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Automotive/1995 Plymouth Neon shuts down

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Expert: - 4/19/2009


Question
My 1995 Plymouth Neon (SOHC,AT) will shut down after 20-30
minutes of driving time.  The engine stops, the tach goes
almost to zero, but the remainder of the gauges work as
expected.  When this happens I have to wait 3-5 minutes
before it will restart.  During this time the dash lights
up as expected, the fuel pump will toggle on and the engine
turns over fine.  It just won't start.  I expect that,
since the fuel pump will run on about every third start
attempt, the fuel is delivered but there is no spark.  The
car will then go another 10-15 minutes before the problem
returns.  (I drive 35 minutes each way to work, so I may
experience the problem 1-3 times each way.)  Before, during
and after each instance there are no OBDII codes or service
light.

The interesting thing to note is that this started
happening when the temperatures warmed up above 65F.  After
a few days coping and trying to locate the problem the
temperatures dropped and the problem disappeared.  Now that
the temps are up again the problem returned.

My only thought is that the ECU contains a self-resetting
PTC fuse and this is tripping off the ECU.  Is this a
possibility?  Are there other possible instances of a PTC?  
How can I diagnose this intermittent problem?

Answer
My automotive work being largely custom work on "legacy-technology" vehicles, I can only speak generally ...

The very nature of apparent temperature-dependent intermittent problems is that one often has to be both systematic and creative in finding them.

Inasmuch as you appear to have already gotten into the "nitty-gritty" of thinking through the possible problem areas, I could only suggest something that you probably already know: use a can of "freeze mist" (once upon a time that was freon HFC) and selectively cool those susupect areas.  Intermittent connections will frequently identify themselves when subjected to this type of stress.

Good luck ... 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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