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Air Intake Temp using stock components

 
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Old 29 Apr 2003, 11:37 pm
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Default Air Intake Temp using stock components

The remote temp sensor for the overhead display is located behind the grille, in front of the A/C condensor. It should be the one on the left side, facing the front of the car. The sensor's range is from -49 degrees Fah to 140 degrees Fah. It is a variable resistor sensor, that changes resistance with temperature. It should have a resistance of 9K to 11K Ohms at 68 to 72 degrees. The other sensor is for the NGC Engine controller. They both mount to the same stud and nut, with the ambient temp sensor (for the overhead display on the left).

If you were to extend the harness to allow the sensor to be relocated inside the airbox, or whever the air intake receives it's flow, it would give you a head's up display of the temp of the air going to the intake. It would use the stock overhead display, and provide a much more pertinent reading than the outside air.

Other possibilities would be to monitor any temperature not expected to exceed the sensor's range.

The service manual picture shows the sensor plugging directly into the harness at it's mounting point. You may be able to make an "extender harness" from connectors gathered at a junk yard, or you could cut the connector off and splice in the needed length of wire(s) to extend it to where you want to relocate it to.

Be sure to check that you have the right sensor by unplugging it and checking the display. You may either get a blank display or a check engine light. A blank temp display is probably good; the check engine light would mean you either got the wrong sensor, or the service manual has the positions reversed in the pictorial.

I haven't tried this; just got the idea from looking at the service manual. It should be a nice and fairly easy mod, for anyone that has ever put in a car stereo, and is familar with wire polarity and making inline splices. I would suggest butt connectors and heat shrink tube. Cut the wire first, slide on a piece of heat shrink that is twice the length of the butt connector, crimp, slide the heatshrink over the butt connector and heat the heatshrink tube to seal the crimp.

I may try to do this in the next few days.

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Old 30 Apr 2003, 05:46 am
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I'm betting that it'll work but ...you are gonna exceed the upper limit a lot ! I know with even my gheeto intake that whole tube gets very warm to the touch even when not staying in the boost. I tryed surrounding the filer in an insulated box ( open -top) and it still was transferring heat from the turbo . I'm gonna try relocing battery if possible and routing air intake to grill ala ptdiy coldair intake style and see what happens this weekend.
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Old 30 Apr 2003, 08:08 am
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If you have a service manual, you may want to look into the battery temp sensor and how it ties into the computer to regulate charge rate of the alternator. It is built in to the battery shelf.

In short, moving the battery may start throwing MIL codes if it is separated from the temp sensor that controls the alternator.

On of these days, I am going to try to make a listing of all the monitored functions and the location of their sensors.

I will post the results of the temp sensor relocation project when I try it. I will attempt to make a reversible mod procedure that doesn't compromise the wiring harness.
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Old 30 Apr 2003, 11:28 am
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Thanks...don't have manuals ,yet (waiting for money from selling my 2001's manuals) . So thanks for heads up . I'll just remove battery and look it over . I was just hoping to offset it back into the area occupied by the air box and running the intake over the battery and into the area alongside the radiator .
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Old 30 Apr 2003, 03:06 pm
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Well, the mod was a success, and no wire cutting/splicing is necessary.

The wires to the temp sensor are violet, and green with black tracer. It is the sensor on the left side, facing the engine. The grille should be removed for easier access.

You will be able to confirm you have the correct sensor, by unplugging it and turning the ignition on and observing the temp gauge. It should read -49F or -45C depending on the setting you have it on. After confirming, switch off and remove negative battery lead.

The wire loom that the sensor wires feed into is located along the bottom of the cavity between the bumper and A/C condensor. The loom can be made accessible by pulling out on the 2 center loom holders (plastic) and lifting up on the 2 metal holders that slide into the supports on either side of the condensor.

Remove the tape holding the right side plastic loom holder to gain access to the wires in the loom. Pull out the wires going to the left temp sensor. There is enough slack to allow you to relocate the sensor to the area where the bottom tube from the air box rests above the driver's side front fender. It can be wire tied in place there.

The loom can now have the plastic holder taped back into position, and the loom remounted.

Remove airbox to give access to the mounting location and to aid in passing the wire through the space to the right of the condensor, which looks like a piece of roofing tar paper. It has enough give in it to easily pass the sensor wires through it to the engine compartment. Wire tie the sensor in. The grille can now be replaced.

Now would be a good time to remove the upper and lower silencers from the airbox (if you haven't already done so), before replacing the airbox. Don't forget to reconnect the negative battery wire.

****************

Ambient temp this morning was 73F. I started the car and did some driving and recorded the following:

9:33 AM Trip Odometer set to 0.0 73F outside temp

.4 to .6 miles started rising and stabilized at 86F
1.0 miles 84F @ 60 MPH
1.2 miles 83F @ 60 MPH
1.3 miles 82F @ 60 MPH
1.6 miles 81F @ 60 MPH
1.9 miles 80F @ 60 MPH
2.3 miles 79F @ 60 MPH
3.5 miles 78F @ 60 MPH

3.7 miles - 9:39 AM Traffic light stayed at 78F (short light)

4.0 miles 79F @ 60 MPH
8.0 miles 78F @ 50 MPH
8.3 miles 77F @ 50 MPH

In town, I had to make a few stops, and had someone in the car, so I left the car running with the A/C on. During that time the temp jumped from 95F to 140F, and when I started going again it fell from 140F to 95F. This happened 2 cycles; I was able to see it make the jump one time.

