Cold weather, engine runing rough

[Le_Combattant]

I'm still troubleshoot my issue since it still here.

I'm also waiting lower temp to check compression when the engine is cold to see if there a mechanical issue cold (valve/piston ring) but to be honest, I'm confident in the
fact my engine is "healthy".

But: "prevention is better than cure"

Also, today I removed my 0² sensor to check it visualy.

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On one side, little white pouder (?) and on the other side nothing.
According to some people it's quite normal as modern engine tend to run lean to pass emission test.

For info, my long term fuel trim is at -0.8%

[Le_Combattant]

So today, by -2°C, I took compression of my engine again.

I wanted to know if it was a mechanical issue due to the cold weather (piston ring, valve seal or whatever).
I remove all the fuses in relation to the fuel system and started the engine until it stop.

By the time, oil temp reach 40°C. My issue is present up to oil temp at 60-70°C so it's okey.
I was confident about the health of my engine and here are the results:

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Results are similars.
But one major point: I don't know how accurate my device is. So results are pretty good but we have to be careful.

VW Manuals said: Between 10 and 15 bars for a good engine.

Tomorrow I will run with my coolant temp sensor disctonnected to see, when engine is in open loop runs better or not.
If it's the case, coolant temp sensor is faulty or not accurate for ECU.

[Le_Combattant]

Since I'm focusing/suspecting fuel issue, I did a comparison with my parent's car.
A Skoda Octavia of 2015 equiped with an EA211 CZDA engine (1.4 TSI 110KW).
Mine is a EA211 CJZC engine (1.2 TSI 66KW) but the architecture is the same.

Here is the graph of the high fuel pressure of the Skoda.
It was used few hours ago and some pressure was still inside the high pressure fuel rail:

*I just forgot to include RPM on the first*

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Here with RPM

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When can notice since the moment engine is switch OFF, fuel pressure remain stable and even increase in the fuel rail due to the heat generated by the engine and by the fact, injector/fuel pump are fueltight.

And here, the graph of my Polo.
Car was used until midnight and the test was performed 14-15h later.
Notice how low the fuel pressure in the rail is low.

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Engine was cold so I let it stabilize during 2 minutes.
Then I switch off the engine.

And immediately, high fuel pressure drop like skyrocket.
What I do not understanf/missing is the fact that the "High pressure fuel request" is also dropping and if there is a link between the two (request and actual pressure mesured in the rail).

On the Skoda it stays at 140 bar, factory value for idle (on mine it's 120 bar).

[Le_Combattant]

Hello everybody, hope you are doing well !
I'm still busy with my issue (not as much as before, but still).

I'm more focused on the fuel system and the HPFP and LPFP with the controler.

Today and yesterday, I had the same issue.
Yesterday, after a short drive (less than 10km), the engine was barely hot (oil temp below 70°C) and I stopped it the time I did my sport (1h30).
When I went back to the car and start the engine, it barely hold idle. At least, RPM were below the normal idle (around 300-400 rpm) with check engine light + EPC light.

I switch it off and start again: no issue.
After a scan: no faults.

Today, same issue and even worse: the engine stall after the start (after 1h30 of sport).
Started it again: no issue.

It's not the first time she did this to me, also last year I had the same issue.

With VCDS, the LPFP went smoothly to every level of power/pressure. And from what I can heard, no issue or suspect noise.
Now today I was on the HPFP and the N276 solenoid.

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I'm going to try to measure (time permitting) its resistance and power supply.
On the internet, the value seems to be between 1 Ohm and 1.5 Ohms.

For the power supply, between 11 and 12V also according to internet, but on my schematic: no informations.
Also, I'm going to check that if I disconnect the N276 sensor, I have 235 bars by default (degraded mode):

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When I disconnect the N276 connector, the pressure rises to 235 bar.
The values are quite variable (it's not a perfect 235) between 220 and 235 bars (a little more).

Resistance values are between 15 and 16 Ohms (the engine was still warm, at least when I opened the hood, you could still feel the heat).
Being a solenoid, its resistance will increase with temperature.
I'll be able to try the experiment tomorrow, with lower temperatures and with a cold engine.

