Sensor tweak

KERMA

Vendor , w/Business number
Joined
Sep 23, 2001
Location
here
TDI
99 beetle and 04 jetta
Sensor tweaks

Please note: the state of the art (and our knowledge) has progressed significantly since 2006, when this was first posted. Many of the speculations presented over the course of this thread were just that: speculation.

It was all part of the quest to figure out 'how it works". Lately, this characteristic seems to have been supplanted by an ongoing contest to see who can garner the most shills to overwhelm the forums with second tier advertisements, thereby gaining market share. It's no longer the "TDIClub", it's the "TDIvendorsInfomercialClub". It wasn't always this way.

Back in the day, these forums were a place where new ideas were welcomed and there was a lot yet to be discovered. Now many things are taken for granted, that were unknown or not even thought of several years ago. Posts like this were one aspect of the sense of pioneering and discovery that made Fred's forums so much fun for innovators.

Nowadays, many of the "truths" are simply stuff that was repeated over and over. and eventually gets read by an innocent third party, who repeats it. Eventually, if this cycle repeats enough, the idea goes "viral", which kind of makes it a truth unto itself. Too many of these "truths" are simply based on bad information from the past (ignorance) or even flat-out lies in an attempt to gain some market share advantage over the competition. By and large, public debate and discovery are discouraged, because it interferes with someone's marketing plan. Whole 100-post threads are started and cultivated to "cover the tracks" of vendors to "document" new "problems" that are nothing more than posturing which is intended to cover for an inability to provide a product or service for reasons that are completely unrelated to the contrived technical discussion.

this is not one of those threads.

Please bear in mind, this thread does not represent the current best knowledge, which has been gained over the intervening 6+ years. We've learned that things actually work the way they do for different reasons than was originally speculated "back in the day". I will not be discussing the particulars in public. However, if some guys want to experiment for themselves, and find out "how it works" you may use some of the info discussed here as a guide to develop your own experiments, and come to your own conclusions.

------------------------- Original post follows:

Experimenting with another sensor tweak on the VE-cars. (not PD) Seems to help a lot with smoke and better power to boot, especially in hot weather.

Here it is: cut the wire going to the fuel temp sensor, and also the Intake Air temp sensor, and insert a 2200 ohm resistor in-line in each of them to fool the computer into thinking the fuel and intake air are cooler than it actually is.

If you do just the fuel, the car idles funny, but if you do both, it's good.

Maybe just my imagination, hopefully someone else can try it and verify/refute. Let the discussions begin. ;)
 
Last edited:

Mike_M

Veteran Member
Joined
Sep 23, 2003
Location
Phoenix, AZ
TDI
Black 2002 Jetta GLS
Cool mod, Charlie! (pun intended) Just wondering a few things:

* Would there by any reason NOT to do this if one had a few mods, for example: PP520s and RC2?

* Okay, I know that hot air isn't as dense as cool air, which is why we have intercoolers. But would there be any actual HARM to burning hot air with advanced timing? Would it hike the EGTs dangerously, or try to melt pistons or anything?

* Same for hot fuel...I've seen it said that injection pumps don't like hot fuel. I'm not doubting, but just looking for a definitive word...do we have proof of this? Does pumping hot fuel kill injection pumps (or anything else for that matter)? Would advancing timing with hot fuel hike EGTs dangerously, melt pistons, etc?

* I think I've actually read (will try to dig up the thread) that hot air and fuel actually combusts better, and might yield better MPGs? If there any evidence for this? Would you expect MPGs to go up, down, or sideways? :D

That said, how heavy-duty of a resistor would you need, as far as current? 1/4 watt? More needed? Is less adequate?

Mike
 

KERMA

Vendor , w/Business number
Joined
Sep 23, 2001
Location
here
TDI
99 beetle and 04 jetta
EGT seems lower.

The "heated veggie oil" guys will probably benefit the most. That's what got me thinking about this in the first place. These guys are feeding their injection pumps a steady diet of 200F fuel. That's hotter than the fuel ever gets from the tank. No wonder the mileage and performance suffers if the ECU pulls timing to keep NOx down. The hot fuel does not inherently hurt performance, because some of the truck guys are finding that HEATING the fuel adds HP on the dyno. So it must be the ECU. If it's the ECU, it's an emissions thing.
 

