poor fuel consumption after inlet manifold gasket change

[spudboy6]

i changed my exhuast manifold gaskets the other day and found it was much easier to take the inlet manifold off to do the job, all gaskets replaced with new ones and fitted up ,

everything was cleaned and throttle body re alighned on vag com and after 30 miles checked for faults codes on VCDS and nothing came up , no fuel leaks or blows at any manifolds

consumption before

60 miles to £10 (7.5L )

after

40 miles to £10 (7.5L )

so anyone got any sugestions , all breathers on and not split / blocked and no fuel leaks .

may need a good thrash and some redex ?

[itavaltalainen]

which engine code?

what exactly have you done to change exhaust manifold gaskets?

[spudboy6]

1.8 adz ,
Had an annoying blowing noise under full load so removed the exhaust manifold to check for cracks ect and changed gaskets on the exhaust but couldn't get the two upper exhaust manifold bolts so removed the inlet manifold , cleaned all faces , refitted manifolds , put the two vaccume pipes back on the spi unit , put the two black pipes on the spi unit with arrows (fuel) and didn't remove anything else apart from spi unit and TB and had a new rubber flange on that recently withing last 6 months then coolant topped up and air bled , and I've been on an ecconmey run lately trying to get it back up to decent consumption to make sure it wasn't my foot  ,

Just trying to make sure I didn't miss anything but have been under it on a ramp and checked everywhere and all seems fine and like I said no fault codes

[itavaltalainen]

run a check on measurement blocks on vcds....

you're after block 1, specifically lamda value - check if this works, just connect laptop up, set up logging and put the laptop on the floor and drive around a bit... suspect you may have disconnected the probe or broke a wire (that is if you don't have air leaks - would check with few sprays of brake cleaner)

[spudboy6]

Will have a look when I get back to work , what's the rough values I want to see ?

[itavaltalainen]

lambda should be around 1.... it's the ratio of oxygen available divided by oxygen needed to burn fuel completely

it will be around 0.9 with cold engine idling (maybe even 0.8xx)
with warm engine it should be around 1 idling...
partial load with warm engine will be around 1, even a bit above 1

full load it will go below 1 again - region of .09

the value will constantly change slightly - even in idle. but if you're driving and logging revs, lambda and throttle body angle (think TB angle is in measurement blocks 2 or 3) you should see a larger change than when it sits idling.

above a certain TB angle (i think >75 deg. is considered full throttle by ECU ) you should see a fairly noticeable drop in lambda as it will ignore it and rich up mixture according to a map values.

you can also check TB angle reads back correctly in measuring blocks with engine off... fully open should be 85 degrees (+/- 1...2 deg), closed position is probably around 15....20

[spudboy6]

Nice one for that info !

Since manifold fitted I've put £10 in it three times with a result of

35 miles first £10
40 miles second £10 all on 95ron

I put £10 of 97ron bp ultimate in just now and done 60-70 miles on it (6.5l)

So looking back to normal now but will still carry out the above checks and keep an eye on it

[spudboy6]

Been fishing around today and havent managed to get on VCDS but will in the morning but , I read on a thread elsewhere and apparently a crack in the brake servo hose can cause bad running and consumption and I noticed that on the servo pipe near the manifold has them green caps over two nipples , should they both have a green cap on or one with a cap and one without ?

Need to get this sorted as 40-50 miles on 7.5L isn't right

Can someone confirm the throttle body reset procedure on the 1.8 ADZ with cable throttle ?

[itavaltalainen]

your way of tracking mileage is not the most scientific... gauge and mpg display are not super accurate...
fill up - drive till empty - fill up at same pump will give you much better numbers and average out any environmental changes (weather, traffic, etc)....

will check for TB procedure when i get home from work

[spudboy6]

lambda should be around 1.... it's the ratio of oxygen available divided by oxygen needed to burn fuel completely

it will be around 0.9 with cold engine idling (maybe even 0.8xx)
with warm engine it should be around 1 idling...
partial load with warm engine will be around 1, even a bit above 1

full load it will go below 1 again - region of .09

the value will constantly change slightly - even in idle. but if you're driving and logging revs, lambda and throttle body angle (think TB angle is in measurement blocks 2 or 3) you should see a larger change than when it sits idling.

above a certain TB angle (i think >75 deg. is considered full throttle by ECU ) you should see a fairly noticeable drop in lambda as it will ignore it and rich up mixture according to a map values.

you can also check TB angle reads back correctly in measuring blocks with engine off... fully open should be 85 degrees (+/- 1...2 deg), closed position is probably around 15....20

Just been out with a snap on machine in and my lambda readings are 100% spot on and have no air leaks and no fault codes
Where to look next ?