Cold start issues - 617 - PeachParts Mercedes-Benz Forum

JHZR2 · #1 11-21-2010, 02:19 PM

Hello,

more and more at full cold start my 82 is exhibiting cold start issues. In the 50s-60s type weather, I'm used to glowing until the light goes out, then the engine catching on the first cylinder.

More and more what happens is that I crank and the engine turns over multiple times and doesn't catch. When I let off the key the car didn't start. Try again after glowing again it may catch, but when it does it is misfiring and the speed is 350-500rpm. Giving a bit of throttle helps, but let go too early and it will remain rough. After manually holding the idle up around 750-800 via the pedal, finally it will be able to govern itself at 750 with no throttle.

I used an ohmmeter on the ground to the threaded part of each glow plug and got somewhere between 0.3 and 0 ohm for each one. Battery is fully charged showing 12.78v. During glow the voltage is around 11.

Valves are adjusted, car returns 28-29 mpg consistently, and runs really nicely. The car has some hot idle shake which I've tried to adjust via the (updated) rack dampener pin, but it still exhibits the same just slightly less... Rack dampener may have something to do with it, may adjust it back and put up with the shake (changed shocks no help)...

Any thoughts suggestions based upon this discription?

#2 11-21-2010, 02:26 PM

Have you checked the GP resistance individually from the relay by unplugging the connector and checking all 5 (should be about 0.8 cold)? Also, have you verified that the GPs are actually getting about 11v? I recently replaced the relay on the 240D because it wasn't actually energizing the GPs.

jt20 · #3 11-21-2010, 02:28 PM

Other than regular maintenance items, the first thing that comes to mind is weak fuel hose connections / primer pump.... anything that can let the fuel system lose prime.

Biodiesel300TD · #4 11-21-2010, 02:40 PM

Sounds like classic bad GPs to me. I've never had luck checking the resistance of the GPs I always pull them out and give them 12v. If they glow bright orange then they are good, if they don't then they are bad. Don't touch the GP while you're doing this, they get REALLY REALLY hot.

Also when it starts getting cold you should let the GP run longer than the light is on. The light is just an idiot light. The GPs stay on for about 30sec after the light goes out. If you listen you can hear the relay kick off. Let it run through the full cycle then turn the key. But at any rate you shouldn't have to be glowing the full cycle when it's 50*F outside which make me think its a bad GP or two.

You could also have an air leak in the fuel system. Before you start the car on a cold start, look at the primary filter and see if there it a big air bubble, or if it has the normal little air bubble. If you have a large portion of the primary filter with air, then you've got an air leak.

JHZR2 · #5 11-21-2010, 03:03 PM

No air leak (big one at least) that I can note.

I haven't checked at the relay, as I figured that would merely add on the higher wire resistance. I just know that monitoring dc voltage, I get a nice drop as the GPs load the battery...

dude99 · #6 11-21-2010, 03:10 PM

Pull each glow-plug and hook them each up to a battery or jump box to test for function and pattern. Sometimes they stop glowing at the tip were they're supposed to...

Biodiesel300TD · #7 11-21-2010, 03:28 PM

Also look at the strip fuse. You could have a crack in it and the GP aren't getting the amps then need and thus not heating up all the way.

vwnate1 · #8 11-21-2010, 04:16 PM

No where have the basics been mentoned :

Valve adjust then a Diesel Purge followed by new filters then just for shytes & grins try following the Mercedes cold weather starting drill : throttle to the floor & HOLD IT THERE .

Cycle the glow plugs twice before engauging the starter , do not let off the starter until the engine begins to run on all cylinders , then release the key and ease up on the throttle to keep it runnng , no need to rev it to the moon

This worked to instantly light off the totally worn out engine in my '78 300CD even in 0* F temps . it also works for all my Canadian buddies, the guys in Michigan and Philly , New York , Bostom , Maine and New Hampshire etc. when it's 30* F out so give it a try .

In 50* F weather , the engine isn't supposed to stay running on a cold start all by itself unless the engine is new . give it a little throttle , NEVER pump it

Never forget that this is a 1940's technology machine ,YOU the Operator , must bend to it's needs , not the other way 'round .

layback40 · #9 11-21-2010, 05:08 PM

Every one has made valid suggestions.
If the valves have not been adjusted, do it. You wont believe what a difference it makes to cold starting & running.
Take the GP's out & bench test. You need to see them glow nicely.
Parking the car nose down on a hill with a full tank overcomes any air leak into the fuel. If you you try that & it starts good then you have an air leak into the fuel.

Good luck !!

JHZR2 · #10 11-21-2010, 06:38 PM

Mentioned it at the top. Valves adjusted within last 2k, injectors pop balanced and cleaned within 500. Starting funniness and shaky idle existed before injector job - had hoped it would help...

kerry · #11 11-21-2010, 06:47 PM

The 0 ohm glow plug is definitely bad. All your symptoms point to bad glow plug(s). I wouldn't do anything else before replacing the bad one.

#12 11-21-2010, 06:50 PM

Quote:

Originally Posted by kerry

The 0 ohm glow plug is definitely bad. All your symptoms point to bad glow plug(s). I wouldn't do anything else before replacing the bad one.

I'm guessing that he checked them at the GPs without unplugging the connector from the relay, which won't give an accurate reading.

layback40 · #13 11-21-2010, 06:50 PM

Quote:

Originally Posted by JHZR2

Mentioned it at the top. Valves adjusted within last 2k, injectors pop balanced and cleaned within 500. Starting funniness and shaky idle existed before injector job - had hoped it would help...

Remove all your GP's & bench test them. While they are out clean the carbon from the GP holes.
You can not trust resistance tests when such low values are involved.

JHZR2 · #14 11-21-2010, 06:56 PM

Quote:

Originally Posted by Craig

I'm guessing that he checked them at the GPs without unplugging the connector from the relay, which won't give an accurate reading.

I didn't unplug. I'll have to search for why this important unless someone has the 30sec answer and is willing to type it...

#15 11-21-2010, 07:03 PM

Quote:

Originally Posted by JHZR2

I didn't unplug. I'll have to search for why this important unless someone has the 30sec answer and is willing to type it...

Sorry, I wasn't clear. I don't believe you will actually be measuring the individual resistance of each GP is they are all electrically connected together at the relay. If you unplug the connector at the relay and measure from each of the 5 female connections to ground, you will be measuring the resistance of each GP, including it's wire. Look for about 0.8 ohm.