely try to start on a hot day without the GP relay plugged in just for curiosity's sake.