Has anyone done the new external IAT sensor upgrade? Looks like VF has added this recently. Ran into this on Karl's blog:

http://docwilenracing.wordpress.com/...ger-continued/

It's 928 sensor mounted post of the chargecooler so the ECU can take the more accurate temp reading rather then from the MAF.

Wondering if it's worth the conversion on the stock VF tune.

 

What year is your car? I could not make heads or tails from the pictures what he was doing I did not see the sensor. I was under the impression that on older cars 996 with the new VF kit had a separate sensor going directly into the charge air to throttle body for temp. As far as a re-tune of DME not sure of delta air across the inter-cooler being enough that the computer would not compensate, but interesting to know.

 

I have a '00 996. You can see the sensor that is tapped into the top of the chargecooler, take a look at the 2nd picture here:

http://docwilenracing.wordpress.com/...tall-part-vii/

Here are my thoughts, since the stock ECU tune is slightly rich and now with the air temp of the boosted air taken post chargecooler which is higher then at MAF, the ECU will go leaner and possibly more balanced A/F ratio based on accurate air temp readings?

 

Not sure what you base that comment on regarding the stock ECU tune being slightly rich.

Stock the ECU delivers 14.7:1 (or thereabouts) because with a healthy engine this produces an exhaust gas that is most fully processed by the converters.

If the ECU determines the exhaust gas processing isn't going well it will then vary this air:fuel mixture until the exhaust gas processing returns to acceptable levels or until it runs out of adjustment. If it runs out of adjustment one or more error codes are stored and the check engine light is turned on.

Now under hard acceleration the ECU can enrichen the mixture because it suspends for a while emissions monitoring. But this enrichening doesn't last long.

A supercharged engine is a bit of pain. The MAF monitors incoming air (its mass) and temperature. Now the ECU has some assumptions built in that the air temp will be within reasonable and understood limits by the time it leaves the area of the MAF and enters the engine.

But if a supercharger is involved this can (will) raise air temp so the air temp entering the cylinders is quite elevated. Since the air is under pressure though quite a bit of air gets pushed into the combustion chambers. The amount of fuel will probably be ok -- up to a point that is barring some gruesome/scary boost levels -- and in fact the mixture might be a bit richer than it would be otherwise -- but the air being elevated means the engine may go into detonation mode quicker than it would otherwise. Too quick for the stock ECU to dial back the timing or maybe the ECU doesn't have that much adjustment.

Afterall the ECU is designed to deal with stock NA engines, not these engines fitted with an aftermarket supercharger.

Another problem is the narrow band O2 sensors do not have the sensitivity that the wide band sensors have. This is ok for NA engines but for supercharged egnines, at least in the case of the Porsche Turbos, Porsche uses wide band sensors to more precisely control fueling of the engine. Supercharged engines need precise and proper fueling, at all times.

The only way to know what's going on and that what is going on is ok is to check the engine's output on a dyno during which time fueling can be checked to ensure the fueling is spot on under all (simulated) conditions.

Everything may be just fine. But you want to know this based on actual testing not on guessing.

Sincerely,

Macster.

 

Thanks Macster for your input, by stock ECU tune I meant the standard ECU flash by VF Engineering/GIAC. I will be doing the external IAT upgrade shortly but I don't expect to see much of a change.

 

I plan on tuning mine soon also via dyno and would be nice to see the difference with the IAT, let us know the difference.

 

Macster,

I appreciate your input, however I believe correct me if I am wrong but the stock 996 02's sensors are wide-band. The add on SC comes with a DME tune designed for the added airflow, timing etc and believe that if these parameters are out of spec then they register a fault like a stock NA engine would.

 

So how is the 928 temp sensor wired? Do you have to hack up the oem MAF wiring? What resistor is used for this mod? TIA

 

My info is that only the 996 Turbo (not sure about the GT2/GT3 cars) comes with wide band O2 sensors, and just the #1 sensors. The #2 sensors are narrow band.

The NA engines come with narrow band sensors all around. But I might be mistaken.

What Pid numbers are used to read the sensor voltages? If Mode (service) 1 Pids 14 (bank 1 sensor 1) or 16 (bank 2 sensor 1) then the sensors are narrow (0V to 1V) sensors.

If the Pid numbers are higher, like 24 (bank 1 sensor 1 -- wide band (0V to 7.999V (!))) or 26 (bank 2 sensor 1 -- same voltage spread) then I'm wrong the sensors in your car are wide band.

I was not aware the SC kit came with a custom DME tune. If so then of course it should have the customization in place to maximize the benefit of the SC and yet provide a comfortable safety margin to prevent engine damage.

But then why does the OP have an interest in using a 928 IAT?

Sincerely,

Macster.

 

The sensor is a thermistor (resistor that varies w. temp) with 2 wires, you have to tap into the air temp signal and gnd at the MAF. See doc's site for details on wiring:

http://docwilenracing.wordpress.com/...ger-continued/

 

It is what is used on the newer SC kits along with a resistor (used for setting proper voltage of MAF for new air flow). The IAT would also measure the intake air temp (which is cooler) after the inter-cooler that would/could change the DME tune and gain hopefully more HP. I think the only thing that would change is that you could tune more accurately since the air would be actual before entering the throttle body.

Note:

Just looked at some readings of my car and nothing over a volt with either before/After cat 02's...Must be narrow band.

 

mec0t0 or Ferd,

Have you done any further research on this? What year 928 sensor is used? etc bumping for more knowledge.

 

Color codes on older MAF look different used with a SC, mine is a 2000 Model and Blu/GR is the temp color to cut for IAT sensor and also tap the Brown/White for ground for IAT sensor.

 

I believe all 928 IATs have this pn 92860614300 or 0280130039. It seems that VF is selling the upgrade kit but they did not respond to my emails.

 

That is different than the one I found.

http://www.autopartswarehouse.com/sh...rsche/928.html