Today I drove ~39 miles and used ~7 gallons of gas.

I've got a Walbro fuel pump, 720cc/1,680cc injectors, an adjustable FPR, Racing Beat REV TII exhaust, BNR turbo, etc... It has been tuned, and I used to have no issues with gas mileage at all. When I drove my car out to move out here to Washington, I averaged 22 MPG.

Now: When driving in any gear, my car sputters and jerks. You can smell fuel out of the exhaust while it is idling. The turbo has been smelling weird and has also been smoking a little bit. I have absolutely no gas leaks... My car is running rich as a mother ******, and I need some advice.

 

Just a thing to check... But is fuel leaking out somewhere?

 

You have a major gas leak, it's just not external.

If the fuel system is unbreached (i.e., tank, lines, filter, hoses all intact) then the obvious culprit would be the injectors. Either they are physically distressed (stuck open) or something happened to your tune and they're being told to stay open.
I'd think the former is more likely.

 

I'd check your coolant. :'(

 

also depends on the ECU, you could simply have lost the coolant temp sensor connector or the sensor itself which most EMS will default to a cold state, or rich. most tunes are aggressively rich when cold.

i also think you're exaggerating the mileage. the lower you fill up the less accurate the mileage would be, some filling stations have more sensitive backpressure sensors than others so you could be 3 gallons from full still. being that it's eating that much gas means you're running down in the 6-7AFR range which is going to foul your plugs in no time flat, i'm actually surprised it's still running and didn't foul them 10 miles in.

 

^^Yup, I had a broken IAT that caused it. What EMS do you have? I'd start there... then if it looks normal maybe send the injectors off to be cleaned/tested.

 

A'PEXi Power FC.


I recently removed my A'PEXi turbo timer... I am going to check the ECU for sure. I've seen people talk about the coolant temp sensor before. This may be a stupid question... But I am just curious what it has to do with gas mileage...?

I'd like to believe that it was an exaggeration myself. 14.11 gallons is what the pump stated... (I thought I have only had a 12 gallon tank.) Drove home ~39 miles and used around 7... As stated above.

I may get the injectors tested and re-cleaned. I'll be probing the ECU a bit. Anything else to check for??

 

the tank is 16 gallons but 2 gallons left is pretty much bone dry before it sucks air. the series 5 has an 18 gallon tank.

explained the coolant temp above. if the ECU detects an open circuit or out of range it will run in a defaulted state. almost every engine needs progressively more fuel when cold versus warm to function properly, so if it is defaulted then the engine will run rich.

it's simply a matter of reading your water and intake temps from your ECU and compare them with actual readings. like basically your intake temp will be around 30C and water temp around 85-90C with the engine fully warmed up on an average warm, not hot, day. if one or the other are not changing at all while warming up the car then you likely found it.

 

You might want to pull the plug off the secondaries and drive the car using only the primary injectors and compare and contrast the difference observed as this would provide you with a heads up as to whether the secondary injectors are problematic.

 

s4 is a 16.6 gallon tank, and s5 is 18 and change.

with the PFC you can go thru the sensor check screen, and anything highlighted needs to be looked at.

the coolant temp, on a stock ecu, has a HUGE impact on fuel, there are a few reasons but basically the colder the engine is the more fuel it needs, and if the ecu thinks its -32F then you're lucky it started!

the air intake temp sensor is also one to look at

i've been doing some fuel economy testing, and i think i've learned that Karack is right about the gas pump being inconsistent, even if you use the same one. either that or got 40mpg on the last test loop... my freeway test loop is returning numbers in the 26-40mpg range, and the around town loop is 12-13mpg

 

How do you know you used 7 gallons on your way home? Are you going by the stock gas gauge or did you top off the tank with 7 gallons?

 

j9fd3s, my commander has VTA1, VMOP, and FUEL highlighted. I understand that VTA1 is TPS full range (I have a S4 TPS, which we all know is narrow range.) I currently have that unplugged, though because the TPS I have is a POS. I have a mechanical MOP, so I can understand that the VMOP would be highlighted. FUEL is the one I don't understand... It claims that "FUEL" is the fuel temp sensor. It shows voltage... 4.98v with key to "ON". Does this seem right? Is there a different name for this sensor on the FC?

As for switches, it displays NTR (Neutral Switch), CLT (Clutch Switch), HWL (Exhaust Temp Warning Indicator), PAC (Port Air Control), and CCN (Charge Control) with highlighted black dots next to them.

