Hard to start when hot

PB_NB

Veteran Member
Joined
Nov 20, 2007
Location
Vancouver, B.C.
TDI
1999 New Beetle
cbrpaul said:
Possible side effects of constant cold starts ?

Just trying to look at the angles here !!!
You are right. There are many disadvantages to this work around.

I think who ever is going to perform the mod needs to weigh these factors. For me, I have a plan to reverse the mod once I have the real problem corrected.

Until then, this will certainly buy me some time and save the car from falling appart and me money.

I am going to move towards an RCII soon and see if I can get some extra tweaks done in the areas that affect starting.

Then, with luck, I should be able to undo the mod and return the CTS back OE design. I will look forward to that day.
 

STRANGETDI

Veteran Member
Joined
Sep 20, 2001
Location
East Hampton, CT
TDI
2013 Audi A3 S-Line Premium Plus Quattro - APR Stage II
PB_NB said:
I am pleased to be a new member of TDIclub.com. I have owned my NB for a year now and this is my first experience with a diesel. I must say that out of all the forums that I have used, this one seems to have the most loyal VW owners that I have witnessed.

When I bought the car, the only complaint the former owner had was that the car was sometimes hard to start especially when it was hot.

I put up with this but figured that it was time to do something after throwing another P0380 code, believing that the hard starting and the P0380 were somehow related.

My 99.5 NB was about to get a bunch of new parts; battery, starter, glow plugs, glow plug relay, glow plug harness, $$$ etc...,

Then I signed up with tdiclub.com and came accross the Hammam Mod. I am no stranger to VW ECU's and wiring having performed several gas engine swaps.

I discussed the use of a push button with my wife and she didn't really get it. She drives the car more than I do, so I knew that for this modification to work, I had to automate the process so that she didn't have to worry about pushing a red button at the right time.

Today, I performed the modification but I substitued a simple relay for the prescribed red switch. I tied into the starter solenoid circuit as my trigger and it works. The engine isn't straining to start and there is no button to push.

I used this circuit as my trigger because I wanted to make sure that the 10k resistor was only active when the key was turned to "start".

Here is the wiring plan that I used:
1) Cut and connect the #3 wire (blue and brown or red) from the CTS plug to relay terminal 87a (Normally Closed).
2) Connect the other end of #3 wire to relay terminal 30.
3) Tap into the starter soleniod wire and connect to relay terminal 86.
4) Run a wire to a good ground from relay terminal 85.
5) Connect a 10K 1/4w resistor to relay terminal 87 (Normally Open) and then splice the loose end into the wire connected to relay terminal 30.

I hope this helps those who wish to tackle it.

The only question that I have is the effect on the starter solenoid performance with an extra little current draw to switch the relay.

Pictures of the procedure would be helpful to us non technical types so we can do this. Actual pictures and text always have made various mods and how to's super easy.

I have been having this hot start problem for a couple of years now. In the winter it isn't as bad, just because the engine cools faster.

Thanks for all the info.
 

PB_NB

Veteran Member
Joined
Nov 20, 2007
Location
Vancouver, B.C.
TDI
1999 New Beetle
STRANGETDI said:
Pictures of the procedure would be helpful to us non technical types so we can do this. Actual pictures and text always have made various mods and how to's super easy.

I have been having this hot start problem for a couple of years now. In the winter it isn't as bad, just because the engine cools faster.

Thanks for all the info.
Hi Strange,

Here is a diagram of the wiring that I did:

http://pics.tdiclub.com/data/uploads/69936/Graphic1.jpg

Here is a post with some pics of the Hamman Mod.

http://forums.tdiclub.com/showpost.php?p=1098738&postcount=34

The difference is that I used the starter solenoid circuit and relay rather than the push button. I have not had any CEL's since doing this. And it starts very fast hot or cold. I read that one of the other members is getting a CEL with this mod. I think it is due to the button and holding it down too long after the engine starts trips the ECU into throwing a code for the open circuit. The suggestion was to reduce the resistor to ~4500 ohms. rather than the 10K suggested by Hamman.

Either way, this seems to get the engine started much quicker and easier.

Hope this helps.
 

