Chasing that illusive fault!

[valgamesh]

Hello all,

Some of you know my car, some of you dont, some of you know my eternal problem, some of you dont.

So as the title says, I'm chasing an electrical fault thats been with me since 2011 after a group run up the Bathurst. To put it in simple terms,

Every time I drive the car all electrics will stop for a split second and then turn back on, this causes the car to engine brake and then re-fire back to life ( Super awesome at 110km/h ) sometimes it will do it once and be fine for 15-30min later, other times it will hammer 7-9 times and die completely ( zero electronic register as if battery had been disconnected ) Ive replace countless parts of the car, I've had 2 separate auto-electricians look at it, the first removed immobiliser and put the fuel pump on a separate relay. The second replaced battery leads (useless person).

I've wondered about a number of things in the car, so I removed them, Stereo + sub systems, speakers, head unit completely back to fuse box, central locking back to fuse box, electronics boot release back to fuse box, the after market cigarette lighter back to fuse box, trimmed every wire that was doing nothing ( I even found a wire that halfway to the fuse box had another fuse with no fuse in it ), I removed all the controls for an aftermarket cruise control that was only half wired in. Basically Im getting rid of every bit of electrical part of the car thats not needed just to find this 1 (insert words) problem.

Now heres the weird part:

The car will run perfect, and I mean not a single fault what so ever while it idles, you can rev it, lights, stereo ( when it was in ) push the clutch in and out, brakes... basically anything.

Put it into gear and try to take off and BAM problem, as soon as I get the clutch into the engaged position to take off all electronic play up, engine dies and re-fires, both forwards and reverse, its instantaneous as soon as I get to taking off.

So my questions are:

1. Has this ever happened to anyone else?
2. Is it some epic earthing failure when the clutch comes out while in gear? (take out of gear, rev and clutch nothing happens)
3. Something else?

Im pretty much going to keep with my course of removing electrical parts I can to try and find this problem, but any thoughts or advise would be awesome.

Valgamesh.

[sports racer]

Has to be something with the gearbox or linkages. What electrics go to the gearbox? To the gearshift? Have you disconnected the reverse light switch? Are there any wires that get shorted by the linkages?

Is it OK if you push in the clutch and try different gears without releasing the clutch?

You're running an aftermarket engine management system. Have you contacted the manufacturers to see if they know of this problem?

Any chance you can remove sensors to the aftermarket system (one at a time) and still run the car?

Have you connected a voltmeter to every wire in turn to see what the difference is with it in gear compared to out of gear?

C'mon, there's so many things you can do to track down this problem. I'm surprised the autoelectricians haven't fixed this.

What about the old trick of running it at night with no lights on so you can see if there's any sparking of wires somewhere?

What about starting the car then removing every single fuse, 1 at a time, so you only have the ones necessary to run the car? That will eliminate any outside cause.

Is there a wire rubbing against the clutch pedal or accelerator? Is the accelerator cable hot when the problem happens? Sounds like a stupid question but I once had the cable carrying a current because something else failed.

Is any of the wiring hot to touch?

That should be enough things to try for now before I get serious and get off my arse to show you how to fix it.

[sports racer]

And just to rub salt into the wound mine is running super sweet. I fixed the problem with it occasionally coughing when it was in gear.

[valgamesh]

As far as I can tell, the battery earths to the gearbox/starter, the new fuel relay earths to one of its mounts, & the reverse light is linked to the gear shift. Nothing else

Once the clutch goes in you can cycle through all the gears, nothing happens unless you try to take off in any gear.

The ECU is stock 1985 tech so no contacting/removing sensors.

Meter has been connected to tonnes of things with no change.

The electricians found A problem, assumed it was that, fixed/changed that, seemed to work so said all done give me money see you later.

Been run at night with no sparks appearing.

Removing fuses has been done.

There are loose wires everywhere but nothing touching/hot.

[sports racer]

You said all electrics stop when you lose power. Isolate the circuits that run the engine and run a separate power AND earth line to them. Don't have anything common to the rest of the car (lights, horn, fuel pump etc). The next time you lose power it shouldn't affect the rest of the car. You need to do this because it could be almost anything that's shorting the electrics and by having 2 totally separate electrical systems you can start to isolate what's causing the problem.

Are you running multiple earth leads off the battery? You've got 1 to the motor, do you have another to the chassis?

So you know which fuses are needed to run the engine? Replace them with 1 or 2 amp fuses and see what blows when you lose power. Isolate that circuit and go troubleshooting.

The fact that you lose electrical power to everything when you have this problem makes me think it's a loose connection or it might be an earth lead because you're not blowing fuses. Check and double check all the earth connections. Wouldn't hurt to add a couple too.

You could also run a second small battery in the boot wired into the circuit via the petrol pump. That would give you a second source of power just in case it's the connections to the main battery that are causing the problem.

Have you added any more to the 15kg of wiring you found you don't need? There's a good chance once you get rid of all the crap you might get rid of the problem.

[blis]

I'd be looking closely at the residue from the aftermarket cruise control, pressing the clutch would have to trigger it.