2006 Jeep severe miss at 2,400 RPM

Jehu

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#1
My 2006 Jeep Wrangler runs fine until it's been on the road for about 20 minutes or so. It starts with an occasional, minor miss but soon starts bucking severely. I've figured out that, when it does that, it's like a governor that completely cuts off at about 2,400 RPM. When this first happened a few weeks ago, I parked it and ordered a new, bolt-on, exhaust system with all three cats. After I got that installed, I drove it for a couple of days with no problem and then it started up again. I don't believe it's a fuel pump because I can give it all the gas I want up to 2,400 rpm. I can't even "feather" it above that. Vehicle speed doesn't matter. Just engine speed.

Any ideas?
 

kev2

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#2
Whoa slow down no throwing parts at an issue.... get expensive fast.

OK lets start looking at this step by step... follow a plan.
1) Which engine - Hope its the 4.0L- I love that engine.
2) Next important and EASY!! - when you start the vehicle the Ck eng Lite (CEL) should come on for @3seconds then go out.... does it?
We want to take advantage of the on board diagnostics (computer) -
You might take advantage of the FREE scan at Auto Zone type parts stores, write down all the codes they give you. Don't buy, just get codes checked.

Answer 1&2, if you had a scan done, also tell us any other work or mods done to jeep...
DO NOT throw out the old exhaust.
Thats a start- we will get this figured out. Can you use a DVOM, pressure gauge, test light?
 

Jehu

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#3
4. 0 liter. We agree on that. The fact that it was the last year for that motor influenced me to buy.

I didn't want to create a marathon post with this so I didn't include the entire history. About 2 weeks before the initial trouble, I got an engine code P0431. "Warm up catalyst efficiency below threshold (bank 2)" My smog mechanic told me that it may be a sensor (o2 I assume he meant) or it may be a cat. He reset and told me to drive it for a couple of days. If it stays off, I'll get the smog cert. The code came back the next day. From what I understand, it's most likely a weak cat, possibly a bad o2 sensor or exhaust leak. There's no exhaust leak.

I've been driving the Jeep for several days now and the only engine codes I got were the crank / cam sensors which is understandable with all the bucking it did. I believe that the cats were bad because the p0431 still hasn't come back. At least I didn't waste $325 on the new exhaust system. (I hope)

I have my own OBDII reader. I'm handy with my Simpson multimeter hxxp: www. simpson260. com/260-7/simpson_260-7. htm

I have a fuel pressure gauge but I've noticed that the '06 Jeep doesn't have a port like every other EFI Jeep I've had.

The only other thing is the engine light. Mine goes off right when I start the engine. No 3 second delay. Is that significant?

Thanks for the help Kev2
 

kev2

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#4
not clear - light goes off -GOOD, but what of those codes crank cam sensor still there?
GTG
 

Jehu

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#5
I reset those codes. The position sensors (crank and cam) threw error codes. Those showed up after a few episodes of the severe bucking. My Jeep is a stick shift so it gets a little more severe than it would if it were and auto.

Another thing that bugs me: the miss starts small only after it's been driven for about half an hour or more. After a few minutes of slight missing now and then the gremlins abruptly begin the 2,400 rpm limit. It seems like heat buildup may be a factor.
 

billr

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#6
I think those crank and cam error codes mean something, those sensors should work OK no matter how much the engine snorts and sputters.
 

Jehu

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#7
Happened on the way home today. I experimented a little. I kept the revs under 2400 by shifting early and you wouldn't know there was a problem. Then I tried getting up to about 45 and then downshifted so the revs were over 3000. It was like the engine wasn't even running. No bucking or sputtering. I pressed the gas pedal and it was like I was out of gas. As soon as the revs got down around 2400, the bucking started. It's like there's a rev limiter set at 2400.
 
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#8
Had that narrow speed range miss that did drive me nuts. Maybe not your problem, but was with the spark plugs, NGK's to be specific with a poor ceramic to metal seal. Can't explain it, but even showed up on my spark plug tester varying the pressure between 0 to 150 psi, good clean spark until I hit a specific pressure, think it was around 120 psi, above or below that range, got a good spark, but at the precise pressure, nothing.

