Hi everyone,

I am looking for some insight regarding a fueling issue on my Skoda Octavia 3 RS (2.0 TSI, EA888 Gen 3, CHHA engine, 169kW). The car is currently running an APR Stage 2 tune (ECU + TCU). The issue first appeared right after flashing APR Stage 1 at around 74k km, and now at 86k km, it has become more frequent (sometimes 3x a day, sometimes it gives peace for 2 weeks).

The car drives absolutely fine, pulling hard from the bottom without any issues. It never enters limp mode, and there is NO Check Engine Light (CEL) or any warning on the dashboard. The only way I know there is a problem is by scanning the car and finding this intermittent fault code in VCDS:

• 15007 - Fuel Pressure Regulator Valve (N290) - P0089 00 - Implausible Signal

• Freeze frame data shows it always happens under heavy load: ~5050 RPM, 93.3% load, MAP at 255 kPa, HPFP actual pressure at 19,860 kPa (approx. 198 bar).

What I found during data logging (LOG attached):

• At part throttle, the LPFP easily hits the APR-targeted 7.0 bar.

• Under WOT (Wide Open Throttle), the LPFP holds the requested 7.0 bar from 1300 RPM to 2400 RPM.

• The issue: From 2400 RPM up to 4700 RPM, the actual LPFP pressure starts dropping linearly until it hits roughly 4.6 – 4.7 bar, where it gets stuck and stays there all the way to the 6400 RPM redline.

• Meanwhile, the HPFP target and actual pressures follow each other quite well, actually climbing from 180 bar to 200 bar at 6400 RPM. However, the N290 duty cycle spikes like crazy because it tries to compensate for the missing pressure from the low-pressure side.

Because the low-pressure side drops significantly below the requested 7.0 bar exactly when the fuel demand increases, I suspect the high-pressure pump (HPFP) and the N290 valve are actually fine and just reacting to a low-pressure starvation.
Performance Logs

I also logged airflow.

APR Stage 2
Maximum airflow through throttle:

• 942 kg/h

• at 5495 rpm

Knock retard looks very clean on all four cylinders.

No significant timing corrections.

The car pulls strong and does not feel fuel limited.

My questions for the community:

1. Has anyone experienced this exact linear drop to ~4.6 bar under load with APR software?

2. Is this a textbook sign of the OEM LPFP control module (5Q0 906 093) overheating and pulling back back due to thermal protection, or is the actual in-tank pump simply tired and drawing too many Amps?

3. Which revision of the control module should I get to fix this, or is a PM4 / aftermarket upgrade necessary for APR Stage 2?

Any advice, link to a similar thread, or log analysis would be highly appreciated.

Thanks in advance!

Current setup:

• APR Stage 2

• HJS 200 CPSI downpipe

• Milltek cat-back exhaust (non-resonated)

• Enlarged turbo inlet

• Upgraded turbo intake hose

• Intake restrictions removed/modified

• RacingLine ignition coils

• Fresh oil service

• New oil filter

• New air filter

• New cabin filter

• New spark plugs

The car is still running the factory IS20 turbo.

The HPFP is doing its job just fine. Looking at the linear drop, I suspect the LPFP is a bit knackered.

It was probably already being pushed with the first map, and the increased demand has proven too much for it.

Can you get any further logs? I'm thinking the LPFP current draw and fuel rail pressure (target versus actual) would be good to have.

@OccyVRS here is my log from the ride, could you advise what could be wrong? Thank you
https://log.tunezilla.com/chart/1103065#H8KLCABBGTpqAgNNwo3DgQrDgjAQRMO/ZcOPE2jCtFbDvcKWwpBDasKXwrgQwpvCkmxBw7vDtRpFw6hlDsOzHjPDjsORLT9GwpnDmcOEwpLDl8KlEjrCj1bCplxkYwLChcKUPhl5w6YSwpTCqcORME3DpmXDglPCmg4qEsOvw7oFwpV1B8KcRcKPMy7CsB0OOMOiwoQBVw/CssK/wpFVc13CksOow7/Dg8O2w57CvwEJW8KERsKQAAAA

Sorry not a clue, but out of interest what petrol do you run it on, 99 Octane or higher?

