Hard to start when hot issue.....

bob_diesel

Well-known member
Joined
Jan 28, 2003
Location
Chesapeake VA
TDI
Jetta 99.5, Jetta Sportwagen TDI 2012
My '99 A4 Jetta has been hard to start when hot since I bought the car. This is my third VW diesel and I thought that this car would operate like the others. I was used to putting the key in the ignition and b-a-r-e-l-y turning the key to have the 'beast' start. The timing is good, nothing sticking with the crossover valve, no fuel leaks, everything looks as it should. Recently, I thought that the coolant sensor was to blame. I ordered a new one, and while waiting for delivery I disconnected the plug. The engine started up right away, and with great vigor, very similar to the way the two older models would start. I put the new coolant sensor in, and back to difficult starting.

Question for all:: are there different software versions for the different model years??
My feeling is that this is a software issue since the car started better with the sensor disconnected??
Any and all thoughts.
 

weedeater

Top Post Dawg
Joined
Mar 17, 2001
Location
Reston, VA
TDI
Jetta, 2001, Baltic Green
I guess the search function is not working. This is an issue discussed at length around here.

S/W is not the problem. Timing is the problem. In fact, how do you know it is 'good'? Hard starting when hot is usually a retarded timing problem.

Or a slow starter. But since turning the GPs on (what happens when you remove the temp sensor) solves the problem, I'll bet on the timing.
 

LNXGUY

Top Post Dawg
Joined
Jan 10, 2004
Location
Barrie, Ont, Canada
TDI
'05 Jetta TDI Wagon
I gotta go with the starter on this one... Take it apart, grease it and see if the problem is still there.

Anyone wanna make some bets? :)
 

Herm TDI

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Nov 21, 2001
Location
Richmond, Maine...The far side of Witsend
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2002 Golf GLS Malone Stage 3, P+520 nozzles, 11MM Inj pump, Sachs VR6 clutch, Stelth Race Pipe, Immo Deleat, EGR Deleat
I'm working on a 99 (A-4) Golf with this very same problem.
The timing is set slightly above the mid-line on the timing graph.
Its not the starter because once the eng. temp sensor (ETS) is disconnected the engine starts flawlessly.

So far I've swapped (with known good units) the electrical load reduction relay and the GP relays. This proved no change in the problem.
I've already replaced the ETC. The GP all check good (.4 to .7) Ohms.

With the ETS unplugged I'm getting battery voltage (12.6 VDC) at each GP harness terminal.

Here is where it gets interesting. With the ETS connected I am only getting 0.13 VDC to the GPs.

When the engine is dead cold....this engine starts just fine. This problem (warm start) happens ONLY when the engine is at normal operating temp (190*F). Shut off the engine ...wait 5 minutes and it takes excessive cranking to get the engine started. Excessive cranking is defined as 5+> seconds of constantant cranking.

This tells me that the circut wiring is not damaged. All of the GP circut components are working. The only thing left is the ECU. But I'm really hesitent condeming this component untill further trouble shooting and diagnostics have been done.

If someone has an answer to this ..I'd like to hear your input
 

LNXGUY

Top Post Dawg
Joined
Jan 10, 2004
Location
Barrie, Ont, Canada
TDI
'05 Jetta TDI Wagon
My car does the same thing.. Starts up quick when cold, when up to operating temps, 5+ seconds before it starts up. So when you unplug the ETS, when the car is at operating temp it starts up right away?
 

Herm TDI

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Richmond, Maine...The far side of Witsend
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2002 Golf GLS Malone Stage 3, P+520 nozzles, 11MM Inj pump, Sachs VR6 clutch, Stelth Race Pipe, Immo Deleat, EGR Deleat
LNXGUY said:
My car does the same thing.. Starts up quick when cold, when up to operating temps, 5+ seconds before it starts up. So when you unplug the ETS, when the car is at operating temp it starts up right away?
Yes...exactly
 

tdi_greendale

Well-known member
Joined
Jan 18, 2004
Location
West Boylston, MA
TDI
1999 Jetta Silver
Car starts hard when warm.

