If this is your first visit, be sure to check out the FAQ by clicking the link above. You may have to register before you can post: click the register link above to proceed. To start viewing messages, select the forum that you want to visit from the selection below. |
|
|
Thread Tools | Display Modes |
#1
|
|||
|
|||
Scrambler ignition woes (kinda long)
For those who don't recall, some time ago I upgraded my CJ-8's ignition
to the team rush TFI style. Here's a link to the thread... http://groups.google.com/group/rec.a...c61ce5c413e29d Anyway, it gave out on me this weekend and I'm at a loss to explain what happened. Here're the details if anyone has suggestions..... Drove to my destination, no problem. Minor detail - when I turned the Jeep off and took the key out, it kept running. I had to hold the brakes and stall the motor to kill the engine. This has happened before causing me to replace the switch. This switch is so new that I doubt it is a switch problem. Hmmm. After being there for several hours, I got ready to leave and the Jeep wouldn't start. It would crank and crank, but no start. Checked for fuel delivery into carb - ok Pulled spark plug and checked for spark - nada. Aha said I, Jeep is brain dead. Typical for the motorcraft style brain. Went to Autozone for a new brain, plugged it in, zip. Checked for spark out of coil - nada. Opened up the distributor cap just to have a look. Looked like the contacts were burned pretty bad and the tip of the rotor was flaky - like a well used spark plug. Odd, but nothing screaming major problem. At this point I noticed that both of the wires going to the coil (hot side and tach lead) were melted over a two inch or so span about 6 inches or so away from the coil. No other melted wires anywhere and no other melting on these two. Definitely not like an overload. Also checked all fuses at that point and none were blown. The only heat source near the melted section is a heater hose. That shouldn't be hot enough to melt wires. Also, even though melted, there were no shorts in those wires. At that point, I put the original brain back in and checked a couple things. I got 12 volts at the hot side of the coil with the key in the on position. That indicated a problem with the brain because there should only be around 4-6 volts there until the switch is in the start position at which time the brain is supposed to jump it up to 7-9 volts (there is a ballast resistor in this system). I put the new brain back in and rechecked the voltage at the coil. Voltages were as expected. I checked the resistance of the coil (between positive side and tach terminal) and got zip. I had no idea what it should be. I went back to autozone and got a new coil, cap, and rotor. The new coil has .6 ohms between the positive and tach terminals. That seems to indicate the old coil is bad. But here's the concern... Just for grins before I go all the way back to where my dead Jeep awaits (several miles and $$ of gas away) I decided to take the brand new brain back to autozone and have it checked. Their checker says it is bad. So, 1) Is there any reason why a the old brain going bad would cause the old coil to die? 2) Is there any reason why a bad coil would cause the new brain to die? And finally, 3) Any idea why only a small section of wiring would melt? |
Ads |
#2
|
|||
|
|||
Scrambler ignition woes (kinda long)
Small section of wiring burned? Don't you need a diode in that system's
power to make it work because it feeds the alternator's excite as well?? A diode will pop now and then. If they are hanging two wire strands together, vibration will kill them. If the diode blows short, the engine won't shut down. That would imply a ground loop issue to me overloading the diode. Mike 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's Canadian Off Road Trips Photos: Non members can still view! Jan/06 http://www.imagestation.com/album/pi...?id=2115147590 (More Off Road album links at bottom of the view page) Clap Trap wrote: > > For those who don't recall, some time ago I upgraded my CJ-8's ignition > to the team rush TFI style. Here's a link to the thread... > > http://groups.google.com/group/rec.a...c61ce5c413e29d > > Anyway, it gave out on me this weekend and I'm at a loss to explain what > happened. Here're the details if anyone has suggestions..... > > Drove to my destination, no problem. > Minor detail - when I turned the Jeep off and took the key out, it kept > running. I had to hold the brakes and stall the motor to kill the > engine. This has happened before causing me to