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#1 HDWildBill OFFLINE  

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Posted May 04, 2013 - 11:12 AM

Our Son bought a used 2002 Jeep Liberty with a V6 4WD.  Since he has had it he has been plagued with off and on warning light's, one being the oil light.  But when it was checked out he had good oil pressure.

 

Well the other day he gets ready to leave work and it cranks but runs really rough and just barely will go.  He took it to a shop and they diagnosed a bad #2 coil pack.  So he goes gets new plugs and a new coil pack but when he gets over here it is running OK.  So we changed out the coil pack and all the plug's.

 

 The next day he drive to a town about 20 miles away goes in to a store and comes back out and boom it is running rough again and this time it keeps shutting down.  He made it to a shop and once again the computer says bad coil pack on #2.  The guy swaps out the coil pack with #1 and no change.  So according to my son the mech does a compression check and says no compression you need a new engine.

 

I don't buy the new engine.  It has been my experience that when something mechanical goes it doesn't come and go.  I think there is something electrical going on, a loose connection or bad sensor something like.  I just wanted to get opinions from you more experienced mechanic's.  Thanks


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#2 WNYTractorTinkerer ONLINE  

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Posted May 04, 2013 - 11:29 AM

I think you may have determined the cause-  Check your ground connections @ the battery and the frame..  Then look over the positive side while your at it..  My $$$ is on a bad ground causing all kinds of electrical havoc..  Sounds like that is what is causing the poor cranking.  Try this-  If you have a load-tester-  Load test the battery.  make a note of what reading you get.  Now load test the battery (+) POS side to the Engine case or metal bracket (if you can find one-  they are using more & more plastic these days!)  If the reading is close, the ground is adequate and I'm full of BS..  If it's not-  You found your problem..  

 

As far as the compression I'd want a 2nd opinion..  Test it yourself.  There are lots of reasons for low compression and most times a stuck valve is at fault..  Yank the valve cover and evaluate your valves..  It's an engine just like your lawn mower but with a couple more parts but it's still the same stuff!!   Good Luck Grasshopper!  :dancingbanana:

 

 

PS-  My wife took her van to the shop because it wouldn't start on occasion..  They charged her 3 bills to replace the starter..  A while later the same thing starts happening again and she asks me to look @ it.. I know when I looked @ the battery what the problem was..  The negative terminal was covered with fluffy white corrosion!  I got out the corrosion cleaner and cleaned the thing up.  Then brush cleaned things and reassembled and gave it an anti-corrosion treatment.  Turned the key and it started right up..  **I know why she keeps me around now..  Every once in a while I help things out!


Edited by WNYTractorTinkerer, May 04, 2013 - 11:38 AM.

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#3 olcowhand ONLINE  

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Posted May 04, 2013 - 11:33 AM

Yes, a bad ground creates all kinds of weird stuff.  The components will backfeed, searching for a ground.  That can feed through all sorts of things, causing codes to go off.  I am NO electrical guy, period, but I've experienced such things myself.  


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#4 chris m OFFLINE  

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Posted May 04, 2013 - 12:25 PM

Bill I have had problems like this on a Chrysler Cyrus (v-6) It was the Crank positioning sensor. I have had to change it 3 times in 2 years.

 

But... there are so many things that can cause this. Heck I had a GM that did the same and it was corrosion under the ignition module, which was right under the coil packs.

 

I am not buying that it needs a new engine! I know Chrysler has had issues with the Liberty engine, but being this comes and goes and the fact that it says coil pack #2 problem, is leading me to think there is a bad connection on something.

 

Good luck, I hope you can find it with out to much trouble.


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#5 DougT ONLINE  

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Posted May 04, 2013 - 02:06 PM

Does that engine have a timing belt or chain? The first question is how much do you trust the shop doing the checking? There's nothing electrical that would fix low/no compression in a hole. Maybe ask to see it with the guage? Now, the fact that something electrical could have caused an internal failure, maybe a burnt hole in a piston. Is the code for misfire or primary coil circuit?
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#6 olcowhand ONLINE  

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Posted May 04, 2013 - 02:36 PM

The only way there can be "no compression" , then run fine later is a sticking valve, or carbon breaking loose & a chunk getting under a valve, then later being freed.  I'd sure have to see the gauge, or better yet, take the reading myself before I'd believe it.


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#7 JDBrian OFFLINE  

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Posted May 04, 2013 - 04:17 PM

I don't have much to add except that if this engine has variable valve timing it is remotely possible that an electrical glitch could cause a valve to malfunction and stay open when it should be closed. The real clue would be to know what actually is sensed to produce the coil pack error. 


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#8 superaben OFFLINE  

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Posted May 04, 2013 - 04:50 PM

Yes, a bad ground creates all kinds of weird stuff.  The components will backfeed, searching for a ground.  That can feed through all sorts of things, causing codes to go off.  I am NO electrical guy, period, but I've experienced such things myself.  

