Coolant temp showed 63 this morning and IAT at 77.
Both seem to make sense to me as the coolant is still colder from last night. And the ambient air temp is currently 77.

 

Just throwing another one over the wall but I’ve heard of throttle bodies wearing out and have seen a utube showing a prominent gap between the TB valve and housing after high mileage
obviously that could cause a rough idle but no idea if it would cause a lean condition?
No harm in checking you’ve done so much elimination so far
you know what they say
‘every no just gets me one step closer to the yes’

 

Britman,
Thanks for the quote, it made me smile.

That is a good thought, but I would have expected to see this come up in my first smoke test.
Also, they actually build in a leak by drilling a hole in the butterfly valve!

 

Apologies i didn’t know that
I think we all want you to solve this
the motor IMHO is a good one
mine is sounding tight still and runs nice at almost 300k no reason with a proper schedule of maintenance that it’ll go on a lot longer.
biggest issue seems to be the manifold
Blessings my friend

 

Those readings of 63 and 77 tell you there is a problem there. Attempting to apply logic here is hampering your diagnosis. Unless the engine was in sunlight where the intake was allowed to get heated , I would start my diagnosis there.

 

I'm going to throw this out here,
First , those of us that have been burned using some aftermarket oxygen sensors learn to stick with OEM.plus they are not all the same.
Second, A lazy or incorrect oxygen sensor takes too long to correct mixture problems and the idle speed reflects this.
For all the time, effort and expense strongly suggest installing 2 Motorcraft sensors from Ford in there and forget about that possible problem. If you know what to look for in your data stream, you can look at oxygen sensor cross counts and it will be obivious if there is a problem there.

 

Hanky, I'm not sure I understand your logic there.
Can you elaborate?

Since the nigh time air temperature got down to below 50 at night, the antifreeze would get that cold.
And since I did not check the reading until it was over 70 degrees outside in the morning, The ambient air temperature, if reading correctly would be in the 70's.
A thin rubber tube would heat up to ambient air temperature much, faster than 5 quarts anti-freeze inside an engine.

If I recall, the IAT is part of the MAF on this year van, so I can try changing the MAF again see what happens.

And, yes, you are correct the van sits outside in the sun.

 

Thanks for the idea. I went ahead and tested as you suggested with starting fluid and there was no change in engine speed or STFT or O2 sendor readings.

 

Hanky,
Can you elaborate on the oxygen sensor cross count ?
How many per second is considered slow or fast?

Thanks!

 

Well, for those that would like to hear about a solution. (or should I say "work-a-round"
I finally went ahead and dropped the gas tank and replaced the fuel pump as everything else in the fuel system had been replaced.
It made no difference.

I realized that the engine ran well, but the fuel trims were out of spec just enough to trigger a CEL and the lean codes, P0171 And P0174
After testing everywhere for vacuum leaks and several smoke tests, nothing was found. You can read the prior info above.

I finally gave up and realized I was never going to be a ble pass smog if I did not do something.
I did notice a slight improvement in the fuel trim settings when the fuel rail pressure was increased by temporary plugging the vacuum line on the fuel rail pressure regulator.
(Remember this is a 2003 year model so the fuel pressure regulator is still mechanical)

So that got me thinking. I noticed from working on an Audi that the regulator on 99 - 2003 VW and Audi looked identical to the one in my 5.4l Ford V8.
But the VW regulators from these years regulates to 4 bar pressure (~58psi) instead of the 3 bar pressure (~43psi) of the Ford.

I went down to the old pick-n-pull and grabbed a 4bar regulator from a 2003 VW for $10 and sure enough it fit perfectly in my Ford fuel rail.
With the slightly higher rail pressure it brought my fuel trim levels perfectly into spec!

So, although I never found the issue, raising the fuel rail pressure a bit completely resolved the issue and the van runs great.
Now just another 80 miles of driving to put all of the sensors in "ready mode" and it's off to the smog shop to get a certificate!