1.8T Basically Inhaling Fuel

[TobiqueSlang]

So I bought another b6 a few weeks ago that's had a pile of work done to it by the original owner and for the most part it runs great and it has no issues other than the usual gremlins.

The main issue I'm having with it though is that it's using about 30% more fuel than my other 1.8T and I'm just curious if anyone would have any ideas as to why?

the vacuum system is a mess but I guess you could say it's been "simplified" to an extent. SAI delete, catch can and a boost gage have been added. N80 still functions normally. Car has also been straight piped and CAT deleted but both O2 sensors are in place and function

No tuning done to the ECU, only thing changed on the motor outside of the vacuum system is that it's an AMB block with an ATW head (from a jetta with VVT)

Would the vacuum work cause the motor to run so rich or is there another explanation I might not be looking at?

[Mike Tries]

Sticky or dirty fuel injector? I've seen this personally on a car, and a simple cleaning brought it right back. I just pulled it out and cleaned it on the bench.

Is the CEL on?

[TobiqueSlang]

From what I know of the car the motor has been fully rebuilt from the ground up and has about 50K km on it.

I haven't pulled the injectors out yet but it's a good place to start.

CEL is on but all I have is an OBII reader and the only thing it shows for a code is "failure to connect with TCM" but I'm not sure why it would say that since it's a 6 speed manual... unless it was a swap from an auto?

There's a lot about this car that weird that I haven't had a chance to figure out. Kid was building a "race car" but a lot of the work he had done to it was already on my list to do to my other B6 so I figured I'd spend $5k to save $15k and then kind of start making things more "stock" afterwards.

So the first thing is to figure out the rich fueling issue.

[Gin+]

I'd look at fuel trims to start with.

[Mike Tries]

Yeah, while you've got them out, since they're right there anyway, might as well see what they are. A full rebuild might have included new injectors... and hey, why not upgrade them at the same time? Maybe they're monsters and the car doesn't know to account for them?

[TobiqueSlang]

I'd look at fuel trims to start with.

I've been going off what the message centre has to say vs the fuel gage. theoretically I should be getting roughly 600km on a full tank but I'm getting probably a little less than 400km. if I'm watching the message centre when it's set to the L/100km, depending on what gear I'm in it averages about 14L/100km at 2200rpm flat. normally that would be somewhere between 7-9L.

Even if I have the live feed up on the code reader I'm not sure it would tell me any different but I'll try it.

Mike- As for the injectors, I haven't pulled them out yet but near as I can tell they look like they're just stock bosch.

[Kevin C]

It's not always just an engine issue. Tires, alignment and brakes can reduce fuel efficiency. The other issues can be the general state of the engine like how good are the rings. Mods are always suspect. With the mods it has I wonder if the ECU has been tuned. Are you getting a CEL for the SAS pump and the missing converter?

[Mike Tries]

I've been going off what the message centre has to say vs the fuel gage. theoretically I should be getting roughly 600km on a full tank but I'm getting probably a little less than 400km. if I'm watching the message centre when it's set to the L/100km, depending on what gear I'm in it averages about 14L/100km at 2200rpm flat. normally that would be somewhere between 7-9L.

Even if I have the live feed up on the code reader I'm not sure it would tell me any different but I'll try it.

Mike- As for the injectors, I haven't pulled them out yet but near as I can tell they look like they're just stock bosch.

I think what Gin+ meant by looking at fuel trims involves querying the car for what it's trying to do. Generate a log file maybe? Or look in VCDS? There's a variable called "fuel trim". Maybe log it and see if it's out of whack in one direction or the other. The code reader you have, if it's generic and not connected to a laptop, might not help you. Consider an eBay cable and some logging software, or perhaps the Ross-Tech VCDS.

edit: Also, check the part numbers on the injectors. The Audi TT 225 hp used Bosch injectors, I think, and they had a higher flow rate for a given duty cycle. I don't think you can just hook those up and have the car compensate automatically for the change. Or... maybe it can handle the Audi TT injectors, but not some even larger Bosch injector? There are folks here more versed in this than I am. I just mean that you should take a look at the part numbers and verify, that's all (if they're stock 1.8t Audi injectors, then my speculation doesn't help anyway).

[Gin+]

Could also be a variation in fuel senders.

[TobiqueSlang]

It's not always just an engine issue. Tires, alignment and brakes can reduce fuel efficiency. The other issues can be the general state of the engine like how good are the rings. Mods are always suspect. With the mods it has I wonder if the ECU has been tuned. Are you getting a CEL for the SAS pump and the missing converter?

Not getting any codes for either of those, I know there's been some recoding done ie. the immobilizer has been deleted from the BCM... but not the ECU. the only code I have showing is "failure to connect to TCM" otherwise everything seems fine so I would assume that the cat and the SAS would have also been recoded as well.

I've only got access to a generic OBDII reader right now but VCDS is on my list of things I need if I want to be able to diagnose anything accurately via the ECU.

as far as I'm aware the ECU doesn't have any tuning done to it and aside from an aftermarket K03(Chinese) running around 10psi The motor is rebuilt but entirely stock with the exception being the ATW head, the exhaust and the vacuum system being re-routed.

Really what I'm after is confirmation, assuming everything computer and motor related is stock. What would a likely culprit be for such a rich condition? injectors, exhaust or vacuum or all 3? or anything else in addition I should look into?
I'm basically going to be firing a parts cannon at it over time anyway to return it more of a stock existence but this rich running condition is the first thing I'd like to try and alleviate since gas is almost $2L again.

[Cybersombosis]

How old are the O2 sensors? I’d try known good used sensors if you have a set you can swap in. We just had a 2001 come in with a lean condition caused by the secondary O2 sensor. Don’t know if it can cause it to go rich but if you have a set to swap in, it’s worth a try.

[Mike Tries]

Isn't there an easy way to check for fuel injector operation without even disassembling the car? Start engine, put one end of a length of fuel line up to your ear, then put the other end up to each injector? I think that should work. You'll hear them clicking away. Listen for one that sounds different than the others. I'm suspicious that one isn't operating correctly, though, the one time I saw that (Mitsubishi Galant) there was a code for it.

Did anybody ask about spark plugs? What do the spark plugs look like?

[TobiqueSlang]

Isn't there an easy way to check for fuel injector operation without even disassembling the car? Start engine, put one end of a length of fuel line up to your ear, then put the other end up to each injector? I think that should work. You'll hear them clicking away. Listen for one that sounds different than the others. I'm suspicious that one isn't operating correctly, though, the one time I saw that (Mitsubishi Galant) there was a code for it.

Did anybody ask about spark plugs? What do the spark plugs look like?

I'm going to pull all of this and look at it if I have a chance this weekend. I haven't had a lot of time to really go over the engine so I guess I made this thread a little prematurely to look for suggestions before I get too far into it. but I did ask how old the coils and plugs were before I bought it and he said they were new... but I suppose that doesn't mean they're right or actually any good.

FYI a screw driver makes a pretty good ghetto stethoscope too for listening to things like injectors.