Starter and Idle Probems-76 300D - PeachParts Mercedes-Benz Forum

79Mercy · #1 08-12-2009, 08:59 PM

I drove the car this morning and for some reason it stalled when I came to a idle. It just barely re-started. I got to a gas station and it died as soon as I took my foot of the pedal. Would not re-start, the motor would turn very slow almost as if the battery was dead. The battery was 5 years old so I decided to get a new one due to the age of it.

After it sat for awhile I jumped it and it started, but I had to drive with 2 feet all the way home or it would die at idle. I replaced the fuel filters, air filter, and replaced the injector return lines today. It still will not idle when hot and in gear.

When it stalls the starter turns the motor over very slowly, even on the brand new battery. After the car has sat and cooled down thestarter will start the motor no problem. Does this sound like a bad starter? It is a 13 year old starter from Pepboys

When the motor is cold it idles perfect, but when hot it wants to stall when in gear. Im thinking I just need to turn up the idle a bit. What do ya'll think?

Thanks

Diesel911 · #2 08-12-2009, 09:20 PM

Not sure if the Starter is related to your idle issue. Most likely separate issues.

Simple things first:
One of the causes of the Engine running poorly hot can be valve clearances that are too tight; as the valve clearances get tighter with wear. Some members have reported have zero clearance; being unable to get a feeler gauge in.

In the past I had a small air leak that only showed up when the Engine was hot. My fuel inlet hose was hard and no amout of clamp tightening helped. For a few dollars I replaced the hoses with 5/15 fuel hoes and that cured it.

If you have the old style Hand Primer Pump with the hard Plastic Knomb on it they are noted for causing air leaks also.

Since the begining of the year some members have had Fuel Supply Pump issues or problems with the IP Over Flow Valve (big thread by cervan on this; it controls the fuel supply ressure).

Out of curioisity while the Engine is at idle you might clamp the Cigar return hose quickly; long enouth to see if the idle smooths out. This would override the Over Folw Valve and you would be creating more pressure than the Over Flow Valve can do. If the Idle smooths out it could be an indication of a problem with the Over Flow Valve not holding enoug pressure at idle.

To check the Fuel Supply Pump pressure is more complicated as you need some way to dampen the Gauge as the needle jumps around too much.
I bought a liquid dampened Gauge for this purpose and made a fitting to do the check but never have gotten around to doing it. (I am not having a problem; but it is good to test something when it is operating normally so you know what normal is.)

You did not say if while the idle trouble was happening if there was an abnormal smoke?

79Mercy · #3 08-12-2009, 09:26 PM

yes, I think both are seperate issues, the starter has nothing to do with the engine not wanting to idle hot.

Sorry, I should have put this in the first post.

I did a valve adjustment last week, only 3 valves were out of spec.

The W115 300D has a different style primer pump than the W123. Its more of a big button mounted directly to the fuel filter housing.

Air leaks are a posiblility, though I see no visable fuel leaks.

Diesel911 · #4 08-13-2009, 12:41 AM

Quote:

Originally Posted by 79Mercy

yes, I think both are seperate issues, the starter has nothing to do with the engine not wanting to idle hot.

Sorry, I should have put this in the first post.

I did a valve adjustment last week, only 3 valves were out of spec.

The W115 300D has a different style primer pump than the W123. Its more of a big button mounted directly to the fuel filter housing.

Air leaks are a posiblility, though I see no visable fuel leaks.

The problem with Air Leaks is that tiny clearances let air in but the viscosity of the Fuel and Atmospheric Pressure that is around 14.7 psi can keep the Fuel from leaking out.
When the supply pump starts moving Fuel you now have a negative pressure inside of the Fuel Hose and 14.7 psi trying to push in.
In the Fuel Hose example that happend to me I had no external Fuel leak.

Did the hot rough idle problem show up before or after the Valve Adjustment?

Diesel911 · #5 08-13-2009, 12:52 AM

Does your Fuel Injection pump have a Mechanical or a Pneumatic Governor?

Is it possible to squirt some thick oil or put some grease around the Hand Primer Button to seal it to see if it is leaking air?

Does your Fuel Filter look like item #5 with item #128 as the Hand Primer:
http://www.detali.ru/cat/oem_mb2.asp?TP=1&F=115114&M=617%2E910&GA=722%2E109&GM=716%2E003&L=760%2E101++++++++++++++765%2E700&CT=M&cat=143&SID=07&SGR=120&SGN=04

Perhaps the gasket item #7 could be the source of an air leak.
When it is running good what is the idle speed?

jt20 · #6 08-13-2009, 12:55 AM

what are the chances your alt. is overloaded and forcing your engine to slow to a halt?

Could this load be from a fault in the starter?

edit: a bit far out, I suppose.

jt20 · #7 08-13-2009, 01:15 AM

actually, can't a dying battery put a high demand on the alt? That might make more sense, especially since the battery is weaker at higher temps and you live in Fl.
this would explain the inability to start as well.

edit: I see you replaced the battery and it still happened. Ignore my ramblings.

barry123400 · #8 08-13-2009, 08:35 AM

Quote:

Originally Posted by jt20

what are the chances your alt. is overloaded and forcing your engine to slow to a halt?

Could this load be from a fault in the starter?

edit: a bit far out, I suppose.

Alternator can not absorb enough energy to kill a normal idle. It can seize though and burn the belt off.

Kpmurphy · #9 08-13-2009, 10:51 AM

Did you get traped under the car? How is everything going.

kerry · #10 08-13-2009, 10:59 AM

You should have a manual idle speed control knob on that car I think. Is there a problem with that mechanism.

Diesel911 · #11 08-13-2009, 05:32 PM

Guys I thought he said: "When the motor is cold it idles perfect, but when hot it wants to stall when in gear. Im thinking I just need to turn up the idle a bit."
I don't see anything here or in the origional post to indicate a Battery or Alternator problem as it starts OK when cold.

79Mercy · #12 08-13-2009, 09:43 PM

So today I pulled tank strainer only to find out that there isn't one installed, just a metal plug...... Thats wierd......

It still turns over very slow when hot, bad stater?

There are no little air bubbles in the clear filter while running, at any engine speed.

The idle adjustment cable is fine.

I did do a diesel purge, wonder if that could have lowered the idle? I seems that I read a post where a guy stated the idle dropped after using diesel purge.

The alt puts out 13.5volts at an idle. The battery voltage is 12.7, but drops to 10.5 when starting, thats normal.

So I think I need to adjust the idle on the IP and install a new Bosch reman starter.

sasquatchgeoff · #13 08-13-2009, 10:44 PM

Might want to check delivery capacity on that lift pump - should be 150 cm³ after 30 seconds at idle - those little primary filters are .6 mm mesh (600 µm) and can put a lot of unnecessary load on the pump if clogged with big particles that your missing tank strainer did not filter. Probaly need to invest the $19 for a tank strainer as well.