new (to me) 240d won't start - PeachParts Mercedes-Benz Forum

newdieselowner · #1 11-07-2004, 06:50 PM

Hi I'm new here, so bear with me.

I bought a 78 240D last week. It test drove well on two occasions, then drove 60 miles home on the interstate and did great. But then it wouldn't start the next morning and i haven't been able to start it since.

I've searched around here a little. I've checked the glow plugs and looked for fuel leaks. I repalced some of the fuel lines that looked older and bled the fuel system. I replaced the battery cables. The glow plugs are filament type, and they are all getting volatge, but i don't know what kind of voltage is normal. I can also see a small pocket of air in the fuel prefilter that i can't get out, is this ok? or should i have absolutly no air visible?

Any advice would be much apppreciated.

John

#2 11-07-2004, 07:04 PM

A little air in the prefilter is not a problem. Mine ('80 300TD) always has it. I've changed it several times when it got clogged, and I always fill the new one with vegetable oil (I'm burning WVO blends) usually including a little air. No problem. Lots of questions like yours have been discussed many times here; further searching is encouraged. Good luck!

BrierS · #3 11-07-2004, 07:12 PM

Welcome aboard.

Just went out and looked at one of my diesels to confirm what I remembered about the pre-filter and air bubble. Right or wrong, it has had an air bubble at the top since I have owned it. Runs good. Of course someone may come on and say there shouldn't be one then I'll have to check mine too.

I believe the test for the glowplugs would be resistance. When you went to start it, did you have a glowplug light showing on the dash (yellow on my two)? After they go out I usually wait a total of 30 seconds before engaging the starter. Did it turn over at a reasonable rate?

phantoms · #4 11-07-2004, 07:17 PM

Is it spinning over, but not starting?

Take the Fuel Cap off and see if you here a vacuum when you do. If so, the tank vent may be clogged and the fuel is not getting pulled up to the IP. This is a common problem with cars that have set up for a while.

Is the prefilter clear or does it look dark? May have clogged filters.

Any fuel leaks? If so, it may also be pulling air into the system.

Touch the resistor wire between the first two glow plugs (cyl.1 and cyl.2) very quickly after glowing the plugs. Do not grab it, but rather brush your finger across it very fast. Is it hot, if not you have a glow problem. If it is, you may still have one but it's less likely.

These are just a few things that are easy to check.

BrierS · #5 11-07-2004, 07:17 PM

Copied this from a quick search on glowplugs & ohms.

"Any GP that doesn't read about 0.7 ohms is suspect. Do the 12V test (across battery terminals) on any GP that doesn't read 0.7 ohms. Replace any bad GP."

The search had 4-5 threads regarding 240D glowplugs and I think I saw how they were testing the relay.

From what I have read, you need to know if your glowplug indicator light on the dash appears to be cycling correctly.

newdieselowner · #6 11-07-2004, 07:25 PM

Seems to crank at a reasonable speed... until the battery gets discharged. I've been recharging with a charger. It cranked fast enough to start it when i test drove it anyway. Seems to want to start, its smoking and feels like it starts to fire but doesn't catch.

I saw a tiny amount of fuel on the top of the filter after the drive home, thats what got me replacing fuel lines, i think i got rid of that problem. i will check the fuel cap, but it does seem like fuel is moving through the prefilter (which is clear, btw). perhaps not fast enough.

The wire between all the plugs is glowing red after heating. and the light seems to be cycling properly.

I thought the resistance check only applied to pencil type glow plugs, so i filtered out those threads... am i wrong?

John

whunter · #7 11-07-2004, 07:30 PM

Quote:

Originally Posted by newdieselowner

I saw a tiny amount of fuel on the top of the filter after the drive home, thats what got me replacing fuel lines, i think i got rid of that problem. i will check the fuel cap, but it does seem like fuel is moving through the prefilter (which is clear, btw). perhaps not fast enough.
John

Prime the system after you replaced the filter?

newdieselowner · #8 11-07-2004, 07:35 PM

yup, pumped the hand pump until i got out as much of the air as possible and i got a constant squeaking noise...

whunter · #9 11-07-2004, 07:36 PM

Quote:

Originally Posted by newdieselowner

The wire between all the plugs is glowing red after heating. and the light seems to be cycling properly.
I thought the resistance check only applied to pencil type glow plugs, so i filtered out those threads... am i wrong?
John

This would be a good idea.
http://www.peachparts.com/shopforum/showthread.php?t=107229

For now, this is what you need for testing.
http://www.peachparts.com/shopforum/showthread.php?t=106447

whunter · #10 11-07-2004, 08:05 PM

Quote:

Originally Posted by newdieselowner

Seems to crank at a reasonable speed... until the battery gets discharged. I've been recharging with a charger. It cranked fast enough to start it when i test drove it anyway. Seems to want to start, its smoking and feels like it starts to fire but doesn't catch.
John

Speed is critical for cold starting.
If the starter or battery are getting weak, you will have a very hard time starting.

newdieselowner · #11 11-07-2004, 08:23 PM

I rechecked the glow plugs and they sound ok, according to this link: http://www.peachparts.com/shopforum/showthread.php?t=106447

I get a steady decline in voltage across each plug, about ten at the start and 2 across the last plug. it seems the plugs are working according to everything i've seen so far.

The battery is new and holds a full charge.

I don't really have a good sense for the starter, so a slow starter seems like the best bet so far.

I'll go out and tinker with it somemore.

Also, no vacum when i open the cap.

whunter · #12 11-07-2004, 08:43 PM

Quote:

Originally Posted by newdieselowner

The battery is new and holds a full charge.
I don't really have a good sense for the starter, so a slow starter seems like the best bet so far.

The starter on my 1985 300SD cranks at 700 RPM.
If yours does not crank idle speed, it is getting weak.
I have replaced many starters that the diesel owner swore where just fine, then where shocked at how fast the new starter cranked.

newdieselowner · #13 11-07-2004, 08:56 PM

I like having hard numbers. I ran out to the car to check the cranking speed, before i remembered that this is an automatic and doesn't have a tach. Is there an easy way to hook up a tach? i don't have an optical tach, and all the aftermarket tachs i've seen hooked up to the ignition system on a gaser... hmmm. like i said, i don't have a good sense for this starter, i know it started fine when i test drove it, but that was 2000' lower and in a warmer enviornment, and the po probobly warmed it up first. i'll look at the starter a little bit harder. thanks everyone.

BrierS · #14 11-07-2004, 09:03 PM

I may be off on this however someone will correct me and we'll both learn . . . I have a good commercial grade charger which will jump start a vehicle. However, using my extremely good cables and another vehicle gets the job done much better. This will be a good thread to follow . . .

newdieselowner · #15 11-07-2004, 10:23 PM

Well, most of the home grade chargers i saw yesterday when i was looking had 75-100 amp starting functions, the commercial ones i saw at sears had more like 120 amps.... i think thats better than most cars and light trucks put out from the alternator. I could be wrong. I was just recharging my battery at 10amps between attempts though.

still thinking about my starter.