84SE: Common Causes for Blowing "Engine" Fuse in Block?
03-05-19, 09:36 PM
#28
84SE-EGI helpy-helperton
Thread Starter
Ignition Switch has never been replaced / rebuilt.
This is one of my next troubleshooting areas (*in addition to the Trans Harness & Starter grounds...), as the Ignition Switch is what carries current for Start / crank and Run conditions for the Fuel Pump Relay - aka, Circuit Openning Relay.
I'm fairly convinced the Fuel Pump ground is bad on one of the harnesses and is trying to use the FP Relay feed as the ground, instead. That tiny wire is only meant to keep the FP Relay closed, not serve as the ground for 3-5 Amps of current flow. Does this make sense?
I'm fairly convinced the Fuel Pump ground is bad on one of the harnesses and is trying to use the FP Relay feed as the ground, instead. That tiny wire is only meant to keep the FP Relay closed, not serve as the ground for 3-5 Amps of current flow. Does this make sense?
03-10-19, 11:44 PM
#29
84SE-EGI helpy-helperton
Thread Starter
Fixed!
First off, I want to thank all you guys who posted here with advice and things to look for, especially about building a Test Light rig to help me narrow down electrical shorts. The ongoing help kept me focused on troubleshooting, even as my nerves frayed from trying different things, unsuccessfully.
It turned out to be a loose ground at the main engine ground connected to the Starter bolt. This is the single largest negative ground cable in the system, and the nut holding the ground in place was finger tight, but not making good contact. I removed the nut and terminal, cleaned them up, along with the Starter lug that they attach to so that they'd make a solid connection, and then fixed the Black w/Red Trace wire between the E-F Harness and the Circuit Opening Relay. Installed the correct 20 Amp fuse, and turned the key. Fuse held, so turned to Start. Fired right up!
What happened is that the ground at the Starter came loose over time, lost contact as the primary ground for the electrical system, and the Fuel Pump was trying to find ground to carry the load. The only available circuit was through the Circuit Opening Relay (*aka Fuel Pump Replay) where a thin wire ground is used to operate the relay from the E-F Harness to keep the Fuel Pump running. This thin wire ground for the Relay isn't designed to carry that much current and was blowing the Fuse. Connection of the big ground at the Starter restored the primary circuit, allowing the Fuel Pump Relay to function at it's designed voltage and current, and allowing the Fuel Pump to operate using the correct ground which was designed for around 10-12 Amps, max.
I ran the car long enough to warm it up thoroughly and avoid flooding due to short start and shutdown, and it restarted several times in testing the fix.
Once again, my thanks to the board members for your assistance and patience. I've been driving a 1st Gen for 35yrs (an SA and this FB), and this has been the most frustrating experience to locate something so simple as a ground connection...
It turned out to be a loose ground at the main engine ground connected to the Starter bolt. This is the single largest negative ground cable in the system, and the nut holding the ground in place was finger tight, but not making good contact. I removed the nut and terminal, cleaned them up, along with the Starter lug that they attach to so that they'd make a solid connection, and then fixed the Black w/Red Trace wire between the E-F Harness and the Circuit Opening Relay. Installed the correct 20 Amp fuse, and turned the key. Fuse held, so turned to Start. Fired right up!
What happened is that the ground at the Starter came loose over time, lost contact as the primary ground for the electrical system, and the Fuel Pump was trying to find ground to carry the load. The only available circuit was through the Circuit Opening Relay (*aka Fuel Pump Replay) where a thin wire ground is used to operate the relay from the E-F Harness to keep the Fuel Pump running. This thin wire ground for the Relay isn't designed to carry that much current and was blowing the Fuse. Connection of the big ground at the Starter restored the primary circuit, allowing the Fuel Pump Relay to function at it's designed voltage and current, and allowing the Fuel Pump to operate using the correct ground which was designed for around 10-12 Amps, max.