Eric Dow

Well-known member
Joined
Mar 2, 2000
Location
Austin, Texas
TDI
2005 Jetta Wagon
Readings with different resisters :) Here's some observations of this fix.

1st, the worry about reduced mileage and extra fuel consumption... Don't worry, I have some facts to back this one :) Nope, no problem with extra fuel or reduced mileage. I checked in VAG-COM and also did before and after resistance readings. With the documented proceedure, the resister is in Parallel with the factory temp switch/sender. This means that the electricity will take the lowest resistance path. As the temp goes up, the switch/sender actually lowers the resistance, so the 10k or 4.7k ohm resister actuall get's ignored. When the switch is thrown, the temp goes down to the following, and right back to real temp as soon as released:

10k ohm = -15 degrees cel. Not necessary, too low and turns on glow cycle
4.7k ohm = 2.7 degrees cel. This is good, only starts short glow cycle
3.28k ohm = ~24 degrees cel. This is probably the best setting IMO. It doesn't cycle the glow plugs, but does modify injection timimg and starts real easy.
1.67k ohm = 56 degrees cel. on the warming up side.
Somewhere between 3.28 and 1.67 is where the ECU will stop considering the car cold and assist starting.

So, what I'm getting at is this, no codes with this mod, no lasting affects past the release of the switch after starting. So if you have replaced the temp sender, starter, battery and confirmed that your injection timing is good, and don't want to do any more with your pump, or fear that it's on it's way out, give this one a try :)

P.S. On the New Beetle, it's cleaner to splice the ECU side of the circuit. You can make it totally invisable and put the switch anywhere ya like.

PB_NB said:
Hi Strange,

Here is a diagram of the wiring that I did:

http://pics.tdiclub.com/data/uploads/69936/Graphic1.jpg

Here is a post with some pics of the Hamman Mod.

http://forums.tdiclub.com/showpost.php?p=1098738&postcount=34

The difference is that I used the starter solenoid circuit and relay rather than the push button. I have not had any CEL's since doing this. And it starts very fast hot or cold. I read that one of the other members is getting a CEL with this mod. I think it is due to the button and holding it down too long after the engine starts trips the ECU into throwing a code for the open circuit. The suggestion was to reduce the resistor to ~4500 ohms. rather than the 10K suggested by Hamman.

Either way, this seems to get the engine started much quicker and easier.

Hope this helps.
 

dataiv

Veteran Member
Joined
Feb 12, 2005
Location
Ottawa, ON
TDI
2015 Golf Wagon TDI 6MT
Interesting observations Eric. I wonder though, I don't think that the low temperature reading of -15 C will harm anything. Because the way I see the system operating is you turn the key on, and it reads the temperature, decides how long to glow for (if at all). When you turn to start, and the reading is -15 C for a brief second, this doesn't affect glow plug operation. So, whether the temperature reported by the sensor (resistor) during starting is -15 C or 24 C, it doesn't make any difference with respect to glow plug operation.

I'm not sure, but this is the way I would guess that it works.
 

whitedog

Veteran Member
Joined
Jul 12, 2004
Location
Bend, Oregon
TDI
2004 Jetta that I fill by myself
xbangu said:
I am having this problem for a few month now, is all the wiring the same for a PD?

thanks
The PD is a completely different beast. Look elsewhere for the problem.
 

dqa

Veteran Member
Joined
Jun 1, 2002
Location
Alabama
TDI
RIP: 1999½ New Golf GL TDI satin silver
PB_NB said:
Here is a diagram of the wiring that I did:


1) Cut and connect the #3 wire (blue and brown or red) from the CTS plug to relay terminal 87a (Normally Closed).
2) Connect the other end of #3 wire to relay terminal 30.
3) Tap into the starter soleniod wire and connect to relay terminal 86.
4) Run a wire to a good ground from relay terminal 85.
5) Connect a 10K 1/4w resistor to relay terminal 87 (Normally Open) and then splice the loose end into the wire connected to relay terminal 30.
I was trying to use your drawing and instructions in combination with the drawing by MCathcart of the Hamman mod on this thread (post #316):

Hard to start when hot issue...

