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Sherlock Ohms

The Case of the Shocking Stall

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thrashercharged
User Rank
Iron
The Case of the Shocking Stall
thrashercharged   10/19/2011 10:41:10 AM
It's a little known fact that the high carbon content of black rubber vacuum hoses can make them act as a conductor.  An old mechanics trick to disable cylinders selectively (to isolate which cylinder is misfiring) is to pull the spark plug cables off the distributor, and fasten 1" pieces of rubber vacuum hose between the distributor terminals and the spark plug cables.

The engine is then started (and it'll run because the vacuum hose acts as a conductor), and a ground wire (the old school mechanic would use their grounded test probe light) is run close to each hose providing a less resistive path than the spark plug to ground, thereby forcing that cylinder to misfire.

Yes it works every time.

But back to the point - moving that offending vacuum hose isn't solving the problem but replacing the spark plug wires was.  The guy has a bad cable boot at the offending terminal that isn't insulating properly - probably cracked. This would never happen if the components were in good shape.

JimT@Future-Product-Innovations
User Rank
Blogger
That’s Shocking!
JimT@Future-Product-Innovations   10/19/2011 12:55:03 PM

Kudus on your diagnostics methods, and your conclusion makes total sense. High voltage from a coil reacting with a greasy hose; I believe it.   And the 2c fix of a wire tie is my very favorite solution to so many of life’s perplexing mysteries.  Sorry you had to have the shocking experience to go along with the discovery!

JimT@Future-Product-Innovations
User Rank
Blogger
Re: The Case of the Shocking Stall
JimT@Future-Product-Innovations   10/19/2011 1:06:04 PM
Ouch!  I revise my earlier comment about "makes total sense".  A faulty boot allowing a current leak makes even more sense.  Thanks for taking me back to school!

Charles Murray
User Rank
Blogger
Right-turn sensitive
Charles Murray   10/19/2011 11:27:43 AM
Some vehicles can be pretty sensitive about right turns. A few years ago, my Honda Odyssey believed that the driver side door was opening every time I made a right turn. During the turn, the vehicle's interior lights would illuminate, the "door ajar" light on the dashboard would turn on, and a buzzer would sound. The culprit? A faulty seat belt. Because the seat belt wouldn't retract, it got stuck in the door, leaving a dent on the inside of the door. A plunger switch responsible for monitoring the door status would extend into the dent whenever I turned right, making the car believe that the door was open. The solution: I put a piece of duct tape over the dent. I still carry a role of duct tape in the car wherever I drive.

Tim
User Rank
Platinum
Shock
Tim   10/19/2011 10:18:07 PM
I am sure that the shock from the spark plug wire was pretty jolting.  As a kid, I wanted to see if the spark was firing in our line trimmer.   The only solution I was to pull the sparkplug hook up the boot and hold both the spark plug and the cylinder block with the other while I pulled the starter rope.  Needless to say the rewind spring engaging allowed me to open my hand enough to drop the plug and vow to never do that again.

failureindesign
User Rank
Gold
loose hose stops the show
failureindesign   10/19/2011 10:37:56 PM
On thing I always marvelled at was under the hoods of my Honda Accord, my Chevy Nova and my VW Rabbit: the care and training of various wires, hoses and other miscellania.

The Rabbit had most things tied down (execpt where the dealer had touched something - like when the dealer REMOVED the emission controls because they made the car "dirtier"!!).

The Accord had everything tied down and is still running great after 20 years.

The Nova ... well, let's be kind and just say they meant to tie everything down but didn't get around to it. Even the ceiling liner fell down eventually.

The Rabbit was still running great when I sold it at 115K. The Nova ran for a few years (died around 145K). But the Accord still runs like the day I bought it (20 years and 156K ago).

LoL Like I always say, "It's all in design!" (And it doesn't hurt to be built in Marysville, Ohio either!  :-)

 

WaltP
User Rank
Iron
More Stalling
WaltP   10/20/2011 9:33:27 AM
Had an old  Corvair that I was trying to restore about 20 years ago with a similar problem on right turns.   The motor would sputter and die, but as I coasted through the corner and straightened out, the engine would catch and start going again..  