@Evolution13 only OMV MaxxMotion Natural 100plus (98RON)

Good, but it has an octane rating of a 100 ron min, it is not 98 ron.

@Evolution13 ah, sorry, my mistake. Anyway, the local APR service technician recommended this fuel to me

15 hours ago, Michalson said:

@OccyVRS here is my log from the ride, could you advise what could be wrong? Thank you
https://log.tunezilla.com/chart/1103065#H8KLCABBGTpqAgNNwo3DgQrDgjAQRMO/ZcOPE2jCtFbDvcKWwpBDasKXwrgQwpvCkmxBw7vDtRpFw6hlDsOzHjPDjsORLT9GwpnDmcOEwpLDl8KlEjrCj1bCplxkYwLChcKUPhl5w6YSwpTCqcORME3DpmXDglPCmg4qEsOvw7oFwpV1B8KcRcKPMy7CsB0OOMOiwoQBVw/CssK/wpFVc13CksOow7/Dg8O2w57CvwEJW8KERsKQAAAA

If you have to ask someone on the internet to diagnose an issue for you, then you need to take it to someone that knows what they're doing.

However, that being said, I did have a go with Google Translate.

We're interested in the red, orange, yellow and pink lines. Red is the LPFP pressure, orange is the HPFP pressure, yellow is the HPFP target pressure and pink is the LPFP target pressure.

The HPFP seems good - orange and yellow lines are matching well.

However, the LPFP looks less good. At one point, the controller is requesting 7bar of pressure, but only getting 4.34bar. At the same time, it's asking for 92% duty, which is pretty much WOT. No system should be 2.6bar below the requested pressure. The HPFP is doing a good job of hiding the problem, but it will be putting more strain on itself in the process.

As you get to the top of the pull, you can see that the red line dips below the pink - the LPFP simply cannot keep up with demand. Once you lift off, and throttle falls from 75% to 25%, the LPFP pressure begins to stabilise. To me, that looks pretty indicative of a pump that can't cope.

Whether that is due to the tune, a knackered LPFP, or both, remains to be seen.

I am not a mechanic, and if asked to change the LPFP would get as far as taking the seats out. However, I understand a fair bit, and can read a graph. I would speak to the place that mapped the car - they will be able to suggest the next steps.

That being said, I would be interested to see a WOT pull in 3rd gear or so, if you could post the logs here afterwards. The ECU can sometimes do weird things, and we don't see boost, airflow, etc.

@OccyVRS Thank you very much for your response, I appreciate your time and willingness to help me. I am attaching another fuel log that I recently made + performance log.
Small update:

I checked my old VCDS screenshots and found that this exact fault (P0089 - Fuel Pressure Regulator Valve (N290) Implausible Signal) first appeared almost 2 years ago at 61,778 km, while the car was running a much milder Stage 1 tune (~300 HP).
So the problem existed long before APR Stage 2.

During my latest logs:

• LPFP requested pressure = 7.0 bar

• LPFP actual pressure starts at ~7.2 bar

• Around 2800 RPM, LPFP controller duty jumps from ~74% to ~92%

• LPFP pressure then continuously drops to ~4.3–4.7 bar by ~5000 RPM

• Controller remains at ~92% duty cycle for the rest of the pull

• HPFP pressure remains well controlled (~180-200 bar) with minimal deviation

• No limp mode, no CEL, no misfires, no noticeable power loss

Another detail:

• At 69,000 km I replaced the fuel distribution rail due to a crack/leak.

• The original G410 low-pressure fuel sensor was transferred to the new rail and is still being used today.

Does this point more towards:

• a weak LPFP,

• a faulty G410 sensor,

• the LPFP control module (J538),

• or the N290 valve inside the HPFP?
  