Unfortunately, besides your using a Bosch-style relay and MCathcart using a Radio Shack ice cube, the wiring also seems to be different - you run the resistor from Normally Open to Common, while MC runs it from Normally Open to Normally Closed.

These may be trivial differences, but since I have a pretty weak grasp of auto electrical systems and relay terminology, and I also wasn't sure about where the starter wire would be found, I had to abort my planned mod this past weekend.

I was wondering if you or another knowledgable member could provide some more specifics to help the more ignorant among us. Now that I have a Bosch instead of a RS, I'm ignoring the MCathcart diagram altogether. Having placed your 5-step instructions next to your diagram without confusion introduced from the other diagram, it makes much more sense. However, I need more detailed instructions on steps 3 & 4:
PB_NB said:
3) Tap into the starter soleniod wire and connect to relay terminal 86.
4) Run a wire to a good ground from relay terminal 85.
A. How do find the starter solenoid wire? (Visual descriptions, references to Bentley, Haynes, or ETKA all acceptable)
B. Where would I find "a good ground"?
C. What is the preferred way to tap into the starter solenoid wire?

And one last question...does intermittent failure of my dash engine temp gauge have anything to do with this, or does it just mean that my blue coolant temp sensor is 3 years old and putting in for retirement?
 
Last edited:

PB_NB

Veteran Member
Joined
Nov 20, 2007
Location
Vancouver, B.C.
TDI
1999 New Beetle
Hi dqa,

The wiring in both images is very similar.

You need to look at this as 2 different circuits.

The first one is the trigger that runs from the starter solenoid to the relay and then to ground. That turns the switch on and off.

The other is the resistor circuit which applies the 10k resistor on the normally open circuit when the key is switched to "Start". This circuit returns to normally closed.

Thats about all there is to it. This Mod tricks the ECU into thinking that the engine is cold even when it's hot. It only affects the car while the key is turned to start, otherwise there is no change to the normal running of the engine.

I hope this helps.
 

dqa

Veteran Member
Joined
Jun 1, 2002
Location
Alabama
TDI
RIP: 1999½ New Golf GL TDI satin silver
Thanks for that overview - it does make a bit more sense now.

I'm still at a blockade on the technical questions, any quick pointers?

A. How do I identify the starter solenoid wire?
B. Where would I find "a good ground"?
C. What is the preferred way to tap into the starter solenoid wire?
 

PB_NB

Veteran Member
Joined
Nov 20, 2007
Location
Vancouver, B.C.
TDI
1999 New Beetle
dqa said:
Thanks for that overview - it does make a bit more sense now.

I'm still at a blockade on the technical questions, any quick pointers?

A. How do I identify the starter solenoid wire?
B. Where would I find "a good ground"?
C. What is the preferred way to tap into the starter solenoid wire?
There are 2 wires that connect to your starter. One big one comming off the positive battery terminal and a smaller one a few inches away. That's it, the smaller one. There are many ways to connect to it but longer term connections are always preferred. You don't want any connections to fall apart in a few weeks.

I found a spot on the wire a few inches from the starter. Then I took a small amount of the casing off and soldered my new wire to it. Then I covered the wire in thin layer of rubber sealant and then taped it like crazy.

The ground was easy. I put an eye on the end of this wire and took off a small nut near the wiring loom near the battery. I sanded the coating off the backing bolt surface, applied some dielectric grease to the bolt and put the nut back on holding the eye in place.

I would recommend using the female crimp connections for the wire ends that will connect to the relay. Take to the relay to Radio Shack or a auto parts store to get the right ones.

I tapped into wire #3 on the Temp sensor and soldered the other wires in. Wrapped them up the same way.

The nice part about this is you can completely bypass this mod just by pulling the lead the comes from the starter solenoid at the relay. and test to see if it is working by starting the car and comparing how quickly it starts.

Do some preparation planning and make all the relay connections inside.

If you don't want to solder. You can get some crip connectors that will do the same thing. You can get all these connectors at any auto parts store.
 
