Multiple code misfire only when idling and codes PO420, PO300, PO304 and PO316

Tiny
RICO8940
  • MEMBER
  • 2005 FORD EXPLORER
  • 4.0L
  • V6
  • 4WD
  • AUTOMATIC
  • 102,681 MILES
Vehicle listed above is an XLT with a 4.0 SOC engine. When the car is idling, it begins to misfire. When I am driving, it does not misfire. Plugs, wires and coil pack are new, full tune up done like 2 months ago. Current codes that come up are PO420, PO300, PO304, PO316. I think the engine doesn’t misfire either when I have the heat on but normally does when I am warming it up or idling.
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Friday, October 29th, 2021 AT 10:21 AM

3 Replies

Tiny
MASTER ASE TECH
  • MEMBER
Hi, I'm Dan. Looks like you have a P0316, which is a code for misfire at start up, meaning when the engine is cold. Also the P0304 points to cylinder #4. Those older 4.0 Ford engines have a tendency to have issues with the intake manifold rubber gaskets. (See attached picture). As the engine ages, the gaskets shrink and leak when cold, but swell up just enough when warmed up. Try to see if you can hear a whistling at t first start up. The next step would be to have a shop smoke test the intake manifold to look for leaks.
Another approach may be to just change the gaskets as the repair is pretty straight forward and can be done in an afternoon easily. Also, the parts are inexpensive.
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Friday, October 29th, 2021 AT 1:48 PM
Tiny
RICO8940
  • MEMBER
Thank you I appreciate it, I hear like a sucking nose coming from the engine when I first start it but once the RPM comes down, it goes away. I also hear a big hiss when I turn the engine off.
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Friday, October 29th, 2021 AT 4:59 PM
Tiny
JACOBANDNICKOLAS
  • EXPERT
Hi,

I notice it has been a few days since we've made contact with you. Has any progress been made?

I noted that Master ASE Tech indicated a possible intake vacuum leak. Here is a link that explains how to check for leaks. Try it and see if you have success.

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

One other thought is the P0420. That indicates a catalytic converter operating below the threshold. Are there any odd smells coming from the exhaust? Do you experience power loss?

Let me know how things are going or if I can help in any way.

Take care,

Joe
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Sunday, October 31st, 2021 AT 6:28 PM

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