97 Ranger - P1445

No, not a help request but an interesting story....
When #1 son (actually, the only son) got his drivers licence, Dad had visions of the kid wanting to use the SuperCrew.... I was a kid, once, and
had visions of what could happen to said SuperCrew.... especially hauling a racing quad up to the track....
So, in a rush, I picked up a 94 F150 4X4 from a guy I thought I could trust.... so much for that idea..... After the cheque was cashed, I set about making sure the truck was at least safe.... I can't blame my boy for not liking the truck... It runs good and everything, it's just not one of those "fun to drive" feeling units.....
In the mean time, I found a 97 Ranger SC 4X4 with a 4.0... sales dept had taken it on trade.... high miler but started and ran good - didn't feel to bad on the test drive. I went through all the 'usual" stuff - changed fluids and filters - did what brakes needed to be done.... steering, 4X4 system, you name it - I wanted the kid to have a dependable truck.
But there was a nagging check engine light.... P1445, purge flow sensor fault. Now, we have to look and see what possible causes there are - and we find that P1445 is an "electrical" fault. OK... I take a page from AutoZone. The sensor is only 24 bucks, and the partsmonger orders one.... shows up in that nights freight cage and I slam dunk the sensor..... After I wiped the egg off my face, I grab the scan tool and see that that the sensor PID is pegged at 5 volts.... sensor plugged in - sensor unplugged - sensor shorted to SIG - sensor shorted to ground... not difference..... Oh, man!?!?! Am I buyng a PCM? Having the luxury of a breakout box (if you're careful at home, you can "work around" but do NOT speard any of the pins), I hook it up.... Hmmmm.... open circuit on the SIG_RTN line... Phew! - no PCM in my future (I hope)...
To cut a long story short, that includes R&R the intake to be sure the portion of the harness that passes under it isn't hurtin', we discover that the engine in this truck is out of a newer truck.... and the portion of the wiring harness that came with the newer engine had the SIG_RTN assigned to a different pin in the PCM connector.
Moral of the story.... proper testing saved me the cost of a PCM (about $400 or so CA)... if I had started proper testing early enough, I could have saved myself enough money to purchase 26 fluid ounces of Mr Seagrams elixir. Even when we see DTCs generated by a "pattern" failure, we desparately need to apply some logic and diagnosis to the concern.... I once had a DIY customer that had purchased several different DPFE sensors.... the first one he purchased would have been good if he had only hooked the hoses up correctly....
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