so where does #4 fit into this? The only LH2 FI diagram I have shows # 4 as the last fuse in series with BOTH the pumps, and since it's only a 8 amp fuse, I know that can't be true.
• You don't say what diagram you're using, but Bentley 390-46 (grid L2) shows pretty clearly that power from Fuel relay (217) terminal 87/2 goes to Fuse 4, where it branches:
a) thru fuse 4 to the Tank pump (97) and
b) directly off to the Main pump (100).

My neophyte palm tree question is where is #4 getting power? the relay or the ECU? and where is it sending it, obviously not directly to the pumps as my schematic shows.
• Ultimately, fuse 4 power originates at the 25Amp blade fuse (or fuse 6 for '91 an up 240s), then into Fuel relay terminal 30, and out of terminal 87/2 as outlined above.

Is #4 in series with the chip in the ECU/ICU interface or the crank sensor? If so and if the crank sensor's bad and my jumper out, I would also see no spark when cranking?
• # 4 is in series (between) the Fuel relay and the tank pump, which is in parallel with the O2 sensor heater. See item 162 in the referenced Bentley diagram. The crank sensor signal goes only to the Ignition CU, as described the sequence posted earlier above. The 4-to-6 jumper and the crank sensor are totally unrelated to one another. No direct ECU connection either.

How do you check definitively for spark? My old school method, by arcing the coil to ground for a few cranks? I've heard tell this freaks out some other computerized monitoring function.
• It's generally acceptable to pull a plug or use a spare on the end of a plug wire, with the body of the plug in contact with any engine or body metal as a ground, such as a left side upper strut mount bolt, where the plug can be seen while cranking the engine.




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Bruce Young, '93 940-NA (current), 240s (one V8), 140s, 122s, since '63.