 It drove me nuts for months.  Changed the fuel pump, checked fuel lines, rebuilt the carbuerator   Changed the plugs, the wires, the points. battery, battery cables....had the "generator" checked.  There wasn't all that much stuff that could go wrong on car from the early 60's

Finally figured out that the mounting bracket for the coil had rotted away.  I was under "hood" and bumped the coil and killed the engine.  When driving, and you took a corner, the coil would tip over and short against the the body.  Once you straightened out there was enough spring in the coil wire to pull the assembly back....and the engine resume running

Unfortunately that was the begining of the end for that car - the frame was rotted and way too expensive to fix....

Noswad
User Rank
Gold
Sparky McSpark
Noswad   10/20/2011 9:36:00 AM
Working with older cars can be interesting. I once replaced the ignition coil with one of those super coils and also replaced the spark plug wires. Being the tight wad that I am I baught the cheaper set of wires. I started up the car and it had a little bit of a rough idle. By that time it was beginning to get dark outside. I popped the hood and to my amazement there were little spark all around the engine compartment. It looked like one of those physics experiments where you touch the glass globe and sparks are visible all inside the globe.

I went to the auto parts store the next day and baught a quality set of spark plug wires and the problems was cured. Also, the car had much more power with the new coil and I had to go to a colder set of plugs.

rcwithlime
User Rank
Silver
If you were like many of us with "hot" cars
rcwithlime   10/20/2011 3:19:42 PM
we replaced the std mfg's coil with the high output aftermarket ones. Well, you were also supposed to use the resistor to decrease the voltage. If you didn't , you would fry the points, etc.

Object was not to provide too much spark to the distributor and then to the plugs, but to use a coil with enough ummph and "ampacity" to make sure that it provided the spark each and every time. Then, once the spark was provided, it was reduced back down to tolerable levels.

I had done the same thing, saw the same sparks with my wires, burned up points, etc. Back then, there were not a lot of knowledgeable backyard mechanics when it came to electronics. You purchased what magazines touted as better. Unfortunately, if you bought those aftermarket coils used, you did not get the instructions with them, which stated the resitor required and it's p/n.

Amclaussen
User Rank
Platinum
Re: Sparky McSpark and Aftermarket Ignitions...
Amclaussen   10/20/2011 3:27:52 PM
NO RATINGS
Noswad:  I worked on quite a few old cars back in the 70's, 80's and 90's; mainly because my own daily driver car was an old Ford Falcon 289 4-Barrel V-8 (1967 model), given to me by my father.  I had to work on it constantly, improving it in order to keep it driveable in Mexico City, famous for its fast and temerary driving style (either you pass NOW, or you don't pass and other will crash you!")... I tested at least 6 or 7 different brands and types of "specialty" ignition systems: Dual point, Dual points plus transistor switching, Optical, Magnetical, Centrifugal Advance, Vacumm Advance, Combined Advance, computer and sensor advance, single coil, even multiple coil!... silk "wires", metallic wires, resistor plugs, non-resistor plugs, single ground electrode, dual, triple and cuadruple ground electrodes, magneto vs distributor and coil, Capacitor discharge, Multi Spark discharge... ALL of them.

I badly WANTED to "extract" additional Horsepower.  Never got more than a measly couple of the often 15 to 20 promised by the car magazines advertisements, and loudly endorsed by industry paid racers swearing by them!

What I've found was that so called "aftermarket", "Performance" "Sport" or "Competition" labeled ignition systems are only really needed (or, in other words: their installation is distincly felt as an improvment) when the original factory system was defective.

