2000 4.0 Engine rough stutter, popping, on startup - JeepForum.com
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post #1 of 17 Old 06-24-2020, 01:40 PM Thread Starter
Scott8253
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2000 4.0 Engine rough stutter, popping, on startup

147,000 miles on ode.....Just got back from 3 hour road trip, mostly freeway. Last part was through a torrential downpour. Jeep ran fine. Have had no misfire, idle problems etc in past year. Replaced fuel pump myself last year but not fuel filter. I was doing a skid plate replacement so put in new pump anyways.Records indicated from where I got it that filter was recently changed before I bought it and changed the rusty skidplate so didn't replace filter at that time (and it looked fairly new) Did hear constant whine from around fuel tank when pulling in driveway..fuel filter noise? Now engine is shaking badly on startup and barely running and remains that way...depressing gas pedal does nothing. No check engine light, but a "check gauges" light on. Think my fuel filter maybe bad? or possibly coil pack, plugs or injectors? Just amazed how this all could happen overnight with no previous trouble....Before I start trying to hunt it down like to know what you guys may think to check first....

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post #2 of 17 Old 06-24-2020, 02:35 PM
jtec
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well I always start with checking codes.
Can still have codes and CEL is off.

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #3 of 17 Old 06-24-2020, 08:04 PM
paulvon
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The check gages light can come from low voltage, due to low engine RPM.

Does it run fine after it starts and is in netural?

Use a scan tool to check the throttle position sensor if it is ok. Let us know what the readings are related to engine temperature.

Run the Jeep up to temperature then disconnect the air intake from the throttle body. Spray or pour 1 to 2 ounces of Seafoam in and around the throttle body. It will start to evaporate quickly. Wait 1 hour and see how it runs. If it runs better the issue is a dirty throttle body or idle air controller.

Let us know what happens.

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post #4 of 17 Old 06-24-2020, 09:30 PM
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Check your battery terminals for clean and tight connections. That's always where to start. Also, what's the life of your battery. Always start there with unknown and sudden issues in a WJ.

When was the last time you put fresh copper core plugs in your engine? I'd look at the spark plugs second, if there's a good battery and connections, because the fail rate of a coil rail is rare, but it does happen.

The fact that you're not getting a CEL, BUT getting a CHECK GAUGES is weird, but not unheard of. The voltage regulator is a part of your PCM. So, when your PCM is going bad, voltage is going haywire through your system which can cause symptoms similar to spark plug and coil failure.

Also, this could very well be a Crank Position Sensor problem. We call this the CKP sensor, and when it's going bad, can do all sorts of, and cause all sorts of, weird running, or non-running conditions and symptoms, and may or may not set a CEL or MIL code.

What I just typed may sound like a lot of heartache, but it's not that bad. And not so bad that you can't at least diagnose the problems yourself. If you had a strong running engine one day, and a sputtering, misfiring piece of crap the next, the chances are that something electrical and simple is the culprit. No head changes or lower end rebuilds....

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2004 Rocky Mountain Edition. Froggy Bandit. Wife's Daily Driver. PRISTINE! Stock height and may stay that way.....
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post #5 of 17 Old 06-24-2020, 09:47 PM
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Quote:
Originally Posted by paulvon View Post
The check gages light can come from low voltage, due to low engine RPM.

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Not so much in a WJ, sir. Usually, when the Check Gauges light stays on and there's a voltage issue, it's not because the alternator isn't up to RPM. That's old school. The alternator may be faulty, or wiring may be damaged. Those are more consistent symptoms with voltage related to the alternator(generator).

The alternator in our 4.0 i6 WJs is a balancer and a recharger and is there to operate a lot of electronic stuff according to turn of the (21st) century vehicles. Low RPM in our engines does NOT mean low voltage or amperage output. The alternator keeps cranking current into the PCM. It's the job of the PCM in a 4.0 WJ to accept the influx of voltage and distribute it throughout the vehicle at times of operation. Whether at idle, in Neutral in idle, or over a long trip at cruise control settings of 75MPH+.... In other words, the design and function of alternators changed when we stopped calling them generators back when I was a kid.

The alternator supplies voltage to the PCM which then distributes current throughout the vehicle as needed.

