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Unread 11-26-2012, 05:55 PM   #1
ChrisZX2
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'98 Jeep not getting right volts to coil

Here is the more detailed thread I posted on wrangler fourms: http://www.wranglerforum.com/f5/98-j...ml#post3010408

Here is a summery;

98 Jeep wrangler, 2.5. Started dieing randomly when hitting bumps, replaced fuel pump, didn't fix it. Replaced old clogged muffler, and it ran great for a month, but now would not fire with A/C or heater on, would have to turn them off, start jeep, then could turn them on. Now the jeep stopped firing all together.

Replaced CPS, no change. Traced the problem to the two coil wires (that give it power).

From what I read, orange wire is positive, green wire is pulsing ground. Tried new ECU, no change. ASD is good, all fuses good. All connectors good. With old ECU, orange wire gets 12v all the time (one lead on the wire, and one one the pos. battery terminal). The green wire only test .080v when starting, and DOES pulse. New ECU, orange wire acts the same, but the green wire is acting JUST like the orange one, with a consistent 12v (again, testing one lead on the wire, and one one the pos. battery terminal). There is a difference between the ECU's, but nether is working. Could it be BOTH are bad? Seems very unlikely... BTW, at no time have there been any codes, other then for the o2 sensor for cat (sensor 2).

please help......

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Unread 11-26-2012, 08:04 PM   #2
Rubi4MyMrs
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It doesn’t sound like you are checking this right. To check for voltage you need the volt meter connected to the wire being tested & the neg (-) terminal of the battery. You don’t test the neg coil terminal for voltage. There are coil resistance tests & coil & PCM tests for no start conditions in the FSM. Go to this link. Pick your yr then the ignition system chapter.



See online read only FSMs here:
http://www.jeep4x4center.com/knowled...ex.htm#service
You may have to go to the bottom of the page & pick Jeep Resources & online manuals if it directs you to home page rather than the knowledge base.
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Unread 12-05-2012, 12:11 AM   #3
ChrisZX2
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Quote:
Originally Posted by Rubi4MyMrs View Post
To check for voltage you need the volt meter connected to the wire being tested & the neg (-) terminal of the battery.
When doing this, there is no reading at all. I only get a reading with the pos + battery terminal. It's acting like the the positive coil wire, is grounded. Where as the pulsating ground, ether isn't pulstaing with one ECU, and doesn't show much of a reading at all with the other ECU.

Thanks for the link, but it didn't help me much. My last resort before giving up is to pull the dash and look for a short or something (remember, it wasn't stating when the AC or heater was "on").

Thanks for the help.
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Unread 12-05-2012, 02:06 PM   #4
Jonny Jeep
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You will only get postive at the coil for the first two seconds the ignition is turned on or when the engine is cranking or running. Check the orange/dark green wire when somebody is turning the ignition on and off for you.

If you aren't getting 12V at the wire, check for voltage at the socket for fuse 21 in the PDC - again while some body switches the ignition on and off for you. You may have a bad connection either between the ASD relay and fuse 21 or between fuse 21 and the coil/injectors. If you get no voltage at the fuse the bad connection could be in one of the terminals within the PDC, which does happen.

All of the wiring is in the FSMs linked to by rubi4mymrs so the link should have been plenty of help.
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Online factory service manuals (FSMs) and parts lists can be viewed at http://www.jeep4x4center.com/knowledge-base/index.htm
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Unread 12-05-2012, 05:48 PM   #5
Rubi4MyMrs
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Everything JJ says. Some of this is a repeat since he posted as I was typing. But here is some more to test. Fuse 21 is between the ASD & the coil, injectors etc.

When you test the wires at the coil you can get odd readings because of the internal circuit in the coil itself. If you disconnect the wires you won’t get the orange wire seeming grounded for example. If you are not getting 12v at the orange wire you need to find out why not. If the ASD relay is not sending 12v to the coil it is also not sending it to the injectors. That doesn’t mean the relay is bad it can mean its not getting proper signals from the PCM. Also make absolutely sure the fuse 6 in the PDC is good & making good contact with the terminals in the socket. Check it with a meter. Then make sure the #30 terminal in the ASD relay socket has 12v. Then I’m not sure about the ‘98s but in later yrs the ASD will open after a few seconds (signal from PCM) if the key is on but not getting a signal from the crank sensor meaning that the key is on but the starter is not engaged. If this is happening then when you turn the key on (but not to start) to test the ASD it will open & no power to coil (orange wire) etc.

Recheck the 3 connectors at the PCM for pin damage, corrosion or any pins being pushed back into the connector & not connecting fully into the PCM pins.

Make sure the battery is fully charged & the post on the PDC is getting full (battery) voltage.

Make sure fuse 11 in the block behind the glove box is good & making good contact in the block terminals.

If all is good to this point you should be getting 12v at the coil. If not then the PCM is not sending the (ground) signal to the ASD or there is an open wire somewhere.

Once you are getting 12v to the orange wire connect it to the coil. You should still be 12v at the coil terminal.

Now with your test light connected to the positive (+) battery post put the probe on the neg. (-) coil terminal & crank the engine. It should pulse off & on as the engine turns. If not make sure the distributor is turning.

The only common thing I see between engine running & the a/c (not necessarily heat) is fuse 11 circuit. Also possible a bad connection somewhere could be causing a voltage drop when the a/c &/or blower (fan) is running. That is a long shot but possible I suppose.
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