MKV GTI KO4 - Fuel Pressure Question

[jacques1397]

Hi from South Africa,

I have a quick question for you all running K04. Some background, I own a UG MkV K04 with bigger cooler, cold air induction, S3 Injectors etc. Motor was recently rebuilt, due to numerous small problems, so I know its 100% sound.

I had time to log my fueling, boost and AFR.

I noticed for once, no boost leaks, AFR seems on point, little rich/lean, not 100% sure to work that out, but none the less, the LPFP seems to be dropping pressure on higher RPM. Any idea why this will happen? Normal? That's my only conclusion to why she is not as healthy as its supposed to be. I also seems to be having a dirty throttle body, or its faulty, doesn't seem to open to 99.6% as far as I know it should?

Logs below.

Marker

Group 1 - Field 0

Group 5 - Field 1

Group 14 - Field 2

Group 31 - Field 0

Group 31 - Field 1

Group 62 - Field 0

Group 62 - Field 1

Group 103 - Field 0

Group 106 - Field 0

Group 115 - Field 2

Group 117 - Field 3

Group 230 - Field 0

Engine Speed - (G28)

Engine Load

Misfire Counter

Lambda Control - Bank 1 (actual)

Lambda Control - Bank 1 (specified)

Throttle Valve - Sensor 1 (G187)

Throttle Valve - Sensor 2 (G188)

Current - Fuel Pressure

Fuel Rail - Pressure (actual)

Boost Pressure - (specified)

Boost Pressure - (specified)

Rail Pressure - (specified)

/min

%

%

%

bar

bar

mbar

mbar

bar

1​

2560​

46.6​

0​

0.95​

1​

35.9​

60.5​

3.98​

91.77​

730​

730​

93.15​

2720​

120.3​

0​

0.93​

0.94​

88.3​

7.8​

3.99​

115.39​

2280​

2480​

120.75​

3120​

191.7​

0​

0.95​

0.94​

87.9​

8.2​

4.6​

124.45​

2550​

2550​

128.98​

3640​

191.7​

0​

0.78​

0.8​

88.3​

7.8​

3.96​

125.48​

2540​

2540​

128.99​

4120​

191.7​

0​

0.78​

0.79​

88.3​

8.2​

3.6​

124.07​

2540​

2540​

128.99​

4640​

191.7​

0​

0.76​

0.77​

87.9​

8.2​

3.04​

126.35​

2540​

2540​

128.99​

5080​

191.7​

0​

0.76​

0.78​

86.3​

10.2​

2.68​

125.1​

2540​

2540​

128.99​

5440​

190.2​

0​

0.75​

0.76​

84​

12.5​

2.51​

125.53​

2540​

2540​

128.99​

5840​

180.5​

0​

0.73​

0.74​

83.2​

13.7​

2.36​

124.92​

2540​

2540​

128.99​

6160​

174.4​

0​

0.73​

0.73​

80.5​

15.6​

2.3​

123.56​

2520​

2520​

128.99​

Marker

Group 1 - Field 0

Group 5 - Field 1

Group 14 - Field 2

Group 31 - Field 0

Group 31 - Field 1

Group 62 - Field 0

Group 62 - Field 1

Group 103 - Field 0

Group 106 - Field 0

Group 115 - Field 2

Group 117 - Field 3

Group 230 - Field 0

Engine Speed - (G28)

Engine Load

Misfire Counter

Lambda Control - Bank 1 (actual)

Lambda Control - Bank 1 (specified)

Throttle Valve - Sensor 1 (G187)

Throttle Valve - Sensor 2 (G188)

Current - Fuel Pressure

Fuel Rail - Pressure (actual)

Boost Pressure - (specified)

Boost Pressure - (specified)

Rail Pressure - (specified)

