I have a 1986 Dodge W250 318CID truck that I use to plow snow and do work around town. One day, the truck started running terribly. It had no power, an extremely high idle, and severe knocking.
A quick check revealed that the spark advance was going to 53 degrees before top dead center immediately after starting, and the only method of pulling it back was to apply a 18-inch to 20-inch piece of vacuum to the transducer connected to the electronic module. This was more vacuum than the engine generated at an idle, so using a hand pump was the only way to keep the truck running.
The dealer was unable to offer a solution. A call to the Dodge factory service hotline that dealers use didn't offer any help. The distributor was a standard Mopar component with a Hall effect sensor to trigger the computer and thus fire the ignition coil. There was no vacuum advance on the distributor itself, only mechanical. I wired the advance springs to prevent any centrifugal advance, and the condition remained. I replaced the distributor with one from a 1970s era Dodge Coronet, and everything worked fine, although the advance curve did not meet the factory specification due to different weights and springs.
The only difference was that the drive gear on the bottom of the distributor shaft was bronze on the early unit and steel on the truck unit. The early distributor was completely worn out and not usable without rebuilding, but the difference in the gears appeared relevant. I connected an oscilloscope to the output of the Hall effect sensor and found it was sending out multiple output pulses per cylinder on the truck distributor with both Hall effect sensors, but it was clean on the older distributor.
On a hunch, I dug out an old parts degausser and ran the shaft and gear through the coil, and the problem went away. It appeared the steel gear and shaft were becoming magnetized by the wiping action from the camshaft and caused the Hall effect sensor to get false readings. The local Dodge dealer had found this symptom on several other vehicles, and its fix was to replace all components of the ignition system (distributor, coil, computer) at significant cost. It didn't have a degausser, and I didn't offer to donate mine, so I guess it continued to replace parts. The Dodge factory people seemed politely interested, but I never heard whether they changed the design. I haven't heard about this problem on newer models.
This entry was submitted by Bob Humphreys and edited by Rob Spiegel.
Bob Humphreys received electronics training in the US Navy and then worked as an electronic technician and test engineer in the semiconductor industry for 15 years. He built houses during the occasional layoffs, and he built and repaired boats for more than 40 years until age diminished his ability to continue. He is working as a senior process technician for a medical instrument manufacturer in Maine.
Tell us your experience in solving a knotty engineering problem. Send stories to Rob Spiegel for Sherlock Ohms.
The small block Dodge/Chrysler/Plymouth does not *have* any
gear on the bottom of the distributor! Unlike a Ford/Chevrolet, the gear
is on the oil pump driveshaft and the distributor shaft has only a tang on
the bottom of it's shaft that engages a slot on top of the oil pump shaft. Makes it really easy to remove/replace them as you can only install it one of two ways! Could the author be mis-remembering the manufacturer? No one takes out the oil pump drive shaft when replacing a distributor...
EXACTLY! Newer cars are a nightmare to maintain. Maybe they are somewhat maintenance-free for some 3-5 years, but eventually, a belt, belt tensioner, hose, filter, water pump, or spark-plugs WILL need to be changed... THEN the terrible design job of the factory "geniuses" will be immediately apparent!
I've just finished a "revamp" project on my old 1991 Dodge Spirit R/T, consisting of upgrading the original smallish turbo Intercooler and engine radiator with newer, larger units. These units were less expensive than the original replacements, so I decided to go to as large possible sizes, meant for other makes and models of cars. Taking advantage of the disassembly already done to modify the car, I decided to replace the timing belt and tensioner, the water pump and all the accessories belts. Even when I had to remove a lot of brackets, belt covers, the Air Conditioner Compressor, the Alternator and one engine mount, I had just enough space and clearance to perform all the tasks without too much knuckle chafing and bruising...
But looking at the task of water-pump and timing belt replacement on a 2006 Dodge Stratus is ANOTHER matter! Not only is insufficient space to use any hand tool, but component location and disassembly requirements make that otherwise simple task a complete nightmare, probably requiring the whole engine to be dropped from the car.