Last edited:

dqa

Veteran Member
Joined
Jun 1, 2002
Location
Alabama
TDI
RIP: 1999½ New Golf GL TDI satin silver
Finally installed it last weekend, using the 4.7 kΩ resistor suggested by Eric Dow in post #65. While it does seem to start more quickly at times, other times it seems to be as slow as ever. Haven't found any rhyme or reason to when this intermittent performance occurs. The only thing I could think of is a loose connection on the resistor wire - I'll check that this coming weekend. Any other ideas as to what my issue could be?


Other photos: One Two Three
 
Last edited:

poor1

Veteran Member
Joined
May 3, 2003
Location
UK
TDI
MK4
I have read these posts with interest because I have been plagued with the same problem for about three years. Having had the car from new, when it would start hot or cold on half a turn, it is a damm nuisance. It is a common problem VW have not come to grips with.

Before biting the bullet and putting a relay across the temperature sensor I would be most grateful to know whether any of you that did this modification originally have stuck with it and whether it is :
a)still successful and
b)has had no negative repercussions.
 
Last edited:

Hamman

Veteran Member
Joined
Oct 4, 1999
Location
Warren, OH
TDI
No TDI's, but an '84 Rabbit diesel
I have had the setup for a few years and there has been no side
effect. No relay involved for me, but the intermittent extended
use of the glow plugs, etc seems to have no effect.

Dave
 

PB_NB

Veteran Member
Joined
Nov 20, 2007
Location
Vancouver, B.C.
TDI
1999 New Beetle
My car has been starting better, it turns over faster as well. Other than that, I haven't seen any problems and the relay seems to be hanging in there.
 

poor1

Veteran Member
Joined
May 3, 2003
Location
UK
TDI
MK4
I will just throw this in for discussion:

I am told by a professional diesel specialist that "difficult starting when hot is unlikely to be heater plug related as TDI engines need very little extra heat to start when hot". Possible causes: timing or pump overhaul due.

Could it be that allowing the glow plugs to operate is simply disguising a number of other problems which might be due to wear and tear?.

I wonder how many owners who have had this problem might at some time have inadvertently filled up with petrol instead of diesel fuel, thus bringing about extra wear on the pump due to lack of natural lubrication.
 

MCathcart

Veteran Member
Joined
Apr 18, 2001
Location
North Myrtle Beach, SC
TDI
2003 Jetta
dqa said:
I was trying to use your drawing and instructions in combination with the drawing by MCathcart of the Hamman mod on this thread (post #316):

Hard to start when hot issue...

Unfortunately, besides your using a Bosch-style relay and MCathcart using a Radio Shack ice cube, the wiring also seems to be different - you run the resistor from Normally Open to Common, while MC runs it from Normally Open to Normally Closed.

These may be trivial differences, but since I have a pretty weak grasp of auto electrical systems and relay terminology, and I also wasn't sure about where the starter wire would be found, I had to abort my planned mod this past weekend.

I was wondering if you or another knowledgable member could provide some more specifics to help the more ignorant among us. Now that I have a Bosch instead of a RS, I'm ignoring the MCathcart diagram altogether. Having placed your 5-step instructions next to your diagram without confusion introduced from the other diagram, it makes much more sense. However, I need more detailed instructions on steps 3 & 4:A. How do find the starter solenoid wire? (Visual descriptions, references to Bentley, Haynes, or ETKA all acceptable)
B. Where would I find "a good ground"?
C. What is the preferred way to tap into the starter solenoid wire?

And one last question...does intermittent failure of my dash engine temp gauge have anything to do with this, or does it just mean that my blue coolant temp sensor is 3 years old and putting in for retirement?
Very nice drawing dqa. You have your Resistor to the Normally Open contact, this will work but there's a fraction of a second where the ECU sees nothing. My concern is this might throw a CEL. If you connect your resistor from #30 to #87a then when you open the N.C. contact it sees the resistor instantly. Either way will work fine. (If it throws a error just change it to #87a.)

I used a Radio Shack relay 'cause they're cheap and available. Most any N.C. (normaly closed) relay will work (as long as it 12 volt DC). I "think" Mr. Hamman put the resistor across the Normally closed contact. Pressing the button opens the circuit and uses the resistor. Seems like I did Dick my drawing up. (OUCH!) But... I thought I went back and fixed it.

If I ever get caught up I'm going to do my 1998 at the ECU (and not under the hood)! Getting to the starter selnoid wire is a Pain!

