'98 Discovery 1 NAS.

Occasionally, it wouldn't crank. Oddly, if I pulled the "engine management" fuse from satellite box 1 and re-insert it, it would probably crank and start. This solution was so dependable that I got into the habit of going to start it and whenever it failed, I'd just pull the fuse and re-insert it. I could do it without even looking just by feel, and I'd be on my way. That went on for about a year of daily driving. Gradually, it became insufficient, but I discovered a new ritual.

I would pull the 10A engine management fuse, but simply re-inserting it wouldn't work. I would have to pull the 5A ABS fuse next to it as well. Reinsert the 5A fuse after which it would crank but not start (no ignition) then I could insert the 10A fuse and it would start.

Then it began a habit of stalling whilst driving. Evidently, the fuel pump was cutting out. The whole fuel sending unit with pump is just a couple years old so I suspected the relay. If I turned the ignition off and on, I could hear the relays clicking in the passenger footwell, but sometimes I wouldn't hear the fuel pump whine for a few seconds from under the cargo area as it should. It was the under-hood relay module that I suspected. I changed the filter for good measure and swapped out the relay when I got a new one in from TRW. I immediately went from frequent stalling whilst driving down the road and jostling the ignition switch to get the relay to kick on the fuel pump to dependably running without interruption.

The question is, will this also solve the intermittent no-crank condition? I haven't had it occur lately, but I'm not sure I've solved that. There are three relays mounted on a circuit board in that TRW multifunction relay unit. I believe that for the ECM to work, current has to flow from the fuse through that relay unit and then to the ECM. So I suspect that by jostling the fuse I was getting that failing relay to work. I'm not sure how the ABS fuse helped. Maybe it was just superstitious ritual, but it sure seemed to be a dependable workaround. It worked dozens of times when the engine management fuse alone would not.

FWIW, the CKP and the cam sensor were already changed in the last few years.

 

I had a no crank issue a few years ago and the problem was brittle electrical wires on the connection to the fuel pump. I replaced the burned wires and it has been fine. Before replacing the wires I used a bit of diaelectric grease but eventually that stopped working.