What overly optimistic (and dumb) ideas were inside the brain (if any) of the "automotive designers" that create present day automobiles? Can anybody assure that not a single component will fail before warranty ends and needs a difficult and lenghty disassembly before the vehicle is close to its true useful life?
"What's really a total bummer is that his "discovery" went unacknowledged & unrewarded"
Absolutely. This is the penalty for offending the wage slave geniuses 'inside'. Have a wealth of experience in this area.
Solution might be to copyright your solution (& maybe a patent application) (DIY ONLY) - don't waste money on patent attorneys!!!!
Then advise Co you have a solution, cost is $xxxx, disclosure available for $xxx, (or free disclosure with NDA / NCA (Non disclosure agreement / non compete agreement) & 7 days to accept.
Your solution is a very valuable asset & many cos would try to obtain by any means. Many have no qualms about stealing even IP, often advised by their IP counsel to do so - said counsel cognisant that lawyers always win, clients only average 50% win - & that is before costs.
Right now I would like to share some ideas with Fedex - been a customer of theirs for 20 odd years - asked them if I were to disclose it, would they agree to not use ideas without further agreement - reply is (before disclosure ;-) ) 'We do not wish to employ you'.
Newer vehicles have crankshaft position sensors and multiple coils. Not many even have distributors, instead having coils that fire multiple cylinders. Some still use distributors and Hall-effect sensors but not many. Considering the number of trucks, vans and SUV's that had V8 engines with a similar set-up from Chrysler, GM and Ford, there were relatively few that exhibited this problem. The only "unique" aspect of this truck was a 200A alternator, 2 large batteries and a 2000W inverter to power the occasional 115VAC power tool. There may have been eddy-currents drifting around but I was never able to measure anything unusual. This same set-up has run on thousands of marine applications with no ill-effects.
I think this is more an issue of cost rather than the desirable wear feature of steel. It has been my unfortunate experience to machine some different types of bronze that machined as hard as any steel I have come up against. But it is not a cheap substitute and in many cases is hard to justify the expense involved.
One such application involved the weapons industry and the final product had to be Non-sparking, as it was used in a cartridge loading application that involved gun powder. Sparks and gun powder do not mix, so any ferrous material on ferrous material was forbidden, but we still needed the wear characteristics of tool steel. I had to learn more about metallurgy than I ever thought I would need, but in the end the product worked well and the customer was satisfied. Always a good thing.
To back up your remark about no steel being completely without magnitism I remember compass reading when in the Army. You put the compass up to your eye so you could see both the compass needle and the sight wire attached. You lined the needle with the desired azmuth and picked your target with the sight wire. If you did it without removing your steel pot, or laying your weapon aside, the readings were very unreliable. In fact some times the steel pot could pull the needle to which ever direction you looked and if I remember correctly, you might be 10 or 15 degrees off.
I never really questioned from where the original magnetism came, but was well aware of it being there.
As I stated previously, no steel is PERFECTLY unmagnetized. By virtue of entropy, there must be a couple more molecules aligned than exactly 50% in each direction. With the two gears (cam and distributor shaft) rubbing egainst one another, each becomes more and more magnetized over time.
Hall effect sensors incorporate a magent in the design (that's how they work - the Hall sensor senses changes in the magnetic field due to the motion of a distributor cam, "gear" or interruptor wheel). Presumably it's possible for this small magnet to eventually magnetize the distributor shaft, etc.
Another possibility might be a short circuit (or partial short circuit) from the battery to the distributor shaft. Since automobiles use DC, such leakage could cause the shaft to become magnetized over time.
Demagnetization would solve the problem in either scenario, but only temporarily.
Yes, I have magnetized things by rubbing them with a magnet. BUT WHERE did the original magnetism come from? Engine parts are NOT supposed to be magnetic especially gears. And I don't believe that rubbing non magnetic parts with non magnetic parts would cause them to be come megnetized. That was the point.
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