TFI upgrade, blown fuselink

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Johnzi10
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TFI upgrade, blown fuselink

Post by Johnzi10 »

Just finished TFI ignition upgrade and after starting I had a rough idle. Was giving it gas when smelled something and wag shut down. One of the fuseable links was toasted! How do I fix/replace?
2020 Cherokee Limited v6. Wife’s Jeep
2002 Grand Cherokee Laredo Daughters Jeep
1998 XJ Cherokee “the Ghost”
1989 Grand Wagoneer my Covid mental health medicine

Topic author
Johnzi10
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Re: TFI upgrade, blown fuselink

Post by Johnzi10 »

See pics


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2020 Cherokee Limited v6. Wife’s Jeep
2002 Grand Cherokee Laredo Daughters Jeep
1998 XJ Cherokee “the Ghost”
1989 Grand Wagoneer my Covid mental health medicine

Topic author
Johnzi10
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Re: TFI upgrade, blown fuselink

Post by Johnzi10 »

Image
Image


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2020 Cherokee Limited v6. Wife’s Jeep
2002 Grand Cherokee Laredo Daughters Jeep
1998 XJ Cherokee “the Ghost”
1989 Grand Wagoneer my Covid mental health medicine

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Johnzi10
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Re: TFI upgrade, blown fuselink

Post by Johnzi10 »

2redwires, both with a 18 ga fuseable link. Both wires are connected to a round terminal. Connected to starter relay, 89 wag , 360.


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2020 Cherokee Limited v6. Wife’s Jeep
2002 Grand Cherokee Laredo Daughters Jeep
1998 XJ Cherokee “the Ghost”
1989 Grand Wagoneer my Covid mental health medicine

sirrus
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Re: TFI upgrade, blown fuselink

Post by sirrus »

First - find out why did it blow and fix that issue. To replace the fusible link you can get fusible link wire from parts store or amazon, cut the blown link out, put ring terminal on one side and use butt connector to connect it to old wire (real wire, not what remains of fusible link).

At some point I replaced all mine as they were looking bad (chafed and cracked):
Image

Two important things - get correct gauge for fusible link wire (TSM wiring diagrams have it, I’ll check what I used later) and do not replace it with regular wire.
Sometimes we reinvent the wheel not to have more wheels but to have more inventors

1988 Grand Wagoneer - AMC 360 with ProFlo4 MPFI, TF727, NP229 FOR SALE
2021 JLU Willys EcoDiesel - new shiny toy

sirrus
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Re: TFI upgrade, blown fuselink

Post by sirrus »

Checked my Amazon orders, I used 18ga for 3 of them (blue in the pic above) and one 14ga (gray in the pic) for I believe charging wire - last one was replaced later as I upgraded to 150amp alt and that required thicker wire/link (replaced with 6ga wire with 10ga fusible link)

One more thing about new fusible links - keep the length of it about 9 inches, not shorter or longer.
Sometimes we reinvent the wheel not to have more wheels but to have more inventors

1988 Grand Wagoneer - AMC 360 with ProFlo4 MPFI, TF727, NP229 FOR SALE
2021 JLU Willys EcoDiesel - new shiny toy

Topic author
Johnzi10
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Re: TFI upgrade, blown fuselink

Post by Johnzi10 »

I have no idea what fried the link. Has newer alternator (previous owner), I replaced starter relay. Was running when link toasted.
2020 Cherokee Limited v6. Wife’s Jeep
2002 Grand Cherokee Laredo Daughters Jeep
1998 XJ Cherokee “the Ghost”
1989 Grand Wagoneer my Covid mental health medicine
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tgreese
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Re: TFI upgrade, blown fuselink

Post by tgreese »

No one can diagnose this for you remotely. You have to have the Jeep in front of you.

The links are wire that is sized to melt and go open when shorted, before the regular wire in the circuit melts. They have a special insulation around them that contains the melting wire and does not start a fire locally. The link will only melt if it draws too much current, like a fuse. The links are intended to protect the car from a fire when the battery shorts to ground in the event of a catastrophe like a bad wreck.

