I also am trying to track down cold start problem. In warmer weather no problem starts immediately today even in a 48 degree garage when I went to start glow plug light on dash did not go on just yesterday it was. When I tried to start it turned over very fast after about 2-3 seconds starter disengaged and that was it I quickly checked for a bad glow plug and there seem to none all working why the starter is disengageing is another matter that has to be addressed but I probably could of got it started with a couple more attempts but just took the quick sure way and shot a little ether in it fired right up. I was starting to get the idea that maybe the engine is starved for fuel on initial startup. I have read that sometimes the valves go bad in the manual pump and you can get the rebuild kit and not even have to take pump off to replace the valves inexpensive $8 kit. When I did try to pump more fuel with the manual pump I saw it seem to be moving fuel in my see thru lines to injectors but the pump seems to buil no resistance no matter how many times you pump it I am wondering if there is some check valve that may not be working that is letting the fuel back off and not be in the chamber when starting? Or if it could be that my valves are so out of adjustment giving me such a loss of compression? I just did a valve adjustment and thought I had them right on. I only have 1 degree of chain stretch. I did not ever pull injectors to check compression is on my to do list. I have an oliver diesel tractor that has same symtoms of hard starting but with a small shot of ether starts very quickly. I am just about at the point of trying to figure a way of giving it some starting fluid w/o opening hood. I did notice that the car seems to have a lower top end and a little less spunk after the valve adjustment in that it struggles to cruise at 85mph. So things that puzzle me are glow plug light on dash, starter disengageing, and hard starting in 48 degree temps. after sitting a day. Any comments on any of the matters are appreciated.

Starter disengaging could be it got damaged from use of Ether, which should never be used IMO unless it is life or death situation. Did you get some loud clanking noise with Ether start?

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85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

Not to be rude, but please try and use paragraph breaks to separate the information. It's difficult to read a brick of input.

Starter disengaging: Mine did that a few times, a few months ago. Turned out the bolts holding the starter were loose. Has not done it since they were tightened.

Other possibility: your shift linkage bushings are worn out and/or your transmission mount is shot, and as the motor shakes on the start attempt it's moving the linkage enough to activate the neutral safety switch (thinks you are in gear). I had a 240d that did this.

Reduced performance after the valve adjustment: That should never be the case, only the opposite.

I wonder if you got the order wrong of the adjustments, or possibly used the wrong spec.

Did you read the label on the radiator support for the adjustment values? And did you use a "cheat sheet" to ensure you identified the intake and exhaust valves correctly? It isn't that hard to get them wrong (I have done it). If you reversed the adjustment values, it would probably produce the symptoms you describe.

Another possiblity for the lack of top end (not the starting issue) is that you took the throttle linkage apart when you removed the valve cover, and did not assemble it correctly when you reinstalled it. You would not be the first one to do that.

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Mac
2002 e320 4matic estate│1985 300d│1980 300td
Previous: 1979 & 1982 & 1983 300sd │ 1982 240d

“Let's take a drive into the middle of nowhere with a packet of Marlboro lights and talk about our lives.” ― Joseph Heller, Catch-22

The manual lift pump is notorious for letting air in when it goes bad.
Usually though it will also leak fuel when you pump it.
Could still be bad.

As to the glow plugs check them visually that they work.
Pull them out and ground them as you turn ignition on.
They should glow red hot, if they don't they're no good.
If they check out ok then check the strip fuse on the
driver side fender. Check real closely since a hairline
crack won't show up by just looking at it.

Louis.

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Not always the smartest but certainly not dumb?

Pretty obvious that if the lift pump will not build resistance there is a fuel supply problem.

New lift pump could be bad but very unlikely. Relief valve on the injection pump is open or so low in resistance there is hardly any retained fuel pressure present to fill the elements properly.

The last is the two check valves in the lift pump have serious leakage problems. Usually I would expect to see a back and forth type of surging in the primary fuel filter when using the primer pump with this but it would not be compulsory...

A simple test for poor valves in the lift pump might be to introduce say five pounds of air pressure to the output of the lift pump . If it will not hold it then it is pretty conclusive the valves are leaking.

