Hard start problem
AudiWorld Junior Member
Joined: Dec 2023
Posts: 18
Likes: 4
Hi Alexself, I hope this helps. The symptoms you're experiencing with your Audi A4 2.0 TDI, such as difficulty starting when warm and a cool radiator hose despite reaching operating temperature, might be indicative of several potential issues:
- Coolant Thermostat: A faulty thermostat could cause the engine to run cooler than normal, resulting in the radiator hose feeling cool despite the engine reaching operating temperature. This could also affect the engine's warm start performance.
- Fuel System Issues: Problems within the fuel system, such as a failing fuel pump, clogged fuel filter, or injector issues, might cause difficulties in starting when the engine is warm due to vapor lock or reduced fuel pressure.
- Engine Temperature Sensor: A malfunctioning engine temperature sensor could provide inaccurate readings to the engine control unit (ECU), leading to incorrect fuel and air mixture for warm starts.
- Compression Problems: Issues with engine compression, such as worn piston rings or valve issues, might lead to hard warm starts.
- Diagnostic Scan: Using a quality scanner like the Youcanic scanner can retrieve fault codes and provide insights into potential issues with sensors, fuel systems, or other engine components.
- Thermostat Inspection: Check the thermostat for proper operation. If it's faulty, consider replacing it to ensure the engine reaches and maintains the correct operating temperature.
- Fuel System Inspection: Inspect the fuel system components, including the fuel pump, filter, and injectors, for any signs of malfunction or clogs. Clean or replace components as needed.
- Engine Temperature Sensor: Test the engine temperature sensor's functionality to ensure it's providing accurate readings to the ECU.
- Professional Inspection: If the issue persists or if you're unsure about conducting diagnostics yourself, seeking assistance from a mechanic or technician experienced with Audi vehicles might be necessary. They can perform a more in-depth diagnosis and pinpoint the exact cause of the warm start issue.
Thread Starter
AudiWorld Newcomer
Joined: Dec 2023
Posts: 3
Likes: 1
Hi Alexself, I hope this helps. The symptoms you're experiencing with your Audi A4 2.0 TDI, such as difficulty starting when warm and a cool radiator hose despite reaching operating temperature, might be indicative of several potential issues:
- Coolant Thermostat: A faulty thermostat could cause the engine to run cooler than normal, resulting in the radiator hose feeling cool despite the engine reaching operating temperature. This could also affect the engine's warm start performance.
- Fuel System Issues: Problems within the fuel system, such as a failing fuel pump, clogged fuel filter, or injector issues, might cause difficulties in starting when the engine is warm due to vapor lock or reduced fuel pressure.
- Engine Temperature Sensor: A malfunctioning engine temperature sensor could provide inaccurate readings to the engine control unit (ECU), leading to incorrect fuel and air mixture for warm starts.
- Compression Problems: Issues with engine compression, such as worn piston rings or valve issues, might lead to hard warm starts.
- Diagnostic Scan: Using a quality scanner like the Youcanic scanner can retrieve fault codes and provide insights into potential issues with sensors, fuel systems, or other engine components.
- Thermostat Inspection: Check the thermostat for proper operation. If it's faulty, consider replacing it to ensure the engine reaches and maintains the correct operating temperature.
- Fuel System Inspection: Inspect the fuel system components, including the fuel pump, filter, and injectors, for any signs of malfunction or clogs. Clean or replace components as needed.
- Engine Temperature Sensor: Test the engine temperature sensor's functionality to ensure it's providing accurate readings to the ECU.
- Professional Inspection: If the issue persists or if you're unsure about conducting diagnostics yourself, seeking assistance from a mechanic or technician experienced with Audi vehicles might be necessary. They can perform a more in-depth diagnosis and pinpoint the exact cause of the warm start issue.
Thanks for your response
I had a missfire but i fixed it by chaning the injector wiring and repair and adjust all the injectors. I also added new software cause the old was a bad tuning setup. Also got a EGR delete. Ive also had vcds on and checked all. the last faultcode i have is on the climate control.
I have new thermostat and temp sensor that i will try to change and hopefully this will fix the issue.
AudiWorld Senior Member
Joined: Oct 2020
Posts: 975
Likes: 120
From: Michigan
Alex, all,
Once you get the problem sorted out, I recommend a periodic in-tank fuel injector cleaning regime. There are many products available. I have been using Marvel Mystery Oil for quite some time now with good results. Hayabusafalcon.
Good luck.
MMO Not snake oil..... - AudiWorld Forums
Once you get the problem sorted out, I recommend a periodic in-tank fuel injector cleaning regime. There are many products available. I have been using Marvel Mystery Oil for quite some time now with good results. Hayabusafalcon.
Good luck.
MMO Not snake oil..... - AudiWorld Forums
AudiWorld Newcomer
Joined: Oct 2024
Posts: 1
Likes: 1
Yes Sir : I have the answer. Been fighting for months with the exact same issue: starts fine when cold but sometimes doesnt "catch" when cranking warm ( 2.0T engine) Replaced: Both fuel pumps, Crank position sensor, MAF sensor, alternator, key switch,battery, and still same problem ....you wanna know what it was? CAMSHAFT position sensor .... the easiest one to change right in front beside the timing cover. changed that sensor and BINGO!... FIXED.
AudiWorld Senior Member
Joined: Oct 2020
Posts: 975
Likes: 120
From: Michigan
Thanks Mike, for your account of how you fixed it. Bravo. Wow what a troubleshooting saga.
BTW- guys Mike is right, the camshaft position sensor is on top, right up front. Occasionally you may get a cam sensor code, just out of the blue. Pull and clean the sensor. The code will likely reset and not reappear.
That motion sensor is actually a little generator. As the camshaft whirs past a tiny current is generated by the sensor. The ECU looks at this current and interprets camshaft position moment to moment.
Since it is a little electric generator, it has a magnet inside. That magnet will collect tiny ferrous particles which form a brown oily "mud" on the sensor face over time. Pull and clean that from time to time and you are good-to-go.
Thanks again, Mike.
Haya....
BTW- guys Mike is right, the camshaft position sensor is on top, right up front. Occasionally you may get a cam sensor code, just out of the blue. Pull and clean the sensor. The code will likely reset and not reappear.
That motion sensor is actually a little generator. As the camshaft whirs past a tiny current is generated by the sensor. The ECU looks at this current and interprets camshaft position moment to moment.
Since it is a little electric generator, it has a magnet inside. That magnet will collect tiny ferrous particles which form a brown oily "mud" on the sensor face over time. Pull and clean that from time to time and you are good-to-go.
Thanks again, Mike.
Haya....
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