Most times (say 99% of the time), the factory ignition design was perfectly OK in regard to power, economy and emissions.  There were a few occasions where a bigger aftermarket coil gave slightly better results, BUT, there were some other cases when the "bigger" coil only delivered a higher voltage, albeit at the expense of a WEAKER spark, due to a higher internal resistance or a winding construction with too many coil secondary turns.  The only sure way to check if the much over-hyped "competition" coil really worked better, was to measure the emissions, exchanging it two or three times and comparing with the emissions obtained with the factory coil.  Only when a certain combination of older silk and carbon ignition "wires" presented a higher resistance and rendered a more effective spark waveform, the bigger coil worked slightly better, but when using more modern metallic spiral wound ignition wires, the bigger coil actually delivered a weaker, orange colored spark, while the more modern epoxy encapsulated, more compact factory coil reached lower voltage levels, but produced a visibly fatter, higher energy, blue colored spark (and slightly lower hydrocarbon emissions). Dynamometer readings scatter was actually greater than the real horsepower gained by the "improved" ignition vs a proper original ignition.

Even the much touted "Multi-Spark" ignition systems only gave a marginal improvment, at idle and midrange RPM's, but were equal to the standard system at higher RPM's...  My conclusion, after spending several hundred dollars and much testing in several old cars, was that specialized aftermarket ignition components were more a perceived, pychological "improvment" than a real one, unless the factory system was bad (defective coil with shorted turns, leaking capacitors, too high resistance and/or intermittent wires, or poor quality distributor caps (deformed excentrically, tilted top or with carbon traces inside, or were not properly vented, which resulted in a lot of ozone being generated inside).

I'm shure your perceived "much more power" , was only because of the affected performance of the cheaper cables producing a lot of visible arcs bleeding the available voltage to other ground points all around the engine bay, that caused a lot of missing and then reducing the effective horsepower of the engine.

Automobile ignition systems require a definite voltage threshold, and some reserve voltage to overcome the gradual rise in voltage requirement as the sparkplug central  electrode loses its sharp edges and becomes more rounded as a result of erosion in the harsh environment of the combustion chamber, specially in the old days when the thinner platinum or other precious metal electrodes were not common or available.

A much higher voltage in not necessary or desirable, specially when it is achieved by a higher voltage secondary side of the circuit, WITHOUT enough current capability to sustain a proper spark for a long enough duration. A too high initial voltage is of little benefit if the spark cannot sustain a hot, durable arc.  The frequent result is a spark capable of jumping larger gaps, but stinguishing soon and/or producing a weak thin spark with less energy.  An excessive spark energy is not beneficial too, because it erodes the electrodes and places very high dielectric strenght requirements on the rest of the system.

Another misconception is that those special metallurgy electrodes "produce extra power", when actually a thinner electrode can only produce a smaller spark kernel, and frequently is prone to overheating in Supercharged or turbocharged engines... causing pre-ignition. Turbocharged engine fans already have discovered this, and now favor the older plug designs with larger diameter central electrodes, the standard ones that still need to be changed more frequently in order to keep the engine working properly. As they say: There is NO free luch! Iridium, Rhodium or even Gold electrodes do NOT produce more power (but could raise profits for the plug manufacturers, from overly enthusiastic power hungry but ignorant aficionados).

ANOTHER MYTH: multiple gound electrode plugs. Developed in order to maintain at least one firing electrode in the dirty, oily-fuel needed in those grasscutting engines... BUT MORE THAN one single ground electrode only shrouds and shadows the flame front, REDUCING the performance, certainly not enhancing it in any way. (Well, they may enhance the plug manufacturer sales!).  At the last automotive industry Expo in Mexico City, I strongly questioned the salesman from a famous german company for promoting such a wrong product application: it only works better in 2-stroke oil-mixed fuel engines, not in a car engine, unless the car owner pretends to keep the same plug set for many years of use, in which case the extra ground electrodes could be of some help)... After explaining them how the flame front is propated from the spark kernel and it initiates the combustion, finally the crowd assisting to the talk gave me their approval.  Sorry, no more gimmicks for me!  amclaussen, R&D Mexican Petrolum Institute.

Battar
User Rank
Platinum
Re: Sparky McSpark and Aftermarket Ignitions...
Battar   10/21/2011 11:06:27 AM
Thanks for the informative ans well written post.

bellaire
User Rank
Bronze
Another car stall solved
bellaire   10/20/2011 11:31:01 AM
So here is another one. Back in the 60's a friend had a lovely old Daimler. It would run perfectly but occasionally it would cut out going up a hill with a slight left hand bend.

