93 300e won't crank, need help diagnosing
 

Initial problem: failed emissions testing yesterday, due to high hydrocarbons. Drove to local parts shop to get spark plugs, since I was told by emission shop that was the first thing to suspect.

As I got back in car to leave parts store.....car would not crank. Heard fuel pump run briefly and a single click from engine compartment, then nothing. Lights, radio, windows etc all work fine. I tried starting while jigling shifter all around neutral and park to no avail. Guy in store came out with portable battery jumper and tried that too..still nothing. I then figured the OVP relay had gone bad again, since this is how car acted about 4 years ago. So today I purchased a new OVP relay and put it in after work...still nothing (no crank, fuel pump runs, and only an occasional single click when turning key to start). I also had searched forum last night and had decided I would try jumping X27, as per Arthur Dalton's informative posts (hope you are reading Arthur!). But unlike the posts I read last night which all indicated starter engaged upon jumping 12V to middle terminal of x27 today, I got nothing. Only a small spark at terminal/jumper indicating I had current. I am now assuming I have a starter/solenoid problem.

I had to get the car towed back home tonight from auto parts store since I was unsuccessful in getting it started. And I really don't want to buy any more parts unnecessarily (I now have and extra non/refundable $60$ OVP relay). Any suggestions from anyone on how to procede? Arthur?

How easy is it to get at the starter on that car? Perhaps I should rephrase that... how difficult is it to get at the starter on that car? If you can get to the terminals at the starter, you can easily determine if the starter is the problem. (And it sounds like it is.)

If you jumpered from bat + to center terminal of X27 w no crank, then the problem is at the starter/solinoid or a bad ground.[ assuming bat is up on charge]
Take a jumper cable and go from the bat - and go to a good engine ground
and retry with + to x27.

Also, take a good look at the wires going from the X27 to the starter [ behind oil filter]..common for those to have the same problem as the engine wire harness.

Suspect is starter.

hope this flow chart helps

That is a RUN chart..he does not have CRANK.

And we know he has power to X27...so the problem is downstream from X27.

it tells him the 3 major areas to check when the car dont start but doesnt give all things to consider ie bad battery etc

You don't get it.
We are working off the Starter circuit schematic ..and the Starter circuit is the complaint...not Run complaint.

NO CRANK...see that ?????

NVM figured out the suspects causing the problem.

I've had the exact same experience on MB's and had 3 different issues.

1. Defective Battery, most common. I couldn't even jump start. Replaced battery, no more problems.

2. Defective Neutral Safety Switch. Started the car with a push button start switch. Replaced NSS, no more problems.

3. Defective Starter. It started out intermittent, passed bench test at one auto parts store, then failed at another. Replaced starter, no more problems.

Check all the basics first.

hes not getting nothing at x27 which means NSS is out of the picture.
Battery, wiring, corrison, bad grounds., starter solenoid

Thanks for the responses. I tried the grounding jumper as you suggested Arthur, no effect. Lost daylight so no chance to check wires closely from x27 to starter. Priced rebuilt Bosch starter/solenoid today at $180. If I can't find fault in wires from x27 to starter guess I will move forward with replacing that. Anybody have replacement procedure for starter replacement on this rig?

That is the basic idea... except it is not that he is getting nothing at x27... it is that when he brings 12v from the battery to x27, he is by-passing the NSS, K38 relay , and ign sw....
That is the reason we use X27 for the test point..that eliminates all cabin controls upsteam , as you can see on the schematic. So, the problem has to be downsteam from X27.

If he were getting nothing as you suggest [ meaning no power at X27] than the problem would be upstream..NSS/K38/Ign sw/fuse5.

So, X27 is a convienient test point in this circuit to isolate the problem up or down from that point..we use it b/c of it's simple convienience...it can also be used if one gets caught with his pants down somewhere with a bad NSS/K38 circuit..by jumping to that x27, it will get you home w/o a tow truck.
I have seen guys that had a bad NSS and used that jumper for a year to start their car every time the NSS failed. .....:)

Download 15-7100.pdf from FileFactory.com

Download that file

<Anybody have replacement procedure for starter replacement on this rig?
>

The top bolt takes a long extension [ I use a 20" and a 6" combined] and you get way back and sneek in over the top from the upper right side of the tranny.

If that harness is OK, then the suspect is sol or brushes...sometimes you can get a starter with hung up brushes to spin if you give it a smack while someome holds the key over..that will verify starter.

