68 GT 390 Mustang Electrical problem ????

[69 SCJ]

Hello chaps
I seem to be having a problem.
When starting of everything is running fine but after 10-15 minutes when she heats up thats when the problem starts.
It feels like it cuting out and breaking down not smooth and looses power and gets hot but continues to run shit.
Checked and replaced fuel pump no problems their replaced all spark plugs. I have not replaced the spark plug leads  ??
Im thinking my old coil is breaking down ???
Or do I switch switch to electronic ignition ??
Any comments would be appreciated as a starting point.
Thanks heaps guys
And yes its a 1968 390 S Code
Steve 

[Daz 67GTA]

Hi!
Worth checking the coil for sure. Especially if its old. Changing to the Pertronix (replacement of the points) is very easy, but you need to make sure you remove the resistive wire.
Make a call: Do coil and pertronix upgrade at the same time, noting the the existing coil may be the "R" type that needs a resistive wire, so ensure you get the normal GT40 coil if doing the Pertronix.

I did the upgrade in my mates 65 Tbird with the 390. Ran so much better and smoother.

Or... grab a replacement coil and just make sure you get it running correctly again before the upgrade to Pertronix.

[69 SCJ]

Thanks buddy
Great advice
Will do
Steve 

[GEOFF289]

Is the choke opening fully and properly?

[69 SCJ]

Hi Daz
Just checking is this the one you are referring too.
Its on Ebay https://www.ebay.com.au/itm/Pertronix-Ignitor-Conversion-Autolite-Distributor-Points-Electronic-Coil-V8/272479961248?hash=item3f711240a0:g:eDYAAOSwJ7RYSoD6
Also little confused about that resistance you referred too.
Just want to this easy and take coil off and points and replace with this lot.
Thanks for your help
Cheers Steve

[jiffy]

An alternative to the pertronix is the Crane XRi module.
Works with the original coil and resistor wire, but includes a rev limiter. Easy swap too.

https://www.ebay.com.au/itm/FAST-Ford-XR-i-Points-to-Electronic-Conversion-Ignition-Crane-Cams-750-1700-SBF-/192317456175

[scollist]

Here is a video on installing Pertronix.  AutoRestomod are pretty good info source.

Note they talk about Ballast resistor - this is the pink wire from ignition switch to the coil that needs to be bypassed for Pertronix II or Petronix III. Installing relay triggered by existing ignition wire (instead of it going to the coil) to enable a direct 12v feed from battery is probably best option.

https://youtu.be/uQ0smsIO8Js

[SXTY8]

Yep I swapped a crappy electronic distibutor setup that was on my 390 to a MSD system and the difference was fantastic. More power, smoother idling and a bit better fuel economy, but that usually went out the window because I was enjoying the acceleration too much.

[Daz 67GTA]

Hey Steve - I just looked up Pertronix ford 390 and can see that you can save quite a bit of $$ by getting the Pertronix by itself (should only be $120-$130, plus a Bosch GT40 Coil for about $60-$80)

OR.. if Money is no option and you can't be bothered shopping around that one you noted is also fine.

The "resistive" wire as mentioned above is a pink wire that is usually from the ingnition that provides positive voltage to the coil, it drops the the voltage to the coil to 7-8V approx.
The Pertronix wont work with this wire in place. I think Custom mustangs sell a replacement wire with the correct terminals, or if you're handy with wiring you can simply replace it yourself with your own wire.
Hope that helps?

[flatchat]

 probably just the condenser if everything else in the distributer is in good nick

[pmb0186]

I would go through the electrical systems in its entirety
Run the at night look for sparks from leads, cap, coil tracking to ground
measure resistance of leads
replace plugs
inspect cap for cracks
replace point and condenser
inspect coil for cracks
inspect rotor

[Bumblebee]

I had the above done to my GT/CS S Code 390 and it helped. Also consider a carb rebuild if it’s never been done....mine was a mess.

[69 SCJ]

Hello
again
For starters I just changed the Coil WOW running better did not break down at all.
Still getting a little heated.
Im sure this is just the starting point.
I may still get full electronic ignition with another new coil.
Yes I will check cap for cracks and maybe change leads as well.
Also guys I want to do a compression check on the 390 motor maybe used 100klms full rebuild stock.
What numbers should I be getting on my gauge ????
Thank you to all for your great help
Cheers Steve 

[pmb0186]

In respect to compression I would worry about how many PSI you should expect rather the difference between cylinders which shouldn't exceed 10%.
You said it only done 100Km since rebuild ? if so you have a long way to go before the rings seat anything up to 30,000Km so compression may vary a bit and use oil   

[69 SCJ]

B :bow:ig Thanks