1998 GC Laredo 4.0 - question about voltage drop and engine sputters - JeepForum.com
 
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post #1 of 14 Old 02-19-2016, 03:03 PM Thread Starter
dsiglin
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1998 GC Laredo 4.0 - *FIXED* voltage drop and engine sputters

At times while idling my voltage will drop below 14v. I'm guessing this has to do with too low of an idle causing the alternator to not run?

Second and more pressing question - Randomly my engine sputters. No codes have been thrown. Some background on what I've done: Replaced TPS, replaced the Idle Air Control, changed cap and rotor, changed plugs and wires, reset Jeep by grounding positive for 30 seconds, putting Jeep in accessories mode and turning on and off headlights. I've had the fuel pressure checked and it's at 56 with no drop off after car is turned off.

Even with those changes the Jeep sometimes sputters while driving at various speeds (45mph, 30mph). Is it possible a bad O2 sensor could cause the sputtering? Maybe a bad CPS?

Maybe not related but I've noticed that in city driving I get around 11mpg. Seems kind of low given tuneup.

Thanks for your help.


Last edited by dsiglin; 03-12-2016 at 07:56 PM.
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post #2 of 14 Old 02-19-2016, 04:38 PM
JonS
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Read the thread in my signature:


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post #3 of 14 Old 02-19-2016, 04:39 PM
93GCZJ40
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I just had a voltage issue myself, double check to be sure your belt is tightened. It's a 4.0 and the PS pump is your tensioner, as the belt expands over time the tensioner does not compensate for this as the spring tensioner in a V8. My voltage issue was different than yours, but it won't hurt.
As far as the stumble, A lot of people have had success removing the throttle body cleaning it all up really nice and putting it back on, even if it looks clean it may not be.
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post #4 of 14 Old 02-20-2016, 09:38 AM Thread Starter
dsiglin
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93GCZJ - The Throttlebody Position Sensor is new as of two months ago. I had much worse problems - stalling while driving. I replaced the TPS and the spark plugs/wires/rotor/cap and that fixed the stalling while driving. I'll check out the tension on the belt. Should the alternator belt be so tight it doesn't move much? Or should it have some give?

JonS - replacing the TPS and doing a tune up did fix my stalling while driving. So I'm hoping that points to it not being the PCM.
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post #5 of 14 Old 02-20-2016, 10:00 AM
JonS
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[QUOTE=

JonS - replacing the TPS and doing a tune up did fix my stalling while driving. So I'm hoping that points to it not being the PCM.[/QUOTE]

I hope so, but the PCM failures are intermittent. Good luck!


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post #6 of 14 Old 02-21-2016, 11:59 AM
93GCZJ40
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I understand your TPS is new, taking the actual throttle body off and cleaning under it may even further help with the stumble. Most people set their belt to about 1/2 of give or so you can turn it no more than 90 degrees once properly tightened. You'll want to slightly loosen to bolts behind your PS pump, the pivot bolt about the PS pump, the loosen the nut under the PS pump before tightening the adjustment bolt the tighter the bolt the tighter the belt. Not saying this will be a fix but possible, be sure not to over tighten.
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post #7 of 14 Old 02-21-2016, 06:35 PM Thread Starter
dsiglin
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Oh, yeah I forgot to mention I had a shop clean the throttle body and I checked to verify it had indeed been cleaned. It definitely had a ring of crud before cleaning.

"Most people set their belt to about 1/2 of give or so you can turn it no more than 90 degrees once properly tightened."

Forgive me for being dense but what do you mean "turn it no more than 90 degrees"?
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post #8 of 14 Old 02-21-2016, 11:29 PM
93GCZJ40
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Sorry for not clarifying , it means if you take the belt , preferably between the crank and alternator, and turn the belt in you fingers you should be able to turn it no more no less than about 90 degrees
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post #9 of 14 Old 02-27-2016, 09:30 AM
V65Ozzie
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Try disconnecting the front 02 sensor and driving it for a week. it will set a code, but ignore the light. If this solves it, replace the sensor. I spent a year dealing with a sputtering/stumbling issue, read this somewhere, and sure enough......

Retreat? Hell, we just got here......
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post #10 of 14 Old 02-28-2016, 06:32 PM Thread Starter
dsiglin
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Oh, now that's interesting and very cheap to try.
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post #11 of 14 Old 03-01-2016, 07:02 AM Thread Starter
dsiglin
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Unplugged the upstream O2 sensor last night and so we will see if stumbling continues.
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post #12 of 14 Old 03-04-2016, 07:52 AM Thread Starter
dsiglin
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Update. I went ahead and ordered a new O2 sensor because my mileage is so bad. I'm putting it in today or tomorrow.

Something I've noticed. The voltage when running will sometimes be 14.2 and things run fine. Sometimes the voltage will dip and stay down around 14v and that's when it starts acting up. When Autozone tested the alternator it gave them 13.5 which is border line not good. Could this be an alternator on the way out?

The Jeep died at idle yesterday and when I went to start it back up it had a hard time turning over.

Last night I checked battery voltage and it's good. I checked from positive terminal to ground and voltage reads the same as between positive and negative terminal.
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post #13 of 14 Old 03-04-2016, 02:04 PM Thread Starter
dsiglin
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UPDATE to the UPDATE.

I caught the sputter/stumble on video. I was driving and the engine cut out so I fired her back up and parked to see if the engine would stumble again. I got out my multimeter and connected it up to the battery terminals. The voltage did not drop when the engine sputtered. Running the lights I was getting 13.9 volts.

Link to video:
https://drive.google.com/open?id=0B5...FZHT29RRUVid1U
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post #14 of 14 Old 03-12-2016, 07:57 PM Thread Starter
dsiglin
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*THE FIX* - Ignition Coil had three cracks in it. I got lucky on that one, a pretty cheap fix.

I should have inspected it when I changed out the plugs and wires and distributor cap.
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