Cutting a long story short on the 6th or 7th trip to the garage the mechanics could not find anything wrong. They left it running for several hours (petrol was cheaper then) no failure. They opened the bonnet and it ran for another hour then the break through. Remember the days when you changed your antifreeze every 12 months. The garage would tie on a "Bluecol" label with the date. This label had a twisted piece of wire to the bonnet.

It hung down and when gravity and centrifugal force from turning and going up hill was just right, it would swing infront of the air intake and seal it off until the engine stalled. The vacuum would then disappear and the label fall back. The mechanic spotted a slightly dark ring on the label from the air intake!

David12345
User Rank
Platinum
Sparky High Voltage Wiring
David12345   10/21/2011 11:33:54 AM
NO RATINGS
The high voltage path between the coil distributor, and spark plugs seemed to be a common problem area with older cars.  I agree that most of the power gains from aftermarket ignition wires, coils, and plugs was from replacing defective components.  I have multiple instances of this problem:

1) I had a 1969 Corvair.  It ran terribly.  Eventually when I opened the hood (rear) at night, I saw all the Saint Elmo's fire of the blue arcs around the top of the coil and the oil-soaked spark plug wires.  Replaced the o-rings to take care of the oil leaks, degreased the coil, replaced the spark plugs, wires and distributor cap.  It's amazing how well an engine runs when it's not misfiring.

2) Same Corvair I later dropped an 327 Chevy V8 into it.  Wow, what a rocket, but it kept popping back through the carburator and fouling #5 and #7 plugs.  Two problems, A) the #5 and #7 wires were too close to each other and cross-firing from induced voltage, and B) the ballast resistor for the 6 cylinder engine was 1.8 ohms and I needed to change that to a 1.2 ohm ballast resistor for a hotter spark with the V-8 (my bad).

3) A friend had his 1968 Chevrolet Camaro with a small block V8 die by the road.  He had a big 50K volt Accel Coil and aftermarket wiring.  We stuck a wood handled screwdriver in #1 plug wire and held it to the block . . . no spark.  I checked the wires to the coil and distributor.  The wire from the coil was loose in the dirtributor cap.  I snapped it in.  Next test, the car fired-up on 7 cylinders, and I got shocked through the wet wood handle each revolution until I got my happy buddy to shut-off the engine so we could hook-up #1  plug again.

4) Last example, I came upon a group of people trying to get a college coed's 1960's vintage Dodge Dart started.  They had jumper cable out, but it was cranking well, but with no spark.  I found the coil wire was loose and after snapping it in the car fired right up.  They had been working for awhile, and thought it was weird that I jut touched the wiring and the car would then start.  (As if by magic.)

 

OhmsLaw
User Rank
Gold
Re: Sparky High Voltage Wiring
OhmsLaw   11/10/2011 11:37:51 PM
NO RATINGS
My Dad let me drive his 2nd car a 1963 MDB convertible to university 40 yrs ago. One winter storm when it was drifting more than a foot across the highway. My car stopped dead in -20'C weather. No traffic late at niight. I opened the hood and after 10 minutes , it started again.  A few minutes later it died again as quickly as before. I knew it was no spark and then I saw faint corona around the distributor. A crack aha. My intuitition told me it was ice melting that caused the failure and when I opened the hood it froze quickly and then started. Ohm's Law on H2O says insulation is better when frozen. So I sprayed some WD40 and it was good to go home, non stop. Carbon & grease removal gave it another year's life.  

