Fusible link replacement query
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From: Kent, UK
Car: '85 IROC-Z
Engine: 305cid
Transmission: 5-speed
Fusible link replacement query
Ok,
I've had my fusible links burn out again.
Previously, they had burnt out due to a piece of the flywheel cover getting lodged in the nosecone of the starter motor, causing it to jam. I replaced both the fusible links with Dorman 85621 links, although I cut off the crimp and soldered the connection to the circuit, and had to cut off the too-small ring terminals and salvage the existing one.
Annoyingly, they appear to have burnt out again.
My questions:
I think they've burnt out as my car has been very hard to start - I've since learnt this was due to a poor coolant sensor over-advancing the timing, which places a lot of stress on the starter motor to overcome compression. The coolant sensor has been replaced and the car has been much easier to start, however the fusible link has failed now. Could this simply be due to it being weakened by previous stress? If so, I can simply replace the fuselink and carry on without worrying that something else is lurking...
Secondly, why did the fusible link burn out when the starter was under stress? May sound a stupid question, but... the fusible links aren't a part of that circuit, are they? The power to the starter runs from the battery directly to the pole on the solenoid, and then grounds through the motor... so why would the fusible links blow when (in my limited understanding of how electrics work) the 'flow' of electricity doesn't involve the links?
I'm considering replacing the fuselinks with maxi or midi fuses, probably mounted near the battery with a separate power supply directly from the battery, simply so they can be more accessible and more maintainable should I get caught out again. However, will these fuses still blow and protect the car should the starter motor be put under stress again, even though they're nowhere near the starter motor?!
Thanks for my continuing education!
ND
I've had my fusible links burn out again.
Previously, they had burnt out due to a piece of the flywheel cover getting lodged in the nosecone of the starter motor, causing it to jam. I replaced both the fusible links with Dorman 85621 links, although I cut off the crimp and soldered the connection to the circuit, and had to cut off the too-small ring terminals and salvage the existing one.
Annoyingly, they appear to have burnt out again.
My questions:
I think they've burnt out as my car has been very hard to start - I've since learnt this was due to a poor coolant sensor over-advancing the timing, which places a lot of stress on the starter motor to overcome compression. The coolant sensor has been replaced and the car has been much easier to start, however the fusible link has failed now. Could this simply be due to it being weakened by previous stress? If so, I can simply replace the fuselink and carry on without worrying that something else is lurking...
Secondly, why did the fusible link burn out when the starter was under stress? May sound a stupid question, but... the fusible links aren't a part of that circuit, are they? The power to the starter runs from the battery directly to the pole on the solenoid, and then grounds through the motor... so why would the fusible links blow when (in my limited understanding of how electrics work) the 'flow' of electricity doesn't involve the links?
I'm considering replacing the fuselinks with maxi or midi fuses, probably mounted near the battery with a separate power supply directly from the battery, simply so they can be more accessible and more maintainable should I get caught out again. However, will these fuses still blow and protect the car should the starter motor be put under stress again, even though they're nowhere near the starter motor?!
Thanks for my continuing education!
ND
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From: Illinois
Re: Fusible link replacement query
You are right, the fusible links are not in the starter circuit. So that means the even if the starter can't move at all they won't blow. You have a separate issue you need to address. There is most likely an intermittent short causing them to fail.
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Re: Fusible link replacement query
Sounds like this. The Ignition and Headlights are not fused, so maybe start there since those are the only two that really could cause a fusible link to melt, unless you have so many circuits drawing a lot of amps, but not enough to blow the fuse the circuit is on, that is the other thing the fusible link protects
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Re: Fusible link replacement query
Probably from heat. I'm not impressed with of GM's routing of the fusible link wires on early thirdgens...
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Joined: May 2015
Posts: 297
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From: Kent, UK
Car: '85 IROC-Z
Engine: 305cid
Transmission: 5-speed
Re: Fusible link replacement query
Hmm.... I see what you're all saying about the circuits not appearing to be related, but each time the links have blown (assuming that's what's happened again this time!) they've blown on trying to start the car: I turn the car on and the dashboard lights up the MCS starts clicking. Then, as soon as I turn the key, the solenoid clicks and the car goes dead. This suggests to me that it's an overload in the starter circuit that's burning out the fusible links...
