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Sktownsend 03-31-2012 02:46 PM

1997 TJ - sputtering problem and volt surge
I just purchased a 1997 TJ with a 2.5 l engine. It has 132k miles. The jeep was recently tuned up and drove home the first half well. (300 miles total). On the second half the volt gauge surged to 19 volts for 2 mins and then went back down to normal. 30 mins later the truck began to sputter on the hwy at 3000 rpms. It sputter for only a second or two and then back to normal. Off the hwy at lower rpms it seemed to be fine.

I drove it today and it seemed to sputter regularly around town and the volt meter is reguarly going to 19 volts and then back down to 14 volts after a few mins time.

I pulled the codes and I am getting code 12, 25, 43, and 46.

Any ideas on what is going on? The voltage spike I would guess is a bad alternator? The sputtering I am confused as this is my first Jeep. I washed the truck today in the driveway and then took it for a test drive and it was sputtering really bad at that point.

What would everyone suggest?

Curro 03-31-2012 02:54 PM

25 Attachment(s)
12 - Direct battery input to PCM was disconnected within the last 50 key-on cycles
25 - A shorted or open condition detected in one or more of the idle air control motor circuits. Actual idle speed does not equal target idle speed.
43 - Misfire detected in one or more cylinders 1 thru 6. (4 and 6 cyls.)
46 - Battery voltage sense input above target charging voltage during engine operation

Sktownsend 03-31-2012 03:29 PM

any suggestions on what to try tackling first?

shockey67 03-31-2012 09:56 PM

Since it was just tuned up, look for the obvious problems first, check to make sure that the cap is not cracked and that the rotor is firmly seated in place. A loose plug or a loosely fitted plug wire can cause the sputtering or someone may have overtightened a spark plug and cracked it slightly. I would change the alternator and inspect the wiring harness near the battery. Some people tend to spray engine cleaner all over the engine before selling the vehicle. Could have shorted the alternator, if the alternator does not fix the problem, simply bring it back. Good luck

The Ugly Jeep 04-01-2012 07:01 AM

I had similar issues. Thought it was wiring. Replaced wiring harness for the engine. Wasn't my problem. Ended up being the coil. Worth a try for $30.

Sktownsend 04-02-2012 12:48 PM

ok gang....what now? I replaced the alternator, I replaced the coil, distributor cap and rotor and the TPS sensor. Back to square one and it seems to be getting worse.

The truck drove out of the driveway and the check engine light went on and is now reading 12, 24,46, 55. The original codes were, 12,25,43,46,55.

The truck is still sputtering intermittently. It runs fine one minute and bad the next minute. After about 15 mins of driving the voltage gauge will spike while the engine is up anything above 2000 rpms. I tried to run out to the battery and check voltage but the gauge will come right back down within 10-15 secs of idling.

Does this make any sense to anyone?


Sktownsend 04-02-2012 07:22 PM

Latest update.

I put the old throttle position sensor back into the truck and code 24 went away. I found a burnt wire on the crank shaft sensor and went ahead and replaced that. I cleared the codes and then took it for a test drive. Ran great! The volt gauge pegged again, however the multi meter I had hooked up to the alt did not read more than 14.7. My guess is the gauge is acting up.

However, dont break out the party hats yet. The jeep was running fine, so I decided to take the family out for dinner 3 miles down the street. The jeep ran fine for 2 miles and then would not idle the last mile. When we returned from dinner I started up the Jeep and it was idling for a minute while we got everyone buckled into the jeep. It then died sitting there. IT WOULD NOT START BACK UP AFTER. First time for this. I waited a few mins, it started back up than ran 1/2 mile and died. It did this 4 more times. The last time it ran fine for the last mile back home. Pulled it into the driveway and it sat their idling for 20 mins. Drove it around the neighborhood. It was fine.

I am completely puzzled at this point. Does it sound like a ECU problem?


Jerry Bransford 04-02-2012 08:13 PM

My guess on the spiking voltage is one or both of the connectors on the battery are either loose or corroded/dirty. Wire brush both posts and connectors until they are bright and shiny then reinstall them and tighten the nuts securely. NO, you can't tell by just looking at them if the connectors are tight/clean or not. This is one of those jobs you just have to do no matter if they look ok or not.

Sktownsend 04-02-2012 09:55 PM

I was reading on some other posts tonight and found that the coolant temp sensor might cause some problems with firing and running. On the way home tonight the jeep ran horrible for 10 mins, then fine again. I restarted the engine later tonight and it was running very poorly and I unplugged the coolant temp sensor and it ran great. Drove it around ran great. Idled great at around 800-900 RPMS, much much smoother. Do you think this would explain some of the rough running and issues and back firing at random times? I was thinking that maybe it was misfiring when the thermostat was being opened past the sensor with either a bad sensor or bad thermostat.