3​

3440​

91.7​

0​

0.92​

0.91​

88.3​

9​

3.95​

93.24​

1790​

2550​

104.44​

3920​

191.7​

0​

0.88​

0.91​

88.3​

9.8​

4.23​

121.42​

2540​

2540​

125.72​

4560​

191.7​

0​

0.74​

0.76​

87.9​

9​

3.35​

121.54​

2550​

2540​

128.98​

5080​

191.7​

0​

0.74​

0.76​

86.7​

10.5​

2.73​

124.45​

2540​

2540​

128.99​

5560​

187.2​

0​

0.76​

0.76​

84​

12.5​

2.45​

124.56​

2540​

2540​

128.99​

5960​

176.7​

0​

0.73​

0.75​

83.2​

13.7​

2.35​

125.25​

2540​

2530​

128.99​

6320​

168.4​

0​

0.72​

0.73​

82.4​

14.1​

2.34​

124.98​

2510​

2510​

128.99​

4​

6200​

12​

0​

1.99​

0.95​

19.9​

77​

4.89​

122.02​

2510​

2510​

119.75​

Thanks

 

[GIACUser]

You may have tried this but I would do a throttle body alignment (TBA), might not have been done when your motor was rebuilt. (throttle position)

 

[ROH ECHT]

MBs 230 for high fuel pressure in the fuel rail, and 231 for low fuel pressure provide both specified and actual for both and MB 231 also gives the working load of the LPFP in the tank. With that...the low fuel pressure specified/target is never below 4 bar.

The LPFP pressure dropping in high revs, or high load, is almost always related to the LPFP being old and tired. But...it can be from; the fuel filter regulator returning fuel to the tank. You can disconnect the fuel filter's return line (at the filter) which goes to the top of the LPFP, to see if there is any residual fuel in it. If there is fuel in it...you may as well replace the filter. There is also an anti-return/check valve in the LPFP itself, but this is replaced, obviously, with a new LPFP.

One thing you may consider, is drilling the restrictor in the fuel delivery to the HPFP to 5mm. This allows the back-flow from the HPFP to fill the delivery line more easily and allows the LPFP to work less than its full capacity of 91.8%. Let me know if interested and I need to know what fitting it has for the low pressure line attached to the bottom of the HPFP.

 

[jacques1397]

Hi All,

Okay so TB has been aligned, I know it messes around from time to time, then goes into limp mode. But not often. So will have to replace someday, but I usually just re-align it then its fine for a few months.

Main concern is fuel at LPFP side at the moment, then I can sort the TB.

I will start off with logs as specified and then see, I will also check the return valve side, I installed a new 6.6 bar filter a few days ago, so will be easy to see if there is any fuel in return side.

I also read the G410 might be a problem, althoug if unplugged and pressure increases to default as per computer then I might cancel out a faulty fuel pump?

Will run logs and see, post them here if done. Thanks for all the help and advice so far. Seems like MKV fueling is always a problem

 

[ROH ECHT]

I also read the G410 might be a problem, although if unplugged and pressure increases to default as per computer then I might cancel out a faulty fuel pump?

How would it know what the pressure is if the G410 is unplugged, so to set it to a default pressure?

Yes, it is possible the G410 is causing the low pressure report for the low fuel pressures, but the high fuel pressure suffers in the rail as well in the data. So it is likely truly producing low pressure from the LPFP and not just an inaccurate sensor report from the G410. As you can see the rail target is always higher than the rail actual.

 

[jacques1397]

Hi,

Thanks for reply. Will be logging it next week, car going in for front bumper touch ups and new grille install. Going for the Wolfsburg Edition front grille rather then everyday GTI one, so will post pics soon. Then I can hopefully fix the fueling issues.

 

[TSMILEY]

It's all about priorities! HAHA

That's the same grille I'm running in my GTi. I love the look compared to the stock honeycomb. I also got the Euro fog light covers and center lower grille to complete the look.

 

[jacques1397]

Hahahah same here.

Will post pics eventually

Went in to paint this morning. Last min decision, plus I imported them from USA. You dont get it here in South Africa.

Then I can scan the fuel once back.

Thanks all, will keep posted.

 

[jacques1397]

Hi All,

So it took me a bit longer to get her cosmetics fixed. Plan for this week is to have the fueling resolved so the motor can run 100% potential. I will be loggin it soon and posting data here, will run all tests as said above and provide feedback. I personally think its pump related, but will first test.

here some pics