Possible Earthing Problem?

[Hanaldo]

Hey guys,

I'm having a few electrical problems with my car which at this stage are more of an annoyance than a problem, I just don't want it to get any worse. There are two possibilities in my mind that could be causing it, a dodgy earth or a dodgy battery. I have recently done an engine swap on my car, and the problem was there before and it is still there now. I've had the battery tested multiple times and it shows up fine every time.

What's happening is often when I turn the car to accessories to prime the fuel pump (still standard GTT fuel pump, Walbro 550 going in next week), the dash lights will be very very dim and flicker a bit, my volt gauge (aftermarket) will show anywhere from 7v to 10v, etc. When I try to start the car it eventually starts ok every time, but it struggles a bit. Sometimes everything is fine and it will start pretty much instantly, the dash lights will be bright as all hell, the volt gauge will read ~11.5-12.5, etc.

Another thing that often happens is when I change gears or clutch in, the sound system will die. I haven't got a huge system either. It will come back on straight away, but it pretty much just resets. Often when this happens one of my headlights will go out as well, comes back on if I flick them off and back on again.

I had suspected alternator before the engine swap, but seeing as I have changed the alternator with the new engine and the problem is still there I sort of ruled that out.

What could this be? Also sorry if this is in the wrong section, it struck me as a general maintenance type problem...

Cheers guys,

Martin.

[GTRPowa]

First things first. I'd start with getting a multimeter, and testing the voltage at the battery while driving in these conditions. Just run some cables from your battery, out the side of the bonnet and into your cabin, put the meter on them, and drive in the above conditions. If there is a drop at the battery, undo your clamps and test the battery voltage by itself, should be over 12 volts = very healthy.

If the voltage at the battery is fine, you have at least eliminated that from the problem. Also test the voltage at the battery before starting, and while started and check the difference in voltage. If the battery voltage if good without the clamps, put has a large drop when using certain accessories, you could have a dead short that's not fused for some reason. This will cause a voltage drop, and risking a fire.

Does your fuel pump run the stock wiring? Most people bypass them and run a fresh cable to the boot from the battery and put a relay in. I recently wired my pump to the 2 gauge cable I have in there for the amps. No voltage drop for me when priming, or at the fuel pump in any conditions.

Edited August 16, 2010 by GTRPowa

[GTRPowa]

Secondly, depending on how many accessories you are running, it may be good advice to upgrade the earth between the - battery terminal and the chassis/body. Make it a 4 gauge cable with the appropriate lugs at either end. If in doubt even go 2 gauge, but I'd steer clear of 8 gauge.

[Hanaldo]

I've tried using Datascan to monitor the voltage, thing is it doesn't happen very often while driving, it's very unpredictable. The main problem is on start up.

The fuel pump is still stock so I imagine it would still be stock wiring.

[GTRPowa]

Well the things is, whatever you use to monitor the voltage, it's monitoring it at the point you do the test, or have the gauge connected.

Eg, if you had a stock wired fuel pump, I could find 3 differing voltages on the car. The battery, where the dash voltage gauge is, and where the pump is. I can bet all 3 test spots will yield differing voltages.

I don't know what Datascan is? Consult? Possibly it's measuring the voltage at the computer?

What this means though is even if there are voltage sags everywhere, but the battery isn't reflecting the voltage sag, you can eliminate the battery and start looking at wiring.

On top of this, once that earth cable between your - battery terminal and the chassis is overloaded, the returning current needs somewhere else to go. It routes through the engine earth, into the alternator. By overloaded it can be anything from too many accessories, to small of a cable, the quality of the earth connection has diminished. You can pretty much test this without too much work, just get a metre of 8 guage, strip it down, put one end on the - battery terminal, and the other end where the old earth strap meets the chassis. This will reinforce the connection and provide a route for the extra current to head through.

Speaking of engine earths, how are they? I'd also run a meter of 8 gauge from the - terminal to the engine as well. All in all it depends on the earth straps you have on the car. It's one of the overlooked things with engine swaps.

DO NOT PUT IT FROM YOUR + TERMINAL TO THE CHASSIS OR SPARKS AND FIRE GOES EVERYWHERE!

I take 0 responsibility.

Edited August 16, 2010 by GTRPowa

[Hanaldo]

Lol I know, I understand electrics pretty well.

My earth cable is not very quality at all, it is slightly greened which looks like it will be causing resistance. I'm missing 1v between my alternator and my battery, the alternator reads around 14.3v when the engine is one, but the charge going into the battery is only about 13.2v. But this is on the positive terminal, the negative seems ok.

This is why I suspect it is a dodgy earth, the earth cable does not look too healthy at all. How good an idea would it be to get some 8 gauge wires and connect them to multiple chassis points? Or should I use 4 gauge wire?

Edited August 16, 2010 by Hanaldo

[GTRPowa]

Well you have choices, if it's at all possible, I'd simply run a 4 gauge to the normal spot, clean the metal well, use proper lugs, and continue the earth strap with at least 8 gauge to the engine.

Hey I was thinking, you should be able to measure the voltage between the +12 terminal and the chassis somewhere in the car. So you were getting voltage sag because of your earth strap, in theory you should see that on the meter since you're testing the voltage through the strap?

I think with those earth kits you can buy, they normally have what, one earth to the - terminal, one to the chassis, and multiple points of the engine, ie: block, head, intake plenum etc, so one run to the chassis should be sufficient.

You could also test continuity on the strap, but my guess is it will be close to 0 ohms.

I hope my help is helping to find a direction, nobody else posting...

Edited August 16, 2010 by GTRPowa

[t_revz]

if you know your missing 1 volt try putting a multimeter between battery + and alternator + and this will tell you how much is lost in positive side of wiring and the rest of the 1volt is lost through negative cables. Agree with Glen about bumping up size of cables. Skyline battery cables were good when the cars were new but they are getting on. i have 4 gauge from negative to chassis and 4 gauge from positive to starter and 8 gauge starter to alternator. makes a noticable difference

[Hanaldo]

Yeh that's what I did mate, the 1v is missing in the positive lines.

I've connected a number of 8 gauge wires to different points on the chassis, it does seem to be making a difference. Before the voltage was sitting at about 12.3 with the car off, now it sits at about 12.8. Also charges at 14.2 consistently now instead of being around 13.6-14.4

Will see if it fixes the problems

[Hanaldo]

Ok so the extra earth lines didn't work, problem is still there. I am now suspecting it is my alarm/immobilizer that is causing the issues, as from memory these problems started when I had it installed. Would there be anyway of finding out for sure, before taking it back to identimark (I think they are a bit dodgy)

[t_revz]

you said above the 1v was missing in the positive lines but in the latest post you upgraded the earths and it didnt fix it.... did you fit various earth straps or positives or both. if it started after fitting imobilizer etc then check the voltage at the fuse panel as something may have been disrupted