Lean on both banks (P0171 & P0174)

billr

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Make
Ford
Model
F-150 2WD
Year
1999
Miles
unk
Engine
4.2L V-6 auto trans (4R70W)
I'm going to start by taking fuel pressure. Where is that test port located? It is nowhere obvious...
 

Mobile Dan

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I think it is driver side near dipstick, but on the other side of the valve cover. Probably tucked under that wide upper intake.
1619228125032.png
 

billr

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Thanks, I found it. Kind of a pisser to get to. Now I have to come up with a fitting to screw onto it. Yeah, it is standard "tire stem" Schraeder, but I only have one screw-on chuck and it won't depress the valve stem enough to open it. This chuck is made to be tightened with a wrench, and I think the gasket in it can't be compressed for the stem depressor to work. Maybe I can get a wrench in there tomorrow to tighten it, but it is way too cold to continue tonight (down to 52F now).
 

billr

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Fuel pressure is about 39 psig, with no vacuum to FPR; dropping down to about 30 psig when the engine is idling (and idle vac applied to FPR). That seems kind of low to me, I m used to seeing 44 psig (3 bar) as the lowest for all EFI but the old GM "quadrajet"-like TBI. What is the spec for FP on this engine? We drove around with the gauge attached, the FP seemed stable.

My son thought he heard a hiss from the intake area, but I used a stethescope to listen all around and found nothing.

When driving around, the LTFTs both hit 14.8 pretty often. STFTs moved around a lot, even went slightly negative at times, but tended to be in the 25-32 range. Yeah, it seems like it is running lean!

TPS goes from 20% to about 95%, never any lower than 20% even right after KO no crank/start. That seems bogus to me. Can anybody confirm that Ford considers closed-throttle to be 20%?

MAF also looks odd to me. At idle (700 rpm) MAF is under 0.5 #/min; my calculations are that this 4.2L engine should draw about 1.3 #/min at idle. Anybody know good "real world" numbers for MAF on this engine?
 

billr

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OK, what is the MAF flow for a 4.2L (256 cid) engine idling at 700 rpm in N/P?
 

grcauto

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ROT for maf at idle is 1 gram per second per liter of displacement. Concentrate on the low fuel pressure.
 

billr

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OK, 4.2 g/s = 252 g/min = .555 #/min; pretty much what I m seeing in live-data. Agreed, I'll turn my attention elsewhere. Besides, we inspected the MAF; no grid in this one to get crudded up, just two precision resistors and they looked very clean.

My understanding is that KOEO FP should be 28-45 psig. That is, 36.5 psig +/- 23% This beast, at 39 psig meets that fine, and such a wide tolerance on FP means there is little to look for regarding how well it is being regulated. A drive with gauge attached showed no drop-out of FP, even though the codes got reset. I'm not saying it can't be FP, just that I can't do much more to check it without installing a transducer an logging data.

How about vacuum leaks? I have read elsewhere that these engines seem prone/sensitive to vac leaks at the manifold. I can't hear anything, and am reluctant to flood that area with propane or some other fuel to see if engine sound or STFT changes. What else could I try, smoke test maybe?

Can I rule out EGR, does that ever cause too much O2 (lean) without a misfire being detected?
 

Mobile Dan

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Any exhaust noise when cold? Loose, broken manifold bolts at head?

Cracked PCV hose?

Look at the EGR/intake gasket in reply #3. Also, the intake runner valve rods might be leaking where they enter the manifold.
 
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