I know what you mean about heat down there - I also have headers, which probably doesn't help. The starter motor also seems to struggle when the car is hot, which might also be stressing the circuitry.
I know what you mean about heat down there - I also have headers, which probably doesn't help. The starter motor also seems to struggle when the car is hot, which might also be stressing the circuitry.
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From: Illinois
Re: Fusible link replacement query
Which one(s) are failing? Is it all of them? It sounds like all of them when you say the whole car goes dead. Are they getting physically damaged? Possibly too close to a header tube?
Also it’s not that the circuits don’t appear to be related, they are, they both draw from the same battery and the battery cable. Amperage drawn by the starter motor will not be drawn through the links as they are the feed, and therefore, the start of their respective circuits. Without the links connection at the solenoid the circuits have no difference of potential since the other ends of said circuits are chassis grounds and they obviously cant back flow from a source that isn’t there. This is all assuming everything is connected correctly but honestly I can’t think of a way to connect these in a fashion that would draw starter motor amperage through anything other than the cable. If you look at the diagram, you will see that if you are blowing all of the fuses at once that is very abnormal since they are all feeding different circuits and they would all have to be drawing excessive amperage at the same time for seemingly the same reason or cause on three or four separate circuits. This is almost immediately dismissive of the starter motor stress theory (well the circuit design itself is even more dismissive) since it is only connected and drawing from the same source of the amperage. Now the links are physically in the same location so physical damage to all is a good probability, heat damage is a good probability. If you are blowing one it is almost certainly a short to ground through a failed component or damaged wire. Intermittent being a wire vibrating or otherwise moving a little to run through the insulation and eventually contacting a chassis ground. Loose or dirty/high resistance connections can also cause problems. Even make sure the links have the correct amperage capacity.
Sorry for the long winded response!
Also it’s not that the circuits don’t appear to be related, they are, they both draw from the same battery and the battery cable. Amperage drawn by the starter motor will not be drawn through the links as they are the feed, and therefore, the start of their respective circuits. Without the links connection at the solenoid the circuits have no difference of potential since the other ends of said circuits are chassis grounds and they obviously cant back flow from a source that isn’t there. This is all assuming everything is connected correctly but honestly I can’t think of a way to connect these in a fashion that would draw starter motor amperage through anything other than the cable. If you look at the diagram, you will see that if you are blowing all of the fuses at once that is very abnormal since they are all feeding different circuits and they would all have to be drawing excessive amperage at the same time for seemingly the same reason or cause on three or four separate circuits. This is almost immediately dismissive of the starter motor stress theory (well the circuit design itself is even more dismissive) since it is only connected and drawing from the same source of the amperage. Now the links are physically in the same location so physical damage to all is a good probability, heat damage is a good probability. If you are blowing one it is almost certainly a short to ground through a failed component or damaged wire. Intermittent being a wire vibrating or otherwise moving a little to run through the insulation and eventually contacting a chassis ground. Loose or dirty/high resistance connections can also cause problems. Even make sure the links have the correct amperage capacity.
Sorry for the long winded response!
Last edited by PaulyC; Jun 30, 2018 at 06:43 AM. Reason: Add info
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Re: Fusible link replacement query
as soon as I turn the key, the solenoid clicks and the car goes dead
That's a bad connection in the main battery circuit. The problem is the cable connections to the batt or starter or block, or a bad cable itself, or possibly even a bad batt.
Not a fusible link in any case.
Fusible links are the same thing as fuses, just in a different shape. When they blow, they are then ... blown. They don't repair themselves or grow back. They can be intermittent, especially at the ends, if poorly installed; but that's not your problem in this instance.
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Thread Starter
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Joined: May 2015
Posts: 297
Likes: 2
From: Kent, UK
Car: '85 IROC-Z
Engine: 305cid
Transmission: 5-speed
Re: Fusible link replacement query
Sofa, you were, once again, right on the money.
I had, er... *cough*
erm....
*cough*
not tightened up the battery terminal enough.....
*looks at shoes and shuffles away.....*
I had, er... *cough*
erm....
*cough*
not tightened up the battery terminal enough.....
*looks at shoes and shuffles away.....*
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