Do you own a multimeter? Start disconnecting things and see how the resistance to ground through the downstream end of the burnt fusible link changes. Look at the wiring diagram and start with the circuits that are downstream from the link that melted. Go from the link down into each of the circuits, measuring the resistance to ground. You should be able to isolate the problem this way. Note that it takes a lot of current to melt the link, so the change in resistance should be really big once you localize and remove the problem.

You need to fix the problem before you replace the link.
Tim Reese
Maine beekeeper's truck: '77 J10 LWB, 258/T15/D20/3.54 bone stock, low options (delete radio), PS/PDB, hubcaps.
Browless and proud: '82 J20 360/T18/NP208/3.73, Destination A/Ts, 7600 GVWR
Copper Polly: '75 CJ-6, 304/T15, PS, BFG KM2s, soft top
GTI without the badges: '95 VW Golf Sport 2000cc 2D
Dual Everything: '15 Chryco Jeep Cherokee KL Trailhawk, ECO Green
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Johnzi10
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Re: TFI upgrade, blown fuselink

Post by Johnzi10 »

Thanks Tim, I looked at the wiring diagram and the fuse link that fried was the ignition switch wire. Do I check starter solenoid or column switch? I’m such a noob, but appreciative of any help! Have a multimeter, ignorant of proper usage in this application.
2020 Cherokee Limited v6. Wife’s Jeep
2002 Grand Cherokee Laredo Daughters Jeep
1998 XJ Cherokee “the Ghost”
1989 Grand Wagoneer my Covid mental health medicine
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tgreese
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Re: TFI upgrade, blown fuselink

Post by tgreese »

Resistance to ground is an indication of how much current can flow.

If you have a short, that branch of the circuit will have very low resistance to ground, once you isolate it. Isolating the circuits will be the most challenging task.

You understand what I mean by downstream? By convention, current flows from positive to negative. It's the reverse at the atomic level, but you can assume postitive-to-negative without changing the outcome. Upstream will be the source of current (positive), and downstream, at the end, will be a sink (negative). The body steel or the frame is the ultimate sink, since it's connected directly to the battery negative post (negative ground).

You need to find the branch of the circuit downstream of the melted link that is least impeded (lowest resistance) to ground. This should be very low resistance, like 1/10th of an ohm. Low. 1/10th of an ohm will conduct 120 amps at 12V. This is Ohm's law, V=IR. You need something like 100 amps to melt that link, I'd guess.

Normally these circuits will use some reasonable amount of current. If you measure 10 ohms, that's 1.2 amps. Not nearly enough to melt the wire. That circuit is ok.

The bad circuit will have low resistance to ground, very much less than an ohm. It's hard to measure these low resistances accurately, but you don't care. Instead, you want to find the circuit with sufficiently low resistance to melt the link, compared to the others. Once you isolate it from the other circuits, it should be easy to find that circuit, if you measure.
Last edited by tgreese on Sun Jun 06, 2021 6:10 am, edited 2 times in total.
Tim Reese
Maine beekeeper's truck: '77 J10 LWB, 258/T15/D20/3.54 bone stock, low options (delete radio), PS/PDB, hubcaps.
Browless and proud: '82 J20 360/T18/NP208/3.73, Destination A/Ts, 7600 GVWR
Copper Polly: '75 CJ-6, 304/T15, PS, BFG KM2s, soft top
GTI without the badges: '95 VW Golf Sport 2000cc 2D
Dual Everything: '15 Chryco Jeep Cherokee KL Trailhawk, ECO Green
Blockchain the vote.
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tgreese
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Re: TFI upgrade, blown fuselink

Post by tgreese »

