'89 560SL no spark
 

Got the call at work from a weepy wife stuck on the side of the road. Car died, won't start.
When I get there - I determine no spark @ coil but have no test equipment w/me.
I immediately think coil-to-computer, hoping it is the coil. Are there any tests I can run with a VOM as far as V drops, resistance etc. beyond the obvious that will confirm the diagnosis?
Proper specs would be greatly appreciated.

Some Findings
 

OK, ran a few electrical tests on the coil & am not convinced it is the culprit.

Primary winding seems OK with continuity between posts & about .15 ohm of resistance. No continuity to ground. Is that too low?

Secondary winding measures about 9k continuity between the output & either Primary post. Again, no continuity to ground.

I am assuming the small diameter Primary post is NEG?

So it seems there are no shorts to ground & it shows continuity where it should, but is the resistance OK or do my readings indicate internal shorts in the coils?

11+ V is present at both primary posts with key on & it drops slightly (about 1V) when cranking.

Removed coil to clean it up & cleaned ground wires connections to mounting bolt. No joy.

Anyone have any thoughts?

Whether it is a bad coil or a bad computer (EZL) you are likely going to need a new coil. The outfit that sold me a rebuilt EZL would not warrant it unless I purchased and installed a new coil at the same time. Apparently a bad coil can blow the EZL.

The test specs for the coil are in the online manual in the EGv7 sticky above, but my attempts to test a coil showed a dud one as good.

A coil is only about $75 so why not change it out anyway?

Sorry I am in the wrong forum, the sticky is on Benzworld.

See http://www.startekinfo.com/StarTek/outside/11883/?requestedDocId=11883 sec 15-540

Oh, I was wondering why I couldn't find it! Thanks.

Depressing though, about the diagnostics.

OK, don't have all the test equipment (engine 'scope) but I do have a BK Precision 'scope I might be able to cobb into the system.

So far, all VOM checks are within spec.

(Ignore pre-edited post, I was measuring the wrong connections.)

battery , altenator?

Success, sort of
 

So I went to the pull-a-part this morning & snagged a couple of Ign modules & a coil. Got them out of a 560SEL & a 420SEL, the only 2 on the lot. Numbers are not an exact match.

Swapped in the coil w/old module - no joy.

Swapped in a module & it starts right up. Joy.

Shut down right away & came in to post this.

How critical are module p/n's?

First, I do not know for sure but suspect the current module IS NOT original. P/N is BOSCH 0 227 400 695/MZB 0 410 545 67 32 (03), it has worked for years. I suspect it was a heat failure because the heat sink goo did not look to be making good contact; many ripples due, I think, to a missing hold-down bolt.

The unit I got out of the 560SEL is BOSCH 0 227 400 624/MZB 004 545 53 32.

The 420 SEL is a SIEMENS 5WK6 114/MZB 004 545 55 32.

So I figure the best match is the BOSCH unit from the 560SEL but am looking for trouble or just being overly cautious?

I see parts distributors list the BOSCH 0 227 400 695 (same # as the bad unit I just removed) as the replacement for all years/models of 560's & a BOSCH 0 227 400 693 as the replacement for a 420. So I surmise something is different (mappings maybe?) & I should avoid the module from the 420.

Would I be correct in assuming the different #'s (695 vs 624) from the 560SEL are just an older variant? Although I do not trust ebay, both are listed as 560SL replacements there.

Anyone want to chime in?