  FUEL LOG:
  https://log.tunezilla.com/chart/1103634#H8KLCAB4wpw7agIDTcKNw4EKw4IwEETDv2XDjxPDqGoVw73ClsKQQ8K0S1zCiE1JwrZQw716wo0ieMKZw4PCvMOHwozDt3Qtw7fCi8OOw6JSLcOrw5IIQ0Avc8Kpw7oUAsOFwpzDn8KZZMKWGk3CqMOTOE3DrsOhw6LCpl0HVU03w7vCgCbDtgc8w6PCiB3Dthhxw4AJZ8OwAMOmAMOiw6/DimrCpS1Zw613w4JjCC82BTTCg8KRAAAA
  
  PERFORMANCE LOG:
  https://log.tunezilla.com/chart/1103636#H8KLCABbwp07agIDTcKNw40Kw4IwEMKEw59lw48Tw6hqw7HDp1lCDsORLnEhNiXDmULDtcOpNcKKw6BlDsOzfcOMeE/Dl3LCv8OoLC7DlcKyLsKNMATDtDLCl8KqTyFQw4zDucKdSWbCqcORwoQ6wo3Dk8OkHi5uw5p1UMOVdMKzD2hif8OAM044woMHMGPChz1GHHAMIMO+wq7CrFbDmsKSw5V+JzzChsOwAi/CvHU2wpEAAAA=

I would change the sensor and see what happens. The DTC logged is saying there is a mismatch between the pressure commanded and the pressure recorded. I don't believe in coincidences, so I would absolutely change the sensor. I suspect the LPFP is still a bit knackered, given how the pressure drops during acceleration and then recovers, however the sensor could be at fault.

That said, I would also be prepared to change the LPFP itself, and keep an eye on things. I'd certainly take it easy to be honest - the HPFP is doing a lot of work.

Stick an upgraded LPFP while you're at it - can't hurt, and offers some future-proofing.

@OccyVRS thank you for your response. Before I try to replace the G410 sensor as a precaution, I will do the first LOG with 1/4 of the fuel tank and then with a full tank. I have received a recommendation that the LPFP could have a problem when it has less fuel in the tank. The P0089 error appears sporadically

4 hours ago, Michalson said:

@OccyVRS thank you for your response. Before I try to replace the G410 sensor as a precaution, I will do the first LOG with 1/4 of the fuel tank and then with a full tank. I have received a recommendation that the LPFP could have a problem when it has less fuel in the tank. The P0089 error appears sporadically

That sounds like a plan. As long as you are careful with WOT, I would try a few things, speak to a few people and get some more logs before throwing money at it. These sorts of problems can have strange causes, and there's no point replacing the LPFP and other parts if a sensor, or sender, is bad.

@OccyVRS Thank you again for your time and advice.

@OccyVRS just for fun. I did 2 more LOGs today. The first LOG with only a reserve amount of fuel in the tank and the second LOG with a full tank of fuel.

Again the same scenario
LOG with reserve amount of the fuel:
https://log.tunezilla.com/chart/1104387#H8KLCADDq1w9agIDTcKNw4EKw4IwEETDv2XDjxMwWsKrfkvDiCHCtUtcwohNScK2wqDDvXobRcOoZQ7Ds8KGN8OOw5E9PwfCmcOYw4TCksKXwrkSDh7CrUzCucOIw4oECiltGXnDohLClMKpw5Ewwo7Dpm3DgkvDmhxUJD7DtAsqw6sOOMKLDjccccOCGT0uwrjDgm52wrI/w4nCosK5w45Jw7TDv2E7w68/wrRww4kbwpAAAAA=

LOG with full tank of fuel:
https://log.tunezilla.com/chart/1104388#H8KLCADDsFw9agIDTcKNw4EKw4IwEETDv2XDjxMwWsKrfkvDiCHCtUtcwohNScK2wqDDvXobRcOoZQ7Ds8KGN8OOw5E9PwfCmcOYw4TCksKXwrkSDh7CrUzCucOIw4oECiltGXnDohLClMKpw5Ewwo7Dpm3DgkvDmhxUJD7DtAsqw6sOOMKLDjccccOCGT0uwrjDgm52wrI/w4nCosK5w45Jw7TDv2E7w68/wrRww4kbwpAAAAA=

I'm starting to think more and more that LPFP is behind the problem.