But recently my rental home in Winnipeg gas furnace stopped and it was freezing out. I knew the previous renters replaced the furnace motor at my suggestion for rent reduction. It had an electronic spark ignition for a pilot light but the wire beside was to sense the flame temp and that sensor wire was free to rotate in the bracket. So I surmised that the wire moved, which relocated the flame sensor wire which stopped the furnace from going from pilot to operating mode. 1st I used some adhesive which can hold the sensor wire at high temps. Then I bent the wire so it sensed the outer cone of the blue flame rather than the center.  Voila, furnace fixed and it shouldn't drift with vacuum service.  It was wise I used an insulated handle pliers to adjust the flame sensor wire as it tends to arc from the ignitor to flame sensor with metal filling the gap when the pilot arc starts. (otherwise hit the furnace kill switch,adjust then turn on and wait 45 seconds or so until arc starts on pilot gas. ) Murphy & Ohm's law says YOU don't want to be the path of least  resistance.

Rob Spiegel
User Rank
Blogger
Re: Sparky High Voltage Wiring
Rob Spiegel   11/16/2011 2:56:10 PM
NO RATINGS
Hi OhmsLaw,

Id like to use either or both of your stories as a Sherlock Ohms posting.

If you're interested, it need to be fleshed out a bit to reach at least 300 words. Also, we would need a short bio. Two or three sentences would be fine. 

This blog depends on real-life stories such as the you have here. So please consider this request.

We can't offer payment, but fame will come in plentitude. 

OhmsLaw
User Rank
Gold
Re: Sparky High Voltage Wiring
OhmsLaw   11/16/2011 10:44:41 PM
NO RATINGS
I sent a short bio 6 mos ago I think.

Start life as a EE Design Engineer in 1975 with Telemetry design, Aerospace design, Nuclear Robotic Inspection design, and other Instruments, then joined to ISL to design T1 Test equipment and manage debug on an ISDN BB WAN in early 80's then Burroughs with Disk Drive Test Eng10 yrs then IRIS with AUtomated Meter Reading on ISM cell network, then COntract Mfg Eng Mgr... now retired. doing home reno's.

Not much time to re-write it. Both would be fine.

THe case of the intermittent stalled car in sub-zero (C) freezing weather. 

My Dad let me drive his 2nd car a 1963 MDB convertible to university 40 yrs ago. One winter storm when it was drifting more than a foot across the highway. My car stopped dead in -20'C weather. No traffic late at niight. I opened the hood and after 10 minutes , it started again.  

A few minutes later it died again as quickly as before. I knew it was no spark and then I saw faint corona around the distributor. A crack aha. My intuitition told me it was ice melting that caused the failure and when I opened the hood it froze quickly and then started.  THis was before the days of cell phones and I had no CAA or AAA. SO it was fix it or freeze to death or walk a mile in the blizzard.

Ohm's Law on H2O says insulation is better when frozen. So I sprayed some WD40 to displace the water with its magical mix of fish oil used to prevent rust in military parts and I was good to go home, non stop without the moisture causing flashover on the carbon impregnated distributor crack.  . Carbon & grease removal gave it another year's life and WD40 saved my life.
                            = ~ =
Case of the furnace with no flame just an ignitor pilot flame. 

Recently my rental home in Winnipeg gas furnace stopped and it was freezing out. I knew the previous renters replaced the furnace motor at my suggestion for rent reduction. It had an electronic spark ignition for a pilot light but the wire beside was to sense the flame temp and that sensor wire was free to rotate in the bracket. So I surmised that the wire moved, which relocated the flame sensor wire which stopped the furnace from going from pilot to operating mode. 1st I used some adhesive which could secure the roating sensor wire at high temps. Then I bent the wire so it sensed the outer cone of the blue flame rather than the center.  Voila, the sensor heated up quickly and the main flame started a few seconds later.  The furnace appeared to be fixed and it shouldn't drift with vacuum service.  It was wise I used an insulated handle pliers to adjust the flame sensor wire as it tends to arc from the ignitor to flame sensor with metal filling the gap when the pilot arc starts. (otherwise hit the furnace kill switch,adjust then turn on and wait 45 seconds or so until arc starts on pilot gas. ) Murphy & Ohm's law says YOU don't want to be the path of least  resistance.

