HOW TO tamper with the fuel temp sensor like KERMA

jackbombay

Top Post Dawg
Joined
Mar 12, 2002
Location
Diesel knows best
TDI
A4 Jetta
For more info on what this mod does see the thread Kerma started about it here.

Since we got our first snow of the season I figured it was time to fake out the ECU to think my fuel is extra cool.



I bought a pack of 2200 ohm resistors from Radio shack, they were $.99,



I started by cutting the tape back on the wiring harness where it attaches to the injection pump,



Here is the wire I used, yellow with blue stripe, #7, it is quite thin like much of the wiring under the hood,


Oh yea, it's a lot easier to do this if you remove the vaccum resevoir, two 6 mm allen bolts.

First I cut it and tried to just push the thin wire of the resistor into the wiring insulation, but that was not going to happen, maybe if it was 90* + out, but it wasn't. So I soldered it in, I'm not sure hot hot resistors can get so I did the soldering as fast as I could,



I then coverd it all up with liquid electrical tape,



Here is the first coat, I'll put on a second coat tommorow,



before resistor fuel temp reported in VAG-COM was 16.2* C after the resistor it is 2.7* C :D

BEST FUEL COOLER EVER:D

You can see on the right side of the screen the coolant is 16.2* C the car hasn't run since yesterday,


 

Slave2school

Top Post Dawg
Joined
Mar 20, 2004
Location
Angus, Ontario
TDI
99.5 used to at least...
I had to go out and compare! I get 7.2*C for the fuel temp and 22.6*C for the coolant temp (car has not run today either). Your how-to is great Jack. My IAT was reading 5.9*C That is a cheap intercooler too :)
 

TDIpurdue

Veteran Member
Joined
May 22, 2004
Location
Chicago, il
TDI
My first car: Jetta, '01, silver, automatic
what is the advantage of the computer thinking the fuel is cooler? wouldnt it inject less as cooler fuel is thicker?
 

gottdi

Veteran Member
Joined
Jan 5, 2006
Location
Marysville, California
TDI
2001 TDI Yellow Beetle GLS
Nice mod. You really want that much difference? Seems a bit much. I'd think a little less would be better but then again I am only learning.

Hey! where are you located? Is that Colorado? Snow! Nice!
 

skid9uk

Veteran Member
Joined
Oct 31, 2005
Location
Leicestershire UK
TDI
1998 110
would this be ok on my car? i can get what ever resistiors i need from work today:) do you notice a power increase?

Cheers
 

jackbombay

Top Post Dawg
Joined
Mar 12, 2002
Location
Diesel knows best
TDI
A4 Jetta
I'm in south east Idaho, to quote an old farmer here "we've missed a few summers but we've never missed a winter." :rolleyes: :)

I've only ben on a sort drive so far,the car didn't even fully warm up, after a longer drive where the fuel really warms up I think this mod should keep you from losing power due to retarded injection timing, I'm thinking it'll help MPG more than power.
 

bam_bam_dip

Veteran Member
Joined
Nov 17, 2004
Location
Belton, TX
TDI
99.5 Jetta TDI GL
Now it just needs a catchy name........!!!!! You know, ventectomy, evry, etc.....

Come up with a few and run a poll.
 

gottdi

Veteran Member
Joined
Jan 5, 2006
Location
Marysville, California
TDI
2001 TDI Yellow Beetle GLS
KFC Mod
That's got my vote! :D

Even if a chip can be made to duplicate the same results this mod would be great for those without a mod or with a tuning box. Since neither have the ability to tune it out. Excellent Mod.
 

bam_bam_dip

Veteran Member
Joined
Nov 17, 2004
Location
Belton, TX
TDI
99.5 Jetta TDI GL
Hey Jack, did you do the Intake Air temp sensor as well?? If so, add those pics to your OP.

KFC Mod = Finger lickin' good!
 

jackbombay

Top Post Dawg
Joined
Mar 12, 2002
Location
Diesel knows best
TDI
A4 Jetta
I didn't do the IAT sensor, I live by a huge steep pass and my IAT goes through the roof when I drive over it. My fueling is pretty maxed out, I'm pretty sure my car will smoke some when the IAT gets hot if I add the resistor to the IAT sensor as well... I like a smoke free car.
 

TDIfreak

Veteran Member
Joined
Sep 29, 2001
Location
Finland
TDI
Multivan AHY, Golf CFFB DSG, A6Q 4F 2.7 TDI CANC, 7 meter boat with ALH.
Very nice pics and write up but unfortunately fuel temp has nothing to do with start of injection or 'timing' as you may call it :D .

