Hello and Help!
I have been working on my own 240's for several years and am reasonably competent with mechanics but have little experience with electrical problems and terminology. I have searched this board thoroughly but have not been able to find the information I am looking for in this particular situation. I have been reading this board for years and don't know where else to turn.
PROBLEM: I have a 1990 240. My battery drained overnight when I recently left the glovebox door open for ~18 hours. The next day I got a jumpstart, drove the car to work, ran some errands in the evening (starting the car several times with no problems), and parked it overnight. The next morning, however, the battery was almost completely drained and the car would not turn over. Both nights the temperature had dipped into the low thirties.
INVESTIGATION:
1) POSSIBLE BAD BATTERY: I took the battery (age unknown) to the local auto parts store and had it charged and load tested, which resulted "good," although I am not sure I entirely trust that considering the battery was almost completely drained twice.2) POSSIBLE SHORT: I connected a voltmeter/ammeter in series with the negative lead of the battery (now fully charged), which registered current draw of > 150 mA. The car was turned off (naturally) and the radio and interior lights/clock fuses pulled. I don't suspect the alternator, which puts out 14+ volts, but I disconnected it anyway to eliminate the stuck-diode possibility with no resulting drop in the current draw. Leaving the alternator disconnected, I pulled the remaining fuses in the fuse box (corrosion free) one at a time with no resulting drop in current draw. Stumped, I looked under the hood for the problem. When I pulled the 25-amp fuse for the fuel pump circuit, the current draw on the battery went to zero. Eureka! or so I thought.
3) FUEL PUMP CIRCUIT: I checked the fuse and housing for signs of corrosion (non present) as well as the relay under the passenger-side dash (no corrosion present). With the battery connected, I metered between the red lead (#30 at the relay)and a ground and measured current, which doesn't seem right to me. When I completely disconnected the fuse circuit from the battery (disconnecting the wire from the side of the post) and disconnected the relay, leaving the fuse intact, then checked for continuity between the relay lead and ground, the meter shows continuity. At this point, shouldn't I effectively be measuring the continuity of a loose wire with something it is not attached to? It seems to me (and I may be grossly wrong) that there has to be a short somewhere between the fuse and the relay.QUESTIONS:
The sub-par manuals I have, Chilton and Haynes, have limited schematics and none depicting the fuel pump circuit, so I don't know exactly what I am looking at.
1) Should there be any power drawn by the fuel pump circuit when the car is shut off? I probably would have read about this in other descriptions of battery drain problems and testing procedures.2) Are there any interuptions/junctions in the circuit between the battery terminal lead and the under dash relay lead besides the 25-amp fuse, or is it a straight shot? I tried to visually follow the harness and don't see any "breaks." I have considered running a bypass wire directly from the blade fuse to the relay in order to see if that makes a difference, but am concerned that I may be bypassing some hidden junction.
3) Is there something obvious that I should be taking into consideration, or am I on the right track?THANKS: I have almost run out of ideas and am not yet ready to swap the battery and alternator with the hope of correcting the problem "magically." I have to take a trip next weekend and hope to resolve this problem before then. Otherwise, it looks like I will be pulling the battery cable every time I park my not-so-trusty Swedish steed. Any advice or criticisms this group has to offer will be tremendously appreciated. As I mentioned earlier, I only have a passing familiarity with electrics and electrical terminology, so I will be glad to clarify anything in my description that does not make sense.
Thanks Again,
Ezekiel Woods