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The symptoms were very odd. This is a '74, with a fresh 383 and a four speed. Electric fans, serpentine belt drive and an MSD round it out. Electric fuel pump puts the gas to a rebuilt from new, Holley 650 DP, with mech. secondaries. The car would start off, running smooth, no problems. But as the temperature got up and stayed that way for awhile, the car started running rougher and rougher, until I feared getting home. At other times, once in awhile, I'd feel the engine go dead for half a second, like a hiccup in the ignition. then it would run just fine. Saturday, I took it out and pulling into the supermarket parking lot to fix the high idle, the car suddenly died, completely? WTF? The fuel pump died and the LED switch to the fuel pump relay was unlit. The car cranked, and the engine light was on in the tach, but still wouldn't start, no fuel pump yet, so I popped the hood and checked the Painless Fuse Box. I pulled a fuse or two looking at it and suddenly everything came to life. So I drove it to the gas station and it seemed to do ok. Got out, left it running just in case. Got back in the car, and turned onto the boulevard. It seemed fine, so I ran it through the gears with conviction and suddenly, it died again! I pulled off onto a side street and popped the hood again. Just as before, the fuel pump was dead, the switch was unlit and it wouldn't start. After about four minutes, suddenly came to life again! Took it home, right away and parked it.
Sunday, I checked the battery terminals and found them a little loose, along with the three direct wires to the MSD box , the junction for the Painless 7 circuit fuse box in the engine compartment and the direct feed from the relay back to the electric fuel pump. Retightened them all and then took it out. It was in traffic and suddenly, the engine backfired while idling, just a pop. That's weird. And as the temp went up after an hour, it just wasn't nearly as smooth as it was, when it was cold. Idling was going up and down and again, started running rough. I got back home and it died, right in the driveway. Same thing, totally dead electrically. That was a clue. Grabbed the Power Probe out of the garage and hooked it up to the power junction on the driver's side and I got 12.7 volts solid, right off the bat. Then I started checking things. Everything runs off the Painless 7 circuit fuse box. The MSD, the relay for the fuel pump,the two fan relays and the AEM air-fuel ratio gauge. None of that was running, so I pulled the rubber cover off and put the probe to the various yellow fuses. Nothing. The Painless has a purple 40 amp input fuse. Put the Power Probe to that and got a solid 12.7 volts across both sides of the fuse. Rechecked the yellow 20 amp fuses that go to all of that and still nothing on the accessory, but a solid 12.7 on the fuses that are always on. Three or four minutes later, suddenly the fuel pump came back on and the fans came on. I became instantly suspicious and put the Power Probe to the yellow fuses and I got what I needed to know. Touching the Power Probe to the yellow fuses showed an intermittent 11.7 volts. Instead of a solid green LED and 12.7 on the LCD meter on the probe, I got 11.7 and a blinking red cross, with the probe beeping along with the pulsing of the cross every 1/4 second or so. I put the probe to the junction I created next to it on the firewall and got a solid 12.7 reading. Then I put the probe to the circuit box ground on the back of the engine manifold and got a solid small green LED in the corner of the probe, telling me that the circuit was good. My determination is that I have bad relay on the Painless Aux Fuse Box that is both intermittent and is only misbehaving when hot. When hot, it is not giving a full 12V to the stuff that depends on it, including the MSD. If the voltage to the MSD is bouncing around, so will the ignition. I have two Painless replacement relays coming from Summit tomorrow and this should fix it. I'll follow up to make sure, that fixes it, but it should. The input voltage to the Painless fuse box is solid, the ground is good, the fuses are good, so the only thing left is the relay.
Don’t you just love intermittent problems? Good job on the diagnosis. I had a similar issue with my electric fan relay. Intermittently the relays would “turn on” but not completely make the connection. You could hear them click but they wouldn’t send out the 12 volts. Fixed that with a couple of new relays and back in business.
Hmm. This is good info. I am having issues with my long running LS 3 swap. It has always just fired up with the touch of the key. Now it is intermittant. Some days it will fire right away. Other days it will just crank. Same thing I have tested all fuses and power to them seems right in line. The fuel pump relay will always click and give me plenty of pressure. I'll swap around relays and see if this helps.
Hmm. This is good info. I am having issues with my long running LS 3 swap. It has always just fired up with the touch of the key. Now it is intermittant. Some days it will fire right away. Other days it will just crank. Same thing I have tested all fuses and power to them seems right in line. The fuel pump relay will always click and give me plenty of pressure. I'll swap around relays and see if this helps.
As you've read here, if you're not getting 12V or more to the system, it's not going to run, or it will have a lot of trouble. What I've done in the past is actually ran long test leads to a multimeter and had the hood open and the multimeter on the front of the windshield so I can see what kind of voltage is going through it, while I'm cranking it. You can get the alligator clipped 4 foot leads for pretty cheap and then use a paper clip to slip it into the fuse. I'd do this on the various relays, every time I started it, on the various circuits. Even if you're just going out for a nice drive, go ahead and do this. If it starts, unclip the leads, stash the multimeter and close the hood and go out and have fun. But until you do this, you won't know.