LNXGUY said:
My car does the same thing.. Starts up quick when cold, when up to operating temps, 5+ seconds before it starts up. So when you unplug the ETS, when the car is at operating temp it starts up right away?
I am having the same issue. 1999.5 - starter replaced - glow plugs replaced - new battery - new MAF - this is really annoying. I bought the car with 100k miles on it and it started like that ever since. It now has 170k miles on it. The car starts fine when cold (not like my father's 2003 did when it was new though). I run it for a while (until its up to 190F). Let it sit and then it takes excessive cranks to start (5+ or so). I tried disconnecting the temp sensor and this seemed to help but there is nothing definitive.

My father's 2003 (90k miles) is having an even worse problem, his car starts fine in the cold but when it is warmer out it starts hard, he says it just keep turning over and a light comes on (not sure what light). He stops and trys again. On the 3rd try it starts. Its awful. Seems like a different issue though.

Timing is right within bands also. On mine it seems to start easier if I don't wait for the glowplugs and just start cranking.
 
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mailman

Veteran Member
Joined
Oct 30, 2002
Location
USA - CT
TDI
99.5 Black Jetta TDI
I posted this reply before. I have a 99.5 with the same issue. It is not a timing problem. My timing is set at the top of the graph (advanced) and it doesn't make a difference. New battery, nothing. It's not the starter either, or the anti-shudder valve. No bubbles in the fuel line. It has to be something else.

My understanding of how the software operates (someone correct me if I am wrong) is that when cold, the glow plugs operate and fuel injection begins immediately while cranking. When hot, there is no glow plug operation and fuel injection is delayed until the engine reaches a certain cranking speed (100rpm?).

Is it possible that the crank speed sensor might not be sending a good signal at such a low RPM? Maybe it is a bit out of spec or something. Would be interesting to swap one out with a new sensor or somehow trick the CPU (by sending a generated signal) and see if that makes a difference.

Hey, my 2 cents anyway.
 
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Herm TDI

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Richmond, Maine...The far side of Witsend
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2002 Golf GLS Malone Stage 3, P+520 nozzles, 11MM Inj pump, Sachs VR6 clutch, Stelth Race Pipe, Immo Deleat, EGR Deleat
...Is it possible that the crank speed sensor might not be sending a good signal at such a low RPM? Maybe it is a bit out of spec or something. Would be interesting to swap one out with a new sensor or somehow trick the CPU (by sending a generated signal) and see if that makes a difference.
The engine cranking speed (250 RPM) you are refering to is the minimum "recommended" cranking speed to achive diesel ignition.
This is with a fully charge battery with at least 650 CCA @ 32*F.
However....even with a "weak" battery the engine will eventually still start but hesitently (excessive smoke ect).

However...it wouldn't be that difficault to test your theory by swapping out the engine speed sensor (ESS). The only issue is coming up with a spare ESS.

I'm rather lucky having a full set of A-4 TDI spare relays (that I salvaged from my Golf that was totaled). I use these realys to test & diagnose such problems as this issue.
 

Dana Hanchett

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Mar 6, 2000
Location
Milford, Ma. U.S.A
TDI
2011
IMHO it could be slightly clogged intake manifold. Engine doesn't get a good gulp of air to compress = low cylinder heat = slow start. Add glow plug and get extra heat in cylinder = quick starts. If you preglow and it starts right up forget the starter and battery as you have just place an extra load on the battery.:) :)
 

tdi_greendale

Well-known member
Joined
Jan 18, 2004
Location
West Boylston, MA
TDI
1999 Jetta Silver
engine start hard when warm

Dana Hanchett said:
IMHO it could be slightly clogged intake manifold. Engine doesn't get a good gulp of air to compress = low cylinder heat = slow start. Add glow plug and get extra heat in cylinder = quick starts. If you preglow and it starts right up forget the starter and battery as you have just place an extra load on the battery.:) :)
Not sure who this reply is to but both the vehicles I am discussing had there intake manifolds cleaned recently and were heavily clogged. The problem is that they're starting hard when warm, not when cold. What you're saying is opposite to the issue.
 

