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    Sacramento, CA
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    Norton Commandos & other Motorcycles, Various 4WD Trucks, Mechanics and Machining, Welding incl TIG, MIG, O/A Gas, etc., Property Management, Computers and Networking (Linux, Servers, etc),
  1. Just wanted to close this thread out with the resolution so others can hopefully benefit. The owner had purchased a new but cheap Crank Position Sensor as the symptoms pointed to the CPS. That sensor was checked and was just slightly low on the resistance check, and seemed to be putting out ~0.5 VAC when cranking. After miles of wire tracing, and epic growling and gnashing of teeth, another, higher quality CPS was installed, and the Wrangler started up and ran. Moral of the story- don't trust the cheapest part in the list...
  2. Moses, thanks for your suggestions and for all of the invaluable info on your site. That Fluke 1587 meter is interesting, but costs almost more than than the Jeep was purchased for. Honestly, this is a very black and white problem. The Jeep was running and being driven daily, then suddenly there is no spark or fuel signals. The owner and I spent several days cleaning grounds and sensor plugs, and tracing circuits with both resistance readings and audible signal. From all I've read so far (Please correct me!), only the WOT switch has the ability to completely stop the gas injection signal. I've verified that the WOT switch is not closed while we are cranking the starter. I have seen no mention of any condition other than failure of the Crank Sensor (CPS) which would prevent the spark signal while cranking the starter, we have cleaned and verified the sensor leads and tried a replacement part, no luck. The Jeeps owner hauled it to a local professional diagnostic shop but they were also unable to find any other faults. I have done lots of electronic equipment diagnosis from vacuum tubes to modern surface-mount fabrication. I'm confident I can replace any of the components on the ecu board except the microprocessor, but I was hoping someone might have specific information about which components (the large, heat-sinked transistors) on the board are the source of the spark and injection signals and likely to fix the failure if replaced. I guess I'll just wing it, and get a backup replacement from ebay just in case.
  3. Hi Guys! I've scoured these pages the last couple days, but can't find anything that matches my specific dilemma. I have a 1990 Wrangler w/ 150k miles on it, recent acquisition by my future son-in-law. It was running relatively fine, but it quit suddenly on a recent trip. It started cutting out when hitting bumps, then finally quit altogether. After dragging it home, hitting the forums, swapping a few parts, following all the sensor tests and wrapping my head around this TBI setup, I am afraid I have a partially dead ECU. -All ignition parts replaced- Ignition Module, Coil, Wires, Cap and Rotor, Plugs. -The truck will crank the engine just fine, but has NO spark at coil or plugs, and NO gas at the injector. The fuel pump comes on with ignition switch for 1-2 sec, there is fuel in the line at the throttle body, I have not checked fuel pressure yet. -A new CPS was installed, I checked the CPS, 217 Ohms (slightly low), 0.54 VAC while cranking the engine. - All other sensors checked out nominal. There is 5 VDC to the TPS and MAP sensors, so the ECU is not entirely fried. -While tracing the sensor wiring, I found a wire broken internally between the CPS sensor and the ECU (red-white wire tied to pin 28), I'm guessing that was the root cause of the failure. I'm afraid the ECU board may have been damaged in the process of the wire failing while driving. -I am looking for information about what I should be seeing for the output signals for the Ignition Module and Fuel Injector from the ECU. I expect they will be low voltage AC pulses, grounding the DC power supplied to the Ignition Module and the Injector. I have not found any specifications for the AC voltage or pulse duration for either the Ignition at pin 27 or Injector at pin 21 of the ECU. I measured both of these signals while cranking the engine, I got ~0.1 VAC at the injector, and basically zero (0.004 VAC) at the ignition module output. These numbers lead me to believe that the output drivers for these functions are damaged or dead, although I can see no signs of physical damage, no burnt smell, melted traces, cracks, or corrosion anywhere in the ecu components. Is there any function programmed in the ECU which would completely shut down the spark- and injector-outputs based on some combination of other inputs for some safety reason ? Any info on the specific layout of components relating to the Ignition and Injector Drivers in the 1987-1990 ECU would be greatly appreciated! And Thank You to all who have gone before me here, the info trail has been invaluable!!
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