 

That's 100% true on everything these days.  Modern machinery (including compact tractors and cars) is high drain as you turn the key to start the engine and all the electrical equipment.

 

Ben W.


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#9 HDWildBill OFFLINE  

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Posted May 04, 2013 - 05:14 PM

Now for the rest of the story.  

 

I have a good friend, who is a ase Certified mechanic, he does all my mechanical work that I can't do.  He has been out of town and I wasn't sure when he would be back.  He called me today to let me know and we talked about Mike's problem and then we conference called Mike.  What Mike did not tell me is as he was trying to get to the expressway and home he got an oil light heard a loud bang, he thought he had run over something and it hit the car. Right after this a lot of white smoke bellowed from the exhaust and the engine quite.  He could keep it running by keeping the RPM up but it eventually died and he got into a parking lot.  Tim did mention the variable valve timing but neither of us are sure his engine has it, he was more inclined to the thing water in the top of the injector until he heard about the loud bang and smoke.

 

The shop was across the street.  Mike went over to see if they could get a reading from the computer.  Mike said when they pulled the plug the gap was closed and I know for a fact when we put it in the night before it was properly gaped.  He said he stood right there as they did the compression check and that gauge did not move then when the put a shot of oil in the cylinder and redid the check it the gauge still didn't move.  My wife and Mike said that the guy at the shop told them that if we wanted someone else to do the work no problem and that he could leave it there until he could get it towed.

 

In any case my buddy & I are going to call the shop on Monday and talk to them so we will see.  The good thing is he bought an extended Warranty when he bought the car so all it will cost him is $100 deductible.  

 

Thanks for all the help and I'll let you all know what it turns out to be once we find figure it out.


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#10 olcowhand ONLINE  

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Posted May 04, 2013 - 05:18 PM

Wow, did he do the right thing buying the warranty!  Sounds like a possible tossed rod!  That would send the piston up hitting the head and closing the plug gap.


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#11 HDWildBill OFFLINE  

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Posted May 04, 2013 - 05:25 PM

Wow, did he do the right thing buying the warranty!  Sounds like a possible tossed rod!  That would send the piston up hitting the head and closing the plug gap.

 

 

That's what I thought too. If so the rod must have broken close to the crank and had enough clearance not to knock.


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#12 olcowhand ONLINE  

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Posted May 04, 2013 - 05:27 PM

It could also have dropped a valve, breaking the valve off & driving it into the plug.  If this cylinder had been sticking a valve, it might be possible it stuck open so wide the piston hit it breaking it off.  That would explain why it would run good, then bad, then good....until the piston finally smacked it.


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#13 Earl OFFLINE  

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Posted May 04, 2013 - 07:22 PM

We had a 01 Grand Cherokee that would run rough and throw a missfire code occasionally.  Changed the coil pack, swapped injectors, several things to get it figured.  The conclusion I came to (before it was wrecked on icy roads) was that it is either the wiring harness or the injector driver in the computer. 

 

You need to pull the codes yourself.  A decent code reader is around $70 at a local parts stores and are REQUIRED to work on your own vehicles nowadays, the same way an adjustable wrench and flat blade screw driver were in the 60's and 70's.  Make sure the reader reads out the code, not just spits out a number you have to look up in a book.  I have an Actron CP9550.  Bought it from Advance Auto.  I actually have two, lent my first to my Dad and then needed it so I just bought another one.


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#14 JDBrian OFFLINE  

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Posted May 05, 2013 - 06:03 AM

 Extended warranty = good move in this case. Sounds like the engine may be ruined. Even if it only dropped a valve there could be a lot of damage to the cylinder and head. Interesting story! 


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#15 TAHOE ONLINE  

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Posted May 05, 2013 - 01:04 PM

Welcome to the world of the Junk, err, I mean, Jeep Libertys.

The oil light flickering, on/off is the sender unit right above the oil filter, common problem. Our '05 is doing it right now, sometimes it will say on on startup, usually not. Sender unit runs about $18-20 from dealer.

No compression and intermittent running could be valve seat, very common problem inthe 3.7L's. My bet is you pull the head, the valve seat is out or cocked and keeping valve open. Also, they are common for breaking rockers. If you find bad valve seat, I would make sure you have head magnafluxed as they are prone to cracking also. If your mechanic has a video scope, he maybe to snake in the spark plug hole and see damage before disassembling head.

Obviously you have major motor issues, but I believe they have an oil pressured tensioner on timing chain, allowing slack, jumped chain and well, a trashed motor with bent valve, holes in pistons, etc. This motor is like the 4.7 V8, just 2 less cyls just like GM did with the 4.3L, just a 6 cyl version of the 350. I do not think they have variable timing, it has a standard timing chain behing water pump.

please keep us up to date, I'm curious as to problem.


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