Electrical problems that manifest as mechanical problems

Hey Guys,

I guess the below story can come handy for anybody chasing certain mechanical goblins in vehicles.

I've been chasing up a "carby goblin" in my RB30 Nikki carby that I haven't been able to pin point the issue. Apparently it turned out to be an electrical issue rather than carby mechanical issue.
Carby has been hesitating for a while and regardless of my "fiddling" with internals and tuning, it kept
doing it. I dropped the Long Range tank(the only petrol tank in my rig) to rule out any electrical issues with the pump and electrical connections to the petrol pump(pump is an in tank one). I wired up a redundant external pump and cleaned and replaced the bad connectors. However the four wires that come out of the pump(two for gauge sender & two for the pump) are kinda customized(extended) to join the main wire harness at the back of the chassis.
I was going to get to those joints and clean/replace them as well, but it was pretty hard to access it 'cos of the LPG tank, so I kinda forgot about it. The carby was still hesitating and stalling I was ready to tear apart the carby again to rebuild it(again). But, I hit some luck by accident. During my effort to squeeze the fuel tank fill hose through the tight spot between the chassis & body, where the above rear joint of pump+sender wires joins the harness was damaged. One wire was broken from the joint and that wire was the +12V wire to the pump. I found out 'cos the petrol wasn't pumping at all after putting the tank back in & connecting all the wires. It was almost impossible to access it. There was no extra length in the wires to pull them down. Then the all the dust/crud under the vehicle makes it impossible to look up(though I used goggles). After giving the bottom rear of the vehicle a high pressure wash to get rid of some of the soil/crud I was able to reach the wire joints and repair it. I also cleaned/replaced other three connectors as well(four wires all together).
Today, I was preparing to get to the carby problem(it's a petrol only issue obviously), but it turned out that the vehicle was running ok now on petrol. I immediately realized the weak connection to the pump +12V wire at the back where I repaired must have been causing these carby issues by intermittently not pumping petrol properly.

It was an absolute PITA of a job to repair/replace those wire joints with the access being pretty difficult, but in the end it's well worth it.

I've had this experience quite a few times so far with seemingly mechanical problems turning out to be electrical, mostly with the fuel system(both LPG & petrol).

I'll upload couple of pictures tomorrow.

The reason I thought the above problem was carby mechanical issue, 'cos the I could always see the float chamber petrol always half full through the float chamber glass, so I thought it couldn't have been a petrol pumping/pressure issue, but it apparently was 'cos the weak electrical connection to the petrol pump has been starving the float chamber of fuel when try to drive on petrol(it idled fine).

So the moral of the story is,

Always rule out electrical problems that might be related to wires/connections before getting into mechanical domain, particularly with older vehicles like mine(1990 built year)

P.S.
I pasted some Carbon Conductive Grease on the connectors after cleaning them, & then joined them. I also pretty much dust/water sealed the wire joints by caking some generous amounts of hard setting silicone sealant, so it won't be bothered by water/soil/dust in the future.

Good find, Dom. As our old faithful vehicles become older the problems will only multiply. I dread having to "Upgrade" as the electrical complexity of engine control has increased exponentially.

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Originally Posted by mudnut

Good find, Dom. As our old faithful vehicles become older the problems will only multiply. I dread having to "Upgrade" as the electrical complexity of engine control has increased exponentially.

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Yeah, it all comes down to whether you have time to investigate these electrical goblins. Most of the time, it's more economical and time saving to rewire the suspecting wires/connections with brand new wires+conduits. I did that for the redundant petrol pump, but didn't do that for the in tank pump. :icon_bonk:

If you got time to spend locating these weird electrical issues, then I would say keep the vehicle. Paying an auto sparky for these time consuming troubleshootings can get expensive.
What I've been doing lately whenever I get some spare time is to check all the connectors under the chassis, under the bonnet & inside the car(under dash, etc) and replace the dodgy ones. I've been also adding more earth connections to body & chassis.
There's nothing much I can do about old wires broken in the middle where I cannot see any damage from outside at all, but I've been replacing raggedy looking wires whenever I come across a one or when it's possible to do so.
I intend to keep this bastard for a while, so time spent on it might worth it. ;) :D

Considering that it appears the real culprit of the issue's been discovered, I might have overkilled it by installing a redundant external petrol pump and adding extra exclusive plumbing & wiring for the external pump. It was bit of work 'cos I had to do it in a way I can use it just by flicking a switch and plugging in a hose, comfortably without having to muck around under the car. I guess it may come handy one day. If not, it's good experience for other future projects. Nothing's wasted. :)