Start problem developing... - PeachParts Mercedes-Benz Forum

fred98050 · #1 11-01-2010, 11:46 PM

1980, 300TD.

First start of the day is becoming harder than usual. Outside temp still in the 40s. I cycle the glow plugs twice before starting, the engine starts ok, runs for few seconds then quits. Try 2 or 3 times and it starts and runs ok. I suspected defective plugs, but when the car eventually runs It does not smoke at all which makes me believe that it might be fuel related (or both).

Otherwise during the day the car start and runs well.

- Converted to new pencil type/ parallel plugs 7 months ago.
- Looked for fuel leaks but can't find any.
- Fuel filters ok.

Any suggestions?

Thank you

kerry · #2 11-01-2010, 11:55 PM

Check the glowplugs. Pump the primer pump a bunch of times before starting it first thing in the morning and see if it makes a difference. If it does, that might indicate a fuel problem.

bustedbenz · #3 11-01-2010, 11:57 PM

1. How many miles? Could you be feeling the first effects of an engine which is wearing out and losing compression? Maybe over the summer you crossed a low-compression threshold which is now making starts harder.

2. Try giving it an artificial fast idle on your very first crank. The 240D has a twist-knob for this purpose, but I'm pretty sure your car doesn't. So just hold your foot at about 1/8 or 1/4 pedal when you cold-start it. It should start on the first try, run at that faster idle. Once the tachometer (if you have one) is registering, holding it at 1000-1100 would be plenty fast. Ten seconds of fast idle and then slowly (if you yank your foot away suddenly, it might stumble and die instead of re-idling) remove your foot, and you should be idling normally.

Maybe you shouldn't have to do that. But until the problem goes away or makes itself more pronounced and therefore obvious to find, there's a good way to only have to run the starter once in the morning. *should* work.

fred98050 · #4 11-02-2010, 12:09 AM

Quote:

Originally Posted by kerry

Check the glowplugs. Pump the primer pump a bunch of times before starting it first thing in the morning and see if it makes a difference. If it does, that might indicate a fuel problem.

Great idea. I'll try at the morning.

Thanks

fred98050 · #5 11-02-2010, 12:14 AM

Quote:

Originally Posted by bustedbenz

1. How many miles? Could you be feeling the first effects of an engine which is wearing out and losing compression? Maybe over the summer you crossed a low-compression threshold which is now making starts harder.

1- 289k, it might be the case. If you have a low compression should, once the engine runs, have more smoke than usual?

2. Try giving it an artificial fast idle on your very first crank. The 240D has a twist-knob for this purpose, but I'm pretty sure your car doesn't. So just hold your foot at about 1/8 or 1/4 pedal when you cold-start it. It should start on the first try, run at that faster idle. Once the tachometer (if you have one) is registering, holding it at 1000-1100 would be plenty fast. Ten seconds of fast idle and then slowly (if you yank your foot away suddenly, it might stumble and die instead of re-idling) remove your foot, and you should be idling normally.

Maybe you shouldn't have to do that. But until the problem goes away or makes itself more pronounced and therefore obvious to find, there's a good way to only have to run the starter once in the morning. *should* work.

2- The car is fitted with a fast idle knob. I will check and see if it is adjusted correctly though.

Thanks

layback40 · #6 11-02-2010, 02:20 AM

Well its not the hot of summer any more so no air con problem. As a matter of normal maintenance you should pull all the GP's & test them now before it gets any colder.

vstech · #7 11-02-2010, 09:02 AM

define the amount of time you spend "cycling the glow plugs twice"

fred98050 · #8 11-02-2010, 11:17 AM

Quote:

Originally Posted by vstech

define the amount of time you spend "cycling the glow plugs twice"

(Ignition on: Wait about 10seconds after glow light extinguish)x2

fred98050 · #9 11-02-2010, 11:22 AM

This morning: 42F.

pump the primer pump a few times (as per Kerry).

High idle knob on.

Cycle the glow plugs only once.

Car started and ran first crank, no hesitation what so ever....

I'll check the glow plugs anyway but I must have some other problem..

kerry · #10 11-02-2010, 11:34 AM

Air leak in your fuel lines most likely. Look for wet spots. Could be the primer pump itself. Do you have the old white topped screw down style or the newer spring loaded version? Older version has a reputation for leaking.

vstech · #11 11-02-2010, 11:36 AM

Quote:

Originally Posted by fred98050

(Ignition on: Wait about 10seconds after glow light extinguish)x2

that's better than some do with the MB glow cycle, but depending on models, the full glow cycle is 40 seconds. the light comes on anywhere from 3 to 15 seconds, so at best you are giving the glow plugs only 1/2 their cycle before attempting start.
try this if the starting problems continue, turn the key to the glow position, then wait until you hear the click of them turning off, or watch your dome light, it'll brighten when the plugs turn off. then try starting.

if pumping the primer solves your starting issue, next time pay attention to the sounds the primer makes. how many pumps before you get the buzz signifying fuel returning to the tank? does your primer leak ANY fuel when pumping?

fred98050 · #12 11-03-2010, 12:10 AM

Found a very small fuel leak coming from the line near the primer pump (new style).

It is so small that I almost missed it. Don't know if this could be the problem or just part of it.

Got the parts ordered today...

I'll see.

Thanks everyone for your much appreciated help.