83 240D hard to start
 

Does anyone know if vacuum is req'd to start a 240d? Does the vacuum fuel shut off use the vac to switch off the fuel or to enable fuel flow? My 240 has just developed a reluctance to start first thing. Not temperature related, just hard on first start, turns over well, appears to have fuel at IP, just doesn't fire for ages. Wondering if the low vac at idle (10) is a factor....

Once it has been started once, it's easy to start for the rest of the day...

1983 240D, auto

I don't think vac has any bearing on starting. I'd look at glow plug function and if fuel might be bleeding away on shut down.

Thanks; the vacuum tested ok today. I like the fuel bleeding away idea. I have a clear, generic inline fuel filter just before the lift pump,it has fuel in it...perhaps there is a check valve in the IP to maintain fuel pressure and it's weak? If so, any idea if it can be changed/examined in-situ?

The first start of the day takes about 60 secs of cranking, sometimes two cranking sessions(with a starter cool down break in between).

The temps are warm enough that the glow plug light isn't coming on; I have tested them, found OK.

I guess you have clean primary & secondary fuel filters.
Did you check the fuel tank screen "filter" ? If this is clogged it will starve power.

...

Yeah, filters are fresh; haven't checked tank screen. Can it be accessed with out dropping the fuel tank?

Power is normal, once running...

Like Tom said sounds like a GP issue, I would check this first.

Here is the Diesel Giant GP troubleshooting info.
Mercedes Diesel Glow Plug Repair

If the problem persists, pump the Primer Pump a few times and if she starts then it could be fuel bleeding off some. with a full tank of fuel, the gravity flow would keep this from happening, maybe a tank below 1/2 this could happen.

Fuel filters would be the next thing to change, and the often over looked tank screen. since this is your summer car and it sits all winter, you could have some bugs growing in the tank. how does the Pre-filter look?


Vacuum is to turn the fuel off and shut the engine down.
However if there is vac applied to the Vacuum shut off valve, then it won`t start.
The brown line at the rear of the Injection pump goes to the vac shut off valve.


Charlie

Dang you guys are fast.

You can change the tank screen, but it would be best to wait until you are down to the reserve light. thin there will be only 3 - 4 gallons to drain.

If the screen is say 3/4 plugged up, then you will have more fuel. the screen is about 3 inches tall. I had the surprise one time when I dropped the screen and got my Baptismal Diesel bath. :D
The fuel hits the Axle, Diff and goes everywhere. I used one of those cement mixing pans sold at home depot, placed under there to catch any fuel. next time I will have a tarp on the ground first, more rags and maybe some oil soak stuff. (Kitty Litter).

As far as dropping the tank. it comes out from inside the trunk, so the fuel line to the Screen has to be unscrewed first anyway. you need a 46mm socket to unscrew the screen.

Charlie

Like others have stated you have a glow plug problem. Would recommend replacing all plugs!

Your glow plug light should come on regardless of outside temperature....there is a temp sensor in the head on the car....it may be hot outside but the cylinders may be cold inside....you need glow plugs....you may also need a relay....

x2

Even in warm weather, glow plugs are needed to start. check your glow plug relay and the wiring going to it.

X3 or 4, Bad GPs are the most likely culprit in a no start situation. One bad one in a 616 will cause a problem as you describe.

That is true. But on a '83 240D, it has nothing to do with starting the engine.

If the glow lamp is not illuminating at all, the issue is not temperature. The problem is that one or more of the glow plugs are inoperative. Or the lamp is burned out. Or the timer unit is malfunctioning.

If you glow the plugs and do not attempt a start, how long does the relay remain closed? You should be able to hear it "clunk" when it opens.

True but it has a lot to do with how long the gp stay on to heat the cylinders....starter, glow plugs and a good battery has all to do with starting...

A hot wire from the battery and quickly touched to the top of the GP will tell the story..no spark= No good. (not for the "looper" type) Thats a quick check if your on the road or dont have your tool box. I have never set a car on fire by doing this:) or has the old mechanic that showed me this quick check:).
The best check is to pull them out (I pull the hard injector lines also) and use that hot wire and a ground wire and see if they quickly get red hot.

I think the only sensor in the later head is for a temp gauge, the early head had one for the GP relay & temp sensor.