[Vwdiesel] TDI Starting Poor

[William D. Hamblen]

There are a lot of threads on the TDIClub forums (tdiclub.com: VW TDI 
Model Specific Discussions:  General Maintenance) about similar 
problems.  Frequently people report that either a new battery or a new 
starter is what's required.

Personally I find that a little hard believe.  My 99.5 Jetta starts hard 
if the engine is warm - e.g. a hot engine that has been sitting for 
10-20 minutes.  So that's a warmer than when your car starts hard.  By 
hard I mean 5ish seconds of cranking so I haven't done much to track it 
down down (it's not nearly as bad as your's).  But it starts fine when 
cold (down to -20F this winter) or when hot (5 min or less of sitting 
with the engine off).  It's been like this for 18 months.

Anyway, the theory is either that you aren't getting the 300RPM 
necessary for the fuel to start pumping because a warm engine is tighter 
and harder to crank so a borderline starter can't quite pull it off; or 
the battery voltage drops too low for the ECU to stay up.

In the first case, my car is audibly cranking at the same speed cold and 
warm (and it sounds much faster than 300RPM).  As for the second case, 
I'm not sure why extended cranking would improve battery voltage! 
Unless a brief but severe voltage dip forces a reboot of some kind that 
takes 20 seconds to complete?  Sounds far fetched to me.

I'd be curious to hear if you figure it out.

On Sun, 1 May 2005, Val Christian wrote:

> I did check the sensor, using a radiometer, and they both agree within
> 2C, using several points.
>
> One new thing I found, is that the ECN does not order preglow when the
> coolant temp is above +5C.
>
> Interesting.  I don't think I'm looking at low compression or other
> old age problems.
>
> Val
>
>
>>
>> I would check the coolant temp sensor for linearity, or is the coolant temp
>> taken off of Vag-Com?
>> Also connector corrosion, etc..
>>
>> -james
>>
>> -----Original Message-----
>> From: vwdiesel-bounces at vwfans.com [mailto:vwdiesel-bounces at vwfans.com]On
>> Behalf Of Val Christian
>> Sent: Saturday, April 30, 2005 11:05 AM
>> To: vwdiesel at vwfans.com
>> Subject: [Vwdiesel] TDI Starting Poor
>>
>>
>> It's finally getting warmer, and my TDI is starting poorer.
>>
>> Symptoms:  Coolant temp between 5 and 15C, and engine may take 20 seconds
>> of crank to get going.  Coolant temp below -8C, and engine starts with a
>> tap of the starter.
>>
>> Coolant temps are using VAG-COM, and correspond to the outside air
>> temperture (OAT).
>>
>> When engine is warm, or OAT above 20C, start is after a rotation or two
>> of the engine.
>>
>> Theory: A short glow isn't happening at initial start in these temps.
>>
>> Assumption: Sensor indicated by VAG-COM drives glow time.  In this temp
>> band, there is 0.0 preglow indicated by VAG-COM
>>
>> Questions:
>>
>> 1. Can the user tweak the preglow cooeficients using VAG-COM?
>>
>> 2. Other problems or issues I should be chasing?
>>
>> Val
>>
>>
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