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Unread 04-04-2012, 09:30 PM   #16
BlueRidgeMark
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Quote:
Originally Posted by elCapitan28 View Post

I get what you're saying about the welding, that it's probably not the direct cause, (I think a spark to the o2 sensor wire is most likely), but for future readers, I wouldn't really recommend welding on a car without disconnecting. Yes, you can probably do it without problems for your entire life, but that's only "probably." Depending on where you're welding, where you're grounded, etc. it can potentially flow where it shouldn't and fry things. Seen it. Might as well avoid it by taking an extra 20 second to undo a terminal. Low risk, you're right, but a quick fix for 0 risk? Even better.

This is wisdom.


The "Hey, it hasn't hurt me yet, so it must be okay!" approach to life is not.



As for testing continuity, be careful. It's quite possible to have partial continuity. You may be able to pass enough current to light a bulb, but have corrosion in the conductor which limits the amount of current that can flow. This can fool you into thinking that things are okay, when in fact, they are not. When possible, try to test a circuit with a load that is close to what the real circuit will draw. If you can't create an artificial load, look at the symptoms. Such a circuit will show proper voltage, and may even light a bulb, when the normal load is disconnected. However, if you connect the load, you see very low voltage at the same measurement point.

I learned this lesson on a call out to a customer that had a radio that would not work. (A business band two-way radio.) Sure enough, the radio was dead. I checked the fuse out near the battery, and it was fine. I unplugged the radio, and checked voltage at the connector. It was fine. To make a long story short, I found there was hidden corrosion on the battery connection. When I checked voltage with a multimeter, it looked fine. But when the radio was plugged in, checking voltage at the same point showed close to zero.

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Unread 04-04-2012, 10:35 PM   #17
elCapitan28
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Thanks for the explanation, BlueRidgeMark, but I'm still left a bit confused. I posted the ohms reading from the continuity test with the key off and on. Are you saying to test it when the car is actually running?

And if so, I'm still lost about what the reading actually means. What reading would tell me the fusable lead is still good, and what reading would tell me it's no longer good?

Thanks, everyone
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Unread 04-04-2012, 11:58 PM   #18
Reptile
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Quote:
Originally Posted by BlueRidgeMark View Post
As for testing continuity, be careful. It's quite possible to have partial continuity. You may be able to pass enough current to light a bulb, but have corrosion in the conductor which limits the amount of current that can flow. This can fool you into thinking that things are okay, when in fact, they are not. When possible, try to test a circuit with a load that is close to what the real circuit will draw. If you can't create an artificial load, look at the symptoms. Such a circuit will show proper voltage, and may even light a bulb, when the normal load is disconnected. However, if you connect the load, you see very low voltage at the same measurement point.

I learned this lesson on a call out to a customer that had a radio that would not work. (A business band two-way radio.) Sure enough, the radio was dead. I checked the fuse out near the battery, and it was fine. I unplugged the radio, and checked voltage at the connector. It was fine. To make a long story short, I found there was hidden corrosion on the battery connection. When I checked voltage with a multimeter, it looked fine. But when the radio was plugged in, checking voltage at the same point showed close to zero.
Good point. Voltage readings don't take into account the amount of current that can actualy go through, that is because voltage testing is just a measure of electrical force.

I believe what you are referring to is conductivity. Continuity and conductivity testing are pretty similar, except one gives a yes or no type of answer, the other gives an actual figure of how strong it is, which will matter if you're going to run a bunch of amps through that wire. The resistance readings that he performed are exactly that.

Quote:
Originally Posted by elCapitan28 View Post
Thanks for the explanation, BlueRidgeMark, but I'm still left a bit confused. I posted the ohms reading from the continuity test with the key off and on. Are you saying to test it when the car is actually running?

And if so, I'm still lost about what the reading actually means. What reading would tell me the fusable lead is still good, and what reading would tell me it's no longer good?

