JefCooks Posted February 14 Share Posted February 14 Hi Everyone, I tend to overshare and explain the entire situation in my posts and they can get a little long so if you want the short version, skip to the next paragraph. Over the weekend I was leaving work and my truck wouldn't start. Typical crank no start. I made it to work perfectly fine and had not been having any issues with it so this was really out of the blue. I towed it home and started doing some diagnostics. Air filter is fine and it's getting good fuel so it must be a spark issue. Immediate thought was CPS sensor but it tested good with the multimeter. So I pulled a boot off a spark plug and cranked, no spark. Opened up the distributor cap and everything in there looked good. Tested the wire from coil to distributor and it is only getting intermittent signal. Took the multimeter to the ignition coil and it's getting proper 12V constant and 10+V signal. Secondary resistance is right on but primary resistance is low (.5 Ohm vs .85 Ohm for aftermarket coils). The ignition coil is ~13 months old and I splurged on the Accel coil thinking it would last longer and give better spark, I was wrong. So I got out the 30 yr old oem coil, plugged it in without removing the Accel and the truck fired right up. Turned the truck off, swapped coils, bolted in the OEM coil including an attached cable guide for some loom and a random ground wire but again, the truck wouldn't turn over. I removed the random ground wire from the ignition coil mounting bolts and the truck fired right up. While the truck was running I reattached the ground wire and nothing happened. I turned the truck off and then back on and it started fine. The next morning I was leaving for work and again the truck wouldn't start with the ground wire attached so at this point I think the ground wire is messing something up. It's relatively large gauge and goes immediately into a wire loom so I'm hoping to not tear the loom apart to track this thing down. Does anyone know what that wire grounds out? Thanks Link to comment Share on other sites More sharing options...
cruiser54 Posted February 14 Share Posted February 14 Of all the stuff you shared, you left out make, model and year. Link to comment Share on other sites More sharing options...
cruiser54 Posted February 14 Share Posted February 14 Link to comment Share on other sites More sharing options...
JefCooks Posted February 14 Author Share Posted February 14 It’s in my signature but it’s a ‘92 4.0 AW4 4x4 Link to comment Share on other sites More sharing options...
Duncan Moody Posted March 15 Share Posted March 15 On 2/13/2024 at 11:09 PM, JefCooks said: Hi Everyone, I tend to overshare and explain the entire situation in my posts and they can get a little long so if you want the short version, skip to the next paragraph. Over the weekend I was leaving work and my truck wouldn't start. Typical crank no start. I made it to work perfectly fine and had not been having any issues with it so this was really out of the blue. I towed it home and started doing some diagnostics. Air filter is fine and it's getting good fuel so it must be a spark issue. Immediate thought was CPS sensor but it tested good with the multimeter. So I pulled a boot off a spark plug and cranked, no spark. Opened up the distributor cap and everything in there looked good. Tested the wire from coil to distributor and it is only getting intermittent signal. Took the multimeter to the ignition coil and it's getting proper 12V constant and 10+V signal. Secondary resistance is right on but primary resistance is low (.5 Ohm vs .85 Ohm for aftermarket coils). The ignition coil is ~13 months old and I splurged on the Accel coil thinking it would last longer and give better spark, I was wrong. So I got out the 30 yr old oem coil, plugged it in without removing the Accel and the truck fired right up. Turned the truck off, swapped coils, bolted in the OEM coil including an attached cable guide for some loom and a random ground wire but again, the truck wouldn't turn over. I removed the random ground wire from the ignition coil mounting bolts and the truck fired right up. While the truck was running I reattached the ground wire and nothing happened. I turned the truck off and then back on and it started fine. The next morning I was leaving for work and again the truck wouldn't start with the ground wire attached so at this point I think the ground wire is messing something up. It's relatively large gauge and goes immediately into a wire loom so I'm hoping to not tear the loom apart to track this thing down. Does anyone know what that wire grounds out? Thanks Did you figure this out? Link to comment Share on other sites More sharing options...
JefCooks Posted March 15 Author Share Posted March 15 Not really. I replaced the coil with the original working coil and the same thing was happening. I've read about the Crank Pos Sensor reading right but still not working so I replaced that and it fired right up but died about 30 seconds later. I hooked up a fuel pressure gauge and am getting steady 32psi while running, no excessive leak back with engine off and pressure actually went up as the engine died because of vacuum. I checked resistance on the MAP and Throttle Pos Sensor, both were good and no dead spots on TPS. I just ordered 2 NTK crank sensors because the symptoms improved with the new CPS but since it's still dying I suspect it was a dud. I also ordered an 02 sensor because I don't have an oscilloscope to test mine and even if it's good, a spare would be nice. I'll report back later this week. Link to comment Share on other sites More sharing options...
zomeizter Posted March 17 Share Posted March 17 An electrical schematic will tell you what's connected to your ignition coil... Link to comment Share on other sites More sharing options...
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