- Joined
- Oct 30, 2024
- Messages
- 6
- Reaction score
- 1
- Location
- Illinois, USA
- VCDS Serial number
- C?ID=328688
Hey All. I've been chasing a strange idle surging issue on my MK7 Alltrack. This issue has been on going for a couple months but I've never received any codes from it so basically just have a couple symptoms to go off of and process of elimination. The car is modified with a Walbro 525lph in tank pump, multiport injection (980cc), and ethanol content sensor among numerous other modifications. The car also drives completely fine, pulls great through redline, has never stalled or had fuel cuts under load or anything like that.
I used VCDS to look at High Pressure Fuel Specified and Actual. When I look at my values as the car idles, the specified amount seems to fluctuate between 46 bar and up to 60 bar, never remaining consistent. The actual still remaining close to specified. Is this normal? In the research I've done, it seemed that specified should remain at a consistent value and not fluctuate but I haven't been able to find a definitive answer. When I shut off the car and monitor the Actual fuel pressure, it does continue to go up to the low 60s bar which is to be expected.
What I've replaced and tested has lead me to believe it could be related to either fueling or tuning, but wanted to rule out what I can before I discuss with my tuner. I've replaced the PCV, EVAP Purge Valve, pre-cat O2/Wide-band sensor, intake manifold MAP sensor, pre-throttle body MAP sensor on the charge pipe, Spark plugs, and coil packs. I've smoke tested the car at the intake inlet and intake manifold and found no leaks and thoroughly looked at all fuel lines, connections, and injector seats and have found nothing. LPFP pressure is strong and consistent as well, and I've also done a compression test hitting 175-180 across all 4 cylinders.
The only current symptoms and oddities I've noted are:
-slightly rough idle surging with inconsistent rev dips, meaning no continuous pattern like you'd see with a vacuum leak.
-as idle surges you can hear a loud rattling coming from the HPFP
-VCDS shows that the specified fuel value is not constant and is constantly changing
-If I blip the throttle at idle, it smooths out to something more normal for a little while but will eventually start doing it again.
I've ordered a new updated revision HPFP and new cam follower to rule out any internal issues with it, however since I've never thrown a code for low fuel pressure I still have some degree of doubt that the HPFP is failing since under load everything looks and feels fine. It's just at idle and that rattle noise I hear as the idle surges along with the fluctuating specified high pressure values. Any other thoughts are very appreciated.
Here's a video from the engine bay of the rough idle and the noise the fuel pump makes when the idle surges:
And here's a video of the high pressure fuel specified and actual values at idle:
I used VCDS to look at High Pressure Fuel Specified and Actual. When I look at my values as the car idles, the specified amount seems to fluctuate between 46 bar and up to 60 bar, never remaining consistent. The actual still remaining close to specified. Is this normal? In the research I've done, it seemed that specified should remain at a consistent value and not fluctuate but I haven't been able to find a definitive answer. When I shut off the car and monitor the Actual fuel pressure, it does continue to go up to the low 60s bar which is to be expected.
What I've replaced and tested has lead me to believe it could be related to either fueling or tuning, but wanted to rule out what I can before I discuss with my tuner. I've replaced the PCV, EVAP Purge Valve, pre-cat O2/Wide-band sensor, intake manifold MAP sensor, pre-throttle body MAP sensor on the charge pipe, Spark plugs, and coil packs. I've smoke tested the car at the intake inlet and intake manifold and found no leaks and thoroughly looked at all fuel lines, connections, and injector seats and have found nothing. LPFP pressure is strong and consistent as well, and I've also done a compression test hitting 175-180 across all 4 cylinders.
The only current symptoms and oddities I've noted are:
-slightly rough idle surging with inconsistent rev dips, meaning no continuous pattern like you'd see with a vacuum leak.
-as idle surges you can hear a loud rattling coming from the HPFP
-VCDS shows that the specified fuel value is not constant and is constantly changing
-If I blip the throttle at idle, it smooths out to something more normal for a little while but will eventually start doing it again.
I've ordered a new updated revision HPFP and new cam follower to rule out any internal issues with it, however since I've never thrown a code for low fuel pressure I still have some degree of doubt that the HPFP is failing since under load everything looks and feels fine. It's just at idle and that rattle noise I hear as the idle surges along with the fluctuating specified high pressure values. Any other thoughts are very appreciated.
Here's a video from the engine bay of the rough idle and the noise the fuel pump makes when the idle surges:
And here's a video of the high pressure fuel specified and actual values at idle:
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