Sylphy G11 performance issue

nkt · March 13

Guys, I recently bought a Nissan Sylphy G11 2005 as my first car. It was fine when I did a test drive, but after I bought it, I took it to a service station (my bad for not going to the dealer) and did a regular service. When they emptied the engine oil there wasn't much oil and it was dark coloured. The previous owner said he used 20w50 oil so I used the same during the service. However, after I returned from the service, there was a significant hesitation in the engine, which even stopped on a small hill. Once I started again and revved a little it was kind of okay. At this point, the check engine light was lit and the code was P0171 lean condition.

So after this, I took it to A*W and they suggested doing a tuneup. I did it from A*W and they replaced the spark plugs and also discovered there was a heavy sludge formation. They removed the valve cover and cleaned most of it by hand and suggested changing oil in shorter intervals. They also recommended to change the injectors as they were kind of damaged. So once I returned from A*W the pulling power was good on the engine but right on the next day the CEL came on again and the performance was kind of bad again. It was again a lean condition. After this, I did the below,

- replaced injectors with refurbished ones (didn't fix anything)

- replaced the oxygen sensor (was really good right after it was changed but went back to the same problem in a couple of hours of driving, live data scanned shows proper values )

- started to use 95 octane petrol (slight improvement in the performance and responsiveness, somehow the P0171 code is now gone the CEL is not lit and there are no other error codes)

- replaced the fuel pump motor (had a significant improvement in cold starts and pulling power)

- replaced air intake manifold gasket (no improvements)

But still, the hesitation is there. it's most noticeable when I fully press the accelerator, it starts with a wired low rumbling sound and the sound goes away after it picks up rpms. And sometimes the engine revs around 3000 rpm but doesn't pull the car enough relative to the rpm. I have also noted during this time the rpms increase incrementally like a little bit and a little bit and not smoothly and feels like the engine is trying to push away air. However, on high gears, the performance is really good and I can cruise around 100 easily.

Recently I did a break service at automiraj and when they lifted the car we saw there was a small hole in the resonator in the exhaust line. Not sure if this is the cause for that.

Has anyone had any similar experiences? I'm really fed up with going to makabasses because no could identify the root cause.

I would appreciate if anyone could give any ideas about probable causes.

Chung Myung · March 13

1. Check for Additional Vacuum Leaks

Since you replaced the intake manifold gasket, there's still a chance of leaks elsewhere:

PCV valve and hoses – A stuck-open PCV valve can cause excessive air intake.
Brake booster hose – If there's a vacuum leak here, it could cause hesitation.
Throttle body gasket – If not sealed properly, it can create an air leak.

2. Throttle Body & MAF Sensor Cleaning

Throttle body – If it's dirty or sticking, it can cause poor throttle response. Clean it with throttle body cleaner (not carb cleaner) and do an ECU throttle reset if needed.
Mass Air Flow (MAF) sensor – Even if the live data seems normal, a dirty MAF sensor can cause intermittent issues. Try cleaning it with MAF cleaner.

3. Check Fuel Pressure Again

Since replacing the fuel pump motor helped, ensure the fuel pressure regulator and fuel filter are working properly. A weak regulator might not deliver enough fuel under load, causing hesitation.

4. CVT or Transmission Issue?

The part where you mentioned,

"engine revs around 3000 rpm but doesn't pull the car enough relative to the rpm"
suggests a possible CVT transmission slip (if your car is CVT).

Check CVT fluid condition – If it's dark or burnt-smelling, consider changing it (but be cautious with CVT fluid changes if it's never been done before).
If it's not a CVT, check for clutch slippage in an automatic or manual gearbox.

5. Exhaust Backpressure Issue?

You mentioned:

"feels like the engine is trying to push away air."
If the catalytic converter is partially clogged, it could cause power loss and hesitation.

Try removing the upstream O2 sensor (temporarily) and see if power improves.
Check for unusual exhaust smells, rattling, or excessive heat from the catalytic converter.

Next Steps:

Spray test for vacuum leaks (carb cleaner near intake components).
Clean throttle body & MAF sensor.
Check fuel pressure at high RPMs.
Check transmission behavior (if CVT, test for slip).
Test for a possible clogged catalytic converter.

-ChatGPT

Edited March 13 by Chung Myung

nkt · March 13

On 3/13/2025 at 7:31 AM, Chung Myung said:

1. Check for Additional Vacuum Leaks

Since you replaced the intake manifold gasket, there's still a chance of leaks elsewhere:

PCV valve and hoses – A stuck-open PCV valve can cause excessive air intake.

Brake booster hose – If there's a vacuum leak here, it could cause hesitation.

Throttle body gasket – If not sealed properly, it can create an air leak.

2. Throttle Body & MAF Sensor Cleaning

Throttle body – If it's dirty or sticking, it can cause poor throttle response. Clean it with throttle body cleaner (not carb cleaner) and do an ECU throttle reset if needed.

Mass Air Flow (MAF) sensor – Even if the live data seems normal, a dirty MAF sensor can cause intermittent issues. Try cleaning it with MAF cleaner.

3. Check Fuel Pressure Again

Since replacing the fuel pump motor helped, ensure the fuel pressure regulator and fuel filter are working properly. A weak regulator might not deliver enough fuel under load, causing hesitation.

4. CVT or Transmission Issue?

The part where you mentioned,

"engine revs around 3000 rpm but doesn't pull the car enough relative to the rpm"
suggests a possible CVT transmission slip (if your car is CVT).

Check CVT fluid condition – If it's dark or burnt-smelling, consider changing it (but be cautious with CVT fluid changes if it's never been done before).

If it's not a CVT, check for clutch slippage in an automatic or manual gearbox.

5. Exhaust Backpressure Issue?

You mentioned:

"feels like the engine is trying to push away air."
If the catalytic converter is partially clogged, it could cause power loss and hesitation.

Try removing the upstream O2 sensor (temporarily) and see if power improves.

Check for unusual exhaust smells, rattling, or excessive heat from the catalytic converter.

Next Steps:

Spray test for vacuum leaks (carb cleaner near intake components).

Clean throttle body & MAF sensor.

Check fuel pressure at high RPMs.

Check transmission behavior (if CVT, test for slip).

Test for a possible clogged catalytic converter.

-ChatGPT

Expand

I did test for vacuum leaks and there were none. The idle is rock solid at 700 rpm.
MAF sensor was also cleaned during the tuneup

I checked the gear oil and It looks red too. Do you know a place where they check the fuel pressure?

Chung Myung · March 13

On 3/13/2025 at 10:41 AM, nkt said:

I did test for vacuum leaks and there were none. The idle is rock solid at 700 rpm.
MAF sensor was also cleaned during the tuneup

I checked the gear oil and It looks red too. Do you know a place where they check the fuel pressure?

Expand

Well you'd have to find the factory fuel pressure spec somehow to do that... if you're based around Kandy Nandana motors and Knight auto works have been recommended by the forum members before

It can't hurt to replace the fuel filter too if you haven't done it already when you replaced the pump.

nkt · March 13

On 3/13/2025 at 10:57 AM, Chung Myung said:

Well you'd have to find the factory fuel pressure spec somehow to do that... if you're based around Kandy Nandana motors and Knight auto works have been recommended by the forum members before

It can't hurt to replace the fuel filter too if you haven't done it already when you replaced the pump.

Expand

I'm in colombo mate. Fuel filter was also replaced when I replaced the pump motor