From all my study on what's going on is that once the car (Tdi) is hot the amount of Fuel needed to start the engine is not quite enough. (I disagree with that the Glow Plugs help once it's hot.) When the engine is cold the ECU tells the system "Mo' Fuel" ( & fire the Glow Plugs) and once it's hot, leans the fuel out to where once the engine is running all is fine but shut it down and try to re-crank it and.... and ... and.. Ckack, clack, clack'da clack it does start after a few revolutions but not instantly. What's funny to me is with owning a total of 8 Tdi's not all have this problem. The best "cranker" we had was a 2000 Jetta that would crank as soon as you bumped the starter (it also got 53 mpg).

They're still great cars even with this little problem!
 

poor1

Veteran Member
Joined
May 3, 2003
Location
UK
TDI
MK4
Hot start

1)Could clarify please MCathcart. You say, "if it throws an error, change it to 87a." Is this a typo, you already have the resistor connected between 30 & 87a.

2)I have had mine from new (1989) and then it started on half a turn hot or cold. I suppose compared with a petrol engine which sometimes need such long crank we have been spoilt.

Oddly enough a few months ago I replaced the fuel filter as a matter of routine maintenance and the hot starting improved dramatically. Maybe there had been a slight air leak, or maybe it is due to the filter housing now being mounted marginally higher (not deliberately) than it was.

With a forum such as this and quite a number plagued with this problem it would so useful to find a common denominator.
 

dqa

Veteran Member
Joined
Jun 1, 2002
Location
Alabama
TDI
RIP: 1999½ New Golf GL TDI satin silver
poor1 said:
1)Could clarify please MCathcart. You say, "if it throws an error, change it to 87a." Is this a typo, you already have the resistor connected between 30 & 87a.
Actually he's referring to PB_NB's drawing (last seen in my post #69) which I used to assemble my device seen in post #74. That drawing and my device have the resistor connecting 30 and 87, not 87a.

You can actually see the electrical tape covering the resistor in my photo, coming off 87 on the far right. That red wire loops back to the blue connector at the top, going to 30 on the far left.
 

poor1

Veteran Member
Joined
May 3, 2003
Location
UK
TDI
MK4
Hot Start

Thanks for the clarification.

In post #74 you say there was an intermittent start problem after doing the modification. Did you manage to eliminate it or is it still the same (intermittent).

By the way, did you realise there are mountable Relay Sockets available very cheaply ($2). Even relay sockets with blade type fuse provision. If this was going to be a permanent fixture using a socket, it would not be so obvious that a modification had been done to the wiring.
 

dqa

Veteran Member
Joined
Jun 1, 2002
Location
Alabama
TDI
RIP: 1999½ New Golf GL TDI satin silver
poor1 said:
In post #74 you say there was an intermittent start problem after doing the modification. Did you manage to eliminate it or is it still the same (intermittent).
I haven't actually done anything about it yet. I should clarify that I've only got intermittent improvement compared with before the mod; there is no new intermittent problem resulting from the mod.

Right now I'm waiting on new glow plugs, which had triggered a CEL a couple weeks before I did the mod - I'm not sure whether this could be interfering with the proper operation of the mod. At that point I'll also strip off the electrical tape and verify the intactness of the resistor, and its connections. If I'm still getting only intermittent improvement, I'll try switching the resistor to 87a as recommended by MCathcart.
poor1 said:
By the way, did you realise there are mountable Relay Sockets available very cheaply ($2). Even relay sockets with blade type fuse provision.
Tell me more - do you have a picture or link so I can get an idea?
 
Last edited:

PB_NB

Veteran Member
Joined
Nov 20, 2007
Location
Vancouver, B.C.
TDI
1999 New Beetle
There are some good points raised here. This problem seems to be happening to the older TDI's around 1999 or so. It could just be age or some air leaks allowing loss of prime.

I think the underlying problem may still remain in the software and the aging mechanical items only enhances it.

The mod adds a resistance and tells the ECU that it is colder and adds the GP cycle increase. I think there is a change in the injection timing during cranking which helps increase the cranking RPM's to start the engine quicker.