For years now I have watched far too many people struggle trying to get decent cold starts on site. The fuel system except for air leakage has been ignored too long in my opinion as a possible source.

Certainly it is more productive to check out valve clearances and the glow plug system first. To me it is not the end of the line if they are not the problem.

Cold fuel has a higher viscosity than in the more pleasant seasons. This can work against you in the design of that fuel supply system I suspect in low ambient temperatures. Another quick test is to close off the return line from the injection pump temporarily and see if cold starts are better.

What is really required though to reduce guessing is a 0-30 pound liquid dampened pressure gauge applied to the base circuit of the injection pump. The car will reward you with better operation overall with getting the fuel supply system up to what it should be.

I will repeat what I found on my 1977 300d. There was no particular issue when I decided to tune up the fuel supply system. It is so cheap to do I just felt why not as it probably had never been checked.

I found a few issues that where just tired parts or wear and tear that one could expect on a car that old. The improvement overall in the car was really noticeable when rectified. So it was far from time wasted.

The real advantage to a simple guy like me is it gets you familiar with the fuel supply system so that when there are serious issues with it you will have far less trouble tracking them down.

Some think my 77 is fast for a N/A nonturbo engined car. Really though I suspect it is normal and what they have compared it too. Most likely just have easily solved issues existing from age and use.

Remember that the lift pump on a 617 N/A and 616 N/A provides a weaker output lift pump pressure originally than the turbo lift pump as well that can factor into all this. Personally I think putting a turbo lift pumps spring in the weaker pump is a good upgrade as well. This slight modification was felt needed as the years went by with the 617 engine by the manufacturer. So it was a production change with the 617s with turbos. It was not a case of the weaker lift pump was unable to supply enough fuel volume as it was. It had to do with other things I believe.

Recent filter change? How is the tank strainer? You can view the tank strainer by removing the first aid kit, and removing 4 screws. Then remove the fuel sender unit, the nut is the same size as the tank strainer (huge).

Always goes with the simplest and cheapest solutions, especially with our old Mercedes it tends to be the 20-30$ part that goes bad.

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Nosce Te Ipsum "Know thyself"

Thanks for all the great replies on thinking them all over I think I might take a closer look at the strip fuse in the relay. I find it very strange that the g.p. light on dash seems to work and not work currently not work but when I check all the glow plugs they check out ok and when I did check to see if they all got voltage seems they were all getting 10.8 volts which I thought is strange in that the sitting battery is putting out about 12.6 but I guess some gets lost along way. This is one of those very tricky problems to hunt down. This morning with temps. at 30 and with the car plugged in lower radiator hose heater it did start w/o any starting fluid but was a little hesitant . I will keep monitoring the situation. The car starts fine 8 months out of the yr.

While thinking things over. The fuel supply system may or may not be contributing to the hard start problem.

Still if you cannot build good resistance while pumping the primer pump you do certainly have a problem . Cheap to deal with is a benefit as well.

Almost no problem I can think of on these cars is cheaper to deal with. Hard start at 30 degrees while plugged in is really pretty bad.

The quick light off with either in those conditions basically could be you supplying enough fuel to start on perhaps. If you substitute diesel fuel in a spray bottle instead of the either and the engine lights off quickly. It would prove that not enough fuel is being provided at starter rpms to start. As rpms pick up you get a little more fuel pressure building to allow it to run.

Again I like simple tests. Open up the breather to get a clear shot at the intake while someone else is cranking. The diesel fuel oil will not process through the air filter the same if you are leaving the filter on with the either.

There may be a terrible price to pay when running low fuel pressure on these engines for a long time anyways. Besides all the more obvious problems. If the injector pumps arm moves all the way to it's stop with another person pressing the fuel pedal to the floor. That is another indicator of why you struggle to see 85mph. You may be starving the engine for fuel with low fuel pressure.

The best way to check the glow plugs is to remove them and connect jumper cables to the appropriate sections, do just the tips glow?

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83 SD

84 CD

if the voltage drops to 10.8 on a battery with 12.6 at rest, then the glows are pulling in...

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!