I ran the car long enough to warm it up thoroughly and avoid flooding due to short start and shutdown, and it restarted several times in testing the fix.
Once again, my thanks to the board members for your assistance and patience. I've been driving a 1st Gen for 35yrs (an SA and this FB), and this has been the most frustrating experience to locate something so simple as a ground connection...
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maikelc (03-19-19)
03-11-19, 05:02 AM
#30
ancient wizard...
I would imagine the starter cranks engine noticeably faster now,certain if you had checked running charge voltage at battery previous to your”short”problem you would now find that to be .2-.5 or more volts higher,may or may not see that in running engine voltage shown in voltmeter in dash.
Pretty good bet you’ll see your headlights are a tick brighter than you’re accustomed to.
Pretty good bet you’ll see your headlights are a tick brighter than you’re accustomed to.
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LongDuck (08-02-19)
03-12-19, 12:23 AM
#32
84SE-EGI helpy-helperton
Thread Starter
Starter never seemed phased by it...
But, yeah - everybody go out and clean up your ground at the Starter Mounting Bolt right now. I'll wait here.
03-12-19, 07:55 AM
#33
Waffles - hmmm good
iTrader: (1)
Related but different. I have never replaced my battery cables on my 80 SA. When its really damp and cool out I have been having issues getting the car started.
Raise your hand if you think its the cables? Yeah, I think it is too. I think 40 years out of a set of battery cables is pretty good.
Raise your hand if you think its the cables? Yeah, I think it is too. I think 40 years out of a set of battery cables is pretty good.
03-12-19, 08:51 AM
#34
84SE-EGI helpy-helperton
Thread Starter
Related, but different - Battery Cables...
(Raises hand) I have to admit that these are still the original OEM Battery Cables in my SE, too. I've just never had a reason to change them, and living in the dry desert, there's very little corrosion risk.
I forget who posted the list of AutoZone parts #'s to effectively build new cables from random Battery Cables commonly available, but it was literally about $35 worth of tid bits and done, apart from cutting a section of insulation out of the Negative lead for the body ground at the DS fender apron.
I have installed new Cable Ends several times over the years, though. Might be a good time for that project for both of us,
Also, here's the picture of the SE Circuit Opening Relay (*aka Fuel Pump Relay) for future reference:
I forget who posted the list of AutoZone parts #'s to effectively build new cables from random Battery Cables commonly available, but it was literally about $35 worth of tid bits and done, apart from cutting a section of insulation out of the Negative lead for the body ground at the DS fender apron.
I have installed new Cable Ends several times over the years, though. Might be a good time for that project for both of us,
Also, here's the picture of the SE Circuit Opening Relay (*aka Fuel Pump Relay) for future reference:
Last edited by LongDuck; 03-12-19 at 08:58 AM. Reason: Inserted Picture.
03-12-19, 03:23 PM
#35
ancient wizard...
My Se has original battery positive and negative cables. There is no reason to replace them. I'm fortunate to be 2nd owner of this car now for 26 yrs. Original owner kept it garaged as have i and the wiring throughout is in excellent unmolested condition.
Sometimes battery cables need to be replaced due to corrosion or physical damage. If the cables physically look good,they can be voltage drop tested to determine how much resistance is in the cable. If they test good,there is no reason to replace them,save your money and put it somewhere else,unless you feel the need for shiny new shi*.
I prefer the original look of oe cables and think enough of them to strip them from cars i've scrapped and come across in junkyards. Not all passed testing but many did,they're keepers stashed in my hoarding room.
So test your cables before tossing them aside for something"new" that you have to cobble together that will look like you did just that. If you have to,you have to...
Sometimes battery cables need to be replaced due to corrosion or physical damage. If the cables physically look good,they can be voltage drop tested to determine how much resistance is in the cable. If they test good,there is no reason to replace them,save your money and put it somewhere else,unless you feel the need for shiny new shi*.
I prefer the original look of oe cables and think enough of them to strip them from cars i've scrapped and come across in junkyards. Not all passed testing but many did,they're keepers stashed in my hoarding room.