As someone said you only get less fueling by fooling the ECU to think the fuel is cooler. So in a way you get lower exhaust temps :p .

In addition to IQ and rpms, the only thing affecting start of injection is ...

COOLANT temp!
 

Mike_M

Veteran Member
Joined
Sep 23, 2003
Location
Phoenix, AZ
TDI
Black 2002 Jetta GLS
TDIfreak said:
Very nice pics and write up but unfortunately fuel temp has nothing to do with start of injection or 'timing' as you may call it :D .

As someone said you only get less fueling by fooling the ECU to think the fuel is cooler. So in a way you get lower exhaust temps :p .

In addition to IQ and rpms, the only thing affecting start of injection is ...

COOLANT temp!
That pretty much directly contradicts what VAG-COM reports, and what the TDI timing chart says, not to mention what KERMA and others have specifically researched, and what many others have felt by the "seat of the pants" before and after fuel cooler installs.

I'm not doubting your knowledge level, because I don't know you at all...just pointing out the inconsistency. Where do you get this info?

Mike
 

GuyGuy

Veteran Member
Joined
Apr 19, 2001
Location
Rockland Ontario, Canada
TDI
2012 Passat Comfortline DSG
this is my next mod for sure but i bought 2kohm resistor, so i know it will drop the temps but not as much.

should i bother with it or spend anothe .99c and get some 2.2kohms

thanks
 

FlyTDI Guy

Top Post Dawg
Joined
Nov 3, 2001
Location
PNW
TDI
'01 Jetta GLS
Hey guys... this resistor mod does not drop fuel temps nor does the TDI Timing graph have anything to do with the ECU retarding timing under hot fuel/intake temps.
 

truman

Top Post Dawg
Joined
May 18, 2000
Location
columbia,MO,usa
TDI
'05 Passat Variant, Still miss the 03JW
FlyTDI Guy said:
Hey guys... this resistor mod does not drop fuel temps nor does the TDI Timing graph have anything to do with the ECU retarding timing under hot fuel/intake temps.
Please explain
 

jackbombay

Top Post Dawg
Joined
Mar 12, 2002
Location
Diesel knows best
TDI
A4 Jetta
FlyTDI Guy said:
Hey guys... this resistor mod does not drop fuel temps
Nobody ever claimed it did except for some of us in jest.

FlyTDI Guy said:
nor does the TDI Timing graph have anything to do with the ECU retarding timing under hot fuel/intake temps.
I just ran some Vag-logs, I also have some that are only a week old, pre resistor, at WOT there is no difference in start of injection before and after the resistor, :( . Vag logs before resistor recorded 46* C fuel temp and after resistor it recorded 7* C, fwiw.

KERMA said:
You can also watch requested timing at idle change in a veggie oil system after the "switch" from (cool) diesel to heated veggie oil.
I wonder if it may have an effect at say %50 throttle? or is it just at idle/very low throttle settings that Kerma noted :confused:
 
Last edited:

FlyTDI Guy

Top Post Dawg
Joined
Nov 3, 2001
Location
PNW
TDI
'01 Jetta GLS
What I mean is it doesn't drop fuel temps literally. Maybe I misinterpreted GuyGuy's last statement but... the resistor just fools the ECU, it doesn't actually drop fuel temps. As for the TDI Timing graph... the graph shows timing values while in basic settings. There is no ECU intervention while in that mode. It shows your 'mechanical' timing outside the influence of the ECU.
 

jackbombay

Top Post Dawg
Joined
Mar 12, 2002
Location
Diesel knows best
TDI
A4 Jetta
FlyTDI Guy said:
As for the TDI Timing graph... the graph shows timing values while in basic settings.
Kermas original claim was that hot fuel made the dynamic timng retard, not timing in basic settings, but that doesn't seem to tbe the case for my car.
 

FlyTDI Guy

Top Post Dawg
Joined
Nov 3, 2001
Location
PNW
TDI
'01 Jetta GLS
If I can manage to avoid any peacekeepers, I should have some data later tonight. This topic has my curiosity as well.
 

GuyGuy

Veteran Member
Joined
Apr 19, 2001
Location
Rockland Ontario, Canada
TDI
2012 Passat Comfortline DSG
got me thinking, has anyone checked the fuel injected quantity with hot versus cold fuel. maybe the ecu is injecting less fuel in order to maintain proper emissions.

anyways i just checked my resistors and they are 2.2kohms but are 1/2 watt at 2%.

does that make a difference as everyone else has 1/4 watt at 5%.

electronics is not my forte.
 
Top