bad gas milage...carbon build up?

[Johnny Dangerously]

k...i changed 02 sensors
FPR
fuel dampener
injectors
fuel rail
afm
fixed all boost leaks
fixed all exhaust leaks
changed driving habits

gas milage STILL sucks. 230 miles a tank which is roughly 16 mpg

i was told on supraforums before that gay fuckin server thats powering it decided to crash on me 5 fuckin times that carbon build up in the combustion chamber can cause bad gas milage through absorption.

my question is...aside from engine disassembly..is there anyways to dissolve/burn/eliminate/pick up/saturate the carbon deposits in the combustion chamber? i know the only other path is the spark plug holes..i was just curious if there was any way to get in there and collect the mighty annoying but inevitable carbon deposits...

thanks

 

[mkIIIman089]

IIRC, I remember seeing a very strong detergent like system for removing cabon build up but its like a stand alone machine and probably costs a good amount of money, I saw it on 2 guys garage or something a while back. It was probably the most effective way without disassembly though.

 

[Orion ZyGarian]

Seafoam?

 

[Johnny Dangerously]

Seafoam?

seafoam did enter my head..my old man said it worked great on his boat engine (chevy 350)

i was real curious about seafoams effects on the stock HG, tho. I have a stock HG, arp head bolts at 75 ft lbs....dont you think it could possibly eat it up?

 

[Justin]

seafoam did enter my head..my old man said it worked great on his boat engine (chevy 350)

i was real curious about seafoams effects on the stock HG, tho. I have a stock HG, arp head bolts at 75 ft lbs....dont you think it could possibly eat it up?

I have no input on that fact, but I have heard that stuff works really well. Always have been weary of putting it in my engine though....


you said on SF you put in new injectors. How do you know those injectors are good/clean/working correctly?

 

[Orion ZyGarian]

Seafoam wont ever touch it...how could it affect the headgasket?

I've heard as many people like it as would never touch it. I used it myself when I first got my car...not sure if it helped but it mightve. I do suggest changing your oil and plugs right after though

 

[Johnny Dangerously]

I have no input on that fact, but I have heard that stuff works really well. Always have been weary of putting it in my engine though....


you said on SF you put in new injectors. How do you know those injectors are good/clean/working correctly?

the injectors came from my friends car who is getting his 22mpg...they were clean as a whistle.

i give seafoam a try tomorrow along with an oil change..see if it helps. I DO know there is carbon deposits in my combustion chamber..when i went to change spark plugs and my mirror finish cover, u can see it if you shine a flash light in it.

hopefully it does the trick, however i am open to other suggestions. such as that one machine that takes out carbon deposits...any more info on that would be great

 

[turbomk3]

post an update on whether or not it works

 

[mrnickleye]

Those carbon deposits aren't whats causing your low fuel economy. They might cause pinging. Look elswhere to improve mileage. Mine gets 15 town, 20 hwy (but hauls ass).
Those deposits are as dry (and stay that way) as the Mojave Desert sand. What you probably heard is that the carbon build up on the 'back-side' of the intake valve can suck up fuel when you first start the car after it sits for a while. Its like a sponge. This can cause poor idle, and a stall when first dropped into gear.
Then, after 2-3 minutes of engine on, its saturated with fuel, and it stays that way till you stop engine for 10+ minutes, and it dries out again.

Economy areas: Timing, temp sensors, TPS, fuel pressure, injectors (leaking??), AFM, ECU, O2, vacuum leaks, fuel leaks, too much back-pressure in exhaust system, too cold engine operating temp (thermostat at 180* min.) etc, etc.

 

[albertmdh]

i know seafoam works miricles on auto trannies.... makes reverse work again!

 

[Johnny Dangerously]

Those carbon deposits aren't whats causing your low fuel economy. They might cause pinging. Look elswhere to improve mileage. Mine gets 15 town, 20 hwy (but hauls ass).
Those deposits are as dry (and stay that way) as the Mojave Desert sand. What you probably heard is that the carbon build up on the 'back-side' of the intake valve can suck up fuel when you first start the car after it sits for a while. Its like a sponge. This can cause poor idle, and a stall when first dropped into gear.
Then, after 2-3 minutes of engine on, its saturated with fuel, and it stays that way till you stop engine for 10+ minutes, and it dries out again.

Economy areas: Timing, temp sensors, TPS, fuel pressure, injectors (leaking??), AFM, ECU, O2, vacuum leaks, fuel leaks, too much back-pressure in exhaust system, too cold engine operating temp (thermostat at 180* min.) etc, etc.

yeah, well i have NO idling problems, no stalling problems, no start up problems, no hauling ass problems, no drivability problems.

timing..checked, fine...temp sensor, replaced, fine
TPS..fine
fuel pressure...u tell me, i tried two FPRs that work real well on other peoples cars, yet bad gas milage on mine
fuel leaks..none
too much back pressure in exhaust system? I run an HKS Super Drager, Test pipe, and 3" Supersport downpipe with integrated elbow..ported and polished ct26 turbo and ported and polished exhaust manifold....i doubt i have too much back pressure
thermostat is fine, temp goes to where its supposed to...thats a non-issue.
o2 sensor was replaced with a brand new one and reads very well according to the AF guage (which is its only positive use)
no vac leaks...-20 on idle, -18 with AC on
no boost leaks...pressure tested it, its fine, car boosts fine, reponse is normal
AFM..replaced with 3 different kinds...2 regulars and one Lex, no difference


I havent tried changing out ECU's...for some reason i dont think it would change a thing...but if i can get a hold of an 89+ ECU to borrow, ill give it a shot. im still gonna try out the seafoam later today and see what results it brings me. it couldnt hurt anyways, wether it solves the problem or not.

 

[Johnny Dangerously]

What the FUCK? How did you get it to work on a tranny?? You are supposed to put it in your ENGINE...it shouldnt ever touch the tranny either...what?! I'm confused by that statement

they make a solutions for automatic transmissions that work also for your power steering system.

 

[Orion ZyGarian]

Okay thanks...I didnt know that

 

[suprajjang]

damn you are in the same situation as me except i only get about 12 MPG on a stock mkiii :aigo: if you find out what your problem is let me know because i need to fix this also

 

[mrnickleye]

Try getting a hold of a fuel pressure gage setup (friend, borrow from friendly autoparts store, rent, or just pay the hour labor at a reputable shop). Check fuel system for proper pressure, and injector leaks. Its posiible that one or more injectors is not spraying in a nice pattern. The only way to check an injector for the proper spray pattern is pull them, and have them tested. Not cheap by what I've read here on SM.

Please keep us up to date, as we all want to know what solves your problem.