So test your cables before tossing them aside for something"new" that you have to cobble together that will look like you did just that. If you have to,you have to...
03-13-19, 08:02 AM
#36
Waffles - hmmm good
iTrader: (1)
Good advice Mike. I'll definitely do the voltage drop test before moving forward. Rockauto has decent 4 gauge sets that sell for about $35.00 for all three cables (negative is in 2 pieces).
03-19-19, 02:23 PM
#37
Waffles - hmmm good
iTrader: (1)
Got new cables coming in. I used a battery tender to top up the battery to 13.30 volts on my cheapo HF meter. I then started the car no problem, did a run and came back to the garage. I measured the output from the alternator with + on the B terminal of the alternator and - on the battery post. It showed the alternator putting out 13.80 volts, seems good to me. I then put the + over on the batter terminal and it only measured 12.90 volts going to the battery. I think its safe to say theres a dropped there that shouldn't be there and its probably on the positive cable side. So, new cables and cleaning up all the connections is coming up this weekend. Also adding a extra ground near the alternator on the block to help charging and ignition.
LongDuck, sorry I thread jacked you but thought was useful info.
LongDuck, sorry I thread jacked you but thought was useful info.
03-19-19, 05:11 PM
#38
ancient wizard...
Just reading your post Tim,not type voltage drop test i was suggesting and we were talking about battery cables in that post.
Back to what you just posted..13.8 at alternator and 12.9 at battery. Definitely have something going on there almost 1 volt drop and possibly not battery cable at all. Set your voltmeter up like you described,running car,13.8 at alternator and start working your way back from alternator and follow harness back to main fuselink area and check voltage there.What is it? If it's measurably lower at that connection than at alternator,you have resistance in that section of output wire and/or the connections at each end. If that 13.8 reading follows to that connection then the problem is in the feed wire from battery to fuse link. Check the connection of power wire at fuse link for corrosion or overheating and then work your way back to the battery connection for main feed wire looking for faults.
A solid electrical system that shows 13.8 at alternator(that should be 14.0-14.3 volts at alternator with car running and nothing on)should show less than .5 difference at battery,that's 13.3 and that's initially too low before you start turning accessories on.
Find that 1 volt loss in circuit and you will see that in your headlights at night,it'll look like you put brighter bulbs in.Wipers run faster as well as heater motor,dash lights brighter. I believe you're running an FC alt,your car is definitely not getting near what that unit puts out.
Regarding battery cables...or any circuit you want to voltage drop test. You need to load the circuit,make it work while you're testing it. To test battery cables,disable ignition so car cannot start(fully charged battery) put positive lead of voltmeter on positive battery cable and put negative lead of voltmeter on battery cable lug at starter. Crank the engine and note the voltage reading displayed on voltmeter,what it registers will be the voltage lost from beginning to end of that circuit(wire). Same,same for negative battery cable. Test your cables and post back what you find-before you replace/disturb anything. This is your base line. When done repairs,retest. You can get an exact voltage drop reading in wire from alternator to main fuselink and from there to battery feed for main fuse link the same way. Car running,pos lead of voltmeter on alt output post and negative lead on car side of main fuselink. Identify your problem areas,you don't have to replace everything to improve anything...
Back to what you just posted..13.8 at alternator and 12.9 at battery. Definitely have something going on there almost 1 volt drop and possibly not battery cable at all. Set your voltmeter up like you described,running car,13.8 at alternator and start working your way back from alternator and follow harness back to main fuselink area and check voltage there.What is it? If it's measurably lower at that connection than at alternator,you have resistance in that section of output wire and/or the connections at each end. If that 13.8 reading follows to that connection then the problem is in the feed wire from battery to fuse link. Check the connection of power wire at fuse link for corrosion or overheating and then work your way back to the battery connection for main feed wire looking for faults.
