Random misfire with 2.7 - DodgeIntrepid.Net Forums - Dodge Intrepid, Concorde, 300m and Eagle Vision chat
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post #1 of 23 (permalink) Old 03-05-2011, 11:23 AM Thread Starter
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Random misfire with 2.7

Hello,
My 2002 Intrepid (120,000 miles) 2.7 has had a random misfire for a couple years now. Typically it'll happen when the engine is cold , but not always. Pretty much a perpetual check engine light. Here are the different scenarios that show up.

1. About 10% of the times that we leave the house in the morning, pull onto the highway, push down normally on the gas and the engine bogs down and you can't get any speed at all. Let off the gas a couple times and punch it down and suddenly the engine comes to life and all is good.

2. Engine seems to be running fine going down the road, but when you pull up to a stop light, it feels like the engine is running on two cylinders (shakes). Put the car in neutral and the shaking seems to go away. (This isn't a real common occurrence, maybe once a week)

3. Traveling down the highway on cruise at 65mph, everything works fine for quite a while and sullenly you can feel engine hesitations, which go away and repeat themselves until you take it off cruise and punch the gas to the floor.

All these conditions have flashing check engine lights, beeps, associated with them. The Dodge dealer says that it only shows (random misfire). I have a code reader coming next week, so I'll be able to keep a closer eye on it after that.

Some things that have been done to the car up to this point are a new fuel pump, new spark plugs, new coil wires. Throttle body cleaned.

This morning, the engine was running rough so I tried pulling coil power to isolate which cylinder was causing the problem. The front two cylinders (1 and 4) made no difference at all to engine performance. All other cylinders made a big difference when I pulled the power to the coil. I tried a new coil on one of the problem cylinders and it made no difference at all. I checked the compression of the questionable cylinders and it seemed good (about 175 lbs). I then decided to only plug in coils of the questionable cylinders to see if there was any reaction if I tried to start the engine. To my surprise, the engine started on those two cylinders. I hooked up the rest of the coils and now when I tried to remove a coil power to cylinders 1 and 4, I can hear the engine dropping rpms. (This is the random part of the problem that is making the diagnosis so hard)

A Dodge dealer has had the car twice and an independent repairman once.

Any ideas as to what could be causing this? Like I said, I'll have a code reader in a few days, so I'll be able to tell you what is being reported by the computer.

Thanks in advance,
Jack
Fort Loramie, Ohio
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post #2 of 23 (permalink) Old 03-05-2011, 12:21 PM
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Welcome, and wow! Glad to have you, Jack!

Very good post, and thorough diagnosis.

About the only thing I would question, and it may just be my misunderstanding what you said, are you sure it is always #1 and #4?

Some random ideas that come to mind - PCM failure is not unheard of, in fact, the PCM of a fellow member recently went out and when it did, it left the coils "on" 100% of the time, eventually burning out the coils. Also, being a 2.7 you have a timing chain, and as they wear and stretch (or more accurately as the guides wear and the chains slack), valve timing will change slightly. I don't know if this would cause your issue or not.

Replacing the PCM isn't too complicated, depending on if you have SKIMM (grey) key or not.
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post #3 of 23 (permalink) Old 03-05-2011, 11:46 PM
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^^^^^ put me in the PCM corner too....also check your engine wire harness
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post #4 of 23 (permalink) Old 03-06-2011, 06:07 PM Thread Starter
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2.7 misfire code readings

Thanks for the replies.

My code scanner came today and I checked the stored codes (8 of them)
1. PO300 Random Multiple Misfire Detected
2. P0302 Cylinder 2 Misfire Detected
3 through 8. P0351 to p0356 Ignition Coil (A through F) Primary / Secondary Circuit Malfunction.

The top reported fix for the P0300 for this (according to my Actron scanner) is replacing the PCM, followed by the Camshaft Position Sensor. Since it's a random problem, which involves all cylinders, I'm leaning for the PCM. I would "guess" that the camshaft position sensor wouldn't be such a random problem.

I drove the car about 200 miles this weekend and it didn't miss a beat. I'm clearing the codes and will see what pops up next.

Jack
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post #5 of 23 (permalink) Old 03-06-2011, 06:27 PM
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Cam and crank sensors would be random, but wouldn't be isolated to plugs 1 and 2.

Have you cleared the codes and then run it for a bit, then scanned? I wonder how much of the errors you have may be from experimenting?
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post #6 of 23 (permalink) Old 03-06-2011, 07:04 PM Thread Starter
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I cleared the codes and took a 10 minute drive with the car. The car seemed to run good and the check engine light didn't come on, but when I just checked, there is now a P0300 (Random Engine Misfire Detected) code stored.