For me, I did this because I heard of people spending tons of money on batteries and starters and GP's and all sorts of things but those fixes didn't help. I looked at this as cost savings. If my IP is going to fail then at least I can take all that cash I saved and buy another pump if it should fail.

If you have a "hard start when hot" problem simply pull your CTS plug off and try starting the car. If that helps then this fix can help you. Pulling the CTS plug will throw a CEL which you will need to have cleared with a scanner or vagcom.
 
Last edited:

poor1

Veteran Member
Joined
May 3, 2003
Location
UK
TDI
MK4
Hot Start

This post relates to the relay/resistance modification for the Mk4 Golf to aid hot starting. Assuming that the original conception of the modification works reliably and intended to be a long term solution to the problem, as opposed to a temporary hook up, I believe the method described here would make the modification less obvious, with obvious advantages.

Not fitted as yet, but this is a mock up of how I propose doing it.

The Relay mounting block incorporates a provision to mount three flat fuses. The block it self can be mounted to the body by means of a 6mm bolt into a captive nut secured somewhere under the hood.


The picture shows the relay in position on the block. The orange 5 amp “fuse” in the foreground has had the fuse wire removed and therefore there is no connection between the two tabs. The tails of the resistor have been soldered across them. The other fuse (an intact 5 amp fuse) is intended to be connected into the live feed from the starter solenoid to give protection to the solenoid side of the relay, which I consider a desirable feature. All the other wiring will be carried out as previously described under this heading, but obviously into the relay mounting block, as opposed to directly into the relay.

Picture






















http://pics.tdiclub.com/showphoto.php?photo=43419&cat=4021
 
Last edited:

dataiv

Veteran Member
Joined
Feb 12, 2005
Location
Ottawa, ON
TDI
2015 Golf Wagon TDI 6MT
Hello all,

I followed PB_NB's guide, but changed one thing. Instead of connecting the #3 wire from the CTS plug to 87a, I connected it to 30 (common), and then connected 87a (normally closed) to the resistor-free path. 87 (normally open) is still connected to the resistor.

This seemed to make more sense to me, otherwise, when the relay is energized, 87 is not connected to anything and I got a CTS fault code for open/short to plus.

So...

30 is connected to the CTS side of the #3 wire
87 is connected to the resistor and then connected into the wire to the ECU
87a is connected into the wire to the ECU

So, when the relay is not energized (normal operation), 30 is connected to 87a. When the key is in the start position, 30 is connected to 87 (i.e. with the resistor).

Took me a couple hours to do tonight, I took out the battery and battery tray, as well as the air box, so there was lots of room to work.

This works like a champ. Start times when hot are now consistent at about 0.5 seconds of cranking.

The only thing I noticed is that now, always, no matter the actual temperature, after-glow is activated for 2 minutes. Not a big deal I guess, since it always does an after-glow if the coolant temp is below somewhere around 70*C ... so, realistically, there's not many starts that I do where the coolant temp hasn't dropped from 85*C operating temperature to 70*C, so I figure two minutes of after-glow isn't a big deal.

Though, I was reading about the person who did tests with different resistors ... was it after glow they were talking about? (I used a 10K ohm resistor, but could change it easily)
 

PB_NB

Veteran Member
Joined
Nov 20, 2007
Location
Vancouver, B.C.
TDI
1999 New Beetle
dataiv said:
The only thing I noticed is that now, always, no matter the actual temperature, after-glow is activated for 2 minutes. Not a big deal I guess, since it always does an after-glow if the coolant temp is below somewhere around 70*C ... so, realistically, there's not many starts that I do where the coolant temp hasn't dropped from 85*C operating temperature to 70*C, so I figure two minutes of after-glow isn't a big deal.
The afterglow should not be affected because the circuit returns to stock when you let go of the key during cranking. As far as the ECU is concerned nothing has changed and the CTS is sending correct signals to the ECU about the actual coolant temp.

When you changed the wiring, did you put the resistor in the normally closed circuit?

My circuit had to modes:

1) closed with 10K resistance. (normally open)
2) closed with 0 resistance. (normally closed)

Starter controll tripped the normally open.

