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ToniH
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Viestit: 601
Liittynyt: 26 Loka 2005, 20:34
Auto: Mustang GT 5.0 1995

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Viesti Kirjoittaja ToniH » 04 Maalis 2020, 17:48

ja osien kestävyys. Lukekaas Rockauton Newsletterin uusimmasta juttu "Believe in Bad Grounds".

Kopsataan se tähän jälkipolville:
Believe in Bad Grounds
Tom's Story
I have read manufacturer tips about checking ground connections before replacing electronic parts. I have even written articles about checking ground connections, adding ground wires, and using voltage drop testing before replacing parts. But despite all my wisdom, I still went ahead and unnecessarily replaced the Engine Control Module (ECM is Ford's EEC-IV) on my wife's 1993 Ford Tempo when the ECM really "just" had a ground connection problem.

A Hemmings article on Ford's EEC-IV says it is known for "extreme sensitivity to ground circuit issues" and "a high-impedance ground would drive it crazy." Rather than feeling too guilty for not practicing the grounding rules that I preach, I feel like the "crazy" EEC-IV has taught me additional Yoda-level grounding knowledge that is valuable to owners of other computer-equipped vehicles.

Parts that temporarily "fixed" the problem
1. With grounding problems, new parts may bring relief, but that relief may also be increasingly short lived. A grounding problem can persist for years. Replacing parts can temporarily fix/hide the problem for years as well. Disconnecting/reconnecting electrical connectors, removing/reinstalling mounting bolts and/or a fresh, completely in-spec. part might be enough to improve the ground connection. But, the root-cause grounding problem might still be there and possibly worsening.

The fuel pump in my wife's Ford would stop (no sound from fuel tank). A new Ignition Starter Switch fixed the problem for a few years and a new Fuel Pump fixed the problem for a few more years, cleaning the electrical connector on the Body Control Module (BCM contains the fuel pump relay) fixed the problem for another fourteen months, replacing the BCM fixed the problem for two days, replacing the ECM fixed the problem long enough for one round-trip to the grocery store. Forums are full of posts from Tempo, Mustang and other Ford EEC-IV owners with nearly identical stories. They gradually replace all the major parts connected to the circuit, reporting temporary success after every install. Sometimes, they start replacing the same parts for a second time and those new parts fix things for an even shorter period of time or don't help at all.

2. It looks exactly like a desktop computer problem, but that might mean your old PC just had a grounding problem too. After a cold-start, the engine in my wife's Ford would run for about ten minutes and then the fuel pump would shut down. After a minute or two, the fuel pump would come back to life and the engine would restart and run another three minutes. The Ford's OBD I diagnostic connector conveniently has a pin that turns on the fuel pump whenever it is grounded. The fuel pump always ran fine with that pin grounded, so it was not the fuel pump overheating. (The ECM turns on the fuel pump relay by providing a ground, so manually grounding that OBD I connector pin might provide a good ground connection to the fuel pump relay that the ECM no longer has on its own.)

I guessed that an electronic component on the computer's circuit board was overheating, shutting off and restarting after cooling down. That is when I finally replaced the ECM and enjoyed one trip to the grocery store before the fuel pump stalling started again.

Old PCs and laptops also sometimes repeatedly shutdown and restart as they heat up and cool off. The last time I had a PC do that, I called the computer manufacturer and was told to unplug all the cables and hold the computer's power button in for thirty seconds to "drain away static electricity." The PC was not dead, it was just experiencing something similar to a grounding problem.

3. Accept the solution even if you cannot adequately explain it. I spent six long years studying electrical engineering, and I wanted an elegant solution. I had replaced, tested and/or cleaned every part, connector and ground connection I could reach. In the '80s, there is no way Ford Engineers could have known how well every ground path in their EEC IV designs would hold up after thirty years. I decided I would try to enhance their original design.

I took a 12 ft. long battery Jumper Cable (available at RockAuto.com!) and clamped one end to the engine ground near the battery, then with the ignition key on and the car in its broken state, I started clamping the other end of the cable to metal points all over the car while listening for the fuel pump to start up. I had some inconsistent false positives but finally found the sweet spot when I clamped the ground wire onto the large Spare Tire Hold Down bolt in the trunk. With that bolt grounded, the engine/fuel pump stayed running indefinitely and always started up immediately. I am guessing my jumper cable was providing a new ground path for the nearby fuel pump. Maybe the fuel pump's ground path had changed over time, sucking the life out of the sensitive computer's ground path at the front of the car. I would probably have to get my doctorate in electrical engineering to know for sure.

The jumper cables running over the roof of the Ford looked tacky, so I ran some heavy gauge Primary Wire I had on hand from the main engine ground to a new bolt on the firewall and then I ran more wire from the engine ground to three separate new bolts mounted near the spare tire well in the trunk. There was an unused hole and grommet in the right front door jam so the new cable installation is professional-looking and out of sight. All the heavy wire might have been overkill, but I wanted to make sure I did not inadvertently burn up a too-thin wire, and I wanted to be sure that both the computer at the front of the car and the fuel pump at the rear of the car had excellent, independent ground paths.

Tom Taylor,
RockAuto.com
Mustang GT 5.0 '95
Tunturi Start 54cc '73