FlyTDI Guy

Top Post Dawg
Joined
Nov 3, 2001
Location
PNW
TDI
'01 Jetta GLS
Has anyone logged this 'timing pullback'? I'm in the midst of collecting some fuel and IAT temp logs, maybe I'll look at timing as well. A good strong WOT, all gear romp up to 100+ should show it, right? We'll see...

Addendum: If this is such a performance killer, couldn't this be compensated for by Jeff in his RC offerings? If not a new map, perhaps an adjustment to that particular offset/increment into the existing map?
 
Last edited:

Ed's TDI

Top Post Dawg
Joined
Jan 30, 2001
Location
Victoria, BC, Canada
TDI
'01 Bora and '97 A4 1.8T Quattro (future TDI conversion maybe?)
Nice work, Charlie. Funny thing is that Jose and I were discussing this "cooling" vs "heating" stuff while doing the turbo install. I was intially toying with getting a fuel cooler and FMIC and was running it by Jose and he was saying that I should hold off and see the results of the turbo by itself beofre dumping cash that might not result in any more power. He went on to say that there has to be a certain amount of heat in the engine for optimal performance in order to get the most "bang" for you buck and if there's too much cool air or fuel it could actually have a negative effect on producing power. Seems you're providing actual proof with this little setup.

It would definitely be nice to see some more examples of this if someone else could coroborate Kerma's theory.
 

Sootman

Veteran Member
Joined
Jan 30, 2003
Location
Maine Coast
TDI
2011 Golf TDI
KERMA said:
Here it is: cut the wire going to the fuel temp sensor, and also the Intake Air temp sensor, and insert a 2200 ohm resistor in-line in each of them to fool the computer into thinking the fuel and intake air are cooler than it actually is.
OK, I'll bite, which wire? When I look at my Bentley I see the connector for the fuel temp sensor is tested by putting an ohm meter between terminals 4 and 7. For the Air Intake Sensor it's measured between 1 and 2. I realize you are suggesting cutting the wire from the ECU to each od these sensors. Where exactly? Got a picture? I'm pretty dumb with some of these things.

Thanks
 

Mike_M

Veteran Member
Joined
Sep 23, 2003
Location
Phoenix, AZ
TDI
Black 2002 Jetta GLS
KERMA said:
The "heated veggie oil" guys will probably benefit the most. That's what got me thinking about this in the first place. These guys are feeding their injection pumps a steady diet of 200F fuel.
Holy crap! Well, how about guys in the desert? My fuel temps have never been below 150 on the ECU's scale (whatever that translates to in degrees) when I've checked. Mostly I've checked in the summer.

The hot fuel does not inherently hurt performance, because some of the truck guys are finding that HEATING the fuel adds HP on the dyno. So it must be the ECU. If it's the ECU, it's an emissions thing.
That's what I suspected. I remember that gdr703 or TornadoRed or somebody had said something about hot fuel and/or air actually combusting better elsewhere, but I can't find that thread now. :mad: Figures it'd be an emissions thing.

Mike
 

KERMA

Vendor , w/Business number
Joined
Sep 23, 2001
Location
here
TDI
99 beetle and 04 jetta
FlyTDI Guy said:
Has anyone logged this 'timing pullback'? I'm in the midst of collecting some fuel and IAT temp logs, maybe I'll look at timing as well. A good strong WOT, all gear romp up to 100+ should show it, right? We'll see...

Addendum: If this is such a performance killer, couldn't this be compensated for by Jeff in his RC offerings? If not a new map, perhaps an adjustment to that particular offset/increment into the existing map?
Unless that 100+ run heats up the fuel significantly, you won't see anything. But you can defintely tell a difference between a full tank of fuel and when the low fuel light comes on. ANd also on a hot day versus cold day, and after driving all day versus just starting out. You can also watch requested timing at idle change in a veggie oil system after the "switch" from (cool) diesel to heated veggie oil. Idle timing will change from about 2 degrees to about 0.5 degrees, and the car quiets down. This timing change, and the dynamic timing change during driving, have nothing to do with "limiting peak cylinder pressures" for safety, it's all about cutting NOx.

