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Old 04-07-2016, 12:28 PM   #21
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Quote:
Originally Posted by psyber_0ptix View Post
I can pick this sensor up locally from parts stores I imagine?
yes, it's a common GM part.

You want this:
Amazon.com: GM Delphi Packard Intake Air Temperature Sensor # 25036751 w Keyway Connector: Automotive Amazon.com: GM Delphi Packard Intake Air Temperature Sensor # 25036751 w Keyway Connector: Automotive


looking at advance auto parts: http://shop.advanceautoparts.com/p/c...1&prefZC=20151
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Old 04-07-2016, 01:27 PM   #22
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Unplugged it should read like 70* or something. So unplug it. If it still reads 180 then its probably shorted.
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Old 04-07-2016, 07:04 PM   #23
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I unplug slowly falls to 85F

I plug it in it reads 180F

I plug in a new IAT it reads 180F



I re-cut/crimped the wire in case it was a bad connection, same exact thing. I'm using the old MAF wiring, so however it's run from that plug to the megasquirt is as stock. It runs ok enough with it unplugged, but I'd love to take care of this properly.

????

I'm confused
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Old 04-07-2016, 07:06 PM   #24
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Slowly falling might be because of sensor lag.

How is it wired in?
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Old 04-07-2016, 07:09 PM   #25
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It was soldered, i broke those and butt connected them, same results both old and new IAT sensor
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Old 04-07-2016, 07:09 PM   #26
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I mean how is it wired to the ECU.
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Old 04-07-2016, 07:24 PM   #27
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Stock Temp sensor wiring -> Stock ECU plugs -> Brain MS3x adapter

Think the problem is there?

Also, I did install a stereo this Sunday. New speaker cable run from the trunk to doors, RCA cables and a signal wire to the trunk . Nothing to do with the cars harness. Just full disclosure.

Tune attached, but don't know what would have changed.
Attached Files
File Type: msq 2016-04-07_19.18.25.msq (212.9 KB, 31 views)

Last edited by psyber_0ptix; 04-07-2016 at 08:19 PM.
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Old 04-08-2016, 03:08 AM   #28
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doubt its a tune issue
sounds like either wiring or something is funky inside the ms, like a resistor or something ( I have no knowledge of ms intrnals, hit up Scott)
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Old 04-08-2016, 09:46 AM   #29
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what brand/make is the new sensor? does it need different calibration/ ohm vs. temp?
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Old 04-08-2016, 09:56 AM   #30
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Quote:
Originally Posted by 18psi View Post
doubt its a tune issue
sounds like either wiring or something is funky inside the ms, like a resistor or something ( I have no knowledge of ms internals, hit up Scott)
If R4 somehow failed? That's the 5v pull-up resistor.

But I'd expect it to shoot up well past 180F to like 255 or whatever the highest MS would display.

the sensor is just a variable resistor. Based on the temp of the element, it allows some of that 5v voltage to dump to ground.

What's happening here makes me think the sensor is not grounded really and the voltage, regardless of the temperature, it just going all back into the MS. But then it should failsafe to 70 like when unplugged. I dunno this one is odd.

Redo the AIT calibration for GM just in case. Worse case, I can pick up the unit and poke around.
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Old 04-08-2016, 01:12 PM   #31
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When the ignition was off there was a spike to 350f

It hasn't done it since. Just run two new wires to the MS?

I can drop it off any time.
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Old 04-08-2016, 01:38 PM   #32
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Quote:
Originally Posted by psyber_0ptix View Post
When the ignition was off there was a spike to 350f

It hasn't done it since. Just run two new wires to the MS?

I can drop it off any time.
I ground my IAT sensor to the post at the front of the engine with the other grounds. The other wire I run back to the ECU generally.
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Old 04-08-2016, 01:53 PM   #33
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OK, I'll try to get a multi meter out and try a reground first.

From the 92maf wiring,
Red/green is to the ecu
Black/lt green goes to a ground distribution. I'll try to follow that and clean the grounds, then maybe directly ground the se sorry as recommended

Last edited by psyber_0ptix; 04-08-2016 at 02:09 PM.
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Old 04-08-2016, 04:29 PM   #34
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Tried switching to two other grounds available from the maf wiring and cleaned the distribution block by the driver side firewall and the grounds at the head. There's continuity to both and the black/light green is also tied into the head ground.


No change in behavior.
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Old 04-08-2016, 04:37 PM   #35
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Undo radio install?
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Old 04-08-2016, 04:48 PM   #36
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I tried removing the amp fuse. But aside from the signal wire, nothing has changed on the cars side. Power ground an illumination wire is left untouched. All speaker wire is new, signal to amp and rca. But those are all independent of the cars harness.
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Old 04-10-2016, 06:29 PM   #37
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So the multimeter showed that the grounds are fine and the wire back at the ECU wasn't grounding out and was continuous. I snipped the temp sensor wire on the car harness side to see if it was grounding anywere and it was fine. I think it might be the megasquirt.

When completely disconnected it shows a small amount of voltage (1.8ish?), forgot to jot it down before plugging stuff back up for the day.

For now, I'll just restrict my driving to warm days without the iat.

Last edited by psyber_0ptix; 04-10-2016 at 06:57 PM.
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Old 04-11-2016, 05:31 AM   #38
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Open the MS and look for damage.
Or wire the IAT to some other input in your MS as a test for a faulty IAT circuit.
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Old 04-11-2016, 07:37 PM   #39
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Quote:
Originally Posted by Braineack View Post
If R4 somehow failed? That's the 5v pull-up resistor.

But I'd expect it to shoot up well past 180F to like 255 or whatever the highest MS would display.

the sensor is just a variable resistor. Based on the temp of the element, it allows some of that 5v voltage to dump to ground.

What's happening here makes me think the sensor is not grounded really and the voltage, regardless of the temperature, it just going all back into the MS. But then it should failsafe to 70 like when unplugged. I dunno this one is odd.

Redo the AIT calibration for GM just in case. Worse case, I can pick up the unit and poke around.
Whats the lowest possible temp MS will readout? if its like -70F then 180something would make sense.
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Old 04-11-2016, 09:22 PM   #40
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My car is possessed.

I tried wiring the IAT directly at the ECU harness and the temps spiked to 350 then went back to 180. As soon as disconnectng, it would fall as usual. I just plugged the replacement sensor back in and began reconnected the hacked up harness.

WELL.....

As soon as I got everything butt connected temporarily, there TunerStudio sat at 73.

I thought this was the MS default/failsafe but realized the sensor was plugged in; it should have been reading 180. I grabbed a glass of Ice Water and dunked the tip of the sensor in only to find temps plummeting.

Dafuq? I tried wiggling/teasing the wires to see if it would short again or do anything silly to no avail. I resoldered the wires back and just plugged it into the old sensor which was still installed on the coldside. Started the car right up, and it held fine. Drove around, made a couple light ~5psi pulls, watched the IAT increase a couple degrees under load, then drop back down when cruising. AFR is pretty good except for early idle. I might replace the sensor/recalibrate but the car is running again. I didn't do anything. I'm afraid to run it full tilt in case demons decide to show up again, so I'll just monitor over the next two weeks.


This case has left me stumped, I honestly don't know what went wrong or what went right. My speculation is that somewhere among the terminals, the connection was weak either at the MS3x or the ECU harness plugs. Playing with the wires teased them into place to reestablish a solid connection.



/conjecture


Thank you all for chiming in though, I really appreciate the community effort.
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