After those 2 cycles, the temp started tracking higher than 95F, and the highest recorded temp was 112F in stop and go driving with the A/C on. Normal up and down tracking through the 95F previous jump point was observed. End of trip, after 49.2 miles on the trip meter, the temp was 84F.

I don't know if the 2 cycles to 140 and back to 95 before it started tracking properly was a fluke or not. However, in driving under varying conditions I found it would track the intake air temp (at the point where the air enters the air box) fairly accurately, and give a good overview of what the temp of the air getting to the intake is.

The mod is easily reversible, and leaves no tracks. No wires were cut. The tape that was removed to gain access to the loom was easily replaced, and everything is stock appearing.

It is possible to add a DPDT switch to the overhead console, and an extra temp sensor to allow you to toggle between ambient temp and intake temp. I can provide a circuit diagram for anyone wanting to do that.

I took a number of pics, each averaging 60K documenting the steps taken in doing the relocation. I will be glad to email them to anyone who can put the process together for a DIY topic. I may be able to get a web page together and provide a link outlining the process.

As with all mods, do at your own risk. This one seems fairly harmless, and gives a way to tell the air intake temp
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Old 30 Apr 2003, 04:09 pm
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Hey Dalite,

Well done on the overhead sensor mod, I've been interested in engine temp readings and I look forward to seeing what you find out about the monitored functions and the location of their sensors.
Is there any way to increase the temp range so we could monitor the air that passes through the intake manifold?
Thanks and keep up the good work.
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Old 30 Apr 2003, 07:43 pm
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Dalite. Excellent post. Now there's a set of instructions! I've been curious about under-hood temps for a while and now I have a way of checking....with hood seal/without hood seal...airbox with & without insulation....
I'm assuming I can tack on a few feet of wire for temporary test installations without blowing a code?
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Old 30 Apr 2003, 08:49 pm
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Buck,

You will have to splice an extra length of wire to get it any further than the base of the airbox. The connectors for the sensor are small and not standard. There should be no chance of a code from extending them, and since the sensor is plastic covered and in a plastic mounting package, polarity should not be a concern.

The service manual specifically states that the sensor is hard-wired to the overhead console.

On the splice, 4 red butt connectors and some 3/8 heatshrink tube would assure a great, trouble-free connection. I would use 18 gauge wire, to match what the stock wiring seems to be.

The sensor is nothing more than a changing resistance that the display sees as a direct co-relation to temperature. The display sees infinite resistance (open circuit) as -49F, and zero resistance as 140F.

***********************

Here are some interesting tidbits from the service manual:

Since the ambient temperature sensor is in close proximity to the radiator, it can pick up engine heat giving a false “high” outside air temperature reading known as “Heat Soak”. In order to display a more correct outside temperature, the overhead console will not increase the displayed temperature until it detects movement in the compass over a two-minute period, to insure that there is adequate airflow over the sensor. “Movement over a two minute period” is best understood as once in the first minute, then some more detected movement in the second minute.

If the display shows an open circuit OC ( or -49° F (-45° C) then there is an OPEN CIRCUIT or a missing sensor and the condition must be corrected. Keep in mind that after a repair is made, the vehicle may need to be driven to update the temperature for the reasons described above. Even if the engine is cool, it will not increase from -49°F without detecting movement.

***************

The ambient temperature sensor is a variable resistor that operates on a five-volt reference signal. The resistance in the sensor changes as temperature changes, changing the temperature sensor signal circuit voltage to the compass / temperature display unit. Based upon the resistance in the sensor, the compass / temperature display unit senses a specific voltage on the temperature sensor signal circuit, which it is programmed to correspond to a specific temperature.

The compass/temperature display unit then displays the proper ambient temperature.

************************
The thermometer function is supported by the ambient temperature sensor, a wiring circuit, and the compass / temperature display unit. If the display shows OC (-49° F (-45° C) or SC (140° F (60° C),, there is an OPEN or SHORT CIRCUIT and it must be repaired before the VFD can be tested.

******************

Measure the resistance of the ambient temperature sensor. At room temperature (approx. 68°F), the sensor resistance should be between 9-11 Kilohms (9000-11000 ohms). The sensor resistance should read between these two values.

=====================

Resuming my comments: If Open Circuit is infinite resistance, display is -49F, and Short Circuit is 0 ohms, display reads 140F. We can guess from there it is a inverse reading comparator circuit; display shows higher numbers as resistance lowers in reaction to heat.

Another hint is the range of 9 to 11K ohms at 68F; aproximately half of the maximum positive limit.

However, looking at the Short Circuit (zero ohms) = 140F, I can only speculate that unless there is a way to change the input conditioning of the circuit and use a wider range temp probe, there may not be a way to read higher temps.

=================

Strangelove,

We are working with 5 volts here; the first hint that this is a TTL circuit. I will try to take my overhead console down and take a look at the components. If I can identify the comparator IC, I will grab a data sheet and see what could be done to the PCB to extend the reading range.

Theoretically, the display should be able to read up to 999F, using the 3 display digits. The kicke
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Old 01 May 2003, 02:20 am
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Great job....Thank you for sharing !
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Old 03 May 2003, 05:54 pm
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Here s the relocated temp sensor. It is right where the inlet to the air box would sit.
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