You can test the battery at home (at least somewhat) by watching what the
voltage does while you crank. IIRC 10.x volts is okay anything less is a fail.
I bought a meter that plugs into the 12v outlet, it also provides 2 usb ports.
It was useful troubleshooting the failing alternator in my '98 Jetta, it also
confirms the preheat system is working in the ASV when attempting a cold start.
Cheap too.
-Curt
On Thursday, January 24, 2019, 4:10:55 PM EST, Meade Dillon via Mercedes
<mercedes@okiebenz.com> wrote:
The OP has shared offlist that the pre-glow relay was replaced back in
December IIRC.
At this point, however, given the number of less-than-qualified hands that
have been working on the car, I think it would be prudent to go back to a
thought shared earlier and assume nothing, start with fresh diagnosis.
Curt is right on this one, stop making assumptions and test / inspect
everything.
Replace the serpentine belt, ensure the tension device is working
correctly. Ensure the belt is routed correctly - check the owner's manual
(? is the picture there?) for a picture of how it is supposed to be
routed. I've attached a picture to this post.
Battery, even though new, needs to be load tested. Free at FLAPS.
Start the car, measure voltage at battery terminals. If less than 13.5
volts, determine cause. Note that this car should have after-glow feature
in glow plug relay, so wait at least a minute or two after start up to test
the voltage. Cause of low voltage could be bad alternator or bad harness
including the connector at the alternator.
Check cables from battery to starter and from battery to ground; corrosion
can reduce current to the point of no-start.
Check starter for tight battery cable connection (the big thick one).
Check ground strap between engine bottom and body of car.
Intermittent fault in glow plug relay draining the battery: make a
semi-permanent installation of a test light at a glow plug connection, so
the light is visible while driving the car, and if it lights up when it
shouldn't be lighting up, then you've got a bad pre-glow relay.
Check for parasitic draw as discussed ad nausea, with some test at the
battery.
If the glow plug relay is good, alternator is good, battery is good, cables
/ harnesses are good, another possibility is a weak starter.
-------------
Max
Charleston SC
On Thu, Jan 24, 2019 at 1:49 PM Curt Raymond via Mercedes <
mercedes@okiebenz.com> wrote:
> I was thinking that if you left your test light on for a few minutes you
> could get past that bootup stage.
> Do you think if you used a fairly large bulb you could use brightness as
> an indicator of draw?
> If our primary thought is that the glow plug relay is at fault that would
> be a pretty hefty draw.
>
>
>
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