Yes, fuel temp derating is a map changed in certain RC tunings.

Fuel temp sensor: pin 7 = yellow/bluestripe
pin 4 = brown/blue stripe

IAT sensor: pin 1: brown/ blue
pin 2: Grey/ Green

Here is a table with the different resistances at various degrees C in case you want to try different resistance values:

C Ohms

0 5000-6500
10 3350-4400
20 2250-3000
30 1500-2000
40 900-1400
50 700-950
60 530-675
80 275-375
100 150-230

This table is the same for IAT and fuel temp.

IAT and MAF affect fueling and therefore peak power, through the smoke maps. Yes, that is changed in chip tuning. You can log these things quite easily on your "hard run". A false low IAT may make more smoke at high load conditions, all else equal. But the advanced timing will compensate for that somewhat when you fool the fuel temp. PEAK timing won't change, still max out at 12 degrees, but part throttle response is definitely affected. PArt throttle timing is what makes it "feel snappy"
 

Mike_M

Veteran Member
Joined
Sep 23, 2003
Location
Phoenix, AZ
TDI
Black 2002 Jetta GLS
FlyTDI Guy said:
Has anyone logged this 'timing pullback'? I'm in the midst of collecting some fuel and IAT temp logs, maybe I'll look at timing as well. A good strong WOT, all gear romp up to 100+ should show it, right? We'll see...

Addendum: If this is such a performance killer, couldn't this be compensated for by Jeff in his RC offerings? If not a new map, perhaps an adjustment to that particular offset/increment into the existing map?
The fuel temp "pullback" is actually well-publicized, in the form of the "TDI timing" graph from VAG-COM...

http://www.ross-tech.com/vag-scope/TDIGraph.html

Mike
 

Mike_M

Veteran Member
Joined
Sep 23, 2003
Location
Phoenix, AZ
TDI
Black 2002 Jetta GLS
KERMA said:
Fuel temp sensor: pin 7 = yellow/bluestripe
pin 4 = brown/blue stripe

IAT sensor: pin 1: brown/ blue
pin 2: Grey/ Green
So, on which pins are we supposed to put the resistors? All 4 listed, or just pins 7 and 1?

P.S. Are those the pins (numbered that way) on the ECU harness? Or on the inidividual sensors?

Mike
 

Slave2school

Top Post Dawg
Joined
Mar 20, 2004
Location
Angus, Ontario
TDI
99.5 used to at least...
You likely put the resistor accross the two pins for each sensor like the evry mod. (My guess, go try it) :D Actualy the wording of the initial post indicates otherwise... "insert a 2200 ohm resistor in-line in each of them to fool the computer into thinking the fuel and intake air are cooler than it actually is. "

Pictures would be great, if I get this done I could post on cold(er) starting since It's going down to about 5C nightly here.
 
Last edited:

KERMA

Vendor , w/Business number
Joined
Sep 23, 2001
Location
here
TDI
99 beetle and 04 jetta
Cut one wire and inster a resistor to raise the resistance value that the ECU sees. Do this in one wire in each sensor. You are trying to0 raise the resistance value, this should be apparent from the resistance vs temp table. Interesting to note that the lower the actual temp gets, the less effect the resistor has.
 

Slave2school

Top Post Dawg
Joined
Mar 20, 2004
Location
Angus, Ontario
TDI
99.5 used to at least...
Excellent so it shouldn't actually matter for cold starting and simply enhances/eliminates some emmissions crippling nox reduction/efficiency reduction. Have you noticed any difference in fuel economy with this mod?
 
Last edited:

jamest

Veteran Member
Joined
Oct 19, 2004
Location
Arizona
TDI
05 Jetta Wagon, 02 Golf
Some pics would be nice. Everything is better with pictures. :) Sounds like an interesting mod. I think I'd like to try it. We have plenty of heat out here in the Sonoran desert.

