Sparking problem
Discussion
Any ideas please. Irregular spark on all plugs timing gun either doesn't flash or irregular, varies between plugs. Replaced all ignition over last 2 weeks to try and resolve, new distributor, leads, coil, plugs. Timing checked and ok, good earth to engine block, 12v at coil. Running out of ideas so thoughts would be greatly appreciated.
Did you check the coil 12 volt supply correctly?
It can only be checked by disconnecting the White/Black and any other cables from the coil negative terminal
Then
Connect jump lead from coil negative terminal to a known good earth (Battery Negative)
Switch ignition on
Measure voltage across coil positive and negative
By carrying out the above test, the ignition supply to the coil is being measured while under load
Perhaps you have already tested the coil supply correctly
Not worth going any further until the supply is known to be good but........
Do you get a steady strobe light when connecting the strobe to the coil king lead?
It can only be checked by disconnecting the White/Black and any other cables from the coil negative terminal
Then
Connect jump lead from coil negative terminal to a known good earth (Battery Negative)
Switch ignition on
Measure voltage across coil positive and negative
By carrying out the above test, the ignition supply to the coil is being measured while under load
Perhaps you have already tested the coil supply correctly
Not worth going any further until the supply is known to be good but........
Do you get a steady strobe light when connecting the strobe to the coil king lead?
Bigfish_74 said:
Reading of 10.5v across the coil with that test. 12.5v at the battery. No strobe on the king lead although I have had previously but maybe not since I put the new coil on yesterday. Gun checked and working ok.
Ok looks like you've done it, forgot to mention check the battery voltage and coil voltage both with ignition on12.5 volts measured at battery with ignition on
10.5 volts measured at coil with ignition on
There is a big volt drop on the ignition supply from ignition switch to coil
With battery voltage @ 12.5, coil voltage needs to be at least 12 volts
If your car's wired the same as the below diagram.....
Brown from battery connecting to Red @ ignition switch plug
Black/Yellow @ ignition switch plug connecting to White of car loom
White of car loom connecting to Fuse 14
White/Yellow/ Plus possibly a Red or Red Dot from Fuse 14 to Rev Counter
White/Yellow from Rev Counter to ignition Coil and loops onwards to distributor amplifier
Check for volt drop @
ignition switch
fuse 14
or rev counter before checking elsewhere
Good luck in finding it
Tried to diagnose the voltage drop by disconnecting all from the coil other than the 12v ignition supply. So a direct earth to battery from coil negative and the single white wire from ignition which has a good 12.5v are the only connections but still get the voltage drop across + - to 10.5v. Also checked with the old coil and the same result, are we sure the coil isn't meant to drop the voltage under load?
Bigfish_74 said:
Tried to diagnose the voltage drop by disconnecting all from the coil other than the 12v ignition supply. So a direct earth to battery from coil negative and the single white wire from ignition which has a good 12.5v are the only connections but still get the voltage drop across + - to 10.5v. Also checked with the old coil and the same result, are we sure the coil isn't meant to drop the voltage under load?
Now you've checked it with a meter and the feed is there ok but now you need to put load on it, try connecting the feed to a headlight bulb and give it a separate earth and it should light the bulb. If it glows dim then there's a problem.Bigfish_74 said:
Tried to diagnose the voltage drop by disconnecting all from the coil other than the 12v ignition supply. So a direct earth to battery from coil negative and the single white wire from ignition which has a good 12.5v are the only connections but still get the voltage drop across + - to 10.5v. Also checked with the old coil and the same result, are we sure the coil isn't meant to drop the voltage under load?
Don't leave the coil powered up for too long, it will overheatYou comment single white wire from ignition which has a good 12.5v
Do you mean there is 12.5 volts at the white ignition supply cable that is connected to the coil + positive and that voltage drops to 10.5 volts when earthing the coil negative
If so
The ignition supply to the coil is dropping by 2 volts when under coil load......this is a fault
Apart from poor or burnt connections, the only other problem could be the fitting of the wrong voltage ignition coil
Some ignition circuits use a 9 or even 6 volt coil and a ballast resistor in series with the coil supply (White cable) to drop the voltage
Fitting a lower voltage coil in a 12 volt circuit could cause a volt drop to increase
Google has the below file
Somebody had this very same problem in the past
See Page 10 Chapter 3 (3.3) – The Ignition System.............last post in 3.3
https://www.tvr.at/grafiken/wedge_epistles_mk2.pdf
Somebody had this very same problem in the past
See Page 10 Chapter 3 (3.3) – The Ignition System.............last post in 3.3
https://www.tvr.at/grafiken/wedge_epistles_mk2.pdf
Bigfish_74 said:
You've convinced me, I'll work it back, maybe a fault at the relays. Thanks again.
Good luck in finding the faultYes, fault could be at fusebox fuse 14
To make life a little easier, check the connections that are easiest to get at before pulling the rev counter or anything else
Bigfish_74 said:
You've convinced me, I'll work it back, maybe a fault at the relays. Thanks again.
You don't need to go any further with checking the coil feed if the bulb lights up fully. You may have a crusty wire under the insulation, internally in the loom. you can check the resistance and that might look ok but it may be failing under load.Penelope Stopit said:
No bulb being used
Coil is the load
Voltmeter is measuring voltage under coil load
As much as 5 amperes of primary current is needed to produce 30,000 volts but he is testing it statically isn't he? Many ignition coils will pass a resistance test but fail a current ramp test. as is the same with feed circuit.Coil is the load
Voltmeter is measuring voltage under coil load
Bristol ave fag said:
Penelope Stopit said:
No bulb being used
Coil is the load
Voltmeter is measuring voltage under coil load
As much as 5 amperes of primary current is needed to produce 30,000 volts but he is testing it statically isn't he? Many ignition coils will pass a resistance test but fail a current ramp test. as is the same with feed circuit.Coil is the load
Voltmeter is measuring voltage under coil load
The coil primary winding is the load on that supply
Once the 2 volts volt-drop is rectified by testing and finding as mentioned above, the OP can then move on and check the HT voltage
In curing the 2 volts volt-drop at the primary supply the problem with the HT voltage may or may not be solved
Yes a high wattage bulb could be used for the load testing of the circuit if there is any doubt about the voltage or condition of the 2 ignition coils available to the OP
Hopefully the OP has now found the burnt or bad connection in the primary supply cable
Bigfish_74 said:
Headlight bulb test, no discernible difference in brightness on the ignition feed/ direct to battery. Working through the fuse feeds visually checking connections and wires for breaks, any ideas how to better test without ripping the loom apart / rebuilding it?
That feed is ok then. that's not the problem. how does it run? will it rev up?Gassing Station | Wedges | Top of Page | What's New | My Stuff