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2004 Taurus, Vulcan, 178K
I had noticed longer crank time to start and occasional “pinging” under load for several months.

A couple of weeks ago, we took the car on a 200 mile trip on the interstate, A/C on and “moving with the flow,” in other words, not wasting any time. In heavy traffic and fast/slow conditions near the end of our journey I noticed misfiring and “pinging” and for the last few miles it was A/C off and pinging, hesitation and misfiring to our destination. Temperature gauge never moved and nothing apparently wrong or hotter than normal under the hood. CEL light went on at the end of our journey after stopping and re-starting the car.

Next morning, I changed the spark plugs, old plugs 20 – 30 K were all reasonably clean, light tan color but gaps were all different. Bottle of Techron and a tank full of mid grade (89 octane, I usually use regular) got us home, 200 miles with no problems however CEL did not go off. Read the code at home; P0171 and P0174, Since the car was now running OK, I re-set the CEL.

Couple of days later, hesitation returned, changed out the MAF sensor. No difference except no pinging. Seems to run better when cold. Problem occurs as soon as it warms up.
Unfortunately I don’t know what stopped the pinging, the MAF sensor, mid grade fuel or Techron? Also, no CEL although still hesitating.

I ran a smoke test, two vacuum leaks were evident:

  • Where the EGR valve connects to the intake manifold. (See attached image)
  • Around the black cylindrical device where the “cap” attaches to the cylindrical body.
    (Near as I can indicate on the other attached Image)

    Next steps:
  • Fix the vacuum leaks and see what happens.
  • I have ELM cable and downloaded ForScan but haven’t used it yet but will attempt to analyze see if anything else wrong.

    This is where I need experienced advice:
  • Do you think the vacuum leaks caused the problem?
  • Or do you think heat or excessive EGR gases caused the vacuum leaks?

    Any advice is much appreciated, thanks, John Kenneth
 

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Congrats, you are right on. Most common cause lean both banks is vacuum leaks and there are lots of sources that can cause that.

PCV connections common. EGR not so common but right up there I am sure.

Much less common fuel pressure low. System can set a code for low fuel pressure with '02 and later.

MAF very low risk of issues unless it is dirty/oily and then not likely to set a lean code.

Best of luck.

-chart-
 

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The first picture is the runner control valve, a very common vac leak point. Gasket is about $10, and takes little time to replace. Easy fix.
 

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Congrats, you are right on. Most common cause lean both banks is vacuum leaks and there are lots of sources that can cause that.

PCV connections common. EGR not so common but right up there I am sure.

Much less common fuel pressure low. System can set a code for low fuel pressure with '02 and later.

MAF very low risk of issues unless it is dirty/oily and then not likely to set a lean code.

Best of luck.

-chart-
Sooo, if only there is only the one code P0174 = fuel system lean bank 2, does that mean it's likely NOT a vacuum leak?
 

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A vacuum could affect one bank depending where it is located. If you didn't check that runner control valve o ring, as in this original post, I would do so. It depends if there is any mixing in the intake to distribute it to all cylinders or just one bank.
 
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