A solid electrical system that shows 13.8 at alternator(that should be 14.0-14.3 volts at alternator with car running and nothing on)should show less than .5 difference at battery,that's 13.3 and that's initially too low before you start turning accessories on.
Find that 1 volt loss in circuit and you will see that in your headlights at night,it'll look like you put brighter bulbs in.Wipers run faster as well as heater motor,dash lights brighter. I believe you're running an FC alt,your car is definitely not getting near what that unit puts out.
Regarding battery cables...or any circuit you want to voltage drop test. You need to load the circuit,make it work while you're testing it. To test battery cables,disable ignition so car cannot start(fully charged battery) put positive lead of voltmeter on positive battery cable and put negative lead of voltmeter on battery cable lug at starter. Crank the engine and note the voltage reading displayed on voltmeter,what it registers will be the voltage lost from beginning to end of that circuit(wire). Same,same for negative battery cable. Test your cables and post back what you find-before you replace/disturb anything. This is your base line. When done repairs,retest. You can get an exact voltage drop reading in wire from alternator to main fuselink and from there to battery feed for main fuse link the same way. Car running,pos lead of voltmeter on alt output post and negative lead on car side of main fuselink. Identify your problem areas,you don't have to replace everything to improve anything...
03-19-19, 06:55 PM
#39
Senior Member
03-19-19, 06:57 PM
#40
Senior Member
i'm glad u figured it out.....hope u didn't push any gray hairs out
03-19-19, 10:48 PM
#41
84SE-EGI helpy-helperton
Thread Starter
The irony was not lost on me on finding it!
Thanks for posting it, and the admonishment about getting grey hair chasing electrical gremlins that are more easily solved by looking at the grounds! I did learn a lot about the wiring diagram, and who knows how that may come in handy in the future. Thanks to all who helped out,
03-21-19, 09:09 AM
#42
Waffles - hmmm good
iTrader: (1)
Just reading your post Tim,not type voltage drop test i was suggesting and we were talking about battery cables in that post.
Back to what you just posted..13.8 at alternator and 12.9 at battery. Definitely have something going on there almost 1 volt drop and possibly not battery cable at all. Set your voltmeter up like you described,running car,13.8 at alternator and start working your way back from alternator and follow harness back to main fuselink area and check voltage there.What is it? If it's measurably lower at that connection than at alternator,you have resistance in that section of output wire and/or the connections at each end. If that 13.8 reading follows to that connection then the problem is in the feed wire from battery to fuse link. Check the connection of power wire at fuse link for corrosion or overheating and then work your way back to the battery connection for main feed wire looking for faults.
A solid electrical system that shows 13.8 at alternator(that should be 14.0-14.3 volts at alternator with car running and nothing on)should show less than .5 difference at battery,that's 13.3 and that's initially too low before you start turning accessories on.
Find that 1 volt loss in circuit and you will see that in your headlights at night,it'll look like you put brighter bulbs in.Wipers run faster as well as heater motor,dash lights brighter. I believe you're running an FC alt,your car is definitely not getting near what that unit puts out.
Regarding battery cables...or any circuit you want to voltage drop test. You need to load the circuit,make it work while you're testing it. To test battery cables,disable ignition so car cannot start(fully charged battery) put positive lead of voltmeter on positive battery cable and put negative lead of voltmeter on battery cable lug at starter. Crank the engine and note the voltage reading displayed on voltmeter,what it registers will be the voltage lost from beginning to end of that circuit(wire). Same,same for negative battery cable. Test your cables and post back what you find-before you replace/disturb anything. This is your base line. When done repairs,retest. You can get an exact voltage drop reading in wire from alternator to main fuselink and from there to battery feed for main fuse link the same way. Car running,pos lead of voltmeter on alt output post and negative lead on car side of main fuselink. Identify your problem areas,you don't have to replace everything to improve anything...
