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Repair Help Please, Cobra Newbie
Helping a friend. Unique 29 FIA, manufactured 1995.
First instance: was driving, turned on a number of electrical accessories (lights, electric radiator fan, etc) then when putting clutch in at stop sign, engine RPM would go low and then all electrical power cuts out - dash, headlights, etc. Engine stalled, car still rolling, so was able to let clutch out and "jump start" engine - and everything came back. Then seemed to run fine if minimal electrical load (no lights, etc). The ampmeter seems moving normally - up to 30 amps under high engine RPM, down to zero, slightly positive at idle. Second instance: same thing as above, but after engine stalled, pulled over to side of road. Car wouldn't start, no lights, gagues, nothing electrical. Pushed car home and still nothing when you turn the key. Owner changed ignition switch (and says original one was fine also). Battery fine, 12.8 V. Master disconnect switch seems fine. I don't have a schematic unfortunately. There must be a relay to send power to fuse block, right ? Where ? Maybe not energizing. But a bad relay wouldn't explain the "cut out at high electrical load" above. Or voltage regulator ? But a bad voltage regulator would not explain why there's no electrical power when key turned on. Hope this is complete background. Greatly appreciate any help!!! |
I'd swap out the voltage regulator and the alternator, both inexpensive to do.
Also, I'd be suspect of the battery at this point as well. Bill S. |
It sounds like an alternator issue to me. If you can swap it out for a good one to see if all becomes well again that would be very telling. If you have a good alternator and still no electrical power, then I would look at the wiring in the starter circuit, in particular the fusible link if you have one.
Here is the relevant circuit from my Unique. Bear in mind I am running a Chevy engine (:CRY:) so your circuit may be slightly different. Wire numbers and colors correspond to the wires in the harness and the manual that came with it. http://www.clubcobra.com/photopost/d...schematic1.jpg |
If he has an electronic ignition the engine is probably cutting out because the idle rpm and accessories are pulling the voltage below the minimum the ignition box requires to function. Is he running a battery gage (some call an amp gage)? If it's going way negative when slowing to a stop or corner with all the accessories on then that would indicate the voltage output of the alternator/regulator is dropping way below what it needs to charge the battery - which means it's probably too low to operate his ignition box.
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Agreed.
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First, bypass your Master-Disconnect switch. If it is marginal, it might give you similar characteristics (if it cuts off the alternator power).
It could be intermittent/bad ammeter or its connections. I would also look for an intermittent short somewhere. Probably close to the alternator main wire (could be internal, too) since it's apparently not showing up on the ammeter. The next this happens, you really should immediately use a voltmeter to trace where the power is not showing up. |
Hi, I am the owner of the car that Delawaredave is trying to help.
A quick question; if an ammeter is bad, will the car shut off? Why? I thought it was only an instrument to read a condition, not a no go item. I used my Power Probe to energize the Batt terminal on the ignition switch. It cranked over when I turned key to start. So I am not getting power to the switch. The RED wires (2) are labeled 25 and 26. A schematic sent by Jim,from the Unique Forum , shows wire 25 going from the ignition switch to the ammeter. I cannot determine where 26 goes. Any thoughts? Thanks, Ken |
Since I have had the problem I have replaced the :
Ignition switch starter solenoid Fuses all good My fuseable link reads 12.5 volts after it so I know it good. It is connected to master cutoff switch. Ken |
12.5 volts seems low. Notwithstanding the fact these systems are referred to as 12 volts, the charging system should be in the range of 13.5 to 14.5 volts. Automotive Charging Systems -* A Short Course on How They Work | CarParts.com
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UPDATE:
Dave and I ran a jump to the ignition switch BATT. terminal. She fired up .Off then on. When I disconnected the jumper lead( Power Probe) the car stayed running. Worked each time. Ammeter showed 30+ when running at 2000 RPM and above. Low idle , slight discharge . I had all accessories on( cooling fan, defroster, head lights, high beams , elec. fuel pump) Oh well, I will just have to wait till the next failure. Ken |
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Have you started the car, pulled the negative cable off the battery and increased the electrical load? Once started, the alternator should run the car and everything on it. If it doesn't, it is probably failing, or possibly the voltage regulator is going. I'd say the alternator.
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After each "instance" in OP, the car was completely dead - no lights, horn, etc.
Diagnosed that we were not getting 12V at the BATT terminal on ignition switch, and:
Circuit then goes through ammeter and then to BATT terminal. So then we ran a jumper lead from battery to BATT terminal on ignition switch. Car was then energized, started, and runs fine. Could the ammeter "stick" and create and open circuit ? Could energizing the other side of the ammeter "unstick" it and resume a continuous circuit ? Somehow an open occurred between circuits 25 and 27 in above diagram - that seems to rectify itself by jumping to ignition switch ? Don't see how it could be the alternator or voltage regulator - they are not part of the circuit in between the ignition switch and battery. |
You might want to search and see if someone installed a thermal breaker somewhere in the main 12v ignition circuit... Do you hear a "click" right before the electrical cuts out?
Or, perhaps the Ammeter itself is shorting out? |
Didn't hear click (but loud car). Cut out when high electrical load (lights, fan, etc, low rpm) and low RPM.
What doesn't make sense is why the car stayed dead after stalling. Bad alternator or voltage regulator wouldn't do this. Maybe some high current cutout in the ammeter? That would reset itself when energized on "other side" of ammeter ? Thanks for your comments! |
All batt current flows thru the ammeter shunt (shunt can be internal to the gauge , or external ) most automotive are internal. If the shunt is intermittently opening due to high current, bad connection (internal) etc, you lose all power except batt to starter power.
Remove the ammeter and connect the ammeter feed wires together and insulate the connection well. Easy to do. At least you will eliminate that as a possible problem, and if all works ok, put in a voltmeter. |
All batt current flows thru the ammeter shunt (shunt can be internal to the gauge , or external ) most automotive are internal. If the shunt is intermittently opening due to high current, bad connection (internal) etc, you lose all power except batt to starter power.
Remove the ammeter and connect the ammeter feed wires together and insulate the connection well. Easy to do. At least you will eliminate that as a possible problem, and if all works ok, put in a voltmeter. |
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