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Golf V 1.9 TDI 105km - Golf V 1.9 TDI smokes heavily on a warm engine

sylweczka2006 27750 16
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Why does a Golf V 1.9 TDI smoke heavily and start badly when the engine is warm, even with no fault codes?

The most likely cause is not the fuel map, but a weak starting system: check the battery cranking current, the battery-to-starter connections, and the starter itself, because a warm TDI needs about 250 rpm to fire properly [#17125571][#19209372] A worn starter can cause exactly this symptom; one user fixed similar hot-start problems by replacing a bent starter brush, after which the car started cleanly both cold and hot [#19209337] Also consider the crankshaft position sensor, since it can lose properties when hot and still not trigger an error code [#17125122] One reply suggested increasing the starting dose in the ECU, but another pointed out that disconnecting the coolant temperature sensor did not change anything, so that route may not help [#17132475][#17132481]
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  • #1 17124489
    sylweczka2006
    Level 7  
    Posts: 8
    Rate: 14
    Hello, I have a problem with golf 5, the car when it is cold smokes from an arrow as soon as it starts to spin, no lights are on, the computer also shows nothing, the mechanic said that you need to upload a new fuel map, had someone similar problem? Thanks in advance for your help.
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  • #2 17124497
    Ireneo
    Level 42  
    Posts: 7818
    Help: 746
    Rate: 2452
    See how warm it fires when you disconnect the coolant temperature sensor
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  • #3 17125056
    sylweczka2006
    Level 7  
    Posts: 8
    Rate: 14
    I disconnected the sensor and still it is
  • #4 17125122
    wojtego
    Level 13  
    Posts: 48
    Help: 4
    Rate: 34
    The crankshaft position sensor may lose its properties after heating and hence firing problems. He won't show an error then.
  • #5 17125571
    seba694637
    Level 16  
    Posts: 549
    Help: 11
    Rate: 113
    Before the mechanics talk you into unnecessary services, check the battery's starting current. Let him stand overnight and then have him checked. A warm diesel needs more electricity to start. Often the first signs of diesel battery wear are heavy firing when the engine is warm
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  • #6 17126778
    sylweczka2006
    Level 7  
    Posts: 8
    Rate: 14
    I noticed that there is a gel battery here, is there a difference? and how to check it?

    Added after 3 [hours] 41 [minutes]:

    and besides, it's not the other way around? he should smoke badly on a cold engine if it was a battery, and a cold one smokes an arrow. It doesn't matter if it's -15 or -20
  • #7 17130780
    seba694637
    Level 16  
    Posts: 549
    Help: 11
    Rate: 113
    At -20 degrees a functional lead-acid battery will have about 50% of its capacity - and therefore a smaller starting current.

    At +20 a fully functional and charged battery will start your car without a problem, but when the engine is warmed up, the demand for starting current is greater. So when the battery does not demand it will run harder on a warm engine
  • #8 17131907
    sylweczka2006
    Level 7  
    Posts: 8
    Rate: 14
    Will you tell me how can I check it? because usually when I had a problem with the battery it would sit down already
  • #9 17132475
    piotrek1994
    Level 14  
    Posts: 191
    Help: 2
    Rate: 8
    The subject of heavy start-up of a hot tdi is well-worn and here the most help with increasing the starting doses programmatically (uploading a new fuel map) Approach someone who performs such services in your area show him how he smokes warm and someone who knows the topic will tell you immediately whether increasing the doses will do the trick. Greetings
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  • #10 17132481
    bodzio012
    Level 33  
    Posts: 1888
    Help: 161
    Rate: 777
    piotrek1994 wrote:
    The subject of heavy start-up of a hot tdi is well-worn and here the most help with increasing the starting doses programmatically (uploading a new fuel map) Approach someone who performs such services in your area show him how he smokes warm and someone who knows the topic will tell you immediately whether increasing the doses will do the trick. Greetings


    After all, he wrote that he disconnected the temperature sensor, so your advice will do nothing, unless it did not disconnect the sensor.
  • #11 17132799
    seba694637
    Level 16  
    Posts: 549
    Help: 11
    Rate: 113
    At a first-class workshop, you can perform a battery inrush current check. It should be similar to the one on the battery case
  • #12 17151666
    sylweczka2006
    Level 7  
    Posts: 8
    Rate: 14
    I also noticed that sometimes it is warm as if the starter is locked
  • #13 17180543
    mihai
    Level 2  
    Posts: 3
    Rate: 2
    I suggest to drive to the Tuner to increase the engine start dose. It helped me
  • #14 17181108
    bodzio012
    Level 33  
    Posts: 1888
    Help: 161
    Rate: 777
    mihai wrote:
    I suggest to drive to the Tuner to increase the engine start dose. It helped me

    Next what she reads ...
  • #15 19209337
    Tom2204
    Level 1  
    Posts: 1
    Rate: 1
    I had such a vw bora, first on a warm long shot and in the last months and on a cold one, as if the battery was at the outlet. One-year battery, and what a mechanic is a different diagnosis, and I have had a few years. Already had to be uploaded map, etc. and the reason was very simple, one brush was a curve in the starter. After replacing them, whether in cold or hot, smokes to the touch. 1.9 tdi agr 90 km
  • #16 19209372
    k124l
    Level 20  
    Posts: 601
    Help: 31
    Rate: 125
    Before you hit the costs, regenerate or replace the starter and improve the current connections on the battery starter. Warm tdi needs around 250 rpm to ignite.
  • #17 21301530
    Gwizdinho90
    Level 2  
    Posts: 6
    Rate: 1
    >>17124497 .
    When I disconnect it smokes on shot.
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Topic summary