Another suggestion: I would get in there with a bright light and inspection mirror and whatever else I needed to inspect every circuit branch downstream from the melted link. You may find the short that way, and you need to get familiar with the circuits anyway.
Tim Reese
Maine beekeeper's truck: '77 J10 LWB, 258/T15/D20/3.54 bone stock, low options (delete radio), PS/PDB, hubcaps.
Browless and proud: '82 J20 360/T18/NP208/3.73, Destination A/Ts, 7600 GVWR
Copper Polly: '75 CJ-6, 304/T15, PS, BFG KM2s, soft top
GTI without the badges: '95 VW Golf Sport 2000cc 2D
Dual Everything: '15 Chryco Jeep Cherokee KL Trailhawk, ECO Green
Blockchain the vote.
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tgreese
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Re: TFI upgrade, blown fuselink

Post by tgreese »

Look here -

https://oljeep.com/gw/elec/89GW_elec/19 ... Switch.jpg

Presuming this is the '89 GW in your sig, the green wire goes to your ignition switch. You installed the TFI upgrade - did you keep the original resistance wire to the coil? Possible your new coil made the ECU fail and short to ground. Usually they would just go open, but it could fail shorted to ground, or try to sink so much current through the coil that it melted the link. Coil failure?

You could unplug the ECU, disconnect the battery, and see what the resistance to ground is at every ignition switch position.
Tim Reese
Maine beekeeper's truck: '77 J10 LWB, 258/T15/D20/3.54 bone stock, low options (delete radio), PS/PDB, hubcaps.
Browless and proud: '82 J20 360/T18/NP208/3.73, Destination A/Ts, 7600 GVWR
Copper Polly: '75 CJ-6, 304/T15, PS, BFG KM2s, soft top
GTI without the badges: '95 VW Golf Sport 2000cc 2D
Dual Everything: '15 Chryco Jeep Cherokee KL Trailhawk, ECO Green
Blockchain the vote.

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Johnzi10
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Re: TFI upgrade, blown fuselink

Post by Johnzi10 »

Thanks Tim. I looked at the same 2 diagrams.the fuse link to the B2 splice is the one that blew. Is access to all the circuits best to get at in the steering column based on the second diagram? As a coincidence, my right turn signal is not operating.
2020 Cherokee Limited v6. Wife’s Jeep
2002 Grand Cherokee Laredo Daughters Jeep
1998 XJ Cherokee “the Ghost”
1989 Grand Wagoneer my Covid mental health medicine

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Johnzi10
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Location: Northern Kentucky

Re: TFI upgrade, blown fuselink

Post by Johnzi10 »

In the spirit of there are no stupid questions, to use multimeter correctly. Set to ohms( which setting?) place red lead on the circuit and black to any good convenient ground and take reading?
2020 Cherokee Limited v6. Wife’s Jeep
2002 Grand Cherokee Laredo Daughters Jeep
1998 XJ Cherokee “the Ghost”
1989 Grand Wagoneer my Covid mental health medicine

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Johnzi10
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Re: TFI upgrade, blown fuselink

Post by Johnzi10 »

Or do I isolate the circuit and place leads from multimeter, one at each end of the circuit?
2020 Cherokee Limited v6. Wife’s Jeep
2002 Grand Cherokee Laredo Daughters Jeep
1998 XJ Cherokee “the Ghost”
1989 Grand Wagoneer my Covid mental health medicine

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Johnzi10
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Re: TFI upgrade, blown fuselink

Post by Johnzi10 »

Your saying check the resistance at the connector from the vehicle to the ECU. Yellow and green are ignition switch and starter relay in to ecu, other is 4wires , 3?to distributor and 1 to coil
2020 Cherokee Limited v6. Wife’s Jeep
2002 Grand Cherokee Laredo Daughters Jeep
1998 XJ Cherokee “the Ghost”
1989 Grand Wagoneer my Covid mental health medicine

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Johnzi10
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Re: TFI upgrade, blown fuselink

Post by Johnzi10 »