Dana Hanchett

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Mar 6, 2000
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Milford, Ma. U.S.A
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2011
tdi_greendale I too thought like you when I had the theory mentioned to me the first time. It is the high temperture of the air in the cylinder that ignites the fuel charge caused by air being highly compessed. That's how compession ignition works. If you can not get a good amount for air in the cylinder the temperture of the air is lower causing a no fire in that cylinder. With the use of glow plugs the cylinders internal air temperture goes up causing a plugged intake manifold engine to start. I guess I didn't understand that when the motor is up to operating temperture that the use of glow plugs helped the situation. That's what I read so that's what prompted my response. Just trying to help. Timing set in the middle of the upper portion of the timing graf will definatly help with slow starting (long crank time) in tempertures that do not require glow plug operation.
 

TMielke2

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Joined
Jul 19, 2005
Location
Charlevoix, MI
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1999.5 Jetta, 1999 New Beetle
This is the exact problem that I am having as well. I have read all the threads regarding timing, mine is in the upper half of the chart on VAG-COM. Nothing has helped.

I have avoided the temptation to wire a switch into the ETS circuit to fool the ECU into thinking it is uplugged when starting warm.

Nothing I have done fixes this. The only change I have experienced is with a change in injector nozzles. The old stock nozzles started a little quicker than the new ones (Sprint 520). I am at 220,000 on my Jetta
 

richieracket

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Jul 27, 2005
Location
New Jersey Shore
TDI
2012 Jetta TDI , DSG
how r u doing with that hard start Herm? I too have one of these "slow to start when warm" buggers here in the shop and have done all that has been discussed here (and other threads) but when warm, she'll crank 4-7 seconds. fire up, no smoke, will run great. This seems to be a relatively common problem. Perplexing.
 

Ann

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Mar 10, 1999
Location
Midcoast Maine
TDI
2009 JSW
Add me to the list. I'm going to set up a session with Herm, but I've done the same as him, and gotten the same results. I've checked the GP harness the same and got the same results! I'm also throwing a CEL code which we will check out also.

My Jetta has a little over 94,000 miles.
 

richieracket

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New Jersey Shore
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2012 Jetta TDI , DSG
very interesting--thanks DeafBug. Still, I wonder why the hard start. I'm going to have to check basic timing again. Wonder if the little bit of play in the cam lock tool amounts to much. Throw off cam timing much? I usually try and shim the play out, but on my own car i don't think i did shim the cam lock. Once i get this Beetle out of the shop (another botched TB---Head is coming off--unbelieveable) I'm going to pull my ride in and do some basic timing checking.
 

Hamman

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Oct 4, 1999
Location
Warren, OH
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No TDI's, but an '84 Rabbit diesel
Just a thought re: ECM's.... Do any of you with this problem
have a car that is chipped or are they all originals CPU's?
I sure would like an excuse to get a rocketchip!

Dave
 

TMielke2

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Jul 19, 2005
Location
Charlevoix, MI
TDI
1999.5 Jetta, 1999 New Beetle
Here is your excuse!

I was running a Wetterauer Chip for a little over a 100k miles. During this time, my hard starting, when warm, after sitting for a bit started.

I installed my ECU that I received back from Jeff at Rocketchip. See my signiture for what I had done. One very nice surpise, the car starts instantly Warm/Cold.

My only question is that I don't know what problem was solved/masked, but I am not going to worry about it. Jeff did say the the cars he has installed the AFN tuning in did seem to start better.

Tom
 

richieracket

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New Jersey Shore
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2012 Jetta TDI , DSG
Hmmmm-my electronics are stock, but that's an interesting monkey in the works. guess maybe we should all check our connections and wiring to ecm first. Be interested to hear from others that have had this situation corrected with chipping or replaced ecm. thanks for the input.
 

tdi_greendale

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Joined
Jan 18, 2004
Location
West Boylston, MA
TDI
1999 Jetta Silver
emc - chipped.

Hamman said:
Just a thought re: ECM's.... Do any of you with this problem
have a car that is chipped or are they all originals CPU's?
I sure would like an excuse to get a rocketchip!

Dave
My father and I have stock electronics. Interested in the chip though but don't want to pay big money. We are strictly for economy. Both our timings were near the upper part of the band before our timing belt changes. It seems after the timing was adjusted to mid-band that we started having poorer MPG numbers and harder starting (can't be sure if the latter though).
 