✨ A Volkswagen Golf V 1.9 TDI 105 km exhibits heavy smoke emission immediately upon startup when the engine is warm, without triggering any error codes or warning lights. Disconnecting the coolant temperature sensor does not resolve the issue. Potential causes discussed include a failing crankshaft position sensor that loses functionality when heated, and insufficient battery starting current, especially relevant for diesel engines requiring higher current at warm start. The presence of a gel battery raises questions about testing methods, with suggestions to measure battery inrush current at a qualified workshop. Another frequent recommendation is to increase the starting fuel dose by uploading a revised fuel map via engine tuning services, which has reportedly helped similar cases. Additionally, mechanical issues such as a worn starter motor—specifically damaged brushes causing starter locking and poor current delivery—can mimic these symptoms and should be inspected and possibly replaced before incurring tuning costs. Improving battery-to-starter electrical connections is also advised to ensure adequate cranking speed (around 250 rpm) for warm ignition in TDI engines. The problem is consistent across temperature ranges, including extreme cold (-15 to -20°C), and is not solely related to battery charge state.
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FAQ

TL;DR: “Warm TDI needs around 250 rpm to ignite.” That benchmark explains most hot-start smoke on Golf V 1.9 TDI. Check starter, battery CCA, grounds, crank sensor, and consider start‑fuel dose. This FAQ shows quick tests and fixes. [Elektroda, k124l, post #19209372]

Why it matters: For Golf V 1.9 TDI owners battling warm-start smoke and long cranks, this prioritizes proven, low-cost fixes before tuning.

Quick Facts

Why does my Golf V 1.9 TDI smoke heavily and crank long when warm?

Warm-starts need about 250 rpm. If cranking slower, fueling lags and unburnt diesel smokes. Common causes are a weak starter, poor battery-to-starter connections, or starter wear. Address these first, then evaluate calibration. This order saves cost and restores clean starts. [Elektroda, k124l, post #19209372]

How do I quickly rule out a bad coolant temperature sensor?

Do a warm-start unplug test. 1. Warm the engine, shut it off. 2. Unplug the coolant temperature sensor. 3. Restart and compare cranking and smoke. If behavior changes, the temperature input is influencing starts. Use this result to guide next steps. [Elektroda, Ireneo, post #17124497]

Can a crankshaft position sensor fail when hot without logging a code?

Yes. A crankshaft position sensor can degrade when hot and misread position. The engine then cranks longer or fails to start. It may not log any fault code, complicating diagnosis. Replace if suspected after other checks. [Elektroda, wojtego, post #17125122]

Does a diesel really need more current to start when hot?

Yes. A warm diesel needs more electrical power to start. Check starting current after an overnight rest and after heat soak. Weak batteries often first show as hard hot starts. Verify capacity before chasing other issues. [Elektroda, seba694637, post #17125571]

How can I check my battery’s starting current (CCA) correctly?

Use a shop CCA test. 1. Let the car sit overnight. 2. Have a workshop measure inrush current with a tester. 3. Compare the reading to the battery’s label value; they should be similar. Replace the battery if results are consistently low. [Elektroda, seba694637, post #17132799]

Is a gel battery a problem for hot starts on the Golf V?

Battery type matters less than available starting current. Focus on tested inrush current versus the label. Any battery that meets its rated starting current should crank the engine adequately. Use a professional tester to confirm. [Elektroda, seba694637, post #17132799]

Could my starter be the real culprit even with a new battery?

Yes. Starter wear, such as damaged brushes, can slow cranking and mimic a weak battery. Rebuilding or replacing brushes restored instant starts on a 1.9 TDI case. Inspect the starter if warm cranking feels sluggish. [Elektroda, Tom2204, post #19209337]

When should I consider increasing the warm-start fuel dose (map)?

Consider it after hardware checks pass. Many hot-start TDIs improve when a tuner increases the start-fuel dose in software. Show the tuner a warm-start attempt to evaluate need. Choose a specialist with this exact service. [Elektroda, piotrek1994, post #17132475]

Disconnecting the coolant sensor makes it start instantly—what does that tell me?

That behavior matches community experience. If unplugging the coolant sensor makes it start instantly, temperature input affects starting. Inspect the sensor and connector, and review warm-start calibration later. This simple check can save time. [Elektroda, Gwizdinho90, post #21301530]

What cranking RPM should I see on a warm start?

Target about 250 rpm during warm cranking. “Warm tdi needs around 250 rpm to ignite.” If the tach shows less, service the starter and connections. Then reassess starting behavior. [Elektroda, k124l, post #19209372]

I feel the starter “locks” when hot—what should I do first?

Address the starter and high-current cables first. Regenerate or replace the starter, and clean battery and ground connections. Poor current delivery can make the starter stall or bind when hot. Confirm cranking RPM after service. [Elektroda, k124l, post #19209372]

Why does it start at −15°C but struggle after a short stop?

Cold weather reduces a battery’s available capacity sharply. At −20°C, a healthy battery has about 50% capacity. A warmed engine then demands higher starting current, exposing marginal batteries. Test and replace if results fall short. [Elektroda, seba694637, post #17130780]
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