Hard to start when hot

justaguy

Active member
Joined
Apr 14, 2004
I have a 98 New Bettle TDI that starts right up when it is cold but once it is hot it cranks from 3-5 seconds before it starts. The car has 40k Miles on it. Right now the MAF is unplugged until I can get a new one. I am not sure if the MAF is the cause of this or is the timing off. Thanks
 

justaguy

Active member
Joined
Apr 14, 2004
I don't see what the starter has to do with this. It cranks just fine. It just takes longer for it to start up when it is hot.
 

Cosmic Green

Veteran Member
Joined
Nov 8, 1999
Location
Udora,Ontario, Canada
TDI
2005 Jetta wagon
I had exactly the same problem a couple of years ago. A new battery cured it. Like it was mentioned, it looks for 250 r.p.m. before injecting fuel into a hot engine. Once the new battery was in, I could tell right away it was turning over faster.
 

Hamman

Veteran Member
Joined
Oct 4, 1999
Location
Warren, OH
TDI
No TDI's, but an '84 Rabbit diesel
Been going through this for four years. Do a search and you'll see lots of info. For me, new starter and battery were only temp fixes (currently running with red top optima)
If you pull the temp sensor plug and crank, you'll see it start up hot immdediately. Be careful if you don't have a vag-com, because you'll generate a CEL. My remedy was to throw a switchable 6,000 ohm resistor into the temp sensor circuit so the engine thinks it's cold when it is hot and won't start.
 

rdkern

Top Post Dawg
Joined
May 21, 2004
Location
Humboldt Co CA
TDI
Passat 1997 silver (sold after 11 years), Jetta 2000 atlantic blue
Hamman - this seems strange. How's your timing? I'm trying to understand how unplugging the temp sensor would fix this problem.
 

MCathcart

Veteran Member
Joined
Apr 18, 2001
Location
North Myrtle Beach, SC
TDI
2003 Jetta
Hamman, I'm with you... I am almost 100% positive battery and starters are not the correct fix. Yes, if spinning the engine faster it will decrease the amount of Winding before it kicks.

Did you try changing the temp sensor or did you test it hot and cold to see what the values were. I have not done my starter yet but comparing our 2001 Jetta to the 1998 Beetle they seem to turn over at the same speed (but the Jetta Tdi) will be running in one Bump of the starter (No Winding). The Beetle will take 3 to 5 seconds. I've considered cleaning the carbon off my injectors. (I'm not here to prove anyone wrong, I'm looking to solve my cranking problem.) I'll try unpluging the sensor today to see what happens.

Mike
 

Hamman

Veteran Member
Joined
Oct 4, 1999
Location
Warren, OH
TDI
No TDI's, but an '84 Rabbit diesel
All i can figure is that when the engine thinks it's cold
(temp circuit absent or high resistance), the timing changes
and the glow plug circuit activates. All I know is that I now have a little red button that I push when I know the engine is hot and it starts up right away!

BTW, I checked everything out from MAF to temp sensor to timing before resorting to this solution.
 

rdkern

Top Post Dawg
Joined
May 21, 2004
Location
Humboldt Co CA
TDI
Passat 1997 silver (sold after 11 years), Jetta 2000 atlantic blue
The gp circuit is not needed with a hot engine. It might mask other problems, but, if all is running correctly, the gps shouldn't glow at all in this situation.

Do I understand that you did change the temp sensor originally and it still wouldn't work?
 

mjbach

Veteran Member
Joined
Jun 1, 2001
Location
Apple Valley, MN
TDI
99.5 Golf
Hamman-Your idea is exactly what I've been looking for! Thanks for posting.

Since March, 2002, we've been throwing money at the same problem you describe. Several starters and batteries have not fixed the problem. In fact, the last starter when up in smoke and left me stranded at the grocery store parking lot. At least it was warrantied.

The long cranking warm start problem started after accidently fueling up with gas.

When we disconnected that temp sensor on the side of the engine, just as you described, it starts immediately--even when the engine is warm.

Replacing that sensor and also the cheaper sensor inside of the fuel pump did not help at all.

The dealership said we'd have to replace the fuel pump which was very expensive. I just tolerated the problem.

I've posted about this many times in the past and it's great to read of your work around idea.