Only problem now is half the time the furnace motor won't cut out after the flame stops. But recycling the power or the slow speed switch on resets the motor to the off state.  Hmmmm.. another Murphy's law.  Perhaps excess dust is insulating the hot air sensor now and reading too is offset on the high side from stiction with hysteresis on the threshold . recycling the power seems to fix it... 

I'll let you know if it is the hot air sensor.

 

 

 

 

 

 

OhmsLaw
User Rank
Gold
Re: Sparky High Voltage Wiring
OhmsLaw   11/16/2011 10:44:42 PM
NO RATINGS
I sent a short bio 6 mos ago I think.

Start life as a EE Design Engineer in 1975 with Telemetry design, Aerospace design, Nuclear Robotic Inspection design, and other Instruments, then joined to ISL to design T1 Test equipment and manage debug on an ISDN BB WAN in early 80's then Burroughs with Disk Drive Test Eng10 yrs then IRIS with AUtomated Meter Reading on ISM cell network, then COntract Mfg Eng Mgr... now retired. doing home reno's.

Not much time to re-write it. Both would be fine.

THe case of the intermittent stalled car in sub-zero (C) freezing weather. 

My Dad let me drive his 2nd car a 1963 MDB convertible to university 40 yrs ago. One winter storm when it was drifting more than a foot across the highway. My car stopped dead in -20'C weather. No traffic late at niight. I opened the hood and after 10 minutes , it started again.  

A few minutes later it died again as quickly as before. I knew it was no spark and then I saw faint corona around the distributor. A crack aha. My intuitition told me it was ice melting that caused the failure and when I opened the hood it froze quickly and then started.  THis was before the days of cell phones and I had no CAA or AAA. SO it was fix it or freeze to death or walk a mile in the blizzard.

Ohm's Law on H2O says insulation is better when frozen. So I sprayed some WD40 to displace the water with its magical mix of fish oil used to prevent rust in military parts and I was good to go home, non stop without the moisture causing flashover on the carbon impregnated distributor crack.  . Carbon & grease removal gave it another year's life and WD40 saved my life.
                            = ~ =
Case of the furnace with no flame just an ignitor pilot flame. 

Recently my rental home in Winnipeg gas furnace stopped and it was freezing out. I knew the previous renters replaced the furnace motor at my suggestion for rent reduction. It had an electronic spark ignition for a pilot light but the wire beside was to sense the flame temp and that sensor wire was free to rotate in the bracket. So I surmised that the wire moved, which relocated the flame sensor wire which stopped the furnace from going from pilot to operating mode. 1st I used some adhesive which could secure the roating sensor wire at high temps. Then I bent the wire so it sensed the outer cone of the blue flame rather than the center.  Voila, the sensor heated up quickly and the main flame started a few seconds later.  The furnace appeared to be fixed and it shouldn't drift with vacuum service.  It was wise I used an insulated handle pliers to adjust the flame sensor wire as it tends to arc from the ignitor to flame sensor with metal filling the gap when the pilot arc starts. (otherwise hit the furnace kill switch,adjust then turn on and wait 45 seconds or so until arc starts on pilot gas. ) Murphy & Ohm's law says YOU don't want to be the path of least  resistance.

Only problem now is half the time the furnace motor won't cut out after the flame stops. But recycling the power or the slow speed switch on resets the motor to the off state.  Hmmmm.. another Murphy's law.  Perhaps excess dust is insulating the hot air sensor now and reading too is offset on the high side from stiction with hysteresis on the threshold . recycling the power seems to fix it... 

I'll let you know if it is the hot air sensor.

 

 

 

 

 

 

OhmsLaw
User Rank
Gold
Re: Sparky High Voltage Wiring
OhmsLaw   11/16/2011 10:44:44 PM
NO RATINGS
I sent a short bio 6 mos ago I think.

Start life as a EE Design Engineer in 1975 with Telemetry design, Aerospace design, Nuclear Robotic Inspection design, and other Instruments, then joined to ISL to design T1 Test equipment and manage debug on an ISDN BB WAN in early 80's then Burroughs with Disk Drive Test Eng10 yrs then IRIS with AUtomated Meter Reading on ISM cell network, then COntract Mfg Eng Mgr... now retired. doing home reno's.

