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Old 03-02-2012, 03:38 PM   #1
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Default IAT reading...Massively high.

Hi Guys

89 NA 1600 with professionally installed (?) homebuilt turbo/intercooler, link G1.

I have idle and hesitant throttle issues (that I know of, presume other issues will reveal eventually too)

After connecting the pc link and running a data log I am surprised to see my IAT reading 80 - 84 deg celsius. This is only a few less than my water temp reading and not what I understand to be normal.

I presume I have one of the following.....

- Incorrectly positioned IAT sensor
- Faulty IAT sensor
- possibly it is accurate and some other issue..?

or maybe even NO IAT sensor and the link is making it up....(unlikely as I figure that is..)

As I didn't build the car, can someone please advise where or even IF the oem car has an IAT sensor and where that might be...?

Or failing that, where is the most common location for mx5 turbo engines to have an IAT sensor positioned...?


Appreciate any advice.

Cheers
Mark
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Old 03-02-2012, 03:42 PM   #2
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Quote:
Originally Posted by mx5-kiwi View Post
As I didn't build the car, can someone please advise where or even IF the oem car has an IAT sensor and where that might be...?
In the stock configuration, '89-'93 Miatas had an IAT sensor built into the airflow meter assembly.

Since your car has a Link ECU, I assume that the airflow meter has been removed.

My memory here is a tad hazy, but I think that the Link system supplied by FM used an IAT sensor built onto a tiny circuit board which was installed into the side of the pipe which enters the throttle body assembly.

edit: Yes, here it is:

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IAT reading...Massively high.-kxuvt.jpg  
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Old 03-03-2012, 01:50 AM   #3
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Hi Joe, thank you for the reply, much appreciated.

Unfortunatley it is not that apparent on this car. We have a manufactured series of S/S pipes for the intercooler etc leading to a cross ribbed rubber elbow that has obviousley been sourced from another vehicle. Nowhere is there a single sticky out thingy like you show.....(Sensor I should say...)

However the car does appear to have a working, variable TPS, did any cars come with the sensor in the TPS unit? (a random thought....)

The more I think about it the more I can't help but conclude the reading is related directly to water temp.......

Would this wire be a OEM loom wire or a self run wire do you think?
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Old 03-03-2012, 01:56 AM   #4
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However the car does appear to have a working, variable TPS, did any cars come with the sensor in the TPS unit? (a random thought....)
No Miata ever did, and while I've not examined the throttle body of every car ever made, I've never seen one with an IAT sensor in it.

It's probably not relevant, though I'd be curious as to which TPS assembly you have. The '89-'93 Miatas with automatic transmissions came with an analog TPS standard (4-wire), as did all '94 and later Miatas, though they are not mechanically interchangeable.

Quote:
Would this wire be a OEM loom wire or a self run wire do you think?
Do you see any aftermarket wires spliced into the OEM ECU harness?

The OEM IAT sensor, as I said, was inside the airflow meter, and thus, the IAT wire will be in the AFM connector, which is on the exhaust side of the engine bay near the shock tower. It's a 7 pin flat connector, and the IAT lead is red with a green stripe.
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Old 03-03-2012, 07:26 AM   #5
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Thanks Joe, your great description found me the unplugged and tucked away afm plug. Unfortunatley no wires spliced in to there.

The link has somehow wired in to the main OEM ECU plugs. I will pull the unit out in the morning and have another look, maybe they have run a lead direct from the link side of the harness.

Your helping a lot so thank you

Thinking ahead, where would the best position for the IAT be? I presume the OEM location is no good for a turbo install as the air compression and subsequent air / air intercooler will change the reading from up at the filter side......

Incidently the TPS unit is a Denso, with 3 wires, however it is a 4 wire plug. position 3 is empty.

Can list the part number on it if interested.....I presume the TPS is on the non cable side of the accelerator shaft just ahead of the intake manifold...
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Old 03-03-2012, 11:23 AM   #6
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You're going to want to place it post intercooler. A lot of people drill and tap the end tank of the intercooler, or you can place it somewhere in the cold side pipes.
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Old 03-03-2012, 12:05 PM   #7
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Quote:
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Thinking ahead, where would the best position for the IAT be?
As Kyle said, anywhere after the intercooler outlet.

Placing the sensor in a location which is behind the radiator (eg, the location in the picture I posted above) can sometimes cause heatsoak problems, to wit the sensor body becomes heated by the hot air coming out of the radiator and causes artificially high readings. A similar problem occurs when placing it on the intake manifold itself.

I'm a big fan of drilling a hole in the end-tank of the intercooler (again, as Kyle said) and placing the IAT sensor there. This is usually sufficient to prevent it from being affected by ambient waste heat from the engine.
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Old 03-05-2012, 04:17 AM   #8
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Okay, just a quick update. After a lot of research it looks like my link is a G3 unit with a G5 software upgrade.

The G3 unit has no hardware/electronic provision for IAT reading, though the G5 does.

Not sure why the IAT is getting a reading but I now realise the IAT reading is exactly the engine temp -4, when the engine temp changes so does the IAT.

I emailed Link and they confirm what I discovered.

So that is a relief in one way (I am not getting 80+ deg C IAT) but somewhat disapointing in another way (no IAT reading or management).

Is having no IAT that big a deal?

Thank you for your help guys. So much to learn!
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Old 03-05-2012, 01:26 PM   #9
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Quote:
Originally Posted by mx5-kiwi View Post
Is having no IAT that big a deal?
It depends on how the ECU software is configured, and I'm afraid that I'm no expert on the Link.

On some (most?) MAP-based ECUs, IAT is used to correct for air density based on temperature. Additionally, with turbocharged / supercharged engines, IAT is sometimes used to retard ignition a few degrees when the intake temps get really high, in order to prevent detonation. This function requires the use of a fast-acting "open element" sensor, which most OEM sensors are not.
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Old 03-05-2012, 01:46 PM   #10
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I ran with out a sensor when i first installed my standalone... it was BAD. Seeing that you're running IC, You're better off placing a sensor ziptied somewhere to the mouth to measure ambient temp than with no sensor at all.
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