Thanks, everyone
First of, all wires will have some inherent resistance, there is no such thing as a perfect conductor. The resistance will increase with lenght of wire and wire gauge.

I would say your readings are very high for an electrical wire. It only takes a brief look at a wire resistance table to figure that out:

Wire Gauge Resistance per foot
4 .000292
6 .000465
8 .000739
10 .00118
12 .00187
14 .00297
16 .00473
18 .00751
20 .0119
22 .0190
24 .0302
26 .0480
28 .0764

Going back to BlueRidgeMark's comments, wire corrosion could definitely be what's preventing the current to go through. That is because corrosion is not very conductive...
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Unread 04-05-2012, 01:23 AM   #19
elCapitan28
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Quote:
Originally Posted by Reptile View Post
I would say your readings are very high for an electrical wire...

...wire corrosion could definitely be what's preventing the current to go through.
So a high ohm reading on a fusable link is bad? Or is the fusable link good, you're just talking about corrosion on other cables? Because I already replaced all leads and both terminals coming off the battery, and cleaned the end of the ground off the alternator, and any other grounds I could find, with a wire brush.
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Unread 04-05-2012, 12:28 PM   #20
Reptile
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Originally Posted by elCapitan28 View Post
So a high ohm reading on a fusable link is bad? Or is the fusable link good, you're just talking about corrosion on other cables? Because I already replaced all leads and both terminals coming off the battery, and cleaned the end of the ground off the alternator, and any other grounds I could find, with a wire brush.
I'm not very familiar with fusable links, but I doubt they're supposed to have an internal resistance. And assuming they did, the readings shouldn't vary, except with temperature (as current goes through). Otherwise it should be very steady. The fact that you're getting variations by moving the wire around makes it suspectious - either wire or fuse. Corrosion isn't only found at connectors but can also occur inside the wiring. You'd only see it if you remove the insulation.
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Unread 04-05-2012, 01:15 PM   #21
elCapitan28
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Well, the computer should be here today, and I've got another vehicle I can swap out the fusible lead, so I'll try both. If neither of those work, I guess next might be completely replacing the wires from the alternator to fuse box/ground (instead of just cleaning connectors)
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Unread 04-05-2012, 04:34 PM   #22
elCapitan28
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fusable link was good. It definitely was the computer. Replaced it with a used one, and it started and went straight to 14V.

...problem is, after that it shut right back off, and I saw the key light. CRAP. The main computer controls the chipped key, so since my key doesn't match the used computer, it shuts it down.

and dealerships can't flash a used computer. (Or won't) Only sell new.
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Unread 04-05-2012, 04:48 PM   #23
elCapitan28
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Anyone know if there's a way to program a chipped key from a different, used computer? Or (my guess) I'll just need a brand new computer flashed to match the vin
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Unread 04-05-2012, 05:31 PM   #24
CJ7-Tim
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I am greatly surprised that the ECU was faulty. I guess there is a first time for everything.

Do you have chip-in-key (SKIM) anti-theft system on your Cherokee, or do you suspect that the ECU you purchased had it ?

If you have SKIM, unplug the module. Then, an ECU needs to be flashed for your VIN either by the dealership (good luck with that) or by an on-line refurbished ECU seller. Next you need to see the dealership to activate the SKIM feature in your new ECU.

If you install an ECU and the SKIM module is still plugged in, it will lock up your "new" used ECU as if you were trying to steal the Jeep.

Option 2 is remove the SKIM module and install another used non-SKIM enabled ECU. This way, VIN re-flashing and Dealership DRB-III SKIM activation are not needed.


SKIM chip-in-key are gray. SKIM Module.
.
sentry-key-module.jpg  
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Unread 04-05-2012, 10:32 PM   #25
Reptile
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Originally Posted by CJ7-Tim View Post
I am greatly surprised that the ECU was faulty. I guess there is a first time for everything.

Do you have chip-in-key (SKIM) anti-theft system on your Cherokee, or do you suspect that the ECU you purchased had it ?

