Bad Gas Mileage [Merged 9-6]

[99GST]

I am still getting some pretty bad gas mileage.

I am only getting about 19.7 mpg with mostly city driving shifting at 4k.
I have already replaced my front O2 sensor and am looking to replace the fuel filter.

I have a 99gst with about 55k miles on it. Should my fuel filter already be bad?

What else should I check or change? I have NKG plugs and Accel wires are on the way.

Thanks,
Nathan

 

[tsi1991awd]

If you are looking into replacing your O2 sensor, I don't know if this applies to you but when I lived in Fairbanks, Alaska , If your car went in for an I/M or emissions and you got between a certian set number of exhaust output and how rich etc. then you qualified for a new and FREE O2 sensor. Thats how I got mine... But I don't know if anyone else does it.

Hey man, yea WA doesn't do that. If you fail emissions, if you spend $150 at an authorized shop toward fixing your car and you STILL fail, they give you a waiver. All they care about is the money.

 

[allrice4g63]

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Hi i am kinda new to the dsm world even though iv been around alot of them, anyways i have been having problem with my 2g talon tsi automatic trans. we swapped the T25 for a 14b also swapped the injectors from a 1g the 14b has a ported 02 housing on stock exhaust. i kinda have two problems for one if i leave my boost setup like stock i boost 8 pounds which i believe is right, but with my mbc hooked up no matter how much i turn it up or down it stays at 14 pounds no spiking no boost creeping just solid 14 pounds, my other problem is i can only brake boost 4lbs and my car will go from completely cold to warmed up in about 1 min and my turbo will glow red even when im not beating on it. my gas mileage sucks im talking like 15 mpg and i get full boost at about 4000 rpms but its like you almost flip a switch at about 5300 rpms and i can feel the car pull until it shifts then it starts all over again. i checked and tested the wastegate, i have replaced the 02 sensor and did a complete tune up i dont know what else it is please help thanks!!!

 

[xioca]

Woah i forgot 2g all had 450cc injectors, but yeah it sounds like you have a boost leak. And you mbc is hooked up wrong.

 

[talon187]

ok the injectors are the same size as you took out. have you checked for boost leaks? sounds like you have a huge one. the other question i have is did you hook up all the coolant lines and oil lines to the turbo ? it shouldnt be glowing it beeing way over worked. i would remove the mbc and see if that fixes your problem as far as boost 14lbs is pushing it on a stock setup

 

[RadDsm]

Arent the injectors the same size? Unless you took them out of a 1g automatic, then they are smaller right?

 

[talon187]

the injectors i thought one a 1g were 450s and the 2gs came with 450s on both autos and manual while the auto 1gs came with 380s or somthing like that

 

[kahl23]

1g autos came with a 13g turbo, not 14b, therefore smaller injectors. 2g's all came with T-25s, therefore all of them had 450s. I'm curious as to why you swapped out your injectors for 1g units, doesn't make sense to me.

 

[allrice4g63]

yeah they are both 450cc, at the time when we swapped the injectors my buddy thought that the 1g ones were bigger but shows what he knows, i just thought i would include that with my post just in case doing anything with the injectors could of messed something up, i have done a boost leak test 3 times was leaking off the jpipe at first fixed that then was leaking where the licp connected to the jpipe i fixed that, i couldnt find anymore leaks but could there be a bost leak out of the injectors??? im just sick of burning my hands on this car i want to get it fixed, the car only has 58k on it and i want to start modding before the snow flys

 

[delta448]

sounds like it's running rich, cause you didn't compensate for the larger injectors. And you mbc is hooked up wrong.

Possibly...

ok the injectors are the same size as you took out.

Unless the 1G already had upgraded injectors.

have you checked for boost leaks?

Always a good idea. And very likely the primary issue here.

it shouldnt be glowing it beeing way over worked.

A big boost leak can overspin a turbo, especially if you're beating on the car and revving the engine over your 5300rpm "switch" repeatedly...

i would remove the mbc and see if that fixes your problem as far as boost 14lbs is pushing it on a stock setup

Maybe 14lbs is pushing it on a 1G with lower fuel pressure and lower fuel cut airflow, but 2Gs can handle a smidgen more, about 16-17 is the consensus with a responsible driver and small turbo like the 14b.

