W124 - 1987 300TD - Intermittent Starting Issue
 

Hi

I have an 87 300 TD that has driven perfectly (aside from new alternator one year ago) since I bought it three years ago. Yesterday I went to the store and when I came out I turned the key and nothing happened, although all the lights on the dash come on as normal. I then moved the auto transmission stick through the gears and wiggled it about a bit and hey presto, she started.

I came home and did some research and found all sorts of possibilities, including parking on a slope, ignition barrel wear, fuel lines/pump, battery terminals and starter motor.

So this morning I got in the car (garaged overnight, by no means 'cold') and tried to start it and it wouldn't crank. Same as yesterday, run through the gears and it started. So I did the easy stuff: I tightened the battery connections and i removed the center console around the gear shift so I could vacuum out any debris/dust. I then tried to start the car and it wouldn't start, so I went through the gears and sure enough she started.

I could be completely wrong, but it seems to me that the car thinks it's in drive when it is in fact in park.

Anyone had this experience before or have any ideas? All input gratefully received.

Since moving the shift lever seems to help it's a pretty sure bet that your neutral safety switch is acting up. That should help narrow down your research.

Many thanks for the super speedy reply, much appreciated.

Regarding the neutral safety switch, do you know of any tests I can conduct to make sure that is in fact the issue.

I could tell you specifically on a W123. On a W124, I'm not certain except to say the general idea is to bypass the neutral safety switch so that it is eliminated from the starting circuit. If the problem goes away, then that's definitely the problem!

If you can look up where the terminals are for your starter wiring (sometimes on the starter itself, other times on a terminal block near the battery) you can also try using a jumper to bypass your neutral safety switch and ignition switch temporarily when you find yourself in a no-start situation (though please be sure the shift lever is in park or neutral before attempting this). This can help narrow it down to those two items, further diagnosis would be needed to narrow it down to the NSS itself.

when it happens again, put shift lever in neutral and see whether it starts. If it starts in neutral consistently then it is the NSS. It is not difficult to R&R but don't get under the car without axle stands.

Uber: Many thanks, will keep you posted.

Ah-Kay: As is always the way, I can't now get it to not-start, it fires up first time every time, although it is warm because I just did a 20 mile round trip.

Next time it doesn't start I will try the neutral position as suggested and let you know what happens.

Thanks for your help, much appreciated.

Check the alignment of the shifter linkage and condition of the linkage bushings. If the bushings get worn out then the lever might not get to the right position to actuate the NSS in Park.

The action between positions should be firm and snappy even after 27 years with new bushings installed. All the detents are in the transmission itself, the console shifter is just a pivot point.

(Note, OP has a 722.3 transmission, this statement is true for 722.3/722.4. 722.6 has a hybrid shifter, P-R-N-D detents from the transmission, 4-3-2-1 detents from the gear selector, since the linkage stays in D on the transmission for 4-3-2-1, those are reported electronically only. On the 722.9, there is no linkage, it's all in the computer, and you have an electrical "wobble stick" on the column or console.)

You will have to get underneath to perform this repair. Proper jacking and support is essential to avoid damage to the car or to yourself.

Although you might be able to reach up under there, especially if you have long arms, and see the condition of the bushings with a mirror with the car safely at rest on its 4 wheels.

Many thanks guys. Will try the neutral option as soon as I can get the car to not-start, the irony being, since it didn't start this morning it has now started every time!

Another check for the shift linkage bushings is the difficulty to get the car to engage park.

Engaging park is smooth as butter, no problems I've detected.

As I said yesterday, problem hasn't reoccurred in 24 hours, having occurred four times in the previous 24 hours, so the plan at the moment is to see if she starts in neutral next time it occurs.

Just to clarify. I have seen the NSS fail to a point where the car will not start, even in Neutral.

I'm only slightly ashamed to admit that I was too lazy to replace the one on my dad's W126 in the winter, so I locked a spare NSS in the "Park" position, plugged it in, and zip-tied it to the bottom of the car....

Glad I saw this post just now, as I am experiencing the same thing happening. Some times it starts right up and then try again and nothing. All I might hear is a click when I turn the key off.

Some history: I have been pouring tons of time into this girl

New glow plugs
Rebuilt injectors
IP seals replaced at same time
Recent new battery
Replaced ground strap on motor
Harness wire replaced as it shorted out and I almost had a barbaque
New harness housing
New 50 AMP GP fuse
Removed and cleaned fuel tank and new strainer
All new filters
Resealed Vacuum pump
New radiator
New alternator brushes
New copper fuses

I purchase lots of stuff from Kent Bergsma (Moly, rebuild kits, hoses, connectors, tools. etc.) I know a little pricey at times but usually worth it in what you get the added knowledge you receive with the parts.

I purchased a new ignition switch. and electrical switch connector for it. But cannot seem to see how it could be even remotely possible to replace them. At this point I am totally stumped. Maybe one of you could throw me a bone here?

The 2 terminals in the fender idea would be a help for me to diagnose the starter at least. Have to work by myself on this! Some direct anyway would be a help. Stumped like Mike

Exit: It's a mind boggler for sure. Since the original post I have gone a whole week with no problems. I hadn't driven the car this weekend so this morning I started it and it fired up first time. I then realized I'd forgotton something, went back in the house, came back out and it wouldn't start, absolutely nothing and it stayed like that for 20 mins. During that time it would not start in neutral. It finally did start and off I went, no closer to knowing the issue, although at least I now know it won't start in neutral.

One thing I have noticed is a small diesel leak from the pipe that i think goes into the Diesel Fuel Thermostat. (I think that's what it is, see picture)

Could that be it?

Attachment 125538

Yep it certainly can be, but more likely IMO the o-ring inside the Thermostat. I had a leak too after fiddling with the pre-filter(yours looks pretty dark may want to change it while your at it) which I guess moved the thermo's nipple enough to cause it to leak. Its a very simple, cheap fix. Depending on where you live, you could bypass it for now(warmer climates) or order the parts and fix it, if its cold where you are I would. OFC R&R any old lines while you are in there as well. Here is the link I found to fix this.

http://www.peachparts.com/shopforum/mercedes-parts-reference-library/235091-om601-602-603-diesel-fuel-thermostat-rebuild-parts-list.html

Treetops

PS-Empty and remove the washer bottle to make life much easier

Thanks Treetops, sourcing what I need as we speak.

It happened again this morning, albeit for a longer period, eventually starting after about 30 mins messing around.

Here are the thing I know for sure: It only occurs when it's cold, even though the car is garaged (garage does get quite chilly).

The neutral safety switch is still in play because this morning it started immediately after cycling through the gears, although it was probably the fifth or six cycle.