Grounding

GT40Mk II with 427 FE cranks but won't start. Has always been hard to start.

- Replaced battery since it was 4 years old. Still not start.
- Battery cable gets very hot during cranking (as does kill switch in the ground wire) NOTE: battery negative is grounded thru kill switch next to drivers seat to bolt on upright where cross bar is connected on drivers side)
- Coil and MSD box check normal
- Plugs all regapped

So, I think I have grounding problem. Where is best place on chassis to ground battery (and motor).

Tahnx
Mark
 

Rick Muck- Mark IV

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GT40Mk II with 427 FE cranks but won't start. Has always been hard to start.

- Replaced battery since it was 4 years old. Still not start.
- Battery cable gets very hot during cranking (as does kill switch in the ground wire) NOTE: battery negative is grounded thru kill switch next to drivers seat to bolt on upright where cross bar is connected on drivers side)
- Coil and MSD box check normal
- Plugs all regapped

So, I think I have grounding problem. Where is best place on chassis to ground battery (and motor).

Tahnx
Mark

I suggest a cable from the block at the engine mount attachment to the chassis where the bracket bolt to the tub. A heavy duty braided cable will work well. You can also run the battery ground to this point so you have a direct path to the block.
 
Thanx for responses ... here's a little more data (not being an electrician my understanding is minimal so your help is greatly appreciated)...

Checking resistance/ohms from my grounding point on chassis (bolt holding in drivers side of cross bar ... note: the same point is used for the battery grounding point and the braided strap I used to ground the engine), the ohm reading is basically zero (ie, .1), so it appears ok.

However, when checking these same two points for voltage under the load of cranking the motor, the volt reading was .6/.8 vs .05 and the cable started getting hot immediately after only cranking a few seconds.

Any ideas? is it simply a bad grounding point? If so, will connect as suggested. Have had this hot feeling ground cable even when car ran well.

Otherwise, what could cause this voltage to flow thru grounding cable? I have a couple of wires needing grounding attached to battery end of ground cable. And, I have a couple wires needing 12volt power connected to positive battery terminal. Primary positive cable is connected to the starter.

Thanx
Mark
 
one other question ... should the cables be replaced since they've had this overheat issue for a long time (ie, can the two cables and strap go bad due to the issue they've been operating under)
 

Rick Muck- Mark IV

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Make sure the cables are big enough for the load and also check the starter. Bad windings in the starter will cause an excessive current draw that will overheat the cables. You can have the starter tested for load draw.

have you ever grabbed an overheated cable? I have and had to pick the insulation that had melted to my hand off....not fun!
 
I have found that having a sizable ground wire connected directly to one of the starter mounting bolts eliminates a lot of problems like this. I believe I added the additional ground cable on mu Superformance GT40 Wiring Diagrams. You might also look for loose connectors at the ends of your grounding cable at the chassis and at the battery ends. Bad crimps can appear, especially if the cable has overheated a few times. The ground cable does not need to be the same gauge as the power cable due to its short length.
 

Ian Anderson

Lifetime Supporter
Do you have a spare charged battery and good jump leads?

If so connect them direct to your starter and then try cranking. Normal battery just powers the rest in fuel pump and ignition

If still slow then it is the starter as you have eliminated the rest of the circuit

Have you tried push starting the car? Does the motor fire up or is there an additional problem?
 
Mark,
I'm still concerned about spark. Even thick cables can get warm/hot if you crank the starter for 30 seconds or a minute. Why is it not firing? We wouldn't be talking about cables if it had fired.
 
I think Rick is correct in suggesting a cabe from the battery to the ground by the starter. Steel is a conductor of electricity, but not a good conductor.
 
I think you have an extreemly long earth. Move the kill switch to the active side of the battery (close to the battery). An auto lecky may correct me here, but i think there may be issues with having the earth on the negative side of your harness, eg a fault may try to find an alternate earth and burn out a smaller path. If the active side is isolated this is less likly to happen. Will also mean your earth cables will be much shorter opposed to routed by the drivers seat.
Cheers, Gus.
 
I'm sure you know this, but make sure all your grounding points are clean of paint/powdercoat/etc. These act as insulators....which is a bad thing for a ground.
 
Mark,
I'm still concerned about spark. Even thick cables can get warm/hot if you crank the starter for 30 seconds or a minute. Why is it not firing? We wouldn't be talking about cables if it had fired.

If the starter is drawing to many amps due to polling or bad earth/power issues due to connections it sucks the life out of the battery and there is nothing left for the coils.
A sure sign of that is as you come of the key it fires.

Mark use a volt meter not an ohms meter as it does not test under load.
You check for voltage drops,google it.
If you have efi most systems when they drop below 9v the ecu wont turn on.
Thats as simple as a volt meter across the battery when cranking.

As Rick said its a bad earth by the sound of it,or it needs an extra one.
Hot leads is a sign of high amperage draw or restriction of flow.

Amp draw on a starter would be around 80 I would think .

Jim
 
Again thanx to all ...

Have battery cable connection cleaned and grounded to cleaned bare metal frame (talked to Dennis Oltoff and he said he uses a bolt where the cross bar is bolted to chassis so that's what I used). Used same grounding point for grounding strap cleaned and bolted to cleaned bare metal engine block. Have taken kill switch out of picture for now.

Will clean all connections to starter.

If I drill a hole in chassis right next to battery box and connect the multiple grounds I previously had connected to negative battery cable, will this screw with all the grounds attached as described provide sufficient ground?

Mark
 
Again thanx to all ...

Have battery cable connection cleaned and grounded to cleaned bare metal frame (talked to Dennis Oltoff and he said he uses a bolt where the cross bar is bolted to chassis so that's what I used). Used same grounding point for grounding strap cleaned and bolted to cleaned bare metal engine block. Have taken kill switch out of picture for now.

Will clean all connections to starter.

If I drill a hole in chassis right next to battery box and connect the multiple grounds I previously had connected to negative battery cable, will this screw with all the grounds attached as described provide sufficient ground?

Mark

That will be fine.

Jim
 
Car wanted to start with lots of smoke, just didn't make it.

All grounds cleaned and sanded. Built up separate grounds to starter, battery, and block. No kill switch breaks in any of the ground lines. Separate ground point for extraneous ground wires built. However, did not sand and clean positive connections...will do that next.

Battery is new but has to be recharged after each starting session. Battery is 96R with 725 cranking amps and 550 CCA. Only size that I found locally that would fit battery compartment.

As it turns out, my Cobra (427 FE SO as well) battery died this weekend (clicking on turning the key). Since there is a lot more room for the battery, so was able to get a bigger battery with 1000 CA and 800 CCA. Cobra started in a heartbeat.

Is the CA/CCA of the 96R battery the issue? Not enough umpf to crank the 427 FE?

If this is the case, what's a high CA/CCA battery that will fit the battery box? I previously had a Continental 96R with 700 CCA, but they don't appear to make it anymore.

Thanx
Mark
 

Rick Muck- Mark IV

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So when your starter is toast and some of the winding insulation has failed, the 70-100 windings of 18-25 gauge wire will effectively be like a 2 gauge cable....and will suck more amps then your battery can supply on a lovely 80 degree beach day. And therefor the cables attempting to supply such amperage will heat up and melt the insulation off in short order. And you your car will not start or not even crank very well.

Redo the ground and power connections and have the starter checked. You can put bandages on a wound, but if the arm is severed you are re-arranging deck chairs on the Titanic,
 
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