So Tim, I understand that a circuit shorted to ground(worn/cracked,etc). The second page you sent shows all the down stream circuits I need to check?
I’m lost on what I’m checking when you say to unplug ecu. Noob.
Do you mean check the circuit resistance at the column switch?
2020 Cherokee Limited v6. Wife’s Jeep
2002 Grand Cherokee Laredo Daughters Jeep
1998 XJ Cherokee “the Ghost”
1989 Grand Wagoneer my Covid mental health medicine

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Johnzi10
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Re: TFI upgrade, blown fuselink

Post by Johnzi10 »

To be clear, I should disco to the ecu and then check each downstream circuit by isolating (remove from switch) then compare resistance of each, with the really low circuit being the one with the short. Then visually inspect or continue to isolate and compare?
2020 Cherokee Limited v6. Wife’s Jeep
2002 Grand Cherokee Laredo Daughters Jeep
1998 XJ Cherokee “the Ghost”
1989 Grand Wagoneer my Covid mental health medicine
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tgreese
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Re: TFI upgrade, blown fuselink

Post by tgreese »

Sorry Johnzi, I'm a bit overwhelmed by your multiple replies. If you don't know how to use a multimeter, there are dozens of YouTube and blog posts that cover it. You will have to take the initiative, learn and think this through. Either that, or pay someone to fix it for you. Check with your local Jeep/4x4 forums for some recommendations.

If you need something more structured, buy one of the many trade books on automotive electrical and read it. Follow along by looking at your Jeep. There are ASE certification text books that will go through it in a more academic way. You should be able to buy a used out-of-date text book cheaply. Check your locak used book stores, or Amazon or Alibris.

https://www.amazon.com/s?k=automotive+e ... =sr_nr_n_2

I suggested some places I might look initially. I would also inspect everything. Refer to the wiring diagram and follow the circuits from the melted link to ground. I would test the new parts I had added. You have the car in front of you - do what reading and learning you need to understand the circuits, measure what you can, and compare that to what your understanding leads you to expect.
Tim Reese
Maine beekeeper's truck: '77 J10 LWB, 258/T15/D20/3.54 bone stock, low options (delete radio), PS/PDB, hubcaps.
Browless and proud: '82 J20 360/T18/NP208/3.73, Destination A/Ts, 7600 GVWR
Copper Polly: '75 CJ-6, 304/T15, PS, BFG KM2s, soft top
GTI without the badges: '95 VW Golf Sport 2000cc 2D
Dual Everything: '15 Chryco Jeep Cherokee KL Trailhawk, ECO Green
Blockchain the vote.
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tgreese
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Re: TFI upgrade, blown fuselink

Post by tgreese »

A side comment about teaching yourself - grade-school education is designed to keep the student engaged, and to shield the student from frustration and confusion while they learn. When you teach yourself, there will be times when you just don't understand, and there is no one to explain it to you. I have been there many times in my work, but I have continued and became expert in that topic. Indeed, an advanced degree is meant to teach you such independence, and prepare you for independent research.

If you are puzzled or frustrated, just put the issue aside and go on. Take notes, draw pictures, solve problems, whatever it takes to clarify the topic. Keep a notebook of what you did and what the result was. Write down the results of any tests or measurements or observations. This will help you. It's work - you will need to apply yourself to learn any subject that's new to you.

And there is no disgrace in seeking professional help. If you don't have the time or inclination to go this route, pay someone to fix it.

Sorry if this sounds highfalutin or preachy - just trying to be helpful.
Tim Reese
Maine beekeeper's truck: '77 J10 LWB, 258/T15/D20/3.54 bone stock, low options (delete radio), PS/PDB, hubcaps.
Browless and proud: '82 J20 360/T18/NP208/3.73, Destination A/Ts, 7600 GVWR
Copper Polly: '75 CJ-6, 304/T15, PS, BFG KM2s, soft top
GTI without the badges: '95 VW Golf Sport 2000cc 2D
Dual Everything: '15 Chryco Jeep Cherokee KL Trailhawk, ECO Green
Blockchain the vote.
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