Mike, let me know if you try this too...
 

indytdi01

Well-known member
Joined
Jul 26, 2004
Location
MO
TDI
01 Reflex Silver
so anyone try this yet. when i get back i want to try it out. can you increase mpg at the same time/?
 

vwdsmguy

Veteran Member
Joined
Jul 5, 2004
Location
Syracuse, NY
TDI
2002 Golf black 5-spd
Sensor tweek

I have been wondering what, I think, has been making my TDI more underfueled or retarded than it should be. I have measured the air temp section of the MAP sensor. This sends a voltage to the ECU relative to the air temp. it sees.
I actually measured the MAP probe temp off the car, measuring the gray wire voltage and reading from a MAP sensor graph what this equates to in C*. My MAP sensor sends a voltage that equates to 60* to 80*F higher than the actual air temp. This has not caused a fault code in the months so far. It may not out of spec enough.
Could this higher than actual air temp. cause the ECU to cut back the fuel??
The MAP is consistantly off about 70* from 60*F to 160*F that I measured. The Air temp part of the MAP puts out about .5V to 1.5V with a 5V input to the sensor. These MAPs cost about $120.00. Is there a way to raise the voltage signal about 1.0V for cheap SOBs like me? Even with this the VAG COM air temp reading seems correct.
I submitted this a few months ago with no replys. You have got my interest now. YES YES
__________________
 
Last edited:

Mike_M

Veteran Member
Joined
Sep 23, 2003
Location
Phoenix, AZ
TDI
Black 2002 Jetta GLS
KERMA said:
Cut one wire and inster a resistor to raise the resistance value that the ECU sees. Do this in one wire in each sensor. You are trying to0 raise the resistance value, this should be apparent from the resistance vs temp table. Interesting to note that the lower the actual temp gets, the less effect the resistor has.
Three more questions, if you don't mind, Charlie:

* Is a 1/4 watt resistor adequate? Too much? Too little?

* Would this affect cruising too? i.e., should I expect more efficiency on the freeway?

* Are those pin numbers you gave at the ECU harness?

I'm guessing from your temp/ohms chart that the tolerance of the resistor (5%, 10%, etc) won't matter...even 20% of 2200 ohms looks like it won't change much after you add the 2200.

Mike
 
Last edited:

shortysclimbin

Veteran Member
Joined
Oct 15, 2004
Location
Virginia currently
TDI
Kubvan, mk2 golf, mk6 golf
Mike,

a 1/4w 5% ressistor should work fine for this. if the ecu was recieving more power than that I would be very surprised. BTW kerma, what about higher or lower values? how did we determine 2.2k?
 

woofie2

Veteran Member
Joined
Feb 11, 2004
Location
Republic of Southern Illinois
TDI
Former TDI owner
KERMA said:
Cut one wire and inster a resistor to raise the resistance value that the ECU sees. Do this in one wire in each sensor. You are trying to0 raise the resistance value, this should be apparent from the resistance vs temp table. Interesting to note that the lower the actual temp gets, the less effect the resistor has.
so what you have done is slide the resistance values so the car thinks it is cooler out than it is, not force it to think it is between 0 and 20*C all the time.

So extrapolated from your original table:
0 5000-6500
10 3350-4400
20 2250-3000
30 1500-2000
40 900-1400
50 700-950
60 530-675
80 275-375
100 150-230

you get the new table by adding a 2k ohm resistor-
-8 7000-8500
0 5350-6400
15 4250-5000
16 3500-4000
17 2900-3400
18 2700-2950
19 2530-2675
20 2275-2375
21 2150-2230
(temp estimated, ohm range calculated from table above, a 2.2k ohm resistor in series would raise the values by 200 ohms, slight change but you get the picture.)

I wonder how this would test in a hotter climate if more fuel sooner would raise cylinder temperatures drastically. (more fuel, hotter air, and more timing advance could mean higher cylinder temperatures, because there is more fuel burning longer.

Someone with a heated grease system could just do this just to the fuel temp sensor, with just a 1k ohm resistor. Thus when their fuel is heated they would not see much differance between diesel, but have more power. and better mileage.

I am thinking about doing this with a DPDT switch to flip between 0 and 2.2k ohm, (switching while the engine is off) to be able to flip to a performance mode when racing.

shortysclimbin said:
BTW kerma, what about higher or lower values? how did we determine 2.2k?
see math above, running a larger resistor slides the graph to a colder temp, by adding restiance your a making the car think it is cooler outside.
 