Dick_Larimore

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Central Indiana
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'05 GL Passat & '05 GLS Passat & '05 Beetle TDI
Re: Why Faster Starts with Coolant Temp Sensor Disconnected

It has been assumed that the reason a hot engine starts faster with the engine coolant sensor disconnected is that the glow plugs are operating. However, if the ECU changes fueling advance and/or the fuel quantity based on the coolant temperature, maybe these changes are what make the engine start more quickly--not hot glow plugs. As I understand the "cold start injector", it operates by kicking up the advance of the fuel injector pump during cold engine startup. It would be interesting to disconnect the glow plug harness from the plugs. When the engine is hot, disconnect the coolant sensor and see if the engine starts quickly. If the engine starts fast, it is not hot glow plugs that make starting faster -- it would either be more fuel injection advance or more fuel injected during engine crank. Injection advance and fuel quantity as the factors affecting startability might explain why some ECU chips make hot engine starting faster. It also makes sense that a cylinder in a hot engine should generate more than enough heat during compression to ignite diesel fuel (glow plugs would make no difference).
 

SCarroll

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Aug 7, 2001
Location
Aurora, CO
I did have a Beetle here that started hard when hot and the performance was down, How is the performance on the majority of these cars? I installed a different set of injectors and it worked great. The car may have seen some gasoline or water in my case to trash the injectors at 110K.
 

mailman

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Oct 30, 2002
Location
USA - CT
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99.5 Black Jetta TDI
Am I the only one who is noticing that every post about the hard starting when warm has a 99.5 model?

I'm almost certain it is a timing advance issue, and maybe the 99.5 models got stuck with an old software rev that was updated for the 00 and up models.

Just a theory.
 

tdi_greendale

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Joined
Jan 18, 2004
Location
West Boylston, MA
TDI
1999 Jetta Silver
How is the performance of the cars with hard start issues?

SCarroll said:
I did have a Beetle here that started hard when hot and the performance was down, How is the performance on the majority of these cars? I installed a different set of injectors and it worked great. The car may have seen some gasoline or water in my case to trash the injectors at 110K.
Performance is fine on both for my Father (80k miles) and I (170k miles).
 

TMielke2

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Joined
Jul 19, 2005
Location
Charlevoix, MI
TDI
1999.5 Jetta, 1999 New Beetle
mailman said:
Am I the only one who is noticing that every post about the hard starting when warm has a 99.5 model?
I'm almost certain it is a timing advance issue, and maybe the 99.5 models got stuck with an old software rev that was updated for the 00 and up models.
Just a theory.
Your theory makes sense. All the cars in this thread are 99 A4's. My hard starting was solved not by a chip (I already had one), but most likely the change to AFN euro tuning maps. Jeff at RC would probably be the one to provide the best insight on this.
Tom
 

amgad

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Marbella, Malaga, Spain
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1998
TMielke2 said:
Your theory makes sense. All the cars in this thread are 99 A4's. My hard starting was solved not by a chip (I already had one), but most likely the change to AFN euro tuning maps. Jeff at RC would probably be the one to provide the best insight on this.
Tom
Anyone come up with any ideas? In my case, the hard starting when warm problem has started gradually (ie. once every so often) and about 10 days ago, it happens all the time. The only logical thing I can come up with is a sensor that has stopped reading, anything else (software) should have been there all the time.

Need help here, ETS been changed, no luck, going to see about the ESS.
 

tdi_greendale

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Jan 18, 2004
Location
West Boylston, MA
TDI
1999 Jetta Silver
amgad said:
Anyone come up with any ideas? In my case, the hard starting when warm problem has started gradually (ie. once every so often) and about 10 days ago, it happens all the time. The only logical thing I can come up with is a sensor that has stopped reading, anything else (software) should have been there all the time.

Need help here, ETS been changed, no luck, going to see about the ESS.
i will know more after my temperatue sensor is replaced. in 3 weeks. That's the only thing I can see. Right now if the heat is on then my temperature doesn't move. If I put it on cold then its right at 190 sometimes, really flaky. Car is running fine once started. My father had that problem also, his is worse, when it was new he said he barely needed to turn it, now its ridiculous.
 
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