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Discussion Starter · #1 · (Edited)
**ISSUE RESOLVED - SEE POST #12

I've just finished up replacing all my coil pack connects and wires, and still am having misfires. So, I decided to measure the resistance on each coil.

First off, I know how to use a multimeter, its set to ohms up to 200 and there is no option lower than that. I know my multimeter is good as I tested it with a few resistors that I have laying around my workbench.

With that said, I know pin 1 is ground on each coil so I connected the multimeter's negative to pin one and the positive to pin two. At first I measured all the resistance with the coils still in the car and after the crazy readings I tried them off the car with the same results.

The readings varied from 1.4-1.8 ohms across the board.

So... Am I doing something wrong, or do I have bad coils?

Thanks guys.
 

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Your meter is not nearly good enough to make a ~1 ohm measurement. Off the top of my head the factory specs the primary side at 1 ohm +/- a few tenths.

Plus, you're only checking the primary side, the secondary side has a diode across it so you can't do a resistance check.

Bottom line is that you can't meaningfully check the coils (other than finding a dead open primary) using a DMM, you have to swap with known good ones. FSM says the same thing.
 

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i was wondering the same thing. Spec says hot resistance should be .48-.98 ohms..
mine checked out at 1.1-1.2. Thing is, the 98 MKIV I have been working on, his coils checked out the same as mine. I was actually at Toyota the other day pricing coils for us. So you are saying that my coils may not be bad after all?
 
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Discussion Starter · #4 · (Edited)
Lagtime said:
Your meter is not nearly good enough to make a ~1 ohm measurement. Off the top of my head the factory specs the primary side at 1 ohm +/- a few tenths.

Plus, you're only checking the primary side, the secondary side has a diode across it so you can't do a resistance check.

Bottom line is that you can't meaningfully check the coils (other than finding a dead open primary) using a DMM, you have to swap with known good ones. FSM says the same thing.
Alright.. So I read this and borrowed a "higher-end" multimeter from my neighbor, they all test between .82-.89 ohms now.. Good call. I also went ahead and pulled codes, I got a 13 and a 47. I do have a FSM so I went ahead and read up on the codes, I'm thinking that 47 is related to the eliminated the trac control. As for 13, I don't even know where to begin.. I know it gives me examples of when the error occurs, but I'm not sure what to do.

Could either one of these codes be causing me to misfire?

**Edit.. I searched a little deeper on the forums, and found a few people with similar issues. Unfortunately nobody posted what the resolution was, any ideas guys?
 

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okay, good info. i have a buddy with an EE degree, I'll see if he has the better DMM and try mine too.
 

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SuBTeK said:
^ Whats crappy is I have a $250 fluke that gave me the incorrect readings.. Its usually pretty accurate :(
$250 is a decent hand-held, but not a lab quality benchtop.

At work I have a Datron 1281, that's about $8,000.00, but it will measure 1 ohm in 4-wire to a few ppm.
 

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SuBTeK said:
Alright.. So I read this and borrowed a "higher-end" multimeter from my neighbor, they all test between .82-.89 ohms now.. Good call. I also went ahead and pulled codes, I got a 13 and a 47. I do have a FSM so I went ahead and read up on the codes, I'm thinking that 47 is related to the eliminated the trac control. As for 13, I don't even know where to begin.. I know it gives me examples of when the error occurs, but I'm not sure what to do.

Could either one of these codes be causing me to misfire?

**Edit.. I searched a little deeper on the forums, and found a few people with similar issues. Unfortunately nobody posted what the resolution was, any ideas guys?

The most common cause of Code 13 is being a tooth or two off on the cam gears. Usually happens when the timing belt is replaced, or adjustable cam gears are installed.
 
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Discussion Starter · #9 ·
Alright, thanks again for your help... I appreciate it! I did just change the timing belt at 60k, but a tooth or two really would cause that? Also, I went out about 30 min ago and reved her up slow, when I do that the misfire seems to go away past 3-4k (unless I hover there), but remains at low idle. Between work and school I won't know if its off by a tooth or not till Tuesday.

If you have any other ideas keep throwing them my way, just gives me more things to go after...
 
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your timing is off. redo your timing belt. and check the timing with a timing light make sure its all good. you tps might be off a little bit also due to the trac elim.
 

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A $250 fluke should be more than accurate enough for measuring coil primaries in the . When the coil reading is high, it is because most people make the mistake of forgetting to subtract out the resistance in the meter leads, connections and input. Set the meter to its lowest setting and check the resistance when the positive and negative test leads are connected (with nothing else in line). This number needs to be subtracted from the reading you get when measuring the coil primary resistance. At the end of the day measuring the primary resistance still tells you nothing since primaries rarely fail and if they do they either read open or totally shorted to mass. I think all Supras suffer from a low RPM (idle) miss especially if plugs are colder than stock and gapped less than stock 1.1mm like with BPU. At least mine does. Aggravating but not an issue if it does not cause stalling. If it was a high speed miss I would be more concerned.
 
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Discussion Starter · #12 ·
Just thought I'd give everyone an update...

I took apart the front of my car and found that I was off about 10 degrees on the crank when the cams were @ TDC :( Went ahead and attributed it to an ID 10T error and re-adjusted. Finished up, started her, and no more real misses.. Still stumbles lightly at idle but nothing like before. So I'm figuring between my blunder and the bad wires in the ignition harness everything is pretty good.

Thanks for all the help guys!
 
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