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Old 05-05-2013, 05:27 PM   #1
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Still Fighting Crazy IAT Temps

I've been trouble shooting high and low IAT temps when data logging. Temps like to hang around -30's but can shoot from -168 to +168. When the real outside air drops bellow about 38 (+/- 3 deg) there's a huge performance lose (feels like a limp home mode).

Tom, last time I talked to you (several months ago) I think we both thought it was likely was a wire intermittent short/ground/open thing.

I think I'm convinced it's not a wire/connection issue, after a lot of inspections and tests.

Last voltage test, same reading at MAF and PCM, (60 deg out)
4.8 Vdc on Input ACT (White/Violet)
4.6 Vdc on Return (Brown/White)

Thinking of replacing PCM, but really don't want to without good reason.

Any Ideas what else to look at?

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Old 05-05-2013, 09:23 PM   #2
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Return voltage seems high. As in the heater isn't working at all.
According to Ford, you should see between 1.7 and 3.5 volts on the signal return (ground).
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Old 05-05-2013, 10:46 PM   #3
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You have a few options

1) get a junkyard MAF or a buddy with a SVT Focus or any 2000 to 2004 Zetec and plug his in , you wouldnt even need to start the car just plug it in and see if the temps are correct

2) get a 2 wire temp sensor from something and remove the wires from the 6 wire MAF plug in and see if you get a correct temp with the key on

3) hate to say buy a MAF because there is nothing more I hate but to throw parts at something with out knowing its bad , I would try option 1 or 2 first

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Old 05-06-2013, 09:29 PM   #4
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Would a bad (high) voltage on the Return cause noticeable problems with any of the other sensors tied to it? (I'll try data logging them tomorrow)

I replaced the MAF couple months ago with no change, but that was before fixing a major engine ground problem.

I'm getting a good 12Vdc at the Green/Red into the MAF, And a good ground on the Black/Orange.

Whats the trick to removing the pins in the MAF connector? Popped the lock block up, but couldn't finagle the pins to release.

Is a non-SVT focus MAF the same?
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