 

[talon187]

yes there could i would use soap and water when do you a boost leak test spary everything intake mainfild turbo intercooler piping vac lines toss the soap and water into a spary bottle and go at it check the turbo for shaft play as wel.

 

[allrice4g63]

as for the coolant lines and oil lines i already checked them and i checked for shaft play there is no shaft play, another thing that might help is that the car sat for 2 years before i bought it. i dunno why somebody would let a car with 58k on it sit with nothing wrong with it unless they know something that i dont. and my mbc is hooked up correctly i have checked and double checked this,

 

[talon187]

have you dissconnected it to see if it boost at 8psi? if it doesnt then you know somthing else is up possibly the wastegate being stuck partly open ive seen this happen a few times

 

[xioca]

Shouldn't he just connect a straight vac line from a pressure source and run it straight to the Wastegate, stock wastegate spring opens at a low psi.

 

[4g63tcrazy]

Sounds to me like a plugged cat or your maf isn't plugged in or is going bad. On my friend's old 2g we forgot to plug the maf in after we got done working on it and it had no power til about 4000 rpm's, but if your turbo is getting hot and still no power it would lead me to think its a clogged cat.

 

[xi Talon ix]

most people turn to boost leaks during problems like this but i think your catalytic converter might be clogged. if your turbo is glowing red it might be "choking" because of the cat. not sure how to check it but take a look at the cat at night after a drive and see if its glowing at all.

haha..4g63tcrazy beat me to it. just glad im not the only one.

 

[allrice4g63]

yeah i have checked the cat at night it doesnt glow, my friend did take out the honeycomb stuff in my MAF. I thought about that to maybe taking that stuff out messed with it or something. I guess letting other people do work on your car is not always good. i was contemplating on getting an exhaust system so maybe ill just replace the cat when i do that but i hate the sounds of automatics with exhaust. another thing is i can adjust the idle to about 1000 but when i put it in drive it drops down to like 500, or i can adjust it to like 2000rpms and ill go for a drive and come back and it drops back down to 800. so the MAF could be a problem. But wouldnt that show a code or a CEL

 

[delta448]

Your MAF is F'ed.
You can't remove all the honeycomb pieces and expect it to work correctly, if at all. 4g63tcrazy was on the right track.

 

[talon187]

yeah taking out the honeycomb isnt such a good idea. now the maf has no idea how much air is coming in. find a new one

 

[KGB Pilot125]

Shouldn't he just connect a straight vac line from a pressure source and run it straight to the Wastegate, stock wastegate spring opens at a low psi.

Wastegate arm should move at around 11.4 PSI

 

[allrice4g63]

OK i checked my wastegate today and it moves at 11-12 psi so that is working fine but i think there is a boost leak somewhere right on my turbo. It sounds like its between the cylinder head i couldnt quite pinpoint it though its not the jpipe at all it seems like its under the turbo almost on the exhaust side which makes no sense. unless its just the turbo spinning is the sound im here but i dont think that is it i tested at 5lbs 10lb 15lbs etc and listened and thats the only spot i could here any leaking anybody that would know why it would leak there please post back thanks.

 

[doober75]

Sounds to me like a plugged cat or your maf isn't plugged in or is going bad. On my friend's old 2g we forgot to plug the maf in after we got done working on it and it had no power til about 4000 rpm's, but if your turbo is getting hot and still no power it would lead me to think its a clogged cat.

exactly what i thought it was too. had the same problem with mine. go check that and report back

 

[scoby41]

exactly what i thought it was too. had the same problem with mine. go check that and report back

He already said it didn't glow..... if the turbo is glowing from a clog, I'm assuming the cat would too

 

[doober75]

whoops didnt see that part..
my bad

 

[allrice4g63]

ok so i have been having problems with my 2g talon tsi 14b swap. i have been getting bad gas mileage and turbo has been glowing easily when i ran a piece of pipe directly from my jpipe to my throttle body bye passing everything my boost went all the way up to 20psi in a second but when i have all the piping hooked up it only runs 14psi is this cause by a boost leak somewhere... possibly stock 2g bov

 

[Burtismaximus]

so you are saying that you are just running a pipe from the turbo to your throttlebody with no ic. are you using a bov????