Jack
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post #7 of 23 (permalink) Old 03-06-2011, 07:10 PM
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I'd try to source a junk yard unit... do you have a SKIMM (grey) Key?
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post #8 of 23 (permalink) Old 03-06-2011, 07:34 PM Thread Starter
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My keys do not have the remote attached (it's a separate fob).

I'm fairly new to the electronics auto repair department. Is a refurb, programed PCM a decent deal at $249.00?
solopcms.com/virtuemart-new-menu.html?page=shop.product_details&flypage=flypag e.tpl&product_id=88&category_id=2

Jack
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post #9 of 23 (permalink) Old 03-06-2011, 08:22 PM
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SKIMM is a starter immobilizer, and the plastic body of the key will be grey, not black - if you have a grey key, you will have to have the dealer (or someone with a DRB tool) help you install it.

That seems to be the going rate for a re-built PCM, but I'd honestly just throw a junk yard unit in it if you don't have SKIMM, and the junk yard car doesn't have SKIMM. MUCH cheaper that way.

No real electronics "skill" required for the swap - just some bolts and plugs. The advantage of going to a junk yard too, is that you can practice disassembly on THAT car, and not risk your own.
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post #10 of 23 (permalink) Old 03-06-2011, 09:00 PM Thread Starter
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I just thought of the fact that my trouble codes (0351 to 0356) were probably set when I had the ignition coil power detached to separate cylinders during testing. At least I assume this would cause that type of code.

Jack
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post #11 of 23 (permalink) Old 03-06-2011, 10:39 PM
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Yup, that's why I suggested clearing the codes then seeing what you are left with.
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post #12 of 23 (permalink) Old 03-08-2011, 11:58 PM Thread Starter
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A bit of an update tonight. I have cleared the codes on two occasions now and after a bit of driving (30 miles or so), it has a "random engine misfire" code stored. No check engine light. The only symptom that I can physically detect is a slight hesitation when you punch the throttle. The Actron code reader says that the #1 fix for this is the Oxygen Sensor, followed by replacing the PCM.

Tonight I cleaned the throttle body and checked the vacuum, which was steady at 19 lbs.

Since I first started this post, none of the intermittent rough idle or severe hesitation problems have shown up. Maybe moving the PCM connectors around helped that problem, or maybe it'll show up tomorrow??

Jack
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post #13 of 23 (permalink) Old 03-09-2011, 01:15 AM
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Unfortunately from HERE, it is one of those things where we say it has to fail worse to know more...

Keep us posted
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post #14 of 23 (permalink) Old 03-09-2011, 09:08 PM Thread Starter
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My wife came home from work today (about 4 miles) and called me out to the garage. She said that the car was running about as rough as it ever has. Super sluggish at low rpms, almost to the point of stalling. The MIL flashed and stayed on. Of course, by the time I get in the garage where the car in idling, it is running smooth as silk. Only new code was another P0300 "random misfire detected". Test drive confirmed that it was running fine.
I know that the PCM is the main consensus as to the problem, but I'm just afraid that the problem will persist after I replace it. Can anyone think of anything else that could cause a random event like this. I assume that most sensors fail completely and aren't intermittent for a long term like it's been for my case.
Thanks much!

Last edited by jmhoying; 03-09-2011 at 09:32 PM.
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post #15 of 23 (permalink) Old 03-09-2011, 09:32 PM
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Quote:
Originally Posted by jmhoying View Post
My wife came home from work today (about 4 miles) and called me out to the garage. She said that the car was running about as rough as it ever has. Super sluggish at low rpms, almost to the point of stalling. The MIL flashed and stayed on. Of course, by the time I get in the garage where the car in idling, it is running smooth as silk. Only new code was another P0300 "random misfire detected". Test drive confirmed that it was running fine.
I know that the PCM is the main consensus as to the problem, but I'm just afraid that the problem will persist after I replace it. Can anyone think of anything else that could cause a random event like this. I assume that most sensors fail completely and aren't intermittent for a long term like it's been for my case.
you might consider a fuel pressure test.....when it comes to a p300 random miss fire things that i've had to do to cure that preblem has been anything from replacing a failing alternator....fuel pump....leaky injector....faulty coil or failing pcm...

Keep in mind i deal with about 18 or 19 intrepids a year + my own and some of them will have a p0300 code to deal with.
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