Not much time to re-write it. Both would be fine.

THe case of the intermittent stalled car in sub-zero (C) freezing weather. 

My Dad let me drive his 2nd car a 1963 MDB convertible to university 40 yrs ago. One winter storm when it was drifting more than a foot across the highway. My car stopped dead in -20'C weather. No traffic late at niight. I opened the hood and after 10 minutes , it started again.  

A few minutes later it died again as quickly as before. I knew it was no spark and then I saw faint corona around the distributor. A crack aha. My intuitition told me it was ice melting that caused the failure and when I opened the hood it froze quickly and then started.  THis was before the days of cell phones and I had no CAA or AAA. SO it was fix it or freeze to death or walk a mile in the blizzard.

Ohm's Law on H2O says insulation is better when frozen. So I sprayed some WD40 to displace the water with its magical mix of fish oil used to prevent rust in military parts and I was good to go home, non stop without the moisture causing flashover on the carbon impregnated distributor crack.  . Carbon & grease removal gave it another year's life and WD40 saved my life.
                            = ~ =
Case of the furnace with no flame just an ignitor pilot flame. 

Recently my rental home in Winnipeg gas furnace stopped and it was freezing out. I knew the previous renters replaced the furnace motor at my suggestion for rent reduction. It had an electronic spark ignition for a pilot light but the wire beside was to sense the flame temp and that sensor wire was free to rotate in the bracket. So I surmised that the wire moved, which relocated the flame sensor wire which stopped the furnace from going from pilot to operating mode. 1st I used some adhesive which could secure the roating sensor wire at high temps. Then I bent the wire so it sensed the outer cone of the blue flame rather than the center.  Voila, the sensor heated up quickly and the main flame started a few seconds later.  The furnace appeared to be fixed and it shouldn't drift with vacuum service.  It was wise I used an insulated handle pliers to adjust the flame sensor wire as it tends to arc from the ignitor to flame sensor with metal filling the gap when the pilot arc starts. (otherwise hit the furnace kill switch,adjust then turn on and wait 45 seconds or so until arc starts on pilot gas. ) Murphy & Ohm's law says YOU don't want to be the path of least  resistance.

Only problem now is half the time the furnace motor won't cut out after the flame stops. But recycling the power or the slow speed switch on resets the motor to the off state.  Hmmmm.. another Murphy's law.  Perhaps excess dust is insulating the hot air sensor now and reading too is offset on the high side from stiction with hysteresis on the threshold . recycling the power seems to fix it... 

I'll let you know if it is the hot air sensor.

 

 

 

 

 

 

Rob Spiegel
User Rank
Blogger
Re: Sparky High Voltage Wiring
Rob Spiegel   11/16/2011 11:06:00 PM
NO RATINGS
Thanks OhmsLaw,

I really appreciate these Sherlock postings. But I still need your name.

 

Rob Spiegel
User Rank
Blogger
Re: Sparky High Voltage Wiring
Rob Spiegel   11/18/2011 12:19:35 PM
NO RATINGS
Hi OhmsLaw,

You can send along your name (for the Sherlock posting) by email if you like:

 

rob.spiegel@ubm.com

 

Thanks much.

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More Blogs from Sherlock Ohms
Sherlock Ohms highlights stories told by engineers who have used their deductive reasoning and technical prowess to troubleshoot and solve the most perplexing engineering mysteries.
Sherlock Ohms highlights stories told by engineers who have used their deductive reasoning and technical prowess to troubleshoot and solve the most perplexing engineering mysteries.
Sherlock Ohms highlights stories told by engineers who have used their deductive reasoning and technical prowess to troubleshoot and solve the most perplexing engineering mysteries.
Sherlock Ohms highlights stories told by engineers who have used their deductive reasoning and technical prowess to troubleshoot and solve the most perplexing engineering mysteries.
Sherlock Ohms highlights stories told by engineers who have used their deductive reasoning and technical prowess to troubleshoot and solve the most perplexing engineering mysteries.
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