If you have the time, I would like to know where you purchased the resistor. THANKS!
 

rdkern

Top Post Dawg
Joined
May 21, 2004
Location
Humboldt Co CA
TDI
Passat 1997 silver (sold after 11 years), Jetta 2000 atlantic blue
Hamman -

Resister in series or parallel to sensor? Or totally different circuit?
 

mjbach

Veteran Member
Joined
Jun 1, 2001
Location
Apple Valley, MN
TDI
99.5 Golf
Bump. Would like to know details, too. My husband is kind of stubborn in not doing this mod. We actually talked about it months ago but for some reason he puts it off. Says it might throw codes, or the sensor has 4 wires and he doesn't know which two to pick for the switch, or blah, blah, blah. Not important to him because I usually drive the TDI and 99.9% of the time it starts even after a longer crank.

Please and thank you!
 

weedeater

Top Post Dawg
Joined
Mar 17, 2001
Location
Reston, VA
TDI
Jetta, 2001, Baltic Green
Series.

You're fooling the ECU into thinking it is cold which changes the timing. Bet your base timing is retarded.

Had this happen on my old Volvo diesel after a TB change. Very hard to start when warm. Turned out to be retarded timing because "the belt stretched" though I think they didn't tighten up the pump bolts.

BTW: I think this mod also can fool the ECU into turning on the coolant glowplugs on a cool/cold day. The ECU looks for a 'pretty cold' temperature (like 0*F) before activating them so this might do it.
 

whitedog

Veteran Member
Joined
Jul 12, 2004
Location
Bend, Oregon
TDI
2004 Jetta that I fill by myself
I think this mod also can fool the ECU into turning on the coolant glowplugs on a cool/cold day. The ECU looks for a 'pretty cold' temperature (like 0*F) before activating them so this might do it.
It is 40 deg. F. So the ambient temp is still pretty warm when the glow plugs come on.
 

rdkern

Top Post Dawg
Joined
May 21, 2004
Location
Humboldt Co CA
TDI
Passat 1997 silver (sold after 11 years), Jetta 2000 atlantic blue
I still wonder about this. Does this turn on the gps, or change the timing? I've got to measure the ohms on my sensor when cold, and also when hot. There is something wrong with a car that doesn't start properly without this. Most don't need this resistor - so it has something that is causing a problem that most others don't. If anyone knows the proper resistance of the temp sensor hot and cold, please let me know. If I can't figure out this problem, I'm sure doggie blanc will.
 

TDIJetta99

Top Post Dawg
Joined
May 17, 2005
Location
Port Jervis, New York, USA
TDI
03... Faster than yours =]
OK my TDI has this same problem... When it's cold, it starts right up, but when hot, about 5 seconds worth of cranking before it starts.. It cranks a lot faster when it's hot too.. With the temp sensor unplugged, it starts immediately when hot or cold with a nice black poof of smoke out the tailpipe. I thought for sure the temp sensor was bad.. When I installed the new sensor, it went back to the normal 5 second crank time when hot... The battery is only a few months old so it's still in good shape. I have no idea when the starter was last replaced but it cranks a good amount faster when it's hot as opposed to when it's cold, so I can rule out the starter. My next step is to check the base timing.. If the computer advances the timing when the engine is cold, that would explain the quicker starting when it's cold (or at least when the computer thinks it's cold) I'm going to a GTG on the 25th... Someone there will have vag-com so I can check the timing then..
 

rdkern

Top Post Dawg
Joined
May 21, 2004
Location
Humboldt Co CA
TDI
Passat 1997 silver (sold after 11 years), Jetta 2000 atlantic blue
Do check the timing. That is a proven cause of hard starting when warm or cold. It's a place to start.
 

Hamman

Veteran Member
Joined
Oct 4, 1999
Location
Warren, OH
TDI
No TDI's, but an '84 Rabbit diesel
Sorry about the delay in reply--- scout camping weekend.
I will try to get pictures of the procdure and a wiring diagram up within the next day or two. The idea behind this
is to set a resistor between the two wires coming out of the harness just behind the temp sensor that DON'T feed into
the temp guage. I can get the numbers on the conductors for you when I get the pictures. The resistor is always in
the circuit and is mostly ignored while the engine is running, but will be the only conductance through the circuit if you send one of the wires (both sides) through to a switch which is a momentary pushbutton normally on.
When you push the button, the only part of the circuit the ECU sees is the resistor, causing the engine to start.


Timing on my car was changed all over the place mechanically
and with Vag-com, having no effect.
 