RXSpeed16... I filled the car up with like 14.11 gallons and ran it down to half tank. According to everyone else, I actually have a 16.6 gallon tank (S4 tank) - Plus today I started my car and it displayed a bit above half tank. So, I suppose I didn't use as much gas as I thought... But it's still a ridiculous amount that was used. Considering I went 39 miles at most. (I set the trip meter thing to check as soon as I filled up.)

Does any of this commander info. raise any red flags?

 

FUEL is for the FD3S which has a fuel temperature sensor in the secondary rail, disregard it.

 

Ah, okay.

The water and air temps change while letting the car warm... But it's been taking my car anywhere from 25-35 minutes to warm up. To get it to heat up faster I have to hold the pedal at 2k+ RPMs.

I am probably going to pull the secondary injector plugs off, as satch had suggested, to see how it runs. Other than that, I feel lost. Car runs like a POS... But I love it too much to quit on it. :-/

 

half an hour is way too long, have you ever replaced the thermostat? my FC is in the same boat, actually its got a lazy thermostat, and warm up takes a long time = wasted fuel

oh and the gas gauge is NOT accurate enough to give you an MPG number. to get something consistent you need to run the tank fairly empty and fill it.

 

another possibility is you lost connection to your map sensor, this is pretty common with the GM sensor adapters. the car naturally thinks you are constantly at 0" vacuum which is overly rich, especially decelerating and idling. check the vacuum line while you're there.

 

I unplugged the water thermo sensor and tried to get a resistance reading, very similar to the method in the FSM. The water/coolant was still warmed at about 25°*C. It read all zeros resistance-wise... If the sensor were screwed, would it display that sort of reading? Perhaps I need to just take the sensor out of the car.

I found something interesting and semi off subject... The commander reads +0.60 Kg/cm2 (boost) with key to "ON" when the BACV is plugged in. When I unplug the BACV with key to "ON"... the commander reads -615 mm Hg (vacuum). Do any of these readings seem "okay"??

I took some voltage readings off of the MAP sensor plugs. What confuses me is that the harness plug has like at least four wires... I forget, and plugs into a three wire GM harness that plugs into the MAP sensor. There is a B/W wire with around 12v with key to "ON" but isn't even used when plugged into the GM harness to the sensor. What's with that?

 

An S4 Boost/Pressure sensor uses the B/W wire while an S5 does not.

 

Not that you would know... But why is the B/W wire not integrated in the Banzai harness to the GM MAP sensor?

How would my car even drive without a proper MAP sensor reading?

 

You could tell by the voltage of the output signal wire if it was working properly. It also depends on the sensor as to how many wires are required. The S5 only has three wires so I would assume that your aftermarket sensor is designed much in the same way.

 

That wire is not needed with a PFC since there is no requirement for 12V to the map sensor. So there is nothing wrong there.

However you do have a wiring issue with your engine harness. The BAC should not be effecting the boost reading on the commander. Neither reading you provided is correct. With the key in the "on" position not running the boost will be somewhere between 0 and -50 as long as you have the 3 bar sensor scaled in the map sensor selection screen.

You need to read our instructions again. The FRT wire needs to be connected.

 

probably broken shielding in the original engine harness. have fun cutting that sucker open and measure resistance values trying to trace it down... or just get another harness.

 

Alright, sure thing! BRB - I could have swore I had FRT wired in, but maybe I don't... It could be why my TPS is a working unit, yet doesn't affect idle at all. - Shitastic idle :-/

Oh, I tested the water thermo sensor at the ECU. Everything checked out okay... 2.8v at pin 2I (car pretty much cooled down all of the way.)


Wait... Can someone tell me the colors of the wires to the BAC? My BAC plug is non-existent, and I just re-installed it with wiring straight out of the harness.

 

If you had the FRT wired properly VTA1 & VTA2 would both be reading the same value, which should be round 1.00v with the TB closed at operating temp if your have thermowax.

The issue is not with the water temps. It is with your map sensor reading, .60 kg/cm2= around 8.7psi of boost, so the ecu is dumping fuel. The fact that your bac connector is interrupting the 5v signal from the map sensor is your issue.

 

So, I have had FRT wired in for a while now... But VTA1 and VTA2 have both been reading 4.99v as of right now. (TPS is unplugged at the moment so the 4.99v reading makes sense.) I will get around to that soon enough, and eventually get the proper 1.00v reading.

The bigger issue is exactly as you stated above. When I completely unplug the MAP sensor with key to "ON" it reads +2.22 kg/cm2... Just something else I noticed.

Can anyone give me the color of those BAC wires?