Additionally, the radiator cap was leaking a bit today. The jeep runs about 200-201 degrees on the gauge. What is everyone running for theromstats? Does it make sense to flush the coolant system, replace thermostat with 180 degree stat and replace the coolant temp sensor.

Sktownsend 04-03-2012 06:07 AM


The terminals were cleaned and checked today. Everything is tight, clean, and no wearing of any sort.

LilYeller 04-03-2012 06:33 AM

I had a problem with sputtering and backfiring, but no voltage spike. Mine was the crank position sensor. best of luck to ya.

ClearH2O 04-03-2012 08:01 AM

I have had similar troubles lately and I have a really simple suggestion that takes all of 5 minutes and costs you nothing. Clean the grounding connection on the engine block. It just above and to the left of the distributor cap on the 2.5l. My jeep ran like new after I did this. I took the nut off and then cleaned the metal until I was sure there were good contacts and then reassembled.

So far it is running with none of the problems I was having before (hesitation, backfire, etc).

Sktownsend 04-03-2012 10:19 AM

ClearH20 thanks for the reply. I cleaned all the grounds yesterday without improvement. The truck is now running fine with the coolant temp sensor unplugged. Drives great, sounds great etc.

Would a bad coolant temp sensor cause misfiring, backfiring, rough idle, and hesitation (only when the jeep is warmed up)? After reading some posts it seems that the coolant temp sensor is in charge or regulating fuel with the MAP based on temp of engine.

wedu22 04-03-2012 10:29 AM


Originally Posted by Sktownsend (Post 2214275)
ClearH20 thanks for the reply. I cleaned all the grounds yesterday without improvement. The truck is now running fine with the coolant temp sensor unplugged. Drives great, sounds great etc.

Would a bad coolant temp sensor cause misfiring, backfiring, rough idle, and hesitation (only when the jeep is warmed up)? After reading some posts it seems that the coolant temp sensor is in charge or regulating fuel with the MAP based on temp of engine.

Sktownsend: I have not had this exact issue...With that being said, it sounds like you found your culprit. Sometimes, you have to use the "KISS" rule (keep it simple) kind of thing....You cleaned the battery post, cleaned the grounds (no improvement) but, when you disconnected the "temp sensor" all appears to be working. So, based on that I would go back to the prior "post" you had read before and reread for the "fix" that was used. In this case, probably changing the cap if it is leaking, flushing the system & quite possibly replacing the sensor. Good luck:thumb:

Sktownsend 04-13-2012 07:15 PM


I think I am back up and running now. Knock on wood. The temp sensor did the trick and I also flushed out the antifreeze, new radiator cap and thermostat. It does stumble at idle when kicking down from cold start to warm until you give it has. Then it smooths out and stays constant. Any ideas?

I'm putting a new muffler and tailpipe on this weekend.

The volt gauge is still periodically spiking to 19 volts, but the meter I have us only registering 14.5-14.8. Any ideas what drives the gauge reading?

Thanks for all the help everyone.

Jerry Bransford 04-14-2012 10:16 AM

Your volt meter registers 14.5-14.8 when placed directly on the battery posts but the instrument cluster volt meter is still spiking to 19 volts? Did you ever remove the battery connectors and clean them throughly as I suggested above? A loose/dirty/corroded battery connector can cause the alternator to surge if its sense lead is not firmly and cleanly connected to the battery.

Sktownsend 04-15-2012 07:59 AM


Thanks for the advice. The battery terminals were cleaned, checked for tightness and all looks fine. I'm abit confused why it is still spiking. It does it sporadically. Yesterday it did not do it at all.


Shelby427 04-15-2012 10:13 AM

Carrying on with Jerry's advice, and since you already did the the battery terminals and ground connections. Take a look a two other spots. #1 the battery connection at the under hood relay/fuse box. That's where the feed comes from for the alternator.

Then to the alternator connections, looking for loose or corroded connections.

Like Jerry said, if the battery is reading 14 volts and the gauge is jumping to 19, something is telling the computer that there's low voltage and causing it to spike the voltage out of the alternator.

That's why you never disconnect the battery leads from a late model vehicle.
Alternator needs to see voltage to operate, if it doesn't it can go full output and fry all kinds of things.

DevilDogDoc 04-15-2012 10:19 AM

Was the iac code ever addressed? And what does the battery temp sensor look like? It also contributes to charging voltage. Maybe the battery itself has issues.

Sktownsend 04-16-2012 06:12 AM

The battery itself appears fine on voltage. I am not sure how to check for temperature of the battery or where the sensor is located. I had to put in a coolant temp sensor in the truck, it then spit back a code for a upstream o2 sensor which went in last night. Now the truck is running perfect. knock on wood! Could the voltage spike be related to some bad sensors?

The voltage spike hasnt come on in a few days now. I will keep everyone posted if it does come back on.

Thanks everyone for the help.

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