TDIJetta99

Top Post Dawg
Joined
May 17, 2005
Location
Port Jervis, New York, USA
TDI
03... Faster than yours =]
What you are doing with the resistor is masking the problem.. My car does it too, but I will not hack up my wiring just to put something in there to fool the computer to get my car to start faster... I will take the time to diagnose the car properly... Until I find out exactly what is causing it, I'll just deal with it taking a few seconds to start. . . Just my $.02
 

Hamman

Veteran Member
Joined
Oct 4, 1999
Location
Warren, OH
TDI
No TDI's, but an '84 Rabbit diesel
I couldn't agree with you more. It wasn't easy making the decision to "cut the harness" and put in the extra crcuit.
However,

1) I do not have the time or the $$ to spend another 4 years on attempting a by the book solution. I suspect in my heart of hearts it may be the pump and if it is, I am NOT going to spend all the $$ to buy a new or rebuilt one.

2) I bought this car to save money, not throw it down a hole trying to find out what the problem is. Besides, I am on my third battery now in 5 1/2 years and I believe it is becuase of the stress of extra cranking. The car at this point is just trasnportation, no longer a hobby. If I had to paint pink flowers on the side to make it work, I'd do it.
 

TDIJetta99

Top Post Dawg
Joined
May 17, 2005
Location
Port Jervis, New York, USA
TDI
03... Faster than yours =]
I can understand where you're coming from... I'd probably do the same thing If I were you... The battery in my car was brand new when I bought it so I should be good for a while... If I was paying a shop or (gasp) a dealer to diagnose this, I would've given up a long time ago... I would've sold my car when I had the coolant migration issue... I'm an auto technician by trade, so it just wouldn't be right for me to add something like that... When I find out what's causing my hard starting issue (and I WILL find it), I'll be sure to post it..
 

Hamman

Veteran Member
Joined
Oct 4, 1999
Location
Warren, OH
TDI
No TDI's, but an '84 Rabbit diesel
Please do, I would just like to know what this is....

BTW I haven't been through for a while, but Port Jervis
is a beautiful place. Think we've been through on our way
home from Burlington, VT
 

TDIJetta99

Top Post Dawg
Joined
May 17, 2005
Location
Port Jervis, New York, USA
TDI
03... Faster than yours =]
yup.. you probably went through it on rt 84.. It looks real nice coming down the mountain into town... It's right where ny, nj, and pa meet.. It's not too bad here, there's the bad parts of town that I think just about every town has though. . There's a few cool things here but all in all it's just a regular town.. I think the best thing is the river trips down the delaware river.
 

wpeets

Veteran Member
Joined
Dec 11, 2001
Location
Chateaugay NY 12920
TDI
2014 TDI Wagen Hers
Hamman totally agree and also looking for your post. I have spent a bundle on the repair and nothing works except the toggle switch which was installed by VW Service at my request about two years ago. Engine always fires up immediatly but CEL stays on. Guess they didn't know about the resistor at that time.
 

Hamman

Veteran Member
Joined
Oct 4, 1999
Location
Warren, OH
TDI
No TDI's, but an '84 Rabbit diesel
I would send all the picture I took, except that I can't figure out how to put them in the post...

So if you want the pictures, I can send them via normal
e-mail if you contact me at ND8Y@arrl.org


Anyway, here are the directions without the pics.

First, go to the back side of the engine where the temp sensor is and remove it for easy access. Find the #3 conductor which is on the upper right of the installed sensor is viewed from the driver's seat. After removing about 2 inches of wrap from around the wires, cut the conductor from #3 about 1 inch from the plug. Strip both ends, and solder in a 18-22 guage two conductor wire. You should have about 5 feet of extra length for feed through the firewall grommet which is just above the brake booster.
Once you have soldered (remembering to tape up afterwords or better yet heat shrink) you will feed the two conductor wire into the passenger compartment and find a place to put a small switch. If you look at the picture, mine is on the side of the console to the left of the ashtray. Part numbers are;

Radio shack 275-1548 momentary pushbutton normally closed
Radio shack 271-1335 1/4 watt 10,000 ohm resistor

Solder the wire onto the switch, being careful not to melt the plastic back of the switch. Once that is done, solder the resistor across the two wires wherever convenient.
Tape up carefully or heat shrink.

Whenever you suspect the car will be hard to start, push the
button. Only hold down while cranking and let up once it starts. It should make a difference.

Dave
 

TornadoRed

Top Post Dawg
Joined
Aug 3, 2003
Location
West Des Moines (formerly St Paul)
TDI
2003 Jetta TDI wagon, silver; 2003 Jetta TDI wagon, indigo blue; 2003 Golf GL 5-spd, red (PARTED); 2003 Golf GLS 5-spd, indigo blue (SOLD); 2003 Jetta TDI wagon, Candy White (SOLD)
This needs pictures.

Login to http://pics.tdiclub.com/ and upload your photos there.
Then link to those photos [image]link[/image]

If possible, do not post mega-sized photos.
 
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