Fuel Pressure Priming Issue

[Andrew429]

Recently been having an odd issue with my car. I go for a cold start and the car stutters for second and then revs up to the normal 1200 rpm for the cold start procedure.
I logged the fueling on vagcom and all numbers on the HPFP side are within normal range, duty cycle in the low to mid 50s idling and actual pressures matching requested. The car also has brand new fuel injectors as I just did the carbon cleaning. There is also no leak down on the HPFP as the system holds the 6.5 BAR pressure after sitting overnight, also no fuel smells.

Then I noticed if a prime it a second time after it does the initial prime when the door is opened it will start up perfect... so I went to auto zone to get a loaner fuel pressure gauge and hooked it up. The car is only priming the system to 20 PSI initially. I then hooked the gauge up to a family members tiguan and that is priming to 40 psi initially.

Would this be a sign that the LPFP is on its way out? I know there is also a control module for the fuel pump which may be worth changing that before the pump itself. I changed the fuel filter ~20k miles ago.

Any insight would be appreciated. I have not found anyone with this same issue on any of the forums.

TIA

 

[Alpinee30]

Mine did the same with Bosch injectors for a few starts after new injectors and cleared up on its own. Do you have the 6.6 bar regulated filter? Could be the module even though it primes with the door open.

 

[Andrew429]

I do have that filter, I ended up ordering the parts and I’ll try the module and new filter before the pump so if that fixes the issue I can just return the pump. I also used the Bosch injectors, it was fine for a couple weeks after installing then this started

 

[Andrew429]

So I replaced the LPFP and the fuel filter. It now primes to around 6 Bar so the old one was definitely weak. However it still is giving odd startups. Runs perfect otherwise, and no issues that I see when looking through Vagcom. Anyone have any other ideas?

Also the car has new plugs and r8 coils

 

[Alpinee30]

Are these fresh plugs after the carbon cleaning or before. Did you use solvent or walnut? If solvent and not fresh plugs after you could have a plug issue, Have you pulled them?

 

[Andrew429]

Fresh plugs before I did the cleaning, and I did almost like a 2 stage cleaning, I used solvent and the cable tie brush to clear out the real thick carbon and then finished the port off with the walnut blaster.
Think the plugs got fouled? I did not pull them as I didn't think twice about them

 

[Alpinee30]

Its possible a plug got fouled . Might see something with VCDS on startup maybe one cylinder has a slight misfire. I imagine you have a slight stumble when ignition hits and then it catches and is fine.

 

[Andrew429]

So I just picked up new plugs, put them in and the cold start was perfect! Hoping that was the culprit! I’ll keep you updated. Thank you!

 

[Alpinee30]

Any like carbon remnants on the old plugs?