Engine rattling at low rpm under load // air in fuel ?

YanCT

Active member
Joined
May 7, 2021
Location
Reunion Island
TDI
1.6 TDI - 207hp - 420nm
Hello all !



The car is a VW Golf MK7 2013 CR 1.6 TDI 105 engine code CLHA mileage 190 000kms

No oil consumption. No coolant consumption. Compressions are as they should.

It looks like I’m having a fuel leak somewhere, it’s like air is getting inside the system.


Engine is ratling at low rpm under load.
Some mornings, Engine hesitates to starts.
Really some mornings, engine takes 5-10 looooong seconds before starting, with a compact and unique white smoke cloud.

Idle is fine and smooth and quiet. Fuel consumption is good.
Engine will never rattle or knock above 2000rpms. No smoke. No smell. No diesel in oil.
VCDS don’t show any fault.

Injectors are brand new Bosch (réf. 04L 130 277 AE), did not solve the problem.
Injection deviation values when idling are :

Inj. 1 : -0.13 / Inj. 2 : 0.01 / Inj.3 : 0.15 / Inj.4 : -0.03

Sometimes the engine will work quietly for few kilometers as I was used before (no matter cold or warm, load or not etc) , but most of the time it will rattle…
I put a can of cetane booster just to check if it was something due to fuel vaporization or timing : did not help to quiet it even a bit.


I really think I have some air in the fuel system, but not enough to get an error code like “pressure too low”.

Does air in fuel can cause rattles / knocking at low rpms ? The engine is not hesitating or getting cuts, it is just loud and rattling…

I have performed the test we can find on youtube Ross-Tech channel to test fuel pressure after warm engine is switched off. The fuel is meant to get warmer in few minutes and expand and will make fuel pressure rise-up.

Here is my experiment :

Values just before switching engine are : Coolant temp. 91°c, Fuel temp. 38°c, fuel pressure 300bars.
When engine is switched off, fuel pressure drops down to 15bars.
In the 5 following minutes, fuel temp rises to 48°c, coolant drops down to 88°c, fuel pressure drops down to 4.5bars.

Fuel pressure never goes up as it should after engine off, despite fuel temp rising up…

I can’t see any visible fuel leak in the engine bay.
 

YanCT

Active member
Joined
May 7, 2021
Location
Reunion Island
TDI
1.6 TDI - 207hp - 420nm
Little update :

If I unplug my fuel press sensor wire, The rattle noise goes away.... totally ! Yes the car goes in limp mode (limited to 3000rpms and reduced power above 1500rpms), but the rattle noise is definitely gone.

Idle gets noisier (more rattle) but still stable and smooth. As soon as I press pedal, engine gets so quiet that I have the impression of recovering original sound... a nice and quiet common rail engine.

Power and torque are the same at low rpms. Maneuvers on idle in reverse and 1st gear are quiet, maneuvers on hills with high torque demand are now totally quiet whereas they were noisy as hell and rattling.


As soon as I plug the wire back, engine gets noisier and rattles at low rpms... and sometimes not at all.
 
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