Another one of my recent workshop experiences....

Mustang turns up recently, owner complains that engine would stall every time he backs off throttle at traffic lights but starts up right away every time and runs fine till he backs off throttle again.

O.K. It is a '65, 289, three speed manual, owner recently fitted a new Bosh electronic dizzy and aftermarket tacho.
Carby is original Autolite two barrel but must be junk so insists to fit brand new 350 Holley to fix problem. No worries. New carby fitted with new fuel pump and new filter, new fuel hoses to fully eliminate further fuel issues. Starts right away but would not idle below 1500 rpm. Check for vacuum leaks, none found, check timing, all ok. Revs clean to over 5000 (not bad for a Ford) but stalls soon as you back off. Same problem.
How long has it been doing it? ..... Since i have fitted the new dizzy and tacho.... owner says.

Ahhahh... Lets look at your wires.
Bosh electronic dizzys have a black and a red wire from the dizzy simply to connect to coil black negative, red positive even a monkey can hook them up. Now you just need the feed wire from the ignition key to to positive side of the coil to make it all broom-broom. Simple as that.
It all looked in order in this puppy...but after some time we discovered the problem.
The owner over enthusiastically disconnected everything without marking which wire went where and by coincidence the car already had a tacho wire running to the negative side of the previous coil so he used that wire connected to the positive side of the terminal and neatly tucked the most important wire away out of sight with black electrical tape. And then he hooked up the aftermarket tacho somehow straight from the ignition switch using the tacho signal wire as feed to the coil.
Does it sound confusing? Like hell it does.... I am still scratching my head wondering how it was running at all.

Bloody backyard mechanics        

You lost me after rack and peanut steering and flux capacitor....and always remember to cut the black wire.

 The problem in a '65 Mustangs engine bay is..... every wire is black.  

So..... which one do you cut?

Quote from: sms777 link=topic=2817.msg16015#msg16015The problem in a '65 Mustangs engine bay is..... every wire is black.  

So..... which one do you cut?

Thats just a build up of grease and oil that gives them the black look

Quote from: GTA390 link=topic=2817.msg16022#msg16022

Quote from: sms777 link=topic=2817.msg16015#msg16015The problem in a '65 Mustangs engine bay is..... every wire is black.  

So..... which one do you cut?

Thats just a build up of grease and oil that gives them the black look

glad I sold my old one Chev's rule:smile:

I'm guessing that he had effectively powered up the coil via the Tacho.  The way the electronics works in a Tacho it would have basically:

A: Not have had full 12volts to coil
B: effectively shorted the B+ side of the coil to ground via the tacho electronics when he got off the throttle.


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Yeah I was thinking along the same lines except I would have spelt it dizzy.....

Quote from: Kroooozer link=topic=2817.msg16033#msg16033Yeah I was thinking along the same lines except I would have spelt it dizzy.....

What do ya expect at 2.30 in the morning.  Bloody S key and Z key are just to close together at that hour

 You are correct cpu, that is exactly what he has done.
Took us a while to figure out since he has used kilometers of black electrical tape to neatly hide all the wires.

Now it runs as good as a Mustang ever will  

Quote from: sms777 link=topic=2817.msg16038#msg16038Now it runs as good as a Mustang ever will  

That bad huh!  



When I rebuilt the Corvette I had an interesting one.

Driving home one day and had to put the wipers on.  That was fine then I turned them off.  They went to the park position and then started to go again.  I pulled over to have a look see, went to get out of the car and the wipers stopped.  I thinks to myself, "hmmm loose wire somewhere, I'll look at it when I get home."  

Further down the road the same happens again, so I pull over again, open the door to get out and they park themselves again.  "Hang on" I says to myself, "every time I open the door the wipers work correctly."  "Maybe a neat feature but I really cant have it that I have to open and close my door every time"

So how was the door and wiper circuits related?  I neglected to connect an earth on the wiper circuit and it found it's own earth, tho it be a bad one, via the interior light circuit which is only active when you open the door.  Only took me minutes to fix it but hours to trace it out on the circuit diagram to find the circuit relationship.  I just had to know.