starting/electrical issues

[Jezza_hr]

Okay, I don't know where to begin with this one, as this issue is a rough one to diagnose and there are several different symptoms that could give clues as to where the issue could be. But here goes.

Since rebuilding my car in the summer and relocating my battery to the boot I have been having an intermittent starting issue where, from time to time, the starter motor and open circuit relay may click on and off on their first and second try and then finally start turning over on the third go. Eventually this either starts the car or kills my battery (where I will then swap in a healthy charged one and get it to start first time) so I eventually end up cycling between two batteries as one discharges over time from all these rough starts. The clue that the battery is about to die is when I'm met with a rapid clicking sound from the open relay as the car is trying to turn over.

However, once the car has been running for a while and has warmed up, the starting issue seems to be next to non-existent, but if the car has been sitting idle for a day or two, the same issue comes back.

When checking over the voltage of everything, there's a standard 12.5V through the the circuit when nothing is running and 14v at both the alternator and battery when it is, so that tells me it should be charging the battery, so I don't think the charge circuit is to blame.

Obviously, one thing that needs to be done when relocating the battery is making sure to get a good ground. Having extensive lengths of 4 gauge wire, I have done my best to ground everything in the best way possible with one ground from the battery to the boot floor and another running to the chassis leg to the front of the car where the block is also grounded, so I assume this wouldn't be an issue?

One other thing that seems to be a problem. Since I'm now running a tachometer signal switch from my Omex to the OEM dials, there seems to be some oddities when using other electrical items in the car. When using the windows or the indicators, the tachometer drops but the engine speed remains the same. I can only assume this a ground issue or something potentially related to my intermittent starting problem? But this also opens up questions for my charging circuit...

Either way, this issue is becoming infuriating, as I live each day wondering if the car will start as I go to leave the house, or if I will end up stranded somewhere. I'm having to keep one battery charged at all times on the off-chance the one in the car dies the next time it turns the starter motor.

Any pointers on where to begin guys?

[pack]

Try a new ground directly on the Engine. And see if you still have issues.

I had some problems with mine, and decided do ground directly to the engine... All problems sorted out!

Regards

[Jezza_hr]

Do you have any other ground wires from the battery set up Pack? I may give this a go and see if it differs my results.

[pack]

Besides the one to the chassis, the regular one, i have that cable directly on the engine block.

There's also a couple wires you can buy, an earthing kit, that provides ground in the engine bay area.... you could make one and try to split the grounds a bit more......

Seems like it's a ground issue....

[allencr]

How're the starter solenoid's contacts?
It doesn't need extra grounds or anything special, it only needs adequately sized wires, equal to or a little larger then original, with good connectors/terminals and good contact between them on everything you've done and on all the original wiring, that's it if the starter hasn't been burned up by now.

It Does Not need a ground cable from the battery all the way from the battery in back to the block in front!! Millions of steel chassis/frames already do that very well. Yours is not an exception.

[jondee86]

I'd say you have a voltage drop problem. 4Ga is not big enough for the
starting current... 0Ga would be much better. And that goes for both the
positive and ground wires. See what the voltage at the starter drops to
while you are cranking.

Cheers... jondee86

[Ivan141]

About the tach signal converter: I assume the Omex item needs a 12v+ and gnd connection, same as the ones I built myself from time to time. If it drops you are probably experiencing voltage dips on the supply circuit when switching on other electronics.

The way those boosters work is they use 12v to charge a coil, and a transistor (driven by your low voltage tach signal) to break the coils ground circuit. That creates big voltage peaks at the output. If for some reason your coil does not get enough voltage to charge, the produced voltage spike may not be high enough to register on your cluster.

Another cause could be jitter on the tach signal, causing it to switch too fast..

[Jezza_hr]

The starter solenoid contacts are fine, I replaced the copper connections during my rebuild and they haven't been in there long.

Voltage drop sounds like the most likely culprit when considering the starting issue coupled with the tachometer drop as Ivan has explained.

I never considered 4 gauge to be an issue as I've witnessed many people who have used it for a battery relocation before and said they haven't had an issue. I have tried a few things to compensate for the voltage drop, including a 4 gauge wire to the junction box from the alternator to make sure there's more voltage making it's way back to the battery.

As Jondee has said, using 0 gauge wire may combat the issue, but if I can rule out every other option before spending out on more expensive cable then that would be a good start. I may draw up a diagram this evening to show how things are setup.

[Jezza_hr]

Right, you can all look at my car schematic prowess and admire the quality of my work

This gives an idea as to how everything is configured right now. I believe the cable is 4 gauge (it might actually be better than that, I'll double check the diameter when I get a bit of the leftover cable in my hands).

One other idea that has crossed my mind is to run the alternator and battery directly to the starter motor and have the live feed coming off of that to the junction box, as it would mean the live feed isn't having a potential voltage drop from anything at the junction box (lights, rad fan and power steering), it would also mean the cable distance could effectively be shorter by close to a metre, as I would be bringing it in via the other hole in the bulkhead. I'll also consider another ground on the off chance that the two coming off the block just aren't good enough.

[jondee86]

To be fair, throwing bigger cable at it is not the best way to solve this
problem. The important thing is the total resistance for the circuits...
battery positive to starter, and engine block to battery negative. That
plus the cranking amps will determine the voltage drop while cranking.

As you have stated, there are plenty of 4Ga installs that work fine. So
if your starter is in good condition and your battery is fully charged,
check the voltage at the starter while cranking. If you have 10V or
better, the 4Ga is not the problem.

Then you need to check that you are getting a full 12V at the COR
while cranking. If there is a bad (high resistance) connection on the
keyswitch power supply, or a high resistance ground, the voltage may
drop low enough during cranking to prevent starting.

Cheers... jondee86