Better yet, if it doesn't start right up, stop right there and get the Power Probe out and start checking! The condition has to exist to see if it's even there. You'll find the dead one eventually. Are the ignition components getting 12V? Yes, no? The Power Probe hooks right up to the car battery and it will tell you, if there's a poor ground too! Something a multimeter won't do without a lot of trouble.
The Power Probe is $139 from Amazon. If any of you work on your car, this is one of the most valuable tools you'll ever have. It is nice to go under the dash with it and just touch the glass fuses on both sides and get the green light and a solid beep, taking ten seconds instead of ten minutes with a multimeter or having to pull fuses to make sure they didn't fail inside the hidden end. It will tell you instantly, whether your circuit is good or not, even with the key in the off position. It will tell you if you have a bad ground and no it's not all or nothing, it can be poor and barely working. The Power Probe led will flicker, letting you know that the ground is of poor quality. I diagnosed a dune buggy in the shop, that wouldn't start in less than ten minutes, doing just that. It wouldn't start, so I got the Power Probe they had and hooked it up to the battery and started running the probe along the auxillary fuse panel. All the circuits showed poor continuity (poor ground). That took three minutes and then went right to the battery and looked at the negative cable, where it hooked up to the chassis. It had a lot of corrosion! I removed the big bolt and we cleaned it up and reinstalled it and instantly, every circuit showed good ground! Then it wouldn't start, but cranked. Put the Power Probe to the coil, knowing that the coil needed 12V and got nothing! Then I pushed the switch and applied 12V to the coil and it wanted to run, right there and then. We ran a four foot test lead to the coil from the battery and it started right up! That's the power of having a Power Probe! The Power Probe also has two bright LED's on the front, that illuminate at all times, so you can see under the dash. $139 sounds like a lot, but really, considering the hours and hours you're chasing down electrical baloney with a lame-o test light or a tough to use multimeter, it's a god send!
Seems like your Painless fuse box is anything but Painless.....
Stuff happens! It worked fine, for well over a year. I ordered TWO replacement relays. One to install and one to have as a spare. Plus, I still like having an auxillary fuse box to run all the extra stuff, like the MSD, the fans, the AEM air fuel ratio gauge and the relay for the electric fuel pump. Beats trying to tie it all on the single accessory spot on the C3 fuse box!
The Power Probe is $139 from Amazon. If any of you work on your car, this is one of the most valuable tools you'll ever have. It is nice to go under the dash with it and just touch the glass fuses on both sides and get the green light and a solid beep, taking ten seconds instead of ten minutes with a multimeter or having to pull fuses to make sure they didn't fail inside the hidden end. It will tell you instantly, whether your circuit is good or not, even with the key in the off position. It will tell you if you have a bad ground and no it's not all or nothing, it can be poor and barely working. The Power Probe led will flicker, letting you know that the ground is of poor quality. I diagnosed a dune buggy in the shop, that wouldn't start in less than ten minutes, doing just that. It wouldn't start, so I got the Power Probe they had and hooked it up to the battery and started running the probe along the auxillary fuse panel. All the circuits showed poor continuity (poor ground). That took three minutes and then went right to the battery and looked at the negative cable, where it hooked up to the chassis. It had a lot of corrosion! I removed the big bolt and we cleaned it up and reinstalled it and instantly, every circuit showed good ground! Then it wouldn't start, but cranked. Put the Power Probe to the coil, knowing that the coil needed 12V and got nothing! Then I pushed the switch and applied 12V to the coil and it wanted to run, right there and then. We ran a four foot test lead to the coil from the battery and it started right up! That's the power of having a Power Probe! The Power Probe also has two bright LED's on the front, that illuminate at all times, so you can see under the dash. $139 sounds like a lot, but really, considering the hours and hours you're chasing down electrical baloney with a lame-o test light or a tough to use multimeter, it's a god send!
Oh great. Another tool for my tool box. Seriously with fuel injection and all the modern circuits on the LS motors this is a good tool to have.
Oh great. Another tool for my tool box. Seriously with fuel injection and all the modern circuits on the LS motors this is a good tool to have.
It will be one of the best tools you'll ever buy! It has a built in alligator ground clip on a 12" lead alongside the harness, so you can power up fan motors on the bench. You can put voltage or ground, anywhere on the car with the rocker switch. You'll wonder how you ever got along without it.
It will be one of the best tools you'll ever buy! It has a built in alligator ground clip on a 12" lead alongside the harness, so you can power up fan motors on the bench. You can put voltage or ground, anywhere on the car with the rocker switch. You'll wonder how you ever got along without it.
I need it right now. I'm about to burn this car to the ground. It was running and for some reason now the electrical part is not firing. Don't know if it is injectors or spark. These LS motors are like computers to me. They live in a cyber world that cannot be seen.
I need it right now. I'm about to burn this car to the ground. It was running and for some reason now the electrical part is not firing. Don't know if it is injectors or spark. These LS motors are like computers to me. They live in a cyber world that cannot be seen.
