Part 2 of fuel pump swap.
Of course I had to have some sort of fail..... it just didn't feel right having a totally smooth project with no issues.
I did a decent amount of idling in the garage with the new fuel pump waiting for the exhaust to arrive. Not a single issue. Drove the car to the gas station to fill up... car would not start. Thankfully I brought my datalogger with me so I could monitor live data and log for later review. I had no fuel pressure and it was hard to tell for sure due to ambient noise but pretty sure the pump wasnt running when 'key on'.
Fuses were good and I swapped the horn and fuel pump relay and lo and behold it started up.... but the horn also worked. Fuel pressure was still dropping/fuel pump cutting out intermittently, sometimes stalling out the engine if I was at idle. Did it a few times while at speed and it would die, then magically come back to life. For the most part though, 30+ mins of driving, it was flawless once it got going.
Next morning, started.....then died, twice. After that it fired right up and I drove to work/back all day no issues. Back in the garage last night I was pulling/reinstalling/swapping relays and sometimes the fuel pump would prime, other times no at all. Narrowed it down to some sort of wiring issue in or below the fuse box itself where the relay plugs into.
At this point 99% sure one of the relay pins for the pump (on the fuse box side) got pushed down/widened out and is just not making good consistent contact with the relay, whatever relay I use. I confirmed this by making a jumper wire basically and testing each pin.... 3 are very snug and tight, one is very loose, no resistance at all.
I spent a few hours trying to make apart the top portion of the fuse box... long story short, it's not worth the effort on this car and I'll probably break the thing. I already did a temp fix (not road tested) by adding a little solder to the loose pin to make it snug. I feel like this is only going to make the problem worse though by widening the gap even more. Probably fine if I never pull the relay again but any sort of removal/reinstall is just going to make it worse and worse.
Replacement fuse panel is like $100, not too bad all things considered. But I already purchased an upgraded wiring harness for aftermarket fuel pumps (not yet installed). It uses the factory fuel pump power line as the signal to trigger another external relay to power the pump directly off the alternator. I am thinking I should be able to actually bypass the whole factory fuel pump fuse/relay and use the original pump trigger wire to trigger the new relay now instead. I just hate this like this because I gotta start cutting some factory harness wires and if it doesn't quite work out, shit starts getting hairy lol.
Datalog of the fuel pressure. Top chart in green is fuel pressure.
[doublepost=1535223785][/doublepost]Well I went thru with my proposed mod to utilize the aftermarket fuel pump harness that I already had on hand and modify the stock harness to completely bypass the factory fuse/relay for the fuel pump. The aftermarket harness just uses bigger gauge wire and connects directly to the alternator to supply more volts/amps to the fuel pump and supposed to handle the increased load of larger fuel pumps / boost a pumps.
Here's the factory wiring, pretty standard
Here's with the aftermarket harness installed. It just takes the factory relay output as the signal to turn on it's own separate relay to turn on and power the pump directly.
My proposed mod... connect the ECU/PCM fuel pump trigger output directly to the new/aftermarket relay.... connecting a green and grey wire under the fuse box.
Done... no turning back now
Happy to report that I think this cured the issue 100% and confirms that relay contact was the issue the whole time. Sigh of relief for now.
