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
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.
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.
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.
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!
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