Hot Start Issue - Log Graphs Inside!

POKTROKT

Member
Joined
Sep 17, 2011
Location
Ontario, Canada
TDI
1999 Audi A4 TDI Avant AFN110
Update: Diagnosed

Called the local diesel repair shop and they asked me to spray cold water on the head of the pump to cool it down after driving the car, this would give them an better idea of the problem. Drove home from work that day and when i got home i sprayed cold water on it, lo and behold car started up. Called them back and they said it was the hydraulic head of the pump, will be replacing the pump soon.
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I've got a 1999 Audi A4 TDI Avant (AFN110)
It has what I thought was a typical hot start issue... things I've swapped, new starter, new crank sensor, new battery, temp sensor. I've bypassed the temp sensor with a resistor and VCDS reads -9 deg C when hot, glow plugs come on and nothing, just cranks over.
The new starter has helped initial starts in the morning and on my way home after work but if it has run for 10 minutes or longer it will not start back up.
Below is a screen shot of a graph with the car running then shut off then cranking with not start. Injection quantity, timing and mass air flow look to be in spec. What should I be looking for to know whether my pump is going bad, I'm mechanically inclined but no TDI guru.
Thanks in advance.
 
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POKTROKT

Member
Joined
Sep 17, 2011
Location
Ontario, Canada
TDI
1999 Audi A4 TDI Avant AFN110
Couple more things,
No Codes
Cleaned the intake manifold
Draws fuel easily through the fuel filter so no clogs
I put a clear line to check for bubbles and there are no air bubbles

Also, I can bump start the car no matter how hot it is, seems if i get the RPM's fast enough it will start.
 
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whitedog

Veteran Member
Joined
Jul 12, 2004
Location
Bend, Oregon
TDI
2004 Jetta that I fill by myself
I wonder if this is similar to the "long start when hot" software issue with early AHL cars?
 

POKTROKT

Member
Joined
Sep 17, 2011
Location
Ontario, Canada
TDI
1999 Audi A4 TDI Avant AFN110
I wonder if this is similar to the "long start when hot" software issue with early AHL cars?
For the longest time I was convinced this was the issue. I cracked the ECU and found that it had been socketed, tune seemed stock so maybe it already had hot start reflash. I did however get tuned chips for it as it was as easy as removing the old chips and installing the new ones, tune has hot start fuel map fix. Also confirmed when i fake the ECU into thinking the engine is cold, still won't start.
 

BobnOH

not-a-mechanic
Joined
May 29, 2004
Location
central Ohio
TDI
New Beetle 2003 manual
How's engine time? All internal combustion engines are hard to start hot if timing is retarded. It just needs to be within range and check if it's been adapted to a different value. Basic mechanical timing is most critical, if the belt is off a tooth or 2 you won't necessarily see that from the ECU.
 

jasantos40

Well-known member
Joined
Aug 11, 2018
Location
EU
TDI
g4 tdi
Battery or starter is slight weak, but it's enough.

Problem is, the ECU, when fuel temperature is above certain temperature, delivers fuel only above a certain RPMs, the RPMs that the starter+battery can't reach on the first cranks.

Spraying the head of the pump is just bringing down the temperature of the fuel temp sensor.

On VCDS, codding for auto transmission will change the start map and will help.

The best would be a ECU remap.

My battery, from my previous TDI lasted 8 years by remapping the start map, a bit of smoke on start, but always started on the first crank.
 

POKTROKT

Member
Joined
Sep 17, 2011
Location
Ontario, Canada
TDI
1999 Audi A4 TDI Avant AFN110
Fixed quite a while ago, figured I should post an update.

To address some of the questions above.
Engine timing – Mechanical timing was in spec.
Battery – New battery
Starter – New starter (valeo)

Eventually the car would not start hot or cold. Bought a new battery, new starter and crank sensor, RPMs were way up and still would not start. Somehow bump starting seemed to get the injection pump spinning fast enough to pop the injectors and it would start.

The fix was a good injection pump, bought an 11mm pump and had it checked and resealed and retrofitted it. Started right up and it’s been running with no issues for a year or about 30000 kms.
 
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