Back to what you just posted..13.8 at alternator and 12.9 at battery. Definitely have something going on there almost 1 volt drop and possibly not battery cable at all. Set your voltmeter up like you described,running car,13.8 at alternator and start working your way back from alternator and follow harness back to main fuselink area and check voltage there.What is it? If it's measurably lower at that connection than at alternator,you have resistance in that section of output wire and/or the connections at each end. If that 13.8 reading follows to that connection then the problem is in the feed wire from battery to fuse link. Check the connection of power wire at fuse link for corrosion or overheating and then work your way back to the battery connection for main feed wire looking for faults.
A solid electrical system that shows 13.8 at alternator(that should be 14.0-14.3 volts at alternator with car running and nothing on)should show less than .5 difference at battery,that's 13.3 and that's initially too low before you start turning accessories on.
Find that 1 volt loss in circuit and you will see that in your headlights at night,it'll look like you put brighter bulbs in.Wipers run faster as well as heater motor,dash lights brighter. I believe you're running an FC alt,your car is definitely not getting near what that unit puts out.
Regarding battery cables...or any circuit you want to voltage drop test. You need to load the circuit,make it work while you're testing it. To test battery cables,disable ignition so car cannot start(fully charged battery) put positive lead of voltmeter on positive battery cable and put negative lead of voltmeter on battery cable lug at starter. Crank the engine and note the voltage reading displayed on voltmeter,what it registers will be the voltage lost from beginning to end of that circuit(wire). Same,same for negative battery cable. Test your cables and post back what you find-before you replace/disturb anything. This is your base line. When done repairs,retest. You can get an exact voltage drop reading in wire from alternator to main fuselink and from there to battery feed for main fuse link the same way. Car running,pos lead of voltmeter on alt output post and negative lead on car side of main fuselink. Identify your problem areas,you don't have to replace everything to improve anything...
Maybe I should write this up in its own thread with my new ground wire install (wires from rockauto) just so folks can easily see all the details. Gems of information sometimes stay buried in various threads and I think its valuable to pull them out and summarize some of them.
03-21-19, 12:38 PM
#43
Copper is copper, it's not really going to "wear out" per say. The protective casing will dry out and crack after many years of heat cycles and flexing from the motor moving within its motor mounts. The terminals will corrode but can be cleaned up with sand paper, a wire brush, a wire wheel, etc. As others have said, follow the electrical path from the alternator bolts, to the transmission bolts, to the starter, to the ground point to the battery. When replacing any of these components it's good to clean off the mating surfaces and wash the bolts of non conductive grease and buildup...and if you painted your engine during a restoration, you'll definitely want to scrape/sand/wirewheel off the paint where the alternator mounts, especially true for any side-mount brackets too.
With that said, I did just replace mine with 2ga high-strand count wire. I'm not sure what gauge the originals are, maybe 4ga? I used some plated wire terminals too. Haven't started the car yet, but I verified the starter motor does work. Jump to post #92 of my build for pics...
https://www.rx7club.com/build-thread.../#post12333857
With that said, I did just replace mine with 2ga high-strand count wire. I'm not sure what gauge the originals are, maybe 4ga? I used some plated wire terminals too. Haven't started the car yet, but I verified the starter motor does work. Jump to post #92 of my build for pics...
https://www.rx7club.com/build-thread.../#post12333857
03-21-19, 01:40 PM
#44
Waffles - hmmm good
iTrader: (1)
True copper doesn't "wear out" but the package as a whole degrades over time. That weakening of the covering starts letting moisture in. That causes corrosion. The corrosion can cause resistance. Resistance reduces the amount of current that can flow. I think it's safe to say after 40+ years, new wires may be in order. Consider this, I didn't have this issue until the recent very damp spells we have had all winter here in Charlotte, NC. Moisture in the air appears to have been some of the culprit here.
Mike, you are correct in that my wipers do work much better now. My fuel pump is noisier too as it sounds like its pumping harder.
Mike, you are correct in that my wipers do work much better now. My fuel pump is noisier too as it sounds like its pumping harder.
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