Last edited:

Slave2school

Top Post Dawg
Joined
Mar 20, 2004
Location
Angus, Ontario
TDI
99.5 used to at least...
Hey guys I tried this mod out.

My observations with a 2.2k restor(s)

Car idles just fine with only the fuel temp modified, and car produces no boost at all (ok 1-2psi) with the IAT sensor modified. Don't ask me why. I used Brown/blue stripe for both the harness and the IAT. After a short test with no boost I stopped and removed the IAT resistor, just twisted the wires back together to get home.

Nadda smoke with stock settings (as we should hope) maybe my imagination but improved throttle response all around.

With the Evrymod on cranked up a bit more....a massive reduction in smoke. Instead of the usual opaque black cloud I usually get when I turn the mod up higher than it should be, I get a haze (an initial black PUFF when standing on it but then fades to grey/white/blue). It doesn't take long for my pump to heat the fuel up either, a trip around the block on a hot day is usually enough to get it up high enough for vag-com timing check.

Thanks for this mod, I'll keep you posted. and any ideas why my car pulled all the boost?
 

Mike_M

Veteran Member
Joined
Sep 23, 2003
Location
Phoenix, AZ
TDI
Black 2002 Jetta GLS
Slave2school said:
Thanks for this mod, I'll keep you posted. and any ideas why my car pulled all the boost?
Only thing I can think is some sort of short or other electrical problem? Maybe wrong wire? Faulty connection, resulting in near-infinite resistance?

I can't imagine why it'd pull all the boost, other than electrical problem with the resistor or the connection.

Would you want to try the gray/green for IAT and see what happens?

Mike
 

Slave2school

Top Post Dawg
Joined
Mar 20, 2004
Location
Angus, Ontario
TDI
99.5 used to at least...
I'll try that tomarrow. But I'm not sure, do the 99's have the same setup as the 00-03? I am sure it was the right wire, and the resistor was good, I tested it out before hand. The electrical connection should have been fine too, not soldered but twisted a bunch and taped up. I'm doubtful there was a prior electrical problem as well. I'm betting it has to do with the car being an early model. REally of the two connections you have to make I thought I was goignt o bugger up the fuel harness, the area is much tighter to work with then snipping the wire that runs along the intercooler tubing.

The fuel sensor mod definately works though, no doubt much much less smoke with the evry turned up *and a warmed up car (so easy to roast the 17's with that up higher now) :D

REally honestly before I only liked to use the evry mod to PO tailgaters, but it is much more useable now, even around town, just a dark gray haze instead of black billowing clouds of death when you floor it.

In theory could you not just replace the resistor in the pump with a wire now and run a variable resitor that you can play with for the temperature outside? :|
 
Last edited:

Slave2school

Top Post Dawg
Joined
Mar 20, 2004
Location
Angus, Ontario
TDI
99.5 used to at least...
Hey Guys, it is 16c outside right now and after about a 15 minute drive my fuel temp reports 11.4c in vag-com. Anyone else tried this yet?
 

dabear95

Veteran Member
Joined
Sep 26, 2002
Location
Roseville, MI
TDI
2002 Golf GLS, Silver
Nope, but I am interested and at the same time worried since we expirance some cold nights in Michigan...



Jason
 

Slave2school

Top Post Dawg
Joined
Mar 20, 2004
Location
Angus, Ontario
TDI
99.5 used to at least...
Fired right up for me tonight, but it's not exactly "cold" yet. I'll let you all know how it works when it does actually get in the sub-0's

While we are on the topic of cold...I'm thinking that since the RC program does de-rate the temp already (I think I read that up there) then folks who aren't chipped can likely run a greater resistance correct?
 
Last edited:

dabear95

Veteran Member
Joined
Sep 26, 2002
Location
Roseville, MI
TDI
2002 Golf GLS, Silver
S2S,
Where did you read that?


I am also interested in Kerma's thermostatic "T" replacement but I'm not sure I want to run it for 8 months and swap it out for the rest of the year...

I know I have a few ponies on the table, but at what cost?

Jason
 
Top