Excesive fuel consumption/jumpy idle

[ALTERNATOR]

Hello everyone

I've got a 2.0l and as the title says, I've got a pretty bad fuel consumption...somewhere around 18l/100km or 13MPG . Ok...I have recently changed: Plugs, rotor cap+dizzy, timing belt+tensioner, oil, filters. Also have done: Valve seats, cleaned and ported the head(as good as I could), changed head gasket, changed valve seals, intake+exhaust gaskets, ported intake+exhaust manifold...Basically everything I could.

The engine pulls great after the head work, I mean really good through the whole rev range. I don't have to rev the nuts off it to get going but the fuel consumption is still pretty bad...I mean come on :shocked:It's not a VR. That's just eyewattering My next guess are vacuum lines. Already have changed the PCV valve hoses and visually inspected the known vacuum hoses. I might be missing some of them. I've already seen that the PCV grommet is in pretty bad shape. Do the vacuum lines influence fuel consumption that much?

It's also been scanned, the laptop says everything is perfect.

[javalin]

>It's also been scanned, the laptop says everything is perfect.
lol - limited fault detection in the mk3's....

Temperature sensor?  Does it come up to temp ok? 90c?

James

[Khare]

Who did the porting? Was it a professional or was it you?

Also, is the throttle body clean?

[xAntiVenxm]

wow thats mental! I have heard of fuel pumps, when they are on the way out, have a sensor that realises this and sets the fuel pump into an emergency-type "limp home" mode.. where the fuel pump will continually run when you turn the car's electrics on with the key, instead of you hearing it power on for 1 or 2 seconds, it just keeps going.
but if vag-com says everything is fine.. how very odd

[ALTERNATOR]

Yup, the needle comes up to 90C in about 10 minutes or so. But if there's another way of checking if it's ok, please share

The porting was done by me, but I don't really think that's the problem, I just gasket matched everything, not really increasing the port size by allot . The throttle body is clean as could be.

[javalin]

VCDS (vag-com) will report the coolant temp - the sensors have twin outputs, one for the dash and one for the ECU.  Should read the same obviously, and as you say 90c in ~10mins.

Coolant temp sensor is a primary source of mixture control for the ECU, when they fail can cause overly rich mixture.

Could also be relating to the upgrades of course.

What engine is it btw?

[ALTERNATOR]

The engine is a 2.0 ADY. The engine ran just the same before the engine upgrades , nothing has changed except for the fact that now it pulls better, allot more responsive through the whole rev range.

Could those vacuum leaks influence fuel consumption that much?

[Khare]

I'm going to say something which may be wrong, but if it's right it may hurt.

Porting is difficult to do right, it required lots and lots of practice as well as the right tools and equipment. I remember porting a throttle body a few years ago and although it wouldn't idle well and the fuel economy was shocking it pulled a LOT harder. Your problem I think lies in the porting, Did you port match the manifolds to the head or did you just make the head and the manifold ports bigger independently?

I think the it's being masked well by a smooth idle and decent power delivery but I think you've affected the efficiency of the engine, thus reducing economy. I'd start by doing a compression test to make sure the valves aren't leaking, as I presume you lapped them in yourself.

[ALTERNATOR]

Well, I port matched the manifolds and the head to gasket size(they're about 1mm larger then what they used to be). Didn't really take out that much material. The thing is, the car had the exact same fuel consumption before I started working on the head I'm pretty sure the valves seal quite good, I tested them with isopropyl alcohol. May I say that the valve were just dropped in there, withouth the springs and retainers and they sealed perfectly. Also tried the test with gasoline, no problem.

[Bandit127]

VCDS (vag-com) will report the coolant temp - the sensors have twin outputs, one for the dash and one for the ECU.  Should read the same obviously, and as you say 90c in ~10mins.

Coolant temp sensor is a primary source of mixture control for the ECU, when they fail can cause overly rich mixture.

Could also be relating to the upgrades of course.

What engine is it btw?

...is the right answer

The coolant temp sensor that feeds the ECU is fecked. Effectively, the choke is on constantly.

As above, use Vagcom to check it out.