Bad Mileage and low on boost (2g maf and 550's)

[Wooley91TSI]

So the car i recently acquired has been getting some seriously bad gas mileage (half a tank according to the gauge) in only 90 miles. Also, at WOT im only seeing a steady 7lbs of boost on the stock gauge. The car is also throwing a CEL, but i havent pulled the codes yet.

Due to my previous experiance with turbo cars this leads me to think boost leak, or o2 sensor, however i have basically no experiance with these cars so i was wondering if it could have something to do with the 2g maf and bigger injectors

 

[USAF 98 GSX]

There are so many possibilities of what could be the problem. Start with basic troubleshooting first. Check CEL codes, check boost leaks, check turbo for shaft play ( make sure it spins freely and no rubbing, which can keep it from boosting correctly), make sure front O2 sensor is working properly. Then to from there. Most likely one of these steps will steer you in the direction of the main issue.

 

[Bud92gsx]

Auto or manual car?

 

[Wooley91TSI]

Auto or manual car?

auto car. anyone know if u can just take these to autozone to get codes pulled or do i gotta bust out the multimeter?

 

[Bud92gsx]

Ahh well auto would explain a little bit.What pressure does the 50os need to flow 550 cc's,because the stock auto fpr is rated about 43 psi.

You may want a 5 speed ecu, and the manual fpr,but check what pressure your injectors want first.Then we will go from there

 

[clipto]

Ecmlink or die!

 

[apckofllamas]

get yourself an aftermarket boost gauge the stock one isnt accurate

 

[Wooley91TSI]

Pulled the codes, came back o2 sensor. Kinda figured thats what it was considering it doesnt come on until 1-2 min after a cold start. Also ordered a MBC, gauge pod, and an aftermarket boost gauge. Will check back in after i get all the parts installed and letcha know if my problem is solved.

 

[Wooley91TSI]

So i swapped the o2 sensor, still have the CEL. Had a buddy with steadier hands a better eyes try his hands at pulling the codes and it seems to be giving me codes 11, 12, and 13 (o2, maf, and iat). Also while under the car i noticed that the rear o2 sensor had been deleted.

So my questions are, Could the rear o2 sensor be throwing the o2 code, and does the 2g maf in a 1g send the codes for MAF and IAT, or should i try a different gen 2 maf?

 

[1G Eclipse94928]

ahh well auto would explain a little bit.what pressure does the 50os need to flow 550 cc's,because the stock auto fpr is rated about 43 psi.

You may want a 5 speed ecu, and the manual fpr,but check what pressure your injectors want first.then we will go from there

reply to this before you start buying parts

 

[Wooley91TSI]

Ahh well auto would explain a little bit.What pressure does the 50os need to flow 550 cc's,because the stock auto fpr is rated about 43 psi.

You may want a 5 speed ecu, and the manual fpr,but check what pressure your injectors want first.Then we will go from there

"what pressure does the 50os need"? not sure if typo. Also, if my fuel pressure regulator didnt have enough PSI to run the 550's, would i be running lean verses extremely rich?

reply to this before you start buying parts

Not sure how thoroughly you read my previous posts. The parts i bough in total were a boost gauge(for a more accurate boost reading than stock), a mbc, and an o2 sensor because i had a CEL for an o2 sensor. i don't see why i shouldn't have bought any of those parts.

 

[Viper588]

So my questions are, Could the rear o2 sensor be throwing the o2 code, and does the 2g maf in a 1g send the codes for MAF and IAT, or should i try a different gen 2 maf?

IIRC rear/downstream o2 should have no bearing on how the car runs, only monitors if cat is working and can/will cause CEL if not removed properly.

do you have any type of tuning device installed?

*edit* just realized you are asking about a 1g, what i started was based on 2g and i do not know if it holds true for 1g as well*

 

[Wooley91TSI]

IIRC rear/downstream o2 should have no bearing on how the car runs, only monitors if cat is working and can/will cause CEL if not removed properly.

do you have any type of tuning device installed?

*edit* just realized you are asking about a 1g, what i started was based on 2g and i do not know if it holds true for 1g as well*

No tuning atm, however if the problem persists i might just go ECMlink because 175 miles to a tank at $4 a gallon will eclipse the cost of link pretty quickly.

