87 240dl intermittent start

87 240dl sedan, B230 LH system, manual, 5spd
I have searched group for same symptoms as this, but no luck.
Son's 240 will just once in a while not start. Engine cranks, etc, but
no fire.
If he starts it 30 times, it might not start but once. I have felt the
pump relay as he cranks it, I don't think it is engaging, that is, I
don't feel the "click" from the solenoid closing. The tank pump
doesn't work either during this problem. About the 5th or 6th attempt
(using jumper cables on all starting attempts to minimize wear on
battery), it starts, runs great, and doesn't stall.
Then it'll start every time, easily, warm, hot or cold, until after
the next 10-15, even 20 starts. Then when it won't start, he cranks it
about 5,6,7 times, let it rest, then try again, and off it goes....or
call me and I rescue with cables, or leave it and come back the next
day. The no-start situations are when engine is cold, in all ambient
temps anywhere from 5 to 65+ deg F. Really stumped here. I have the
Bentley manual, checked the quality of all ground points, they are
clean, etc. Fuel pump relay has been disassembled, looks great, like
new, no cracks.
When the car runs, it really runs well. When on the interstate, it
wants to stretch it's legs and fly!!
Any ideas???
TIA--Tyler

 

Tyler,

The cracks you need to be looking for are not in the PCB material, but the
solder, especially near or immediately around wherever any large chunk of
metal is soldered to the circuit board, these joints were often not heated
as fully as they could have been, when the relays were manufactured, leaving
hairline cracks that while working ok most of the time when new, eventually
erode through spark action and thermal movement, gradually becoming
unreliable, the same fault can be found on many such relays that switch high
currents, including the seat heater relays.
Failing that; when the car won't start, does the rev counter work ok? I seem
to remember that the fuel pump relay gets a rotational signal from the LT
side of the ignition coil, where the wire connects to the instrument
cluster, but this may only apply to our antique UK carb versions.

TTFN, Ken

 

Well, my 240 wagon did the same thing. Eventually, I found the problem was
due to fuse corrosion. The metal on the ends of the fuses deteriorated and
one or more of the fuses intermittently cut power to various critical
circuits.

Replacing the fuses fixed everything.

Even if old fuses are not the cause of your current problem, it's a good
idea to replace the fuses anyway if they are originals.

TKM

 

Oh how I miss (not!) that old 240 fusepanel, I'd quite forgotten the
problems mine used to give me; yes, those fuses can be a right royal pain in
the xxxx, a temporary fix I used to use, was to spin the fuse round a bit
while it was still installed in the panel, the fuses with aluminium links
gave me the most grief, I think some sort of galvanic reaction happens when
they get slightly damp, but the copper ones still needed some periodic
attention.
I drive a 740 now so all this is a poignant memory (pop, pop, splutter,
fiddle, fiddle, spark, fizz, start, vroom!), but the 740 keeps me busy in
it's own peculiar way.

TTFN, Ken Phillips

 

Ditto my '86 240GL - it stopped dead just out of the drive, I found the fuel
pump fuse askew in the socket so I replaced it with a new one. Being 16amp,
it passes a fair current, which eventually corroded it forming the classic
"cruddy contacts" that was the bane of my Navy days!