2004 Special Edition WJ. LOADED!
2004 Rocky Mountain Edition. Froggy Bandit. Wife's Daily Driver. PRISTINE! Stock height and may stay that way.....
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post #6 of 17 Old 06-25-2020, 06:26 PM Thread Starter
Scott8253
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I didn't see a TSP check on the code reader I borrowed but will look again. No codes came up on anything. It does seem to run much better in drive and reverse than Park or neutral but still a little rough..going to try the sea foam you suggested next- leaning toward that may be the problem Then rent a fuel pressure tool to check on the rail. I want to avoid replacing fuel filter because to me its a PITA so I'll leave that to last.
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post #7 of 17 Old 06-25-2020, 06:41 PM Thread Starter
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The check gages light goes out in drive or reverse, only on in park with very rough idle. The city I bought it from says they replaced spark plugs at 100,000 but couldnt find records to back it up. (I won it at auction last year with 143,000 miles....) already replaced leaky radiator, oil pan, skid plate, fuel pump, water pump...So also going to look at plugs in meantime and replace. Thanks everyone for suggestions, will see what happens these next few days....
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post #8 of 17 Old 06-27-2020, 05:39 PM Thread Starter
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Rented a code reader and no codes come up. Same day I did the cycle key a bunch of times to see if code comes up on odometer, nothing came up. Went out today and tried the key on off and finally got a p1594 (overvoltage) code. Going to check alternator voltage tomarrow and all the grounds. Also the battery gauge needle remains off when key on but other gages work and odometer mileage flickers sometime at idle . Maybe a dumb question but if regulator on alternator is bad and causing wrong read to PCM then this could cause the super rough idle? Hope I found the cause before I start throwing parts at it....
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post #9 of 17 Old 06-27-2020, 10:47 PM
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Sounds like you have a bad connection somewhere, I would be checking those grounds first. Uniblurb's ground write up is awesome for this.

'00LMTD-4.7l,242hd,D30,D44A,3.73's,True-trac front,Spartan rear,4" short arm lift,JK'sW/32's
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post #10 of 17 Old 06-28-2020, 03:40 AM Thread Starter
Scott8253
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Quote:
Originally Posted by Bigrigr View Post
Sounds like you have a bad connection somewhere, I would be checking those grounds first. Uniblurb's ground write up is awesome for this.
Thanks for putting me on to this ground write-up. Looks like I'll be checking and cleaning all today. Keeping my fingers crossed....
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post #11 of 17 Old 06-30-2020, 12:33 PM Thread Starter
Scott8253
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Quote:
Originally Posted by Mattyjm View Post
Not so much in a WJ, sir. Usually, when the Check Gauges light stays on and there's a voltage issue, it's not because the alternator isn't up to RPM. That's old school. The alternator may be faulty, or wiring may be damaged. Those are more consistent symptoms with voltage related to the alternator(generator).

The alternator in our 4.0 i6 WJs is a balancer and a recharger and is there to operate a lot of electronic stuff according to turn of the (21st) century vehicles. Low RPM in our engines does NOT mean low voltage or amperage output. The alternator keeps cranking current into the PCM. It's the job of the PCM in a 4.0 WJ to accept the influx of voltage and distribute it throughout the vehicle at times of operation. Whether at idle, in Neutral in idle, or over a long trip at cruise control settings of 75MPH+.... In other words, the design and function of alternators changed when we stopped calling them generators back when I was a kid.

The alternator supplies voltage to the PCM which then distributes current throughout the vehicle as needed.
With engine barely idling I get a jumpy 15.6 to 16.6 volts across battery and dim interior lights, flickering odometer light. Only one time did I get a code 1594 (overcharge) and never again. So it looks like alternator is overcharging battery. No codes now...I ordered a PCM. Even if thats not the problem looks like I needed a new one. When I removed the old one the case was open a little in one corner (or not sealed). Can't get the old PCM out of mounting bracket because the 3 torx screws are rusted in solid so rather than drilling out. I got a used mounting bracket and new screws for cheap.

While waiting for PCM I will get alternator tested. If still no go I will start changing plugs, injectors, crank sensor, fuel filter etc. It probably needs or going to need all that stuff anyways since I don't have any service records for where I got it last year. Still think its something electrical that fried since I drove through a 30 minute torrential downpour and then would barely idle the next morning after running fine all the time in past year until morning after the rain.
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post #12 of 17 Old 07-01-2020, 06:29 PM
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I Believe that if your new PCM is a good unit, your problems will be solved. The PCM is your voltage regulator and was most likely damaged by moisture on the inside of the unit.

2004 Special Edition WJ. LOADED!
2004 Rocky Mountain Edition. Froggy Bandit. Wife's Daily Driver. PRISTINE! Stock height and may stay that way.....
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post #13 of 17 Old 07-02-2020, 06:17 AM Thread Starter
Scott8253
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Originally Posted by Mattyjm View Post
I Believe that if your new PCM is a good unit, your problems will be solved. The PCM is your voltage regulator and was most likely damaged by moisture on the inside of the unit.
I ordered a PCM from Flagship One in New York. Day after ordering I read the BBB reviews about this company which were bad.
My bad, so just want to give a heads up to others. I'll post my experience whenever I get the PCM, which according to some reviews, could be a long time.....
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post #14 of 17 Old 07-03-2020, 10:58 AM
Officerfriendly
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Humm interesting
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post #15 of 17 Old 07-03-2020, 11:31 PM
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Waterluver on here is a better source for replacement PCM's It seems.

'00LMTD-4.7l,242hd,D30,D44A,3.73's,True-trac front,Spartan rear,4" short arm lift,JK'sW/32's
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