A good thing to always have and is very cheap is a Lisle Spark Plug Wire Tester. Unlike most of the testers people use, where they are pulling the boots off, this one, works inductively and you only have to lay the tester next to the wire to see if it has current running through it. The magnetic field from the pulse of high current going through the wire, expands invisibly out from the wire and excites the lamp inside the tester. If it's not starting, stop right there, get out of the car and have somebody crank it over, while you're holding this tool against the wire. That will eliminate that possibility. I've used this tool often and as mentioned, it's a quick way to check all the plug wires while it's running too.
Keep a pad of paper close by and write down your observations or at least track them mentally and then start isolating the various circuits and seeing if you're getting what is supposed to be coming out of them. Check for poor grounds on all your relays. There has to be metal to metal contact and even a coat of fresh paint can disturb that and not let the circuit complete or complete poorly, because if there is no return to the source, whether it's through the car frame or engine block, then there's no circuit and your device, be it a relay or a lamp won't work or work really poorly. Keep in mind, that there are areas of the car that are great grounds (cast iron engine block and the frame are good examples) and areas of the car, that are poor grounds. It could be metal, but if it's mounted on a rubber isolator or fiberglass, that's a sucky ground!
When you get the Power Probe, you can start by checking all the voltages and grounds. Here is a helpful course on the basics and of course, there's a gazillion You Tube videos on how to use this must-have instrument. It is surprisingly easy. I taught one of my Shop Buds in ten minutes how to use it.
Regarding the Power Probe. No need to hook it to the battery, behind the seat. That's a PITA. Instead, use the power junction in the engine compartment for the positive and any good ground for the negative.
I have some of the noid lights on their way also. I have never used the power off the battery. I always use the under hood terminal block plus I have another dist block on the passenger side. Iuse this for the computer feed and fans and so on. I ran a #6 wire off the starter lug to the terminal strip. So I have plenty of "power strips" to use under the hood.
Good deal! Let us know, what you find so we can gain some knowledge from your experience. I'll do the same, when I get the new Painless relay from Summit tomorrow.
Ok, I got the relays from Summit today and before I started, I got the Power Probe out and checked the aux fuse box again. Again, the same broken up voltages across all the fuses, with the ignition on. Replaced the relay with a new one and same thing. Earlier today, the guy from Painless Products told me to check the Circuit Breaker. That's the little square brass box, with the two studs and two bolts sticking out that supplies power to the aux fuse panel. I thought it was just a junction box, but no, it's a circuit breaker. That too, showed wonky voltages on both the input and output terminals. The battery voltage was steady as a rock. So I decided to see if I could isolate this problem and I hooked up a test lead to the power probe, so I wouldn't have to hold it. The other end, went to the junction box and of course, the power probe stayed on, reading 12.7 V. Turned the ignition key on and immediately got beeping and broken up voltages, so I started pulling the fuses out of the aux panel, one by one and on the third one, the intermittent baloney stopped. With the fuse out, I disconnected the power probe and applied it to the empty socket, again, broken up voltages. But and here's a big but... None of the other fuses on the panel were misbehaving anymore! That happened to be the supply to the AEM air fuel ratio gauge, something which had never given me trouble in the three years I had it. So leaving the fuse out, took it for a drive tonight and the car totally behaved.
Now to see why that wire is making the fuse panel and the circuit breaker all weird. But at least I got it isolated now and know what it is. It could be excess resistance or a near short circuit or an unnatural load almost tripping the circuit breaker, but not quite. Something to investigate. With the ignition off, the power probe to the empty socket shows an iffy connection. I'll check that too.
That is kind of what I’m expecting to find. Some odd circuit pulling power out or not grounded very well.
It's going to be something, that's for sure. I was wrong on the relay, but that drove me to the next step: Isolating the problem. Indeed I did find it, but now, I have to find the cause. I'll be using my multimeter now, to test the resistance on that circuit as well as the amperage running through that circuit when it's on.
I figured it out. It was the AEM air fuel ratio gauge that caused the problems. First I checked the ground from the AEM gauge and it showed good. Then I actually disconnected it from the harness cutting the wires under the dash. I put the fuse back in the #3 fuse back and then used the Power Probe on the now disconnected aux fuse power wire and it totally checked good. The disconnected ground wire totally ohm'd good as well With the ground connected directly, I then used the Power Probe directly to the input wire to the gauge and used the switch on the power probe. I got the exact same symptom as at the fuse box. I even ohm'd the gauge harness and it had zero ohms. The pins were all straight too. The conclusion is that I believe the gauge has a internal circuit problem where it's intermittently grounding out the power input wire. Runs great now! The aux panel is totally stable. Problem solved!
06-02-2019, 11:57 PM
The problem was something very weird.
It worked fine, for well over a year. I ordered TWO replacement relays. One to install and one to have as a spare. Plus, I still like having an auxillary fuse box to run all the extra stuff, like the MSD, the fans, the AEM air fuel ratio gauge and the relay for the electric fuel pump. Beats trying to tie it all on the single accessory spot on the C3 fuse box!
It will be one of the best tools you'll ever buy! It has a built in alligator ground clip on a 12" lead alongside the harness, so you can power up fan motors on the bench. You can put voltage or ground, anywhere on the car with the rocker switch. You'll wonder how you ever got along without it.
