1985 300td hiccups at cold idle - PeachParts Mercedes-Benz Forum

kerry · #1 09-09-2002, 05:01 PM

My recently acquired 1985 300TD is a joy to drive but I have noticed one oddity. When the engine is cold, at idle, it will hiccup a few times. This only happens for a minute or two until it warms up. Anyone know what it is? The engine does not have the manual idle control like my 1977 300d so I assume there is a mechanical/electrical/vacuum substitute that may be causing this. It is not a real problem but I wonder if it might be at 10 below. I believe it goes away if I give it a little more fuel.

surfblau · #2 09-09-2002, 05:19 PM

Doesn't it sound more like you have a glow plug that may be bad or on its way out? Real easy to test with an ohmmeter.

Thats about all I can offer (based on a glorious 6 months of mb diesel experience).

later

#3 09-09-2002, 08:39 PM

When it's cool out (below 60 or so) it's not uncommon for a diesel to studder once or twice after started cold. Just revv it a bit and you'll be fine. I consider it normal.

MVK · #4 09-09-2002, 11:54 PM

One or more of the glow plug must be weak and about to fail( if not failed already). Check them one by one. If the problem is more severe on a coler day, its mostly the glow plug.

MVK

ck42 · #5 09-10-2002, 08:52 AM

Kerry, Please pardon the thread hi-jack but this sounds almost exactly like what I've just started experiencing....except mine smooths out after only about 5-10 seconds.

I've read several times in the past about just measuring the resistance of the GP to check them but never paid any more attention because it was starting perfectly.

Well, now that I need to check them for the first time, I'm not sure EXACTLY how.

Can someone tell me WHERE to connect the leads on the GP and what sort of resistance I should read?

surfblau · #6 09-10-2002, 11:15 AM

Does anyone know the resistance value the glow plugs are supposed to be???

I think that tcane has the correct proceedure.

ck42 · #7 09-10-2002, 11:40 AM

surf:

allrighty then....

.3 - .9 ohms

Thanks!

Chris
'85 300SD

GregS · #8 09-10-2002, 12:27 PM

I replaced my glowplugs and my car still hiccups. I never figured out why, so I have just lived with it. Yes, the valves are adjusted, filters are clean, etc., etc. When it is really cold, below 40 for example, the car may stall. One deep seated fear I have is that there is low compression in one cylinder which keeps it from firing until it warms up a little - hence the hiccup. In any event, the car otherwise runs perfectly, so I don't worry about it.

If you solve the problem, please let me know.

Greg
'84 300D, 166k

ck42 · #9 09-10-2002, 01:11 PM

Greg,

Ja....the low compression thought has crossed my mind as well. When the car gets home tonight, I'll check things out....hopefully a GP is all it is.

Chris

engatwork · #10 09-10-2002, 02:43 PM

My 1985 300D (with 150 psi comp in the #5 cyl) stumbles pretty good during cold start. I have to keep bumping the throttle to keep it running. I replaced the gp's and checked the timing and the initial start is fine - I just have to keep giving it some fuel to insure it keeps running. When sitting at a redlight at idle it shakes pretty good but when cruising down the interstate it runs fine. I am seriously considering just running it till it won't go anymore.

goldenbear · #11 09-10-2002, 06:02 PM

Kerry,

A faulty glow plug is the likely culprit. It's probably coked up with carbon as a result of not being driven properly/lots of city driving. Try letting the plugs glow for an extra 10-15 seconds AFTER the light goes out b/f cranking and see if this helps.

kerry · #12 09-10-2002, 09:11 PM

I may be completely mistaken but it doesn't seem to me to be a missing cylinder. It's not as if just one cylinder is not firing but if the engine is shut off momentarily as if the fuel supply is cut off.
I may not have enough experience with diesels to be making this judgment but I know that when my 300d starts in the cold and it only hits on a few cylinders for a few seconds until it catches, it doesn't sound or feel like this 'hiccup'.

ck42 · #13 09-10-2002, 09:19 PM

"...but I know that when my 300d starts in the cold and it only hits on a few cylinders for a few seconds until it catches..."

This pretty much sums up what I'm experiencing. Before I go chasing a wild goose, can someone tell me if this type behavior is to be expected and that 'they all do that' or is this a legitimate issue?

Chris
'85 300SD

kerry · #14 09-10-2002, 09:51 PM

I think that can be expected in cold weather. I happens to mine when the temperature is below about 10 degrees. It must be typical because the starting instructions in the manual say don't disengage the starter under these circumstances but wait until the engine fully kicks in.
However, since last winter I have learned that if I wait 40 seconds after the glow plug light goes out, the engine starts much more quickly. We'll see if that holds true when the weather turns colder.

ck42 · #15 09-10-2002, 11:02 PM

Difference here is that it's happening on frosty 75F mornings.

....still have that block heater ready to go this winter tho just in case.

Chris
'85 300SD