Was actually getting blowby blowing out the spark. A friend had a similar problem, with six identical part number plugs, except after removing them, one of the six had a different electrode configuration. He replaced that plug and cured his narrow speed range miss.

Really getting back to basics, check your plugs. Yeah, last thing I checked, never ran into this before.
 

kev2

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#9
kinda which came first DTC or drivability issue- I think the drivability issue is the result of a problem with those sensors NOT the sensors codeing as a result of the drivability - dont clear any codes yet, trust me.

OK you have a scanner great, is it capiable of p1xxx codes and does it allow freeze frame view?

Running into an RPM 'wall' some checks I would start with...

Exhaust - you said NEW it is stock replacement - DO you have a Vacuum gauge? for backpressure ck.
Intake - check filter and associated ducting - NO K&N or snorkle please let us know.
FUEL - fuel pressure is a must check - ATTACHED a fuel rail dia - confirm no test port after looking. ........
Item #9 is test port-

Taking a SWAG - have you replaced a gas cap?
 

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Jehu

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#10
The P0431 code is still staying away. I'm pretty sure that the cats needed replaced.

My engine code that comes on after the bucking starts is p0344. I've had that code on other rigs from bad spark plugs but, like you said, cause or effect hasn't been determined. I'll keep watching those.

My scanner is a 5 year old cheapo. I can only read and clear basic codes. I have a new one coming that uses Torque on Droid OS. Amazon says it should be here Tuesday.

I don't have a vacuum gauge. I'll look into acquiring one.

Stock intake. I've researched the benefit of cold air, etc. It didn't seem worth it.

I want to check the fuel pressure. The #9 port on your diagram exists on all my previous Jeeps including two XJ's sitting in my yard but not this one. Maybe there's a sensor that can be interfaced when I get my new scan tool.

Gas cap? Interesting. . . I'll swap with another rig.

I've been running the new exhaust for a few days so I figgered that I should retry the smog. The heater isn't resetting. The mechanic told me that I need to start it cold in the morning and let it run for a few minutes before taking off. The OBD EVAP isn't reset either.
 
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#11
My guess is that you have a "cam sensor/oil pump drive" problem. I suspect that the PCM goes into a "reduced power" mode when this problem occurs.

Check out this ugly link... http://www.jeepforum.com/forum/f9/2005-06-jeep-opda_cps_distributor-failure-1144202/

Looks like Jeep tried a new "synchronizer" design that was no better than the last one.
 

kev2

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#12
DAnica is seeing the same thing I am - as soon as you posted the P0344 code it started coming together..
hope we are wrong.
Strongly suggest you look into jeep TSB E05R, a inssue with OPDA*, you could call chrysler 800#, you will need build date and vin #. Hopefully your the origional owner or have a good dealer - do they still call them 5star?


*Oil Pump Drive Assy- drives the CMP
 

Jehu

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#13
I had that exact sound off and on for years. It never seemed to be a problem other than the annoyance. Could that be what's causing my "rev limiter" problem?
 

kev2

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#14
yes - the PCM is not sure of CMP it defaults... does not know where the cam actually is.
this is an issue that will get $$$ fast

Forget My thoughts of fuel, air or exhaust being a likely issue - This is where to look - p0344

Are you origional owner? -
follow Danica's link as homework -
removing the Assy for an inspection - not for the average DIYer..
 

Jehu

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#15
I'm getting a little depressed here. I am the original owner but the "laughing monkey" sound is supposedly a design weakness from engines made before mine.

The procedure for removing for inspection doesn't look anymore complicated than R&R on a distributor. It even has the oil pump slot that needs to remain aligned.

I'm wondering if there's any danger of losing the oil pump drive over this. Is this a case of "park it until it's fixed"?

I am the original owner and I'm a little irritated that most of the tech docs are dated before the manufacture date of my jeep (March, 2006).