Now for the power supply:
-5V after ignition (engine off)
-5V engine on

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So I'm quite a little be confused and bored by this issue :banghead:

[amer6R]

what about making some measurements when cold and hot?
Maybe its some kind of electrical gremlin

Maybe tug s bit on the connectors, see what happens

[Le_Combattant]

what about making some measurements when cold and hot?
Maybe its some kind of electrical gremlin

Maybe tug s bit on the connectors, see what happens

Because depending of the temp of the engine, the internal resistance of the N276 solenoid will increase..maybe to far away from original spec.
My car is almost 11 years old, 184300 km and is doing only highway.

Just by curiosity, I want to see if there any difference. The thing is, even on VW workshop manual, Wiring Diagramm, I can't found the spec for my N276 internal resistance.
I have to rely on internet only.

[Le_Combattant]

So I took the resistance of my N276 solenoid.
It was around 17°C and engine was dead cold.

11.8 Ohms. So 4 Ohms lest than yesterday with a "hot" engine.

[RUM4MO]

Typically a wire wound coil resistance increases when the coil windings get heated up.

I seem to remember that from either a high school or university experiment - and I'm very old now!

[Le_Combattant]

Typically a wire wound coil resistance increases when the coil windings get heated up.

I seem to remember that from either a high school or university experiment - and I'm very old now!

Even if you are old you are right hahaha.

The thing is, what are the factory spec...

[Le_Combattant]

So today I decided to investigate the LPFP:

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First try, ignition "ON", the LPFP prime the circuit just over 2.5 bars:
https://youtu.be/18rXd6RqqVU

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According to my VW documentation, the low pressure fuel pump must regulate between 2 and 6 bars depending on engine requirement.

Now with VCDS, I can test the low pressure fuel pump on it's entire power range, from 0% to 100%.
Pressure almost reach 6 bars:

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Now, an other video with the following sequence:

-Ignition "ON", pump priming
-VCDS test of the pump (pressure reachs almost 6 bars)
-Engine start with revs up to 2000 rpm
https://youtu.be/SJiQtxjRtQ4

What do you think?

If we follow the VW doc: no problem. The values are in the specs (4-7 bars via the VCDS).

Now I find it hard to believe that there isn't a problem, knowing that with the engine running, I have 1 bar, 1.5 bars, whereas the regulation should be between 2 and 6 bars.

So does this pressure change according to the load? Possibly, but I have no way of knowing.

[Le_Combattant]

Hello all !

So after many months of searching, I took the decisiont to replace the LPFP inside the fuel tank.

Because brand new part from VW cost more than 320 euros, and OE solution are crap (even if they came from the same manufacturer, here Continental/VDO-Siemens), I went for a second hand option from Ovoko.
I found a seller, reselling LPFP with the last revision (6R0919051N) for 130 euros.

And with that, low mileage. The one I bough has only 1200 km on the clock. So when I will receive it: good cleaning, quick test and we will see.

[Le_Combattant]

So quick update,

I received this week my brand new "second hand" LPFP.

After little of a cleaning with brake cleaner, she looks almost brand new:





I just have to replace the fuel gauge unit because it's was "bended" during the shipping. And the floating part was damaged. Not a bit deal.
Just 3 wires to remove and swapp with my old unit on my pump.

I also bought this tool to remove correctly the cap:
Cheap and nice design.

[JiSingh1]

This is a definite journey to watch!

Very intrigued if you figure out what caused it or what the fix is.

These polos are very sneaky things and will play up often.

[Le_Combattant]

Well, it's the only issue I have so far.

For an 11 years old car, sleeping outside all the year with 201800 km on the clock, it's not that bad I think ^^

[JiSingh1]

Well, it's the only issue I have so far.

For an 11 years old car, sleeping outside all the year with 201800 km on the clock, it's not that bad I think ^^

Fair enough!

I remember we spoke about gearbox oil a few years ago, trying to look at what was best
Never ended up doing mine.

Currently battling with stop start errors, heavy steering, air con pressure problems, air con energy reduction fault, whistling on acceleration and just horrible suspension on mine