Hi all,
recently I changed out all my GPs, and reamed the ports. After I put it all back together, I went to test it. The GP light comes on as usual, and when I went to start it it didn't even crank. Before I put in the new GPs I tested them and they were all good, and I tested them again after the no crank and still all good. Also, I'm getting 12.5V at the relay fuse. I did not have this problem before changing out the GPs. Any ideas?

Shouldn’t...I didn’t write isn’t related...to replacing the glow plugs. Go back and triple check all of your work focusing on electrical connections. If nothing found transition the diagnostics to a normal no crank situation.

Do the headlights work with the key on? Try moving the gear selector while trying to crank. Try jumping the terminals on the RF fender well to see if the stater turns.

What is the battery voltage before and during trying to crank.

Good luck and keep us posted, we will figure it out.

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"Rudeness is a weak man's imitation of strength" - Eric Hoffer

Check your battery ground and the engine ground strap. The no crank sounds like a bad ground.

Not posting your year and model is not helpful.

I looked up and you have a previous thread about a 300CD so I am assuming that is the one you are speaking of.

This is a good place to start trouble shooting.
On the CD there should be wire Junction/Terminal block on the passenger side fender well in front of the batter. It may still have the plastic cover on it.

You can use a jumper wire or a remote starter switch on that and see if it gets the engine to crank.
The 2 rear most screws are connected to the Positive batter terminal. Using a jumper wire from there to the most forward terminal should get your Starter To crank (if your battery is charged and holding the charge and the ground is OK).
This bypasses the ignition and the Neutral Safety Switch (a bad Neutral Safety Switch will also keep you from cranking.).

If you cannot get it to crank from the terminal block you are looking at a Battery or battery connections (like a bad ground) issue or a Starter issue assuming the wiring is intact.

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84 300D, 82 Volvo 244Gl Diesel

I am going to throw this in perhaps for laughs. In the first few weeks that I had the Mercedes I got into the Car and it would not crank. I called AAA for a tow. As the guy was hooking it up for the tow I went inside to make sure it was in Neutral and I realized I had tried to start the Car with it in Drive.

Of course the Neutral Safety Switch is going to prevent it from starting in drive and it will only start in neutral or park. But I was used to US Cars where you have to return to Park in order to get the Key out of the Steering Colum Lock.

I was too embarrassed to tell the tow guy that I had simply screwed up and I let him tow it home.

Once he was gone I put it in park and it started fine.

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84 300D, 82 Volvo 244Gl Diesel

Yep BTDT with both my kids when they drove the wagon back when they were in high school. First time it was at the high school a mile from our house so I was able to go there and see what the problem was right away. After that I learned to ask that question first.

I actually went to the JY and started collecting the parts for the interlocked ignition to keep that from happening again. But then I sold the wagon to vstech and the parts went with the wagon.

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The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech

Every time I've read this over the years, the same question has occurred to me so I'll finally jump in and ask it:

If I was to use a length of wire to jump, what gauge of wire is appropriate so that I avoid melting the wire and potentially starting a fire?

Thanks for any clarifications.

10-14 gauge. Jump from the battery positive to the solenoid positive. I would get a remote start button though.

When you mentioned the gear selector, I remembered that sometimes the shifter needs a little wiggle to get into the selection. So I tried that, and she started right up. New shifter bushings are on the way. Thanks!

Remember you are only activating the Starter Solenoid and in fact your Glow Plug Relay so you are not dealing with massive amperage. I have done it with 16 gauge wire and in fact the remote starter switch I have also seems to have 16 gauge wire on it.

Also I am only suggesting that you just do it to see if you can get it to crank and not specifically to try to start the engine so you are only going to apply the jumper wires briefly.

Also if you look at the front 2 wires where they are crimped you can kind of get an idea what gauge the wires are.

Also obviously if the jumper wire starts getting hot let go of it.

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84 300D, 82 Volvo 244Gl Diesel

Excellent clarification that also happens to highlight a mistake in my thinking: I was erroneously thinking that I would be passing along the sizeable amperage but on more careful analysis, you are of course correct - the jumping would entail only energizing the relatively low amperage starter solenoid.

Thanks for responding.

You can also jump it on the wheel well with two screwdrivers. Good way to see if your starter works.

If you do that, stand to the side since the car may jump forward if in gear and crash into the garage wall. The key's "crank" may not be working because the NSS switch indicates not in P or N. Same in all cars.

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1984 & 1985 CA 300D's
1964 & 65 Mopar's - Valiant, Dart, Newport
1996 & 2002 Chrysler minivans