87' 420 SEL suddenly not getting power from battery and wont start!! - PeachParts Mercedes-Benz Forum

jriewer · #1 10-22-2008, 08:21 PM

I backed into my garage this evening and shut the car off then realized what a crappy parking job I had done, so I tried to start the car again to re-align the car and that’s when the engine would not start. No noise, no diagnostic lights, no anything. It is as if my battery is completely dead though I put a meter on my battery and I have a full charge. With the key turned to position 1, I tried to see if I could lower the driver’s side window. I hear the faint sound of the window motor trying to operate but obviously it does not have enough power. My headlights will not come on and if I turn on the emergency blinker lights I see a faint glow coming from the red emergency blinker button but that its- I don’t even hear the relay clicking. Its apparent something broke when I turned the key in the ignition, preventing the battery power from flowing to all components of the car. I have a 50 amp start setting on my battery charger which I tried, thinking my battery was not fully charged. When I tried to start the car using this mode, I did get all the dash diagnostic lights to illuminate , but this had no effect on turning over the engine. All I hear is a click. The battery charger also indicates my battery has a full charge. I check all my fuses and tapped on all my relays. I’m suspecting something at the ignition switch it screwed up. Any suggestions?

cliffmac · #2 10-22-2008, 09:36 PM

why not try jumping it from a known running car? just a guess..good luck...

compress ignite · #3 10-23-2008, 02:11 AM

Engine Ground Strap (Looks like a 2" wide braided Copper strap that grounds
the engine to the Chassis)

retroguybilly · #4 10-23-2008, 09:50 AM

I would suspect corroded battery terminals. Clean 'em.

david s poole · #5 10-23-2008, 10:51 AM

the ambient temp has just changed drastically,try tightening the battery terminals or just let it get cold and it might shrink enough to make good contact.seriously though,remove terminals and clean thoroughly then replace and tighten.if still no joy you can check the main ground strap by running good jumper cable from battery ground to good location on engine[saves climbing under car until you know the problem].

jriewer · #6 10-23-2008, 02:14 PM

thanks for your suggestions. I will be checking these thinkgs out this morning. One thing I did notice last night is that when I open the drivers side door, the dome light and the underside door safety lights light up as normal and are getting 12volts. These components are not dependent upon the key being in the ignition to get power which leads me to suspect this is ignition related. Is this reasoning correct?

jriewer · #7 10-23-2008, 02:52 PM

Just checked the contacts and grounding wire and no luck. But I did find that when I turn the key to position 2, about 50% of the time, I am getting full diagnostic lights on the dash and my windows and radio all work but if I turn the key to start the ignition I just get a click. The other 50% of the time the dash diag. lights just give a faint glow with no engine click if I tried the ignition which again tells me this is ignition switch related. I did have trouble in the past with the key occasionally not working at all and getting stuck. A good turn of the steering wheel one way or the other always fixed the key problem. At this point if Im going R&R my ignition should I be looking to just replace the ignition switch?

retroguybilly · #8 10-24-2008, 05:36 PM

I don't know if you've checked and cleaned your battery terminals yet, but everything you're describing is consistent with corroded terminals. The dome light, instrument panel, etc. draw relatively little current, and will therefore work fine even if your battery terminals pretty badly corroded, because such a small amount of current draw won't cause very much voltage drop across a relatively small resistance at the terminals (c.f., Ohm's law), but the starter draws so much current that it will cause a huge voltage drop across even a small resistance at the terminals. (I.e., the voltage drop is proportional to the current draw.) In order for the starter to receive sufficient voltage to fire, your battery connections must be perfect.

jriewer · #9 10-25-2008, 08:19 PM

Cleaned the battery terminals and checked that my grounding strap is good. And I replaced the ignition switch today and still the problem remains. I see that sometimes after I have removed the key from the ignition, some of the the diag lights still remained faintly illuminated like a relay or switch is not resetting. Other times when I turn the key I get all the diag lights illuminated brightly as if I'm getting full power and then when I turn the key to start the engine I just get a click.

Richard Wooldridge · #10 10-26-2008, 10:58 AM

You've got a poor connection between the battery and either ground on the negative post, or between the battery and the positive circuit on the plus post. Take your digital voltmeter and while it is failing measure between the center of the negative terminal and the engine head for voltage. If you see 12v there it's the ground circuit. Then measure between the center of the positive terminal and the alternator's 12v output terminal. If you have voltage there you have a poor connection in that circuit.
It has been my experience that 99.6 % of these problems are right at the battery posts. MAKE SURE you have cleaned those well, and have them tightened well. They MUST be shiny and clean. They can be physically tight and look fine to all appearances but still be failing. You have to remove them to check them! Also, wiggle the wire attached to the starter terminal, and wiggle the wire going from the negative post to it's grounding point. You should be able to find this problem in minutes with a meter.

jriewer · #11 10-26-2008, 04:55 PM

Thanks for the response Richard. Followed your advice, and put the multimeter on the various points you suggested and no voltage reading found at those points. Jacked up the car and checked the starter wiring too and all looks good and secure. I have cleaned the battery terminals several times. Its not a issue of bad contact with the battery or ground. When this condition presents itself I'm get a reading of only 9 volts at the battery - something is draining 3 volts.
I'm wondering; Does the starter get a small amount of voltage during the diagnostic test? Maybe something broke in the starter and is creating a small short that is causing the 3 volt drain. This could explain why half the time when I do turn the key and get full 12.5 volts and then proceed to start the engine all I get is a click from the starter. I think I will disconnect the ground from the starter and see if the 3 volt drain continues during diagnostics. (I have already beaten on the starter with no success.)

Arthur Dalton · #12 10-26-2008, 05:20 PM

Got jumper cables???

Run a jumper from the bat neg to an engine ground and try the starter.

Also, put the headlamps ON and watch them as you try the starter...do the headlamps go out when you try starter..if yes, you have a possibe poor connection at bat terminals or battery ground/feed terminals

If headlamps stay bright, you have a starter feed problem or starter .

Richard Wooldridge · #13 10-26-2008, 10:30 PM

If you truly do have only 9 volts on the center post of the battery terminals you have a bad battery. I would connect a charger and see if the voltage goes right up to 12 volts. If it does, and then drops back down to 9 when you remove the charger the battery has big problems.

jriewer · #14 10-27-2008, 01:19 AM

I disconnected and cleaned the ground to the starter. Now things have changed; I no longer see a 3 volt drop when I turn the key to position 2. the battery goes from about 12.30 to 11.32 volts. all the diagnostic lights stay bright. The headlights are now staying bright when I try to crank the engine (while previously they would completely dim during a crank) but now there is no clicking at all at the starter. I put a meter on the starter and I am getting 11.32 volts at the starter with the key in position 2. I think my starter is no longer working.

Richard Wooldridge · #15 10-27-2008, 09:15 AM

I think it's time to start over again now that you found the poor ground. Make sure that it is in park, then wiggle the gear selector while trying to start it in case the starter lockout switch is flaky. There is a small wire connector on the starter solenoid. You can short it to the heavy positive terminal with a screwdriver to bypass all the lockout circuit and starter switch just to see if the starter will turn the engine over. Do this with the switch off so the car doesn't start, and just for a few seconds. If the starter won't turn the engine over when you do this it means the starter is bad, although since it was working when you began the diagnosis I suspect it's still ok.