If you have SKIM, unplug the module. Then, an ECU needs to be flashed for your VIN either by the dealership (good luck with that) or by an on-line refurbished ECU seller. Next you need to see the dealership to activate the SKIM feature in your new ECU.

If you install an ECU and the SKIM module is still plugged in, it will lock up your "new" used ECU as if you were trying to steal the Jeep.

Option 2 is remove the SKIM module and install another used non-SKIM enabled ECU. This way, VIN re-flashing and SKIM activation are not needed.
It is indeed surprising. I would have thought the ECU'd be last on the list.

Wonder if he can find an alarm install shop that's got a DRB tool to input the VIN in ECU and reinitialize the SKIM (might need a PIN to access the secured access mode) if dealer won't...

Quote:
Originally Posted by elCapitan28 View Post
The main computer controls the chipped key, so since my key doesn't match the used computer, it shuts it down.
Is your key GREY?
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Unread 04-06-2012, 08:45 AM   #26
Reptile
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Read this

http://www.jeepin.com/forum/showthread.php?t=64270
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Unread 04-08-2012, 08:48 PM   #27
elCapitan28
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Yes, the key's grey, and like I said, no dealership will flash a used ECU. It's hard enough to find a used ECU for this specific year, make, and model, and none of the parts places I called could tell me whether the ECU had SKIM activated or not.

Reptile, I really appreciate the link you sent. Looks like there's someone out there willing to basically erase the SKIM option from the ECU, which would be really cool. (I HATE chipped keys. So retarded.) Unfortunately, I foresee a couple problems in my circumstances. First of all, since the original ECU was fried, they can't say whether or not they can fix it. If I send them the used ECU I bought, they could certainly remove the SKIM feature, but apparently that's not the only VIN-specific data stored in the ECU, and they'd have no idea what else to change to be sure this used ECU works in my Jeep.

Their service would be perfect for someone with their original ECU in working order that they want to alter. Besides, to be honest, I'm a bit skeptical. $125 to send my ECU all the way to Florida, for them to do something no one in my entire state is able to do? ...when all there seems to be is one testimonial and a kind of crappy website... eh, I've had enough what-ifs with this repair. I'll just shell out the $425 for a new ECU and get it done tomorrow without the doubts. I'm not saying they're a scam, I'm just saying I don't know.

So tomorrow I'll haul the jeep to the dealership (the vehicle has to actually be there, if anyone's curious--programming requires the computer to be connected to the rest of the modules in the vehicle at the same time) and just get this over with.

Thanks for all the help, everyone.
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Unread 04-08-2012, 10:26 PM   #28
Reptile
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Glad we can help. Totally understand you'd be reluctant shipping your ECU to the other side of the country; I'd be too... it's a little bit of a gamble and you won't know for certain it'll work. You're correct, assuming you would want to get rid of SKIM, from what I understand, not setting the VIN in the ECU can cause other issues, including triggering an error code and potential loss of mileage info. I believe the Jeep should still be able to run though, but someone would have to confirm. I personally haven't dealt direcly with SKIM. I only know a little bit about it after researching the security features of my wife's KJ while installing a remote start module on it (to determine whether a transponder bypass module was necessary)... turned out hers didn't have it; I was able to hotwire it with basically a paper clip at the ignition harness.

The most straightforward approach is to go with the dealer. That will cost you more but you shouldn't have to worry about possible complications, that's their job to do it right. Just make sure you know upfront about the costs, get a firm quote so they won't charge you 'we get you front behind' type of fees... I don't trust them in that aspect.

Good luck. Keep us posted!
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Unread 04-09-2012, 10:21 PM   #29
elCapitan28
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Had to leave the vehicle at the dealer for them to flash tomorrow. Will update soon with conclusion.
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Unread 04-11-2012, 06:57 PM   #30
15tcherokee
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Any word on the new ecu? im am still having the same issues, pretty much exactly like you. Dummy question, anyone have a pic of the fusible link for me?
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