OK, let's be old school about this. First, confirm that your battery is good. Next, if you can get to the terminals on the starter... the big terminal connects directly to the battery positive terminal. You should have battery voltage here at all times. The small terminal energizes the solenoid when you turn the key to "start." Take a screwdriver. Use it to bridge the big terminal to the small terminal. If the starter cranks the engine, your starter is good. If it doesn't, your starter is bad. (Or your engine is seized, but we don't want to go there.) But be VERY careful not to touch the screwdriver to anything else when it is touching the main terminal!

<But be VERY careful not to touch the screwdriver to anything else when it is touching the main terminal!
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1987 W201 190D
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....and what do you think the X27 connection terminal does ???

I think it adds another uncertainty to the procedure, as you said:
Otherwise I think it's fine. Obviously easier, and if it cranks by jumping it there then there's no point in going to my suggestion.

whenever i have a starting problem i suspect fuel delivery, ignition and the starting circuit and elimnate anything that is fine. Check the obivous like fuses etc.

Just because the fuel pump can be heard working doesnt mean the system is up to pressure. I would take a quick fuel pressure test to verify if its working or not.

I would pull a spark plug and see how they look and inspect the ignition system. Also make sure the timing is right.

If these all checked out then I would starting elimnating components in thestarting circuit by making sure i have a good battery, do a few tests with a dvom to check the wiring, make sure the NSS is doing its job and then I would be left with the starter(ignition switch would be elimnated after 12volts was reaching the starter)

Kinda hard to diagnosis problems if you dont have the car in front of you

<Obviously easier,>

Correct ... and that is why they put it there ...cuz you can't get to the wires at the starter on a 124.032 chassis car.
But you have a valid point and that is the old way we did it on an open engined compartment car/truck.
If you read his post, you will see that he has already done his homework and read one of the circuit tutorials I have in the Archieves on this exact chassis procedure ,,,that is how he knew about the X27 shortcut we use for diagnosis on this particular chassis.
The other VERY COMMON failure part on this exact chassis is they had a problem with the harness that went from the X27 test connector to the starter solinoid b/c of bio-degradable wire insulation...so, knowing that, one can see why my next recommendation step is to check that harness for that common complaint before changing the starter...he understands where the diagnostic stand and I credit him for using the Search feature of the Forum.
We are on the same page..and I am aware of this chassis circuity and it's common failures and weaknesses.............

<I would pull a spark plug and see how they look and inspect the ignition system. Also make sure the timing is right.

If these all checked out then I would starting elimnating components in thestarting circuit>

He has a NO CRANK condition.... I would certainly not be checking the timing and ignition system before I got the car to Crank....

Are we reading the same post??????????? Did you see his answers ????

its off topic yes so it obivously doesnt fit this situation.....................

And btw your suggestions for the stalling problem i had a while ago with the 190E didnt solve the problem, paided a dealer foreman nd he didnt solve the problem and I found the problem and I dont have any manufacturing training ether or years of experience....

Yes, we are on the same page. I am not aware of the peculiarities of this chassis, which is why I asked in an early post in the thread if the starter was reasonably accessible. I did not get a response to that question, so I offered a very simple and 100% unambiguous diagnostic procedure. Unfortunately it seems not to be practical in this particular car.

<which is why I asked in an early post in the thread if the starter was reasonably accessible. I>

Very Good.
I was answering your post by mentioning the X27 test connection.
And he knew of it from the Archieves , so There was no reason to explain it in detail. as the thread was a diagnosis for his complaint. But , either way..we have a starter or starter feed problem and we both understand that, as well as he does. ..

<And btw your suggestions for the stalling problem i had a while ago with the 190E didnt solve the problem, paided a dealer foreman nd he didnt solve the problem and I found the problem and I dont have any manufacturing training ether or years of experience....
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>

I remember when you first started posting as a 'Techinician".... [ I believe that's how you spelled it ?]...so why did you even have to ask ???????????

A former tech moving on from it actually but why I posted is I got a bit impatient like we all do and wanted a quick answer but should of know better.

Calmed down and fixed the problem which I paid a MB dealer foreman to fix and he didnt since the problem only came back. I didnt bother bringing the car back to him after I saw what he did to the car.

