Trouble starting, but runs well when it starts - PeachParts Mercedes-Benz Forum

HGV · #1 06-04-2011, 09:36 PM

I have a 1987 300TD with 275k. The car is very hard to start. Need to jump it to get it going. Then it runs well. All six glow plugs are fine. Once it starts it runs great. Full power, everything. I suspect that the fuel is draining back and it needs to be re-primed every time after it sits for a over night.
what is wrong?
Henry

leathermang · #2 06-04-2011, 09:49 PM

Have you taken the glowplugs out and reamed the carbon out of the hole?

kerry · #3 06-04-2011, 09:51 PM

Have you confirmed voltage to the glowplugs? Does it start back up immediately after you shut it down when warm?

HGV · #4 06-05-2011, 12:26 AM

I took the injectors out, inspected the pre-chambers, ran the glow plugs at night and inspected the "glow". Red hot, no problem. I think the fuel is draining back from the injectors and the result is that I need to crank to prime this system before the pistons will ignite.

My questions is, "What will cause the fuel to drain back and need to be re-primed?"

Henry

vstech · #5 06-05-2011, 12:52 AM

many things.
delivery valve o-rings are the most common.
any fuel line leak can cause it though.
best start parking the vehicle with the rear higher than the front until you find the problem
my 87 was that way for a while.

leathermang · #6 06-05-2011, 01:29 PM

Quote:

Originally Posted by HGV

I took the injectors out, inspected the pre-chambers.....Henry

IF you did not take your precombustion chambers out of the engine then you had no way to inspect the most important part of them...
AND , the glow plugs can glow all they want to and not be effective if they are blocked by built up carbon..
so reaming the holes when they are out may be necessary...

HGV · #7 06-05-2011, 04:45 PM

It is not the glow plugs. The car recently had a valve job. I inspected the prechambers then. The car runs just as it should once it starts. When I took the injectors out, I cranked the engine and it took a long time before each high pressure line was spitting out fuel. It is no the o ring seals on the IP. THere is not fuel leak from the lines or under the car.
What would cause the fuel to drain back. I suspect that the only thing it could be is the fuel pump attached to the IP. The IP was rebuilt, so I assume that included the fuel pump. Took a look at the low pressure and high pressure diagram and it is the only device that could allow fuel to leak back.
Does this make sense and how difficult is it to remove and fix?
Henry

leathermang · #8 06-05-2011, 05:25 PM

You could have given us that information in the first post....

Diesel911 · #9 06-05-2011, 07:28 PM

Quote:

Originally Posted by HGV

I have a 1987 300TD with 275k. The car is very hard to start. Need to jump it to get it going. Then it runs well. All six glow plugs are fine. Once it starts it runs great. Full power, everything. I suspect that the fuel is draining back and it needs to be re-primed every time after it sits for a over night.
what is wrong?
Henry

The above in blue sounds resonable.
Bunch of possibles.

Air Leaks in the Hoses or where they attach.

The Valves inside of the Fuel Suppply Lift Pump not seating well.
I so not believe your 87 300TD has a Hand primer so that cannot be the cause.

Newer Model Lift/Fuel Supply Pump Rebuild
http://www.peachparts.com/shopforum/showthread.php?p=2561334#post2561334

You did not mention of parking the Car at night with w Fuel Fuel tank made it easier to start or not. Also if you Drive Way slants you might try parking the car so that it parked with the rear higher than before and see if it improves anything.

HGV · #10 06-06-2011, 01:16 PM

I live on a completely flat street, so parking the car on a slope is not so simple as just parking on the other side of the street. Would help if I could get it started, then I could go park it on a hill. Left it on a charger over night. THe battery was completed drain.
I am sorry for not giving all relevant details of the problem, I just assumed when I said it was not the glow plugs (Which is what I first suspected) that I would be believed. I have had leaking delivery valves seals and have a complete set just waiting for the next time it happens, but those leaks are easier to find. This one is odd. No diesel under the car or in the engine bay. The fuel system is so simple that it must be the delivery pump. Doesn't seem very serviceable. Might just get a new one and take my chances. Maybe just taking it out and cleaning it might work.
Anyone, thanks for the suggestions and the link to the fuel pump thread. Very helpful.
Henry

sixto · #11 06-06-2011, 02:52 PM

Might it be the pressure relief valve on the return side of the IP? Maybe not enough system pressure at cranking revs but enough once the engine catches. I read about pinching the return line between the big filter and hard line on the fender (cigar hose on a 617) to see if the engine is easier to start as a test of the check valve.

Can you do a basic test of the lift pump? Compare output at cranking rpm between drawing from the tank and drawing from a fuel supply higher than the lift pump.

Have you ruled out a clogged tank vent?

Sixto
87 300D

vstech · #12 06-06-2011, 04:44 PM

My favorite trick it to take a shop vac, set it on blow, and pressurize the fuel tank. then start crawling the fuel lines looking for diesel seepage.

sixto · #13 06-07-2011, 02:27 PM

Have you tried first disconnecting the engine shut-off actuator vacuum hose? Maybe the key switch is acting up.

Sixto
87 300D

leathermang · #14 06-07-2011, 03:14 PM

Quote:

Originally Posted by HGV

.....I am sorry for not giving all relevant details of the problem, I just assumed when I said it was not the glow plugs (Which is what I first suspected) that I would be believed.....Henry

LOLOL,
If we took people's word on that sort of stuff we would be of almost no help here on the forum... We have to drill down and see if they understood how and executed the tests for the item which might be in question...
Remember, we are here basically blind except for the description provided by the OP...
WE TRUST NO ONE's original guesses...... if they knew what the problem/solution was they would not be posting on the forum wanting/needing help....

bbboomer · #15 06-07-2011, 03:35 PM

Please don't be offended by the questions, my past experience has taught me these questions have a purpose.
Think of it this way, if you went to the Doctor and said I'm sick a GP would have one set of experiences to draw from to make a diagnosis as would a Heart Specialist, a Chiropractor etc.
Get them all in the same room and the experience base is much better!