Poor starting 300SD. - PeachParts Mercedes-Benz Forum

MotorCityMadman · #1 05-27-2009, 11:24 AM

My 84 300 SD normally starts extremely well. The starter barely rotates to get things going. Lately it has become hard to start. All glow plugs are realtively new and have been tested. The valves were just set in an effort to improve the situation. Cetane boost and injector cleaner are added to the diesel ( I thought I might be getting wvo contamination in my deisel tank).

Does the IP timing slip or is that a rarity? What about injector nozzles? Should they be changed after a certain mileage? Any ideas????

oldsinner111 · #2 05-27-2009, 11:39 AM

Sounds like battery life,or voltage reg. time.
Ma Benz made a stupid ground on these cars.To improve charging and starter speed. I made a extra ground cable from battery to a intake manifold bolt.

Oracle12345 · #3 05-27-2009, 01:02 PM

i would check the wires to the starter and make sure 12 volts is getting down to them, check the resistance of the wires and check ground connections. also consider the battery.

injector nozzles wont have anything to do with hard starting unless they are clogged. As for the mileage its recommended every 100K miles but i just replace them when they are shot which can be diagnosed as hammering sound at idle.

Jarrett · #4 05-27-2009, 01:18 PM

Check glow plug relay. Could be kaput. Would cause hard starting.

tyl604 · #5 05-27-2009, 02:26 PM

What exactly is your problem? Is it grinding and grinding and not firing? Or does it seem like the battery is down sometimes and up others? I have had both problems. The problem with the battery was simple; the battery connection had cracked and it would not clamp down on the battery post tightly enough.

After that was fixed I had the grinding problem; thought it was cold weather. Instead it just needed a valve adjustment - first time in about 225,000 miles. Problem fixed. Starts in probably less than a second now, just like it always started before the recent problem.

MotorCityMadman · #6 05-27-2009, 03:52 PM

Sorry I was unclear. The starter turns it over quickly. It does not fire for a second or two as opposed to the way it normally would fire immediatley.

I will check the glow plug relay but if I am getting the glow plug light shouldn't it be working???

I was told that if the nozzles were old that they would not spray as fine and therefore not ignite as well or quickly.

oldsinner111 · #7 05-27-2009, 04:18 PM

Sounds like your not purging wvo out before shut down.I hope its not a single tank,wvo is a sticky nasty fuel.But OK if you use 2 tanks,I still blend 30% diesel in my veg tank.Makes easier pumping,and not as sticky as 100% wvo.

Diesel911 · #8 05-27-2009, 04:47 PM

Quote:

Originally Posted by MotorCityMadman

My 84 300 SD normally starts extremely well. The starter barely rotates to get things going. Lately it has become hard to start. All glow plugs are realtively new and have been tested. The valves were just set in an effort to improve the situation. Cetane boost and injector cleaner are added to the diesel ( I thought I might be getting wvo contamination in my deisel tank).

Does the IP timing slip or is that a rarity? What about injector nozzles? Should they be changed after a certain mileage? Any ideas????

I have never read of an IP slipping or jumping a tooth before.
However, it is supposed to be possible to jump over some teeth somewhere along the Timing Chain if the Engine is rotated backwards (anti/counter clockwise).
The stock Spray Nozzles that come with the Factory Injectors has the holes drilled in them as in the below pic. During idle all or part of the Fuel is supposed to pass through those holes. When I rebuilt the Injectors on my Car and also almost all of the used Injectors I have pulled at the Junk Yard have had those holes plugged with Carbon.
I think that WVO is even more likely to plug up the Holes in the spray Nozzle.
Concerning the Injectors the only way to know for sure is to pull them out and have them tested or pull 1 or 2 and have them tested just as a sample to see if they are OK.
If you have a High Mileage car and you believe you have the Origional Injectors you might consider rebuilding them.

In the attached pic you can see the Spray Nozzle installed on the Injector and the Central Hole.
You also see a Black Carboned area around the pintel with the hole that is sticking out. If the Metal in the black Carboned area (the area the heat shield does not protect) is eroded deeply or under cut a lot the Injector Spray Nozzle should also be replaced.

MotorCityMadman · #9 05-27-2009, 07:28 PM

Good info guys, thanks. It is a 2 tank system. I suspected wvo contamination and checked the tank valves. One may have been not operating properly and contaminated the deisel tank. I ensured operation of that valve and burned that tank of diesel off. Good fuel + cetane boost was added. Still lacklustre starts compared to what I am used to.

When setting that valves I could have turned the crank backwards. So I guess there is an off chance that the chain slipped. Although, the car still runs well and makes normal power .

I guess I should pull the injectors. So if they are carboned up I assume they can be cleaned and reinstalled. My son has a test rig that we can fire them off with. If there is a problem can you see it in the spray pattern?

I assume you need new washers to reinstall?