replace the switch. > This switch is so new that I doubt it is a switch problem. Hmmm. > > After being there for several hours, I got ready to leave and the Jeep > wouldn't start. It would crank and crank, but no start. > > Checked for fuel delivery into carb - ok > > Pulled spark plug and checked for spark - nada. > > Aha said I, Jeep is brain dead. Typical for the motorcraft style brain. > > Went to Autozone for a new brain, plugged it in, zip. > > Checked for spark out of coil - nada. > > Opened up the distributor cap just to have a look. Looked like the > contacts were burned pretty bad and the tip of the rotor was flaky - > like a well used spark plug. Odd, but nothing screaming major problem. > > At this point I noticed that both of the wires going to the coil (hot > side and tach lead) were melted over a two inch or so span about 6 > inches or so away from the coil. No other melted wires anywhere and no > other melting on these two. Definitely not like an overload. Also > checked all fuses at that point and none were blown. The only heat > source near the melted section is a heater hose. That shouldn't be hot > enough to melt wires. Also, even though melted, there were no shorts in > those wires. > > At that point, I put the original brain back in and checked a couple things. > > I got 12 volts at the hot side of the coil with the key in the on > position. That indicated a problem with the brain because there should > only be around 4-6 volts there until the switch is in the start position > at which time the brain is supposed to jump it up to 7-9 volts (there is > a ballast resistor in this system). > > I put the new brain back in and rechecked the voltage at the coil. > Voltages were as expected. > > I checked the resistance of the coil (between positive side and tach > terminal) and got zip. I had no idea what it should be. > > I went back to autozone and got a new coil, cap, and rotor. The new > coil has .6 ohms between the positive and tach terminals. That seems to > indicate the old coil is bad. > > But here's the concern... Just for grins before I go all the way back > to where my dead Jeep awaits (several miles and $$ of gas away) I > decided to take the brand new brain back to autozone and have it > checked. Their checker says it is bad. > > So, 1) Is there any reason why a the old brain going bad would cause the > old coil to die? 2) Is there any reason why a bad coil would cause the > new brain to die? And finally, 3) Any idea why only a small section of > wiring would melt? |
#3
|
|||
|
|||
Scrambler ignition woes (kinda long)
Mike Romain wrote:
> Small section of wiring burned? Don't you need a diode in that system's > power to make it work because it feeds the alternator's excite as > well?? A diode will pop now and then. If they are hanging two wire > strands together, vibration will kill them. > > If the diode blows short, the engine won't shut down. That would imply > a ground loop issue to me overloading the diode. Hmm - no diode in this system. It's been fine for several thousand miles without it. |
#4
|
|||
|
|||
Scrambler ignition woes (kinda long)
A coil can heat up and short together internally. When you say that the
resistance across the terminals was "zip", do you mean a short circuit (zero ohms) or an open (infinite)? The "brain" as you call it, is basically a signal amplifier and impulse generator. Shorting the output, as with a shorted coil, can burn it out. The brain, on the other hand, can deliver excessive voltage to the coil, heating the windings and melting the insulation, which is after all only shellac. Now you have a chicken and egg problem. The only way to fix it, is to replace the coil and brain with new, together. Does this system have a ballast resistor anywhere? Mike is always blaming faulty grounds. Still, these are old vehicles with rubber mounted bodies and engines. It wouldn't hurt to verify with your ohm meter that everything is grounded properly. A continuity tester might be better, because the light bulb with put some load on the grounds you are testing. Now about the "two inches of wires melted", is that just insulation burned off, or copper strands melted together? This part is just morbid curiosity. Earle "Clap Trap" > wrote in message ... > Mike Romain wrote: > > Small section of wiring burned? Don't you need a diode in that system's > > power to make it work because it feeds the alternator's excite as > > well?? A diode will pop now and then. If they are hanging two wire > > strands together, vibration will kill them. > > > > If the diode blows short, the engine won't shut down. That would imply > > a ground loop issue to me overloading the diode. > > Hmm - no diode in this system. It's been fine for several thousand > miles without it. |