If so, you will see the engine running like it is cold which may have an adverse affect on your fuel consumption. The CTS employs a temperature controlled variable resistor with an upper limit of 7K ohms and a lower value of 200 ohms when hot (close approximations). The high value occurs when the coolant is cold.

By adding additional resistance to the active circuit is like telling the ECU that the engine is cold all the time, resulting in additional fuel at during a prolonged warmup cycle.
 

dataiv

Veteran Member
Joined
Feb 12, 2005
Location
Ottawa, ON
TDI
2015 Golf Wagon TDI 6MT
I first wired it up exactly as you described, but I got a CEL, and what was happening is that when the relay was energized, it become an open circuit. That's when I looked again and thought about it and wondered if you'd maybe described it wrong by accident.

The resistor is not in the normally closed circuit, it is in the normally open circuit. There is only a path through the resistor when the key is at the start position.

Watching in VAG-COM, I turn the key to on. Coolant temp reported is the actual temp as it should be. I shut off the fuel solenoid so it wouldn't start (just for this test). Then, I turn the key to the start position. Engine starts cranking, and coolant temp as reported drops to -13.7*C. Release the key and coolant temp as reported goes back up to the actual temp as it should be. No CEL.

It works exactly as you originally described, only sending the ECU the 'cold' signal when the starter is engaged.

I did also try, while testing, to see what would happen if the resistor was always in place (this is easy to do in my set up with a relay block/plug, I can also easily remove the mod) ... and, of course, the ECU always sees -13.7*C and runs the engine at a higher than normal idle like it does when it is really cold out. So, the resistor is definitely not being seen during normal operation, only during start. As you described originally.

I think I have it hooked up right, as it works exactly as you said it does. The circuit returns to stock after cranking. Are you absolutely sure you don't get afterglow? Check block 12 in VAG-COM. I get 10110000 (post-glow) after a start, even if the engine is actually already warm. It's as though when the ECU sees the lower temps, even just momentarily because of the resistor, it decides after-glow is needed. I'd really like to know if you get the same thing happening.

PB_NB said:
The afterglow should not be affected because the circuit returns to stock when you let go of the key during cranking. As far as the ECU is concerned nothing has changed and the CTS is sending correct signals to the ECU about the actual coolant temp.

When you changed the wiring, did you put the resistor in the normally closed circuit?

My circuit had to modes:

1) closed with 10K resistance. (normally open)
2) closed with 0 resistance. (normally closed)

Starter controll tripped the normally open.

If so, you will see the engine running like it is cold which may have an adverse affect on your fuel consumption. The CTS employs a temperature controlled variable resistor with an upper limit of 7K ohms and a lower value of 200 ohms when hot (close approximations). The high value occurs when the coolant is cold.

By adding additional resistance to the active circuit is like telling the ECU that the engine is cold all the time, resulting in additional fuel at during a prolonged warmup cycle.
 

PB_NB

Veteran Member
Joined
Nov 20, 2007
Location
Vancouver, B.C.
TDI
1999 New Beetle
That's got me thinking. I will check Block 12 when the my wife returns with car from shopping. Should be good and warmed up.

There is also a way to adjust the glowtimes in vagcom. I read it a while ago on this site. Perhaps that is something worth investigation.

I will let you know what I find later on.
 

dataiv

Veteran Member
Joined
Feb 12, 2005
Location
Ottawa, ON
TDI
2015 Golf Wagon TDI 6MT
PB_NB said:
That's got me thinking. I will check Block 12 when the my wife returns with car from shopping. Should be good and warmed up.

There is also a way to adjust the glowtimes in vagcom. I read it a while ago on this site. Perhaps that is something worth investigation.

I will let you know what I find later on.
Other than this, it works great. My glow time adjustment is at the default (I think it's adaptation channel 12). Actually I have everything at the default. I don't really think some post glow is a huge deal. If I recall correctly, if the coolant temp is < 70*C at starting, you get post glow. I tested it at one point, and I'm pretty sure it was around that temp.

Just went out to get a few things at Home Depot and I am sure happy with the way the car starts now.

Looking forward to seeing if the same thing happens for you, because if it doesn't, then I have a mystery on my hands! :eek:
 
Top