 

[KAOI]

$4 a gallon will ECLIPSE the cost of link pretty quickly.

good one


Anyways, my .02... You're throwing 550's on a car that normally sees 390cc so you really need a tune bud.

 

[Wooley91TSI]

good one


Anyways, my .02... You're throwing 550's on a car that normally sees 390cc so you really need a tune bud.

But i'm also flowing approx. 20% more air due to the 2g MAF. Ive read a few dozen threads on the topic of puttin a 2g maf in a 1g with 550cc injectors, and still haven't found an answer to whats causing the trouble codes or the extremely poor fuel mileage (approx 11-12mpg).

Even if the problem was the injectors alone, a 20% fuel abundance wouldnt explain a 50% drop off in fuel mileage.

 

[KuckFatrina]

Also while under the car i noticed that the rear o2 sensor had been deleted.

1g's only have a front O2 so you can check that off your list.

The car is 22 years old so I could inspect all of the hoses and see if any fuel is leaking.

 

[Wooley91TSI]

1g's only have a front O2 so you can check that off your list.

The car is 22 years old so I could inspect all of the hoses and see if any fuel is leaking.

No leaks of puddles of fuel when idiling for 5-10min. first thing i do when picking up a new car. Nice to know if a car is bleeding before you buy it.

 

[Bud92gsx]

reply to this before you start buying parts

This isnt aboot me.So back to the OP, because i'm sure my tuner would say i'm good to go there pal.

 

[Cdc1221]

The reason someone threw out a manual ecu and fpr is because 1g auto cars run 390 cc injectors and only 37 psi fuel pressure. A 2g maf will not compensate for 550s in an auto car, all else left alone. So there's that, which could easily cause it to throw an o2 sensor cel once it starts cycling. Also explains bad mileage since it can't go into closed loop mode at cruise. You're not going to squeeze much boost from a 13g. I couldn't get mine to 10 psi on my setup. As for the maf cel, check the wiring...

 

[Wooley91TSI]

The reason someone threw out a manual ecu and fpr is because 1g auto cars run 390 cc injectors and only 37 psi fuel pressure. A 2g maf will not compensate for 550s in an auto car, all else left alone. So there's that, which could easily cause it to throw an o2 sensor cel once it starts cycling. Also explains bad mileage since it can't go into closed loop mode at cruise. You're not going to squeeze much boost from a 13g. I couldn't get mine to 10 psi on my setup. As for the maf cel, check the wiring...

I though the auto FPR was 43.5psi? I figured that was contributing to my mileage. the maf is flowing ~20% more, and with the auto fpr on 550's im flowing ~35-40% more fuel. I also discovered that at some point in its life it got a 14b thrown on( still in good shape, virtually no shaft play). Im tearing into the maf wiring on sunday but with any luck i'll be picking up an AEM EMS in the next week. that should solve all my problems.

 

[FLASH1970]

Also, if my fuel pressure regulator didnt have enough PSI to run the 550's, would i be running lean verses extremely rich?

The fuel pressure regulator has nothing to do with getting fuel to the injectors. It monitors how much fuel is returned to the tank. If you look on your fuel rail, the feed comes in from the passenger side, and the regulator is on the driver's side of the fuel rail after the injectors. The stock fuel pressure regulator can usually handle a fuel pump flowing about 190lph if I remember right. If you put a 255 pump in there, it is usually too much fuel for the stock FPR to keep in check.

Make sure maintenance is up to date. Fluids, timing belt, ball joints, brakes, boost leaks, CEL's. Once that is taken care of get a way to tune. You'll need a wideband O2 sensor, some way to datalog, and a way to tune in order to compensate for the fuel injectors. A boost gauge and a boost controller are nice to have but if it was me, I would first like to know if my car is getting knock, what the air to fuel ratio is... and get the things needed to control them.

 

[1G Eclipse94928]

This isnt aboot me.So back to the OP, because i'm sure my tuner would say i'm good to go there pal.

That comment was to the op not you, he wasnt answering you so i quoted it.