Vacuum and fuel trim issues 1.8T

james walker

cooling is the key people
May 24, 2007
5,121
2
retford notts
Hi,

Im currently trying to get to the bottom of an issue with High long term fuel trims (+20% give or take) which is showing my car running extremely Lean, struggling with this as the A/F ratio looks ok and o2 looks ok...

I have searched around with Carb spray, washing up liquid for any obvious vacuum leaks but finding it difficult to spot. Dont have access to a smoke test as yet

Symptoms are:

  • Rough idle
  • High LTFT on idle of 25%
  • When revved at 1500, 2500 the trims go back to normal
  • STFT are fine
  • No fault codes
  • Oil level is fine
  • Air filter is fine
  • Spark plugs look good
  • MAF is fine
  • o2 sensor reading is bang on
  • Air fuel mix is nearly bang on
  • Feels stuttery to drive on low revs through the gears, open throttle seems normal
Ive just undertaken a Vacuum test and the results are worrying

At idle (pictured)

8-10 Hg fluttering between the 2

At 1500 rpm

Drops to 3 Hg, increases to 17Hg drops to 5 Hg then settles back to 8-10 Hg

At 2500 Rpm

Drops to 3 Hg, increases to 18 Hg, drops to 5 Hg then back to 8-10 when idling

3000 rpm is the same

Its at a garage for further diagnostics tomorrow but i want to arm with as much information to shorten lead time before its rectified as much as possible

Any advice or experience would be welcome

Thanks in advance
 

Attachments

  • IMG_9393.jpg
    IMG_9393.jpg
    83.1 KB · Views: 93
  • IMG_9394.jpg
    IMG_9394.jpg
    150.9 KB · Views: 90
  • IMG_9395.jpg
    IMG_9395.jpg
    166.1 KB · Views: 97
  • IMG_9396.jpg
    IMG_9396.jpg
    175 KB · Views: 92
  • IMG_9401.jpg
    IMG_9401.jpg
    55.6 KB · Views: 96
  • IMG_9402.jpg
    IMG_9402.jpg
    69.7 KB · Views: 94
  • Screen Shot 2018-07-02 at 17.41.07.jpg
    Screen Shot 2018-07-02 at 17.41.07.jpg
    293.4 KB · Views: 111
Adrian Flux insurance services - discount for forum members.