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Check engine light on and code P0306

Tiny
JVRBKA
  • MEMBER
  • 2004 CHRYSLER TOWN AND COUNTRY
  • 121,000 MILES
My wife's van has check engine light on. The code it p0306. I know it's a #6 cylinder misfire, but I can't figure out why it is misfiring.

The engine light is on. P0306. I've changed the plugs, plug wires, coil pack, and fuel injector, and the light is still coming on. I don't know where to go from here. I thought maybe fuel pressure was low and because the #6 cylinder is the last one on the fuel rail it's not getting enough pressure, but I can't figure out how to test it.

There is no scrhader valve anywhere. I've had the fuel rail out when I changed the injector and there isn't a valve on it to hook a fuel pressure gauge to. How do you check fuel pressure on these engines and is there any other ideas as to what could be causing the misfire?

Thanks!
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Thursday, October 4th, 2012 AT 3:35 AM

15 Replies

Tiny
SATURNTECH9
  • MECHANIC
  • 30,869 POSTS
Does it missfire constantly or just sometimes.
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Thursday, October 4th, 2012 AT 4:04 AM
Tiny
CARADIODOC
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Fuel pressure can't be any different at the various cylinders. All the injectors are fed from the same large tube. I have to guess at the engine size. The 3.0L doesn't use a fuel pressure test port. You pull the supply hose off and insert a tee with a fitting.

You might consider a compression test. Chrysler typically has extremely little trouble with injectors. The spark plugs and wires normally solve 95 percent of misfires, injectors and fuel pump about one percent.
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Thursday, October 4th, 2012 AT 4:07 AM
Tiny
SATURNTECH9
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Thats where I was going is compression thats why I asked if it miss fired constantly?
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Thursday, October 4th, 2012 AT 4:13 AM
Tiny
JVRBKA
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It's a constant misfire. The engine is the 3.8l. So the next step should be to check compression?
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Thursday, October 4th, 2012 AT 5:19 AM
Tiny
SATURNTECH9
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Yes if its constant I would check the compression.
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Thursday, October 4th, 2012 AT 5:34 AM
Tiny
JVRBKA
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If the compression of that cylinder is low, what do I do after that?
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Thursday, October 4th, 2012 AT 10:49 AM
Tiny
SATURNTECH9
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I would check all the cylinders compression and if only the number 6 cylinder was low.I would suspect a valve issue. Then I would do a cylinder leak down test to pinpoint if that's what it is.
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Thursday, October 4th, 2012 AT 3:05 PM
Tiny
JVRBKA
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Ok. I'm going to try and get a compression gauge tonight.
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Thursday, October 4th, 2012 AT 3:07 PM
Tiny
SATURNTECH9
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They rent them at auto zone.
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Thursday, October 4th, 2012 AT 3:51 PM
Tiny
JVRBKA
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Finally got a compression gauge that works. The first one I got had a small hole in the hose, so I had to take it back. The #6 cylinder only had a psi of about 100. The others were around 150. I also poured about a capful of oil in the #6 plug hole and it was still reading about 100 psi.
Where do I go from here now?
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Saturday, October 6th, 2012 AT 3:54 AM
Tiny
SATURNTECH9
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I see the compression shouldnt be less then 100 psi and not vary more then 25 percent from cylinder to cylinder.I would do a cylinder leak down test next.
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Saturday, October 6th, 2012 AT 4:35 AM
Tiny
JVRBKA
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Ok. I'll try and get a leak down gauge in the morning. I've never done a leak down test before. Am I basically just trying to figure out where it's leaking from?
Thanks for all your help so far!
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Saturday, October 6th, 2012 AT 4:40 AM
Tiny
SATURNTECH9
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Yes you need a air compressor to supply air to the tool. You put the cylinder on tdc and see what the percentage of leakage is and where its going. The tool should have instructions.
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Saturday, October 6th, 2012 AT 4:47 AM
Tiny
RONSTAFFORD
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If you compression tested a second time with oil in the cylinder and didn't see an increase in pressure. Then you have a valve seat sealing problem and will have to have a valve job performed.
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Wednesday, March 13th, 2013 AT 4:32 AM
Tiny
CARADIODOC
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There's a couple of things to keep in mind. Did you have a battery charger on it while doing the compression test? If not, the last cylinder is going to read lower than the rest because the engine will be cranking slower. Also, if the engine is cold, things won't seal as well as when it's warmed up.

While 100 pounds is definitely lower than the other cylinders, that should not be low enough to cause a misfire. That cylinder will still be contributing close to the same amount of power as the others. If a valve is burned the compression will be MUCH lower. I had an old Dodge 340 on the racetrack with one quarter of an exhaust valve burned away and at higher speeds you could hardly tell. I'm probably going to be proven wrong, but I'm not convinced yet compression is the cause of the misfire.
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Wednesday, March 20th, 2013 AT 7:44 PM

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