#5
|
|||
|
|||
Scrambler ignition woes (kinda long)
There are typically two to six diodes in every alternator:
http://www.autoshop101.com/trainmodu...timage/12f.jpg If one leaks it will be feeding the ignition through the exciter side of the alternator, like Mike said. God Bless America, Bill O|||||||O http://www.billhughes.com/ Clap Trap wrote: > > Hmm - no diode in this system. It's been fine for several thousand > miles without it. |
#6
|
|||
|
|||
I dread mornings
L.W.(Bill) Hughes III > wrote in message
>... > I get wound up easily and if sum1 sez summat I don't likeI hits or > pushes em i jus swing at em.My mum says that I hav a attitudeb'cos I > am quite strong and do alot of matial arts.She keeps havina go at me > n says that its gotta stop but I dont know how 2 stopmyself b'cos it > is only self defense and I neva hit first unlessthey say sumat I > don't like but my mum doesnt understand.How canI prevent myself as I > am only 12 and soon will hav lotsta ppl aftame |
#7
|
|||
|
|||
Scrambler ignition woes (kinda long)
Earle Horton wrote:
> A coil can heat up and short together internally. When you say that the > resistance across the terminals was "zip", do you mean a short circuit (zero > ohms) or an open (infinite)? The "brain" as you call it, is basically a Sorry - I meant zip as in zero. > signal amplifier and impulse generator. Shorting the output, as with a > shorted coil, can burn it out. The brain, on the other hand, can deliver > excessive voltage to the coil, heating the windings and melting the Which could explain why I measured 12 volts at the coil with the "dead" brain. > together. Does this system have a ballast resistor anywhere? Yes. There is one that drops a 12v source down to 4-6v when the switch is in the run position. > Now about the "two inches of wires melted", is that just insulation burned > off, or copper strands melted together? This part is just morbid curiosity. Just insulation. And it really doesn't look "burned." There are no "burn" marks, it just looks melted with no discoloration of the insulation in that region. |
#8
|
|||
|
|||
Scrambler ignition woes (kinda long)
Clap Trap wrote:
> For those who don't recall, some time ago I upgraded my CJ-8's ignition > to the team rush TFI style. Here's a link to the thread... > > http://groups.google.com/group/rec.a...c61ce5c413e29d > > Anyway, it gave out on me this weekend and I'm at a loss to explain what > happened. Here're the details if anyone has suggestions..... > A follow up for anyone who's interested... Got 'ol Sparky running again today. Turns out the coil was for sure fried. It was actually busted open. Replaced the coil, ignition module, and the melted wiring section and it purrs like a kitten again. Now if I could just find that HEI distributor I bought a couple years back, I could slap it on to avoid a future brain death.... |
#9
|
|||
|
|||
Scrambler ignition woes (kinda long)
An exploded coil usually means there is no resistor and you're
cooking it with a full thirteen, fourteen volts. Put a meter on it. God Bless America, Bill O|||||||O http://www.billhughes.com/ Clap Trap wrote: > > A follow up for anyone who's interested... > Got 'ol Sparky running again today. Turns out the coil was for sure > fried. It was actually busted open. Replaced the coil, ignition > module, and the melted wiring section and it purrs like a kitten again. > Now if I could just find that HEI distributor I bought a couple years > back, I could slap it on to avoid a future brain death.... |
#10
|
|||
|
|||
Scrambler ignition woes (kinda long)
L.W.(Bill) Hughes III wrote: > An exploded coil usually means there is no resistor and you're > cooking it with a full thirteen, fourteen volts. Put a meter on it. There is a resistor. The coil is getting 4-6 volts when the motor is off and the key is in 'on,' 7-9 volts when the key is in 'start,' and 11-12 volts when the engine is running. |
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
Canisters "Discontinued"? Kinda long :( | Daniel Paisley | Jeep | 1 | April 21st 05 04:16 PM |
'88 325is instrument cluster probs...kinda long | JimV | BMW | 4 | March 21st 05 09:55 PM |
Interesting Ignition Revelation | Randall Brink | VW air cooled | 21 | February 10th 05 12:26 AM |
passat instrument cluster ( kinda long) | starburst | VW water cooled | 0 | December 7th 04 04:17 AM |