Tex06 Posted January 1 Author Share Posted January 1 May have found a solution.... time will tell. Looks like by rear tailight ground had corroded a touch, despite the coating I put on it a few years ago. Willing to bet the one I added as per Cruiser54's tips has done the same. Cleaned with the key in the on position when I had a non-start condition (only time it has happened with the temp over 60!) and could hear the pump prime when I reconnected it I'll wait for the next cold snap and if there's no issues I'll declare it fixed (and redo the ground on the pump itself). Link to comment Share on other sites More sharing options...
cruiser54 Posted January 1 Share Posted January 1 Ever seen this? CRUISER'S MOSTLY RENIX TIPS IMPROVING THE FUEL PUMP GROUND JANUARY 3, 2016 CRUISER54 60 COMMENTS The fuel pump and fuel tank sending unit ground at a sheet metal screw up behind the spare tire on an XJ, and behind the driver’s taillamp on an MJ. Not only is a sheet metal screw a lousy way to ground things, this ground path is long and travels through some connectors that are prone to corrosion and moisture. Locate the black wire on the HARNESS side of the fuel pump/sender 3 wire connector. Remove a 6″ length of the split loom covering. Strip back about 1/2″ of insulation from the BLACK wire. Take your new ground wire, preferably at least 14 gauge and 12 to 18 inches long as needed, strip it about 3/4″, and wrap it around the exposed part of the harness plug wire.Solder the connection. Tape it up and reinstall the split loom covering. At the other end of your new ground wire, add a crimp on eyelet. Attach the eyelet under a bolt that goes directly into the chassis. Be sure to clean the attaching point til shiny and apply OxGard to the contact surfaces. Link to comment Share on other sites More sharing options...
Tex06 Posted January 9 Author Share Posted January 9 On 1/1/2024 at 1:46 PM, cruiser54 said: Ever seen this? CRUISER'S MOSTLY RENIX TIPS IMPROVING THE FUEL PUMP GROUND JANUARY 3, 2016 CRUISER54 60 COMMENTS The fuel pump and fuel tank sending unit ground at a sheet metal screw up behind the spare tire on an XJ, and behind the driver’s taillamp on an MJ. Not only is a sheet metal screw a lousy way to ground things, this ground path is long and travels through some connectors that are prone to corrosion and moisture. Locate the black wire on the HARNESS side of the fuel pump/sender 3 wire connector. Remove a 6″ length of the split loom covering. Strip back about 1/2″ of insulation from the BLACK wire. Take your new ground wire, preferably at least 14 gauge and 12 to 18 inches long as needed, strip it about 3/4″, and wrap it around the exposed part of the harness plug wire.Solder the connection. Tape it up and reinstall the split loom covering. At the other end of your new ground wire, add a crimp on eyelet. Attach the eyelet under a bolt that goes directly into the chassis. Be sure to clean the attaching point til shiny and apply OxGard to the contact surfaces. Yup. Did it back in 2016. Re-cleaning the grounds hasn't solved the problem. Still getting no fuel somedays. Isn't fixing it now. Have I mentioned that I hate intermittent electrical issues? Next step is checking my other grounds, I'm starting to wonder if maybe my body isn't grounded well, although that should give me a lot of other issues too. Link to comment Share on other sites More sharing options...
gogmorgo Posted January 9 Share Posted January 9 Forgot to plug in my block heater last night, my MJ cranked a touch slower than normal but fired right up at -28°C. Been a weird winter, this is the coldest morning we’ve had so far. I “fixed” a buddy’s alternator once at the side of the road by adding a 10awg ground wire between the battery and body. Have you noticed if any of your fuses or fusible links might have an issue? I’ve seen fuses fail from vibration or something that causes them to crack, sometimes they connect sometimes not. I feel you though on intermittent issues. Sometimes just poking around will be enough to “correct” a fault, push a loose connection back together or something, and then you don’t really know what happened. Definitely frustrating, makes you want to rip it all out and replace everything. Link to comment Share on other sites More sharing options...