Anytime I get a car to fix with a problem whether its friend, family etc its fixed right the first time and its work I can be actually proud of. I dont know how a MB dealer foreman coulda thought doing what he did to try solve the stallling problem worthy of charging someone.

i agree with slk230red, the starter lockout switch, assuming this is an automatic. keeps you, as a supposed idiot user, from starting the car in gear. i have had the same thing happen.

I finally got a chance to take another look tonight after work (still light out thanks to time change). You were right Arthur, the wiring harness insulation from x27 to starter is almost completely gone....dust. And the x27 wires run right beside the oil filter....and I guess I didn't mention in my first post that I had an oil change before the emissions inspection. And it looks like fresh wiring insulation dust has been deposited from oil filter manipulation in that area. I'm thinking/hoping now that my no crank condition is the harness rather than the starter/solenoid? Nevertheless, the harness needs to be replaced so I guess that is my next step. There are 3 wires from the x27 switch running down towards starter. It looks like one goes down to the starter/solenoid. Anyone know where the other 2 go? And I suppose this harness is going to be a dealer only part?

Yeah, I kinda figured that , as that was a common prob with that chassis..

The other 2 wires on X27 are oil pressure sw and level. OP is terminal #1 [bk/gn ] and OL is term# 3 [bn/bk ]

Anyway, no way around it except you could run a single wire from X27 center terminal to starter solinoid and then cut the old one off at both ends just to get you back to a normal Start/Crank condition..then order the harness and do it . If you do chose to do that, you can also test the starter/sol by bringing 12v bat + to the new wire just like you did when you used X27 as the test point.
There is a tutorial in the Archieves on that replacement job...might even be in the DIYer section.
The oil filter change is what finally did it in...same happens to the engine harness when they change spark plugs...as soon as they get disturbed , they fall apart..literally.

I'm happy to announce....it's running!! Turned out it was the starter after all, even though wiring from x27 to solenoid/oil press/oil level was almost completely void of insulation. I ended up re-insulating wiring with electrical tape (dealer wanted $140 for new). Got rebuilt Bosch starter for $180 and just now finished install.

Also replaced spark plugs, since I still have to pass emissions inspection after I failed 2 weeks ago (high hydrocarbons). Old plugs were really worn down (electrode tip) and gap was more than double spec. I hope this will be enough to get it to pass tomorrow...... If not, I will be back asking for suggestions.

Thanks all for your help, especially you Arthur, this is really an amazing place!

Brad

Very Good.

And you now know the value of using the X27 connector as a test point for diagnosis of the system...Many do not realize that once you jumper to X27, you have literally eliminated the NSS, Ign sw, K38 relay , and ATA system b/c you have by-passed all these circuits in the Cabin...That is why X27 is the preferred test point. [ it is a mid-point circuit seperation of cabin controls and under hood components]
Another plus of this knowledge is that if anyone does get into a no crank condition b/c of any of those upsteam failure conditions [ which are very common] they can simply use that X27 jumper trick to get the hell home......

Hey Arthur Dalton,
gschira here -owner of '88 300 SE. I followed this whole thread. Very informative from everyone. Would my car have the same x-27 test point, or another similar type test point? If so, where would I find it? I still have no repair manual.
Thanks for ALL the great info...............This site is awsome

Should have X27, but location may be different than 124 ...Check just to the left of the brake reservoir...it will be the VI/WT wire on a 3 wire connector block, if it is there.

Thanx Mr. Dalton. I'll check it out in the am.......

X27 and Archieves
 

Mr. Dalton
I recently joined this site. I have read several post recently where you have mention that the information you are giving on the no crank problem is contained in the archieves. How can I find your writeup on this subject? I have a 1993 300ce that I am having a "no crank" problem with. Can you give me more details on what the x27 connector looks like?

Just search " X27"

X27 search
 

Mr. Dalton,
As stated, I am relatively new to the site. When I do a search of x27, I get 30+ threads that appear. Is your write-up in a thread or the DIY section? I am just trying to understand what I am looking for. Thanks

I will have a tutorial in many of those threads with my Name on it.
There are at least a dozen of them and they will be clear and concise, step by step...and I don't want to do them again when they are there already.

X27 Search
 

Mr. Dalton,

Yes, I have read many of your posts on this subject. I will do the research and pull the necessary information from your previous posts. I just didn't know if there was a single writeup I should be searching for in the archieves. Thanks

Very Good

If you have a problem after reading how it works, post and I will run thru it w/you....