71 280SL starting issue

[jimmbo506]

Okay so Im having this issue with an inline 6 1971 280 SL pagoda,
the car starts and runs fine USUALLY but multiple times after parking it and getting back in usually about 30 minutes later,
there is absolutely no starting the thing, it doesn't even crank. just clicks once.

Now one time it died while at a red light and wouldnt start on us, maybe 20 minutes later we cranked it again and it turned back on,
we have taken it to the best mechanic in our area for these types of cars and hes done all kinds of electrical work to it, still nothing, it
works when it wants to work and when it doesnt it doesnt, happened 2 weeks ago, had a bunch of wiring replaced, but today
we took it to a restaurant and when getting back into the thing it did the same thing again, had to get it towed.
Starting to turn into a real problem getting stranded in it.

We use a battery tender every night to make sure the battery is fully charged, and it is.

Any wisdom out there?
Engine bay: https://ibb.co/B4d9NTg

UPDATE: When the car craps out, all electrical to the dash and everything else goes out as well,
its happened while driving it, it happens when parking it and getting back in, not sure what really triggers it.
upon waiting 30 minutes to an hour its able to restore power, could be a heat issue? Not sure,
I'm going to have the wiring to the ignition coil looked at next.



If i am in the wrong place im sorry please direct me to where I should go, I just don't know where else to go.

[teahead]

What exactly did the mechanic do?

Anything replaced?  Starter?  Ignition switch?

What wiring was replaced?

[jimmbo506]

ill be going to my dads house later today ill grab a picture of work done to it and get back to you.

[MikeSimon]

If it does not crank and just "clicks", there must be a problem with the starter or the power supply to the starter or the starter solenoid. Have you observed other electrical users e.g.: lights, instruments, etc. during the starting attempt? Does your car still have the heat shield over the starter, under the exhaust manifold? Excessive heat is the enemy of currency flow. Resistance increases.

[Jonny B]

These have the transistor ignition. Sometimes there is a wire installed from the transistor unit (under the battery - great place, eh?) to allow for a dwell check. If there is even a small wire making contact the car will not start - ask me how I know. We traced this to a small seemingly haphazard wire laying in the engine bay by the battery. It also may be one of the small wires at the coil grounding out.

When I was out some years back, I came up to a stop light, and the car just stopped. Crank,crank,crank,finally got it going, so was lucky to get it home to start the diagnosing process.

[Shvegel]

If you get a click most likely the ignition switch and neutral safety switch are OK.  As Mike said I would focus on the starter and the main cables. Next time it doesn’t start turn the headlight on.  Do they go out when you hear the click.  I think you are dealing with a bad starter or negative cable at the engine.

[ja17]

Yes starter or starter solenoid most likely.

[jimmbo506]

UPDATE: work done  - https://ibb.co/0DgqkW2
https://www.youtube.com/watch?v=4hJ_hYBCxUk "words from the old man himself"

[teahead]

>$500 and still not fixed?

How frustrating

[stickandrudderman]

This really is so simple.
Ignition on: do you have 12v at the + on the coil?
If yes, then bridge solenoid and main terminals with starter motor.
Does the starter engage/car start?
If yes: ignition switch or wiring faulty.

If no voltage at coil with ignition on, run a wire from + on the battery to + on the coil and bridge the starter connections as previously described.
Doe the car start?
If yes then ignition switch or wiring faulty.

If during either of these tests the starter does not run then suspect starter motor (most likely)or heavy battery cable going to it. (unlikely)

[jeffc280sl]

Maybe this topic should be moved to the Electrical Section.  You have the transistorized ignition system in your late model SL.

To build on Stick's comments.  If the car won't start and there is no voltage at the + side of the coil then you can look at the components and wiring in this circuit. 

Power for the circuit comes from fuse 2 and travels through the .4 ohm resistor.  You should have 12 V on the input side of the resistor.  Do you have 12 V on the input side of the resistor?  Check the value of this resistor with a multimeter.

After this resistor power travels to the transistorized ignition module.  An output of this module travels to the + side of the coil.  I'm not sure how to check the transistor module.  If you have power at the resistor and no power at the coil we can look into this module.

Good luck

[Shvegel]

After looking at the video I would take  hard look at the battery cables.  also there is a ground strap from the firewall on the driver's side to the engine.

[MikeSimon]

If the starter does not crank and just "clicks" I don't think we have to send the OP on a wild goose chase through possible ignition faults. It is most likely a matter of power supply or faulty ground of the starter. Most starters ground through the mounting and a somewhat loose starter will display these symptoms.

[Montreal V8]

    I would agree with Mike on this.  If it is indeed the click is coming from the starter motor, this would indicate the solenoid is being activated, but the starter is not responding. That would mean either the solenoid or starter motor is faulty, therefor the ignition circuit has no bearing on the fault. In the event of a low battery or main wiring fault, the starter is more likely to "chatter" than click, accompanied by flickering warning lights etc.  If access, allows you may try bridging the two LARGE terminals on the solenoid, but extreme care must be taken to avoid a "short" to ground, incurring a large spark accompanied by smoke, a somewhat alarming response, which, over the years, I have managed to experience !!   Good luck.

[Montreal V8]

 Sorry, I should have said "I agree with Mike and Joe --"

[jimmbo506]

okay so the next time the car craps out on us I will test some of these ideas out,
but do those explanations still explain why once it crapped out while the engine was on and running, sitting at a stoplight,
i noticed it has been running a little more rough while stopped in drive.
More often than not its when your trying to turn the car back on, but the issue has happened while the cars running and driving, then wont turn back on
in the same manner.

[franjo_66]

Hi Jim

I had a very similar situation with my 230SL last year. It was actually potentially dangerous as the car would cut out while driving or stopping at lights.

Through a process of elimination we traced it down to frayed wires going to the ignition coil.

Once we renewed the wiring the car started and ran perfectly all the time

Regards
Franjo

[Cees Klumper]

I had my 280SL's engine just stop suddenly while driving. Just like Franjo's car, one of the wires going to my coil was not crimped on tight so at random moments it would just cut out, only to start again after cooling off a bit, 5-10 minutes later.

[Montreal V8]

   Jim (?)    Another apology - I overlooked the engine quitting unexpectedly. Now, looking at the wiring diagram, the battery power for the ignition switch comes from the battery power connection on the lighting switch. This in turn comes from the positive battery cable  on the solenoid. Whilst under my car some time ago, I noticed three wires, secured to one of the oil pan bolts, which went through  a connector. They are a little obscure, and not shown in the 280 SL wiring diagram, but are clearly shown on 280 SE and SEL diagram. These wires are  -  1.  for the solenoid,  2. the ignition resistor bypass, 3. the battery power for the rest of the car.  Should corrosion or a faulty connection on the battery power wire occur, this could cause the faults you are experiencing. The same applies to the power connections on the light and ignition switches.  Hope this is of some help.

[Shvegel]

I just watched the video again.  What is the "kill switch"?  I think that might be your problem.  If you car is acting like you turned off the kill switch when it is dead I would be very suspect.

[jimmbo506]

simple switch on/off kills power to ignition (i believe) but he turned it on while it was running and did not kill engine.
not sure why the engine would idle rough and turn off then not turn back on, but we will more than likely have it removed next check up and go from there.