Sensor tweak

No, if you cut both wires and connected the ends from the ECU with a resistor you'd get a "permanent reading" based on the resistance of the resistor, but that's not what's being discussed here.

No, you asked about cutting one wire and placing inserting a resistor there, mike asked about replacing the sensor with a resistor.

jackbombay said:

No, you asked about cutting one wire and placing inserting a resistor there, mike asked about replacing the sensor with a resistor.

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From what I recall in college the cutting of one wire is all that is required to open up the parrallel circuit . As long as the open part of the circuit is open to ground there should be no (R1)(R2) / (R1 + R2 ) = Rt . It should be just R1 + R2 = Rt ., R2 being the varring resistance with fuel temp of the fuel temp resistor . I went and dug out my electronics books from school .

My question is related to the thought of will a fixed resistor value cause a CEL to be set off ?? Does the ECU look for a varried signal from the fuel temp resistor ??

As previously discussed, replacing the sensor with a fixed value is EXACTLY what the cheapo PD tuning boxes do, and no, it doesn't set a CEL.

DPM said:

As previously discussed, replacing the sensor with a fixed value is EXACTLY what the cheapo PD tuning boxes do, and no, it doesn't set a CEL.

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But we aren't talking about PD's, at least I'm not.

I pulled a 2w 5.2 k ohm out a computor power supply . Can you say wow , I couldn't make it smoke under load in the higher gears . Also with a 1k ohm resister on the Evry mod it would only barely smoke .

Evryone should do this mod

After a week I can say the above mod ;

Increased fuel economy by 20 to 30 % . I exceeded 200 miles before the fuel gage started to move off of full , normally the gage starts to move in the 130 to 150 mile range .

Reduced smoke by 95 % . Up here @ higher altitudes I could make clouds of smoke before , after I couldn't hardly get a wisp of smoke .

INcreased power by around (((((((40 % @ lower rpms)))))) . Higher boost @ lower rpms ( 1,200 to 1,500 rpms ) without extra smoke or higher EGTs . I've noticed that not as much throttle input is required during normal driving .

I thought I explained what I was say but I guess it didn't get completely accross . 40 % at the lower rpms of operation !!!!!! Get It ???

Reduced normal observed EGTs by 150 to 200 * F in my driving . I normally see 600 to 800 * F depending on speed & acceleration & grade up or down or flat . After the change/mod 400 to 600 * F was the norm .

I dont think you got thise results, but as long as you think you did thats ok. There is no way you got a 40% power increase.lol

Update after the fuel temp sensor signal mod

790.6 miles / 13.24 gal LSD = 59.7 mpg US in city driving around Denver CO .

rotarykid said:

After a week I can say the above mod ;

Increased fuel economy by 20 to 30 % . I exceeded 200 miles before the fuel gage started to move off of full , normally the gage starts to move in the 130 to 150 mile range .

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It's about six weeks later, Rotarykid. Has your opinion changed since the initial glowing report?

mpgs still holding @ 58 to 61 mpg US since the mod . 51 to 57 mpg was more the norm before .

I'm heading out on a trip today & wew will see if it helps on the highway .

54.47 mpg on B-50 with LSD & ULSD mixed together over about 650 miles this weekend in the high country of Colorado . Up & down passes from a low of 5,000 ft to a high of around 11,000 ft . From a low of 30 mph going over the passes to a high of 65 to 75 mph through the mountian valleys with a little sprint of 90 mph on I-25 .

Not too bad I don't think .

I'd really like to do this, before the weather gets too hot. But I've never used a soldering iron, and I'd rather not practice for the first time with the wires to my fuel temp sensor or air temp sensor.

You could just practice with some scrap wire, a soldering iron is cheap too. As long as the wire is above the melting temp of the solder it will work fine.

This is something that I'd consider doing, but I've a practical question: where are the wiring connections that are being modified? On the ECU harness or at the sensor end or does it even matter? The thought that occurs to me is that with a few extra connectors matching the ones on the sensors, one could fashion a plug-in module to achieve this that can be removed if necessary.

The weather here in Ireland has warmed up noticeably in the last few weeks (average daytime temps up from 8-10 C to between 16-20 C) and power has definitely dropped off in my Passat so anything that'd bring it back would be nice

What could be interesting for this also is to design a circuit that would offer different resistances to the ecu depending on the resistance of the sensor so that it could tailor the signal to match conditions. With a fixed resistance offset the ecu could end up getting an excessively low temperature signal that would hamper engine performance. If a circuit could tune this out so that ECU never gets an IAT lower than e.g. 10 C it could be very useful.

