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Old 01-23-2014
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CEL and strange temp gauge

I have a 98 4L V6 Ranger. A few days ago my CEL came on. I had it scanned and the codes were P0174 and P0171. This morning while driving my temp gauge went up to normal. Then it fell. Then up to normal. Then fell. Over and over all while driving a consistent speed. Any ideas?

Thanks
Jason
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Old 01-23-2014
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Codes 0171/0174 tell you both sides of the engine, all 6 cylinders, were running too lean, too much "air" in the exhaust.

This could have been a one time event or a long term issue, I would reset computer and see how long before CEL comes on again.
Unhook negative battery terminal for 5 minutes, this will cause computer to reset, codes will still be in the "history" file, but CEL will be off unless codes reoccur.

If CEL comes back on within 5 minutes(cold engine) then it's a computer issue.
If CEL comes back on just after warm up then it is most likely an air leak, vacuum leak is the usual suspect, cracked or loose vacuum hose, dirty or bad PCV valve.

If it takes longer for CEL to come on then could be a fuel pressure issue, '98 should have 65psi of pressure, you can rent fuel pressure testers.

Temp gauge could be related or not.
Lean mix will cause engine to heat up, but it would go above normal so not sure if we are on the same page.
"Normal" means where needle usually is after warming up, right?

If so then needle would go above this with lean mix if you were accelerating then drop down to "normal" when cruising.

Dropping below "normal" means thermostat has opened allowing warm engine coolant to flow thru radiator, this cooler rad coolant then flows into the engine causing gauge to go down a bit until system temp is equalized.
On cold days this can be more noticeable.
But continued drop below normal could mean thermostat is starting to fail, it is opening too much, in cold weather this can produce the up and down needle, but never above "normal", unless it sticks closed, then you get overheating.
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Old 01-23-2014
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I had the code cleared and it took about 1.5 hours of driving for it to come back on. The needle usually is right in the middle of the range when normal. Today it was going up and down from that to low. How long can I run my truck like this? I can't get it to the shop until next monday.

Jason
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Old 01-23-2014
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As long as it is not overheating it is fine.

1.5 hours before lean condition reoccurs seems odd, if that's what the new CEL is.
Assuming that is 1.5 hours of engine running time.
And no this will not hurt engine as it seems to be a minor issue at 1.5hrs between occurrences.

Wondering if there is an air leak in one of the "also runs on vacuum" systems.
Climate control system could be the leak, or EVAP(pulls air from fuel tank via a switch using engine vacuum), so neither system is full time.

Not sure if heater core control is vacuum operated, and it shouldn't effect temp gauge, but........
How is the heat in the cab?
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Old 01-23-2014
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Heh. Hard to say right now as it's -2. But the cab does seem to heat up as normal. It's not facemelting or anything, but about normal. Days like these I'd prefer facemelting.
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Old 01-06-2015
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Any resolution to the problem? Just curious as I have the exact same issue with mine. Temp normal to cold and po171 CEL after about 60 miles of any driving.
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