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Automotive/Electrical problems with 2000 expedition

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Expert: - 9/11/2007


Question
I recently had to replace my alternator in my wife's car.  After a couple of weeks, the car started hesitating and the lights on dash and instruments start blinking when you are accelerating.  I ended up changing out the alternator again and it seemed fine for a day, then started again.  I have no error codes and no idiot lights on.  Autozone suggested a computer chip, but couldn't be specific and they said I needed to take it to Ford.  The local Ford service center is probably the worst in the world, so I won't go there.  So, what might cause electrical disturbances, that doesn't affect the voltage indicator and gets worse under heavy load?  I know very little about cars, but I am an electrical technician, but don't know where to start.  thanks!!

Answer
Given the relatively widespread problems that occur when they do occur, I would expect that the problem is some type of intermittent in a - perhaps the -  main bus.  Further, your having to replace an alternator on two occasions has me wondering if the intermittent might be an intermittent short circuit to the vehicle "ground" (0V chassis common, actually - I like to stick to the CEC/NEC definition of ground!)  

A high-current short circuit on the main bus or alternator feed would have the effect of dropping the voltage substantially, and would thermally overload the alternator.  The engine hesitation and flickering of lights (which are on separate circuits) also suggests that the fault has an arcing component to it.  From the alternator's point of view, this could be even worse than a bolted fault because of repeated short-term transient fault currents that are quite a bit higher than the steady-state fault current that would flow once a bolted fault was established.  I would imagine that diodes were blown.

Note that I dismiss the possibility of the hesitation and lamp blinking being due to the cycling of an autoreset circuit breaker; your instrument lamps and engine controls are independent circuits on separate protective devices and it be quite a coincidence if two or more separate circuits had separate but similar problems and which also chose to act up simultaneously, time after time.

That the voltage indicator does not drop is rather surprising - some are thermally-activated trend-type meters, and the actual transients may be too short to be picked up by these meters.

If you start from the alternator main terminal and worked forward from there, you will probably find your problem in short (sorry about the pun) order.  It likely will be very visible - burns and scorch marks at the point of the fault, probably in near proximity or direct contact with the feeder.  The insulation probably will be missing, first by chafing or abrasion, and subsequently by melting or burning.

The fact that the problem occurs under acceleration also suggests that the feeder moves into contact with the chassis due to the acceleration.

This does not sound at all like a chip problem, but I would not discount a problem eventually happening due to the power quality problems caused by lots of heavy transients due to arcing faults.

Stick to your electrical roots ... the problem is there!

Happy hunting ... EGK

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Ernest (Ernie) Kenward

Expertise

The challenges I most enjoy are thoughtful technical questions of a trouble-shooting nature in both electrical, power electronic and mechanical systems, mainly automotive but also machine control and small-machine PLC applications. Please note, however, that I am NOT a walking shop manual! I DO, however, make it a point to have those manuals and other service literature for those vehicles I DO own, and highly recommend that anyone serious about maintenance or modification of their vehicles do the same; MOST of your answers WILL be found there. For that matter, I do NOT go out of my way to acquire shop manuals for any vehicle I do NOT own! That being the case, any general query to me along the lines of "What is the meaning of this code read from the ECU of my 2015 XYZ?" or "Where is the fuse for the windshield washer pump found?" (try your car's electrical distribution panel for a start!) will not go far. What I do offer is a pretty good collection of literature, insights and hands-on experience with 1950s to 1980's Ford products (plus a developing database of information and practice with the Mercedes diesel cars), along with an engineering perspective and the ability to design and implement custom control, electrical and mechanical subsystems for vehicles. For that reason, I am happy to make my thoughts and efforts available to those who are of like mind and/or are seriously making a point of learning about their vehicles. Use the Opportunity to Learn!

Experience

A key skill in my work and hobby pursuits both is STRATEGIC TROUBLESHOOTING. I am a senior instructor in Electrical Engineering Technology at a leading Canadian polytechnic, my areas being Electrical Power and Industrial Control, electrical and electronics design and manufacturing, and AutoCAD and related CAD/CAE software - plus equipment problem-solving and new equipment design and prototyping. Hobby-wise, I have 30-plus years of experience in auto restoration, mostly in electrical and mechanical systems. Ongoing projects include a 1959 Edsel Corsair, my 1978 Ford E250 class-B motorhome conversion, and the care and upkeep of my Mercedes 300CD. My vehicles become engineering test beds for electrical and mechanical upgrades as ideas present themselves. This includes the design and production of circuit boards to restore or enhance features for which no OEM replacement parts are obtainable, or where better specifications or reliability can be had via newer concepts. Regarding the E250 RV conversion, I designed and continue to revise a custom power distribution system, managed by a Programmable Controller (PLC); this has made most revisions as easy as uploading new firmware as I develop it. The "mini" PLC is a powerful device for custom automotive control systems. One good example (there are many) would be the Moeller "Easy Relay"; these offer a wealth of control, monitoring and variable-and-status display options for such projects. A good example project which has worked well is that one for my RV noted above, which has been on the job - revised in firmware only - for a decade now. It is a load management and charging control system to avoid the sulfation-induced early failure that often befalls deep-cycle batteries used in RV power applications. The battery installed in 2003 lasted long enough to more tnan pay for the PLC that contributed to its longer life ... and the PLC will be there for the next battery as well!

Organizations
IEEE - senior member ... past WCC Student Activities; SME - senior member ... past chair, greater Vancouver chapter chair 318; Edsel Owners' Club - have served in various capacities on chapter executive during seventies; have been Power and Driveline resource on the Edsel Owners' Club "E-team" for more than a decade.

Education/Credentials
Graduate of UBC

Awards and Honors
Certificates of appreciation from IEEE and SME for work in student and chapter activities

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