Tex06 Posted January 16 Author Share Posted January 16 On 1/9/2024 at 12:44 PM, gogmorgo said: Forgot to plug in my block heater last night, my MJ cranked a touch slower than normal but fired right up at -28°C. Been a weird winter, this is the coldest morning we’ve had so far. I “fixed” a buddy’s alternator once at the side of the road by adding a 10awg ground wire between the battery and body. Have you noticed if any of your fuses or fusible links might have an issue? I’ve seen fuses fail from vibration or something that causes them to crack, sometimes they connect sometimes not. I feel you though on intermittent issues. Sometimes just poking around will be enough to “correct” a fault, push a loose connection back together or something, and then you don’t really know what happened. Definitely frustrating, makes you want to rip it all out and replace everything. No, I've checked fuses and swapped them when having issues without any success. 28F today and won't start. Drove it last night to the gym right before the temp dropped (was ~60F). Tried cleaning both grounds (taillight one and the one I added to the fuel pump) with no success. Guess I'll pull the tank and replace the pump at this point.... I'm not sure what else I can do. I might try bypassing the resistor again just for the heck of it. Link to comment Share on other sites More sharing options...
Ωhm Posted January 16 Share Posted January 16 Before dropping the tank, run some preliminary voltage checks first. Using a voltmeter or 12vdc testlight (preferred) check for Battery_Voltage_(B+) on the following pins (use battery_negative terminal for ground): D1_5: B+ (Hot at all times) D1_6: At KEY ON only (B+ (Hot for 2-3 seconds)). During CRANK Hot at all times. D2_4: B+ (Hot during KEY ON and Hot during CRANK). Link to comment Share on other sites More sharing options...
Tex06 Posted January 19 Author Share Posted January 19 On 1/16/2024 at 1:04 PM, Ωhm said: Before dropping the tank, run some preliminary voltage checks first. Using a voltmeter or 12vdc testlight (preferred) check for Battery_Voltage_(B+) on the following pins (use battery_negative terminal for ground): D1_5: B+ (Hot at all times) D1_6: At KEY ON only (B+ (Hot for 2-3 seconds)). During CRANK Hot at all times. D2_4: B+ (Hot during KEY ON and Hot during CRANK). Ohm, where are these located? I'm not a Renix year, just fyi. Link to comment Share on other sites More sharing options...
Ωhm Posted January 19 Share Posted January 19 Sorry. Not paying attention. RENIX years only testing here. Disregard. Link to comment Share on other sites More sharing options...
Tex06 Posted Saturday at 02:58 AM Author Share Posted Saturday at 02:58 AM SOLUTION!!!! Finally got cold enough to where I was able to get extended time in the no start condition. Took a troubleshooting tip I found online and grabbed a hairdryer and started heating components I thought were the issue. Idea being, the heat would let the truck start and help me ID the problem. Did this a couple of times, took at least 20 min each time and seemed to be a different component. Well once, I laid my heat gun on the valve cover and almost immediately the fuel pump primed. It had been pointed at the MAP sensor. I tried to replicate this again the next time it failed to start and the truck didn't start at all. Thinking it was another fluke I started tracing out grounds from the relay. I found out if I grounded any of the relays on pin 85 (specifically the fuel pump or ASD), the fuel pump would run, but continuously and the ASD relay would click. At this point I'm testing grounds, checking voltages everywhere I can, and I remember the MAP sensor, so I unplug it and instantly the fuel pump primed. I crank the truck and she starts right up (running rough bc no MAP input). Plug back in, no fuel pressure on the rail, cranks, no start. Verified this twice. Dig thru the parts bin, found an NOS GM MAP sensor I had stashed away, so I verify *again*, not running with current sensor, unplug, and plug into new sensor. Fires right up (not running great, vac line is still on old sensor). Get the new one swapped in, truck fires right up and is idling noticeably another than it has been (had an intermittent stumble at idle if it started when cold). Old MAP was 8 years old from NAPA, swapped in when I had another electrical gremlin. Wrote them a review on it. TLDR: bad MAP sensor was draining power from computer and not allowing truck to start when it was cold outside. Link to comment Share on other sites More sharing options...
Tex06 Posted Saturday at 03:01 AM Author Share Posted Saturday at 03:01 AM Here's a couple pics of the failed MAP. It's Echlin, NAPA's premium brand. Link to comment Share on other sites More sharing options...
Pete M Posted Saturday at 02:49 PM Share Posted Saturday at 02:49 PM Link to comment Share on other sites More sharing options...
schardein Posted Saturday at 05:59 PM Share Posted Saturday at 05:59 PM Wow. Great info and superb work diagnosing it. Link to comment Share on other sites More sharing options...
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