I've got a 1997 Ranger with the 2.3 "Lima" 4-cylinder, and lately it's been giving me fits.
Looking at the fuel trims, it appears to be a vacuum leak (trims are highly positive at idle and even out at higher load and RPM). I've tried to find a leak by several methods and haven't found anything. I'm probably going to replace the intake manifold gaskets (plus, taking off the upper intake will help me get to the spark plugs and PCV).
I'm also thinking about the fuel system... it doesn't hold pressure well after you shut the key off and I suspect the check valve in the pump is bad. I'm thinking of replacing the fuel pump and filter, since I am pretty confident that these parts are bad, but I don't have very high hopes that it will fix it. I checked fuel pressure with the engine running, and it holds pretty well around 30 psi. I would think that fuel delivery would cause the opposite problem as a vacuum leak, though.
MAF... there's a story.. The MAF that was on the truck is overreporting the air from what I can tell. This caused a rich code to be set (P0172, if I remember right). So I put on a new MAF and it seems to be reporting the air correctly, around 2.3g/sec at idle. Worked fine for a few months. But now with a presumed-good MAF, the fuel trims at idle get so high that it goes into open loop mode, where it barely runs. When I put the bad MAF on, the trims are lower -- because it overreports the air flow -- but it stays out of open loop and at sort of runs OK but not well because the fuel trims are going all over the place.
I keep finding threads on the Ranger forums about problems that are a lot like mine and they all go like this:
I have XXXX lean fuel code, any ideas about what it could be?
Sounds like YYYY, replace parts XYZ to fix it.
I replaced XYZ, and it's still doing it!
OK, maybe try this one other part
I replaced that and it's still bad! Anybody?
[End of thread]
There's never a resolution that makes me think, OK it should be this part.
Looking at the fuel trims, it appears to be a vacuum leak (trims are highly positive at idle and even out at higher load and RPM). I've tried to find a leak by several methods and haven't found anything. I'm probably going to replace the intake manifold gaskets (plus, taking off the upper intake will help me get to the spark plugs and PCV).
I'm also thinking about the fuel system... it doesn't hold pressure well after you shut the key off and I suspect the check valve in the pump is bad. I'm thinking of replacing the fuel pump and filter, since I am pretty confident that these parts are bad, but I don't have very high hopes that it will fix it. I checked fuel pressure with the engine running, and it holds pretty well around 30 psi. I would think that fuel delivery would cause the opposite problem as a vacuum leak, though.
MAF... there's a story.. The MAF that was on the truck is overreporting the air from what I can tell. This caused a rich code to be set (P0172, if I remember right). So I put on a new MAF and it seems to be reporting the air correctly, around 2.3g/sec at idle. Worked fine for a few months. But now with a presumed-good MAF, the fuel trims at idle get so high that it goes into open loop mode, where it barely runs. When I put the bad MAF on, the trims are lower -- because it overreports the air flow -- but it stays out of open loop and at sort of runs OK but not well because the fuel trims are going all over the place.
I keep finding threads on the Ranger forums about problems that are a lot like mine and they all go like this:
I have XXXX lean fuel code, any ideas about what it could be?
Sounds like YYYY, replace parts XYZ to fix it.
I replaced XYZ, and it's still doing it!
OK, maybe try this one other part
I replaced that and it's still bad! Anybody?
[End of thread]
There's never a resolution that makes me think, OK it should be this part.
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