Just put a potmeter where the temp sensor was, turn until you read 10°C on the ecu, measure the resistacne, and put a fixed one in place, problem solved, I don't that it would do any bad to let the ecu think that the fuel temp is 10°C ..

I just tried to do this on my 99.5 ALH Golf and it didn't work.
I first put the 2 res on 7 and 2 pins. The car wouldn't start. Like no fuel was injected. Than I took the IAT one out (2), the car would start but the glow plug light would flash and the CEL would be on. So I took them both out.
I don't have a VAG ready right now since I don't have my laptop anymore.
Any ideas why it isn't working?

Doc I think I diverged from the colour codes given by Kerma, but I'd have to look at it again. Maybe your 99.5 is the same as mine? Who knows. here is what I did though.

"I put the 2.2k resistor on the grey/green line for IAT, works like a charm "

Since I have been chipped I reverted it back, but I may try again, it really did lower the computer temps for me. I wanted to go "stock" chipped for a while

I went by the pin numbers and it happened for the colors to be the same as Charlie mentioned.
I didn't try IAT only. Maybe I should. Too bad it didn't work, I need less smoke

I don't want to steer you astray but I think I had to do it to both of mine to get my car to run properly...fuzzy memories comming back. I know there was a reason I cut both mine..and I think for my car it was that it wouldn't work worth a hoot till I had both the fuel and the IAT done. Pretty sure that was the case anyway, my mind has been known to play trick on me.

Doc_Oc said:

Too bad it didn't work, I need less smoke

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This mod will increase smoke on a car that already smokes.

jackbombay said:

This mod will increase smoke on a car that already smokes.

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Well, all the previous posts were stating the contrary.
I am not talking about evry mod. I am talking about the IAT and fuel temp sensor mod.
I am not saying you are wrong. Especially since it didn't work on my car. But most of the other posters said the smoke is literally GONE.

jackbombay said:

This mod will increase smoke on a car that already smokes.

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I haven't had a chance to try this mod yet, but from my readings here it should not increase the smoke.

If fuel temps are getting high and causing timing to become retarded, that might increase smoke, and the IAT Mod could prevent this. Otherwise the amount of smoke being produced should not be affected, one way or the other.

If your car is right on the verge of smoking or already smokes a bit the IAT resistor will make your car smoke more on hot days.

As air temp increases air density decreases, as density decreases injected fuel also needs to decrease or you will get smoke as there is less oxygen for combustion, so if you trick the ECU into thinking that the air is cooler that it really is you will be closer to or past the point of smoke. For mildly tuned cars this is a non issue...

What you are saying makes sense. It is still to be tested, but it makes sense

But first, what should I do to get it working with the resistors?

Does this mod work on a PD?

I just tried this mod and the car would not run with both resistors in. I put one resistor in the pin 7 Yellow/Blue and one in the pin 2 Grey/green. I removed the resistor from Grey/green and it fired right up. I haven't had a chance to drive it yet, but thought the results were interesting.

I have 18k resistors in the fuel and air temp so that I have -30F for temp. So far 2-4mpg gain and the car is "torquey" at part throttle/low rpm situations.

I have however noticed that the car will smoke for a second or two during cold start because it thinks the fuel and air are so much colder than they actually are. Full throttle smoke is increased as well. My "FAT mod" thread can give more detail.

WolfTDI said:

I just tried this mod and the car would not run with both resistors in. I put one resistor in the pin 7 Yellow/Blue and one in the pin 2 Grey/green. I removed the resistor from Grey/green and it fired right up. I haven't had a chance to drive it yet, but thought the results were interesting.

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Did you get a CEL with the resistor left in the pin 7? I had exactly the same thing happening on mine. But with the resistor in pos 7 I would get a cel and gp light flashing. I didn't have vagcom though to see what the code is.

I always have a CEL. It reminds me to check the engine with my right foot! (Race pipe and intermittent gp circuit malfunction). I did have a flashing gp light from Quantity adjuster outside of specification. I think this was from cranking it when it wouldn't start from the resistor in pin 2. I have cleared the code and will find out if it comes back today. On the plus side, it seems there is more power on tap when the engine is hot. After a romp down the interstate at sightly illegal speeds a stoplight launch was much more spirited than before. I eased into full throttle in second and had to back out due to roasting tires(225 series 17's). Vag com shows fuel temp at 17.4*C (63* F).