And this is shifting at ~3,000 rpms. I've been trying to combat this problem for several months since I bought my GTU. Since the last time I asked about this I have picked up a good TPS and adjusted it correctly. Fuel filter has been replaced twice now and I have new spark plugs and cables and I have no visible leaks. Still the shitty gas mileage plauges me.

I have found several things that could be wrong but no fixes for the problems.

1. Injectors - I have a set of good S4 injectors sitting around. Would these be okay to use in my S5 or do I need to get the S5 injectors replaced or mapped and blueprinted? I don't believe they are leaking since I do not have a problem with flooding.

2. MAF - Needs adjusted? Is there a place I can get some more info on this?

3. Coolant temp sensor - Buy and replace or is there someway to test this?

4. Manifold air temp sensor - Buy and replace or is there someway to test this?

5. Air intake temp sensor - Buy and replace or is there someway to test this?

 

you forgot the Oxygen sensor, i just rewired mine and it does make a difference not huge but noticable. and if the MAF isnt working right then it will dump more fuel in and just get your S5 injectors cleaned at www.cruzinperformance.com for like $12 each and then you should see better gas mileage. ALSO if you have low comrpession you will have worse gas mileage

I'll try and find some of my papers that i use at work to check MAF sensors

 

Opps.... Forgot to mention that I replaced the Oxygen sensor. My compression is good since the car is pretty much fresh out of a rebuild and I've just got done breaking the engine in.

Thanks for the website. I should prolly consider getting that done soon.

Thanks.

 

My first test would be the coolant sensor. There are testing procedures in the factory service and Haynes manual.

O2 sensor doesn't really make much of a difference, and really only during highway driving.

 

well it was noticable for me around 2~3mpg

so would the coolant sensor really make that big of a difference between mileage?

 

How cold is it where you live?

Does the car take a long time to warm up - especially just on idle?

My old Winter car (Subaru) got horrific gas milage because the thermostat was stuck open. That meant that for 99% of the trips I took the engine wasn't heating up. The computer would "combat" this by going ultra rich. Once I got the thermostat in, it made a huge difference. I suppose that would be similar symptoms if the thermo switch was bad.

Just might be something to consider...

 

The coolant sensor can make a huge difference. If it's reading way too cold, the ECU will firehose fuel at all times. This will also poison the O2 sensor, by the way.

 

Where is the ECU's coolant temp. sensor? I'm out of ideas right now. I'm holding steady at 10mpg, and I need to figure this out. $30/week for gas is really getting annoying for just 120 miles. I've done the o2 sensor, TPS is slightly bad (one short to zero ohms at ~1/2 throttle) but in adjustment, and the in tank and in line fuel filters have been changed. Spark plugs made a noticable difference (at least 5 probably 10 hp gain), wires didn't help at all. Also, fuel injectors are freshly rebuilt from cruzin' performance. I do notice, though, that on highway driving at ~60-80 mph, I get 18-20 mpg!!! Any ideas?

 

water thermo sensor is located on the back of the water pump housing below the thermostat neck piece. it's a royal bitch to get to. btw my friend drove around with his completely broken off and his milage was ~15mpg. we shall see how it is now that he has just fixed it.

edit: are you getting any check lights?

 

really? the same one on the rear iron?

mine is broken (ordered a new one, waiting) and it reads cold....

hmm, so it is going real rich now??

 

what's the name of the sensor that plugs into the bottom of the radiator?

 

No sensor on the bottom of my S5 radiator?? There is one on top though. Didn't notice one on the bottom of my S4 but not totally sure..there is also one on top of that one.

 

pulsation dampener!
Does it smell like gas when you turn it off? That would indicate a fuel leak somewhere...

 

I think it would be pretty evident if he was leaking gallons of gas onto his engine.

 

join the crowd.. 9mph here, easy driving, 11mpg freeway, and not alot of power

 

I was getting crappy gas milage- like around 10-11 mpg, then found out that my t-stat was stuck open, and my fan clutch was engaged all the time (fan constantly on). I was wondering why I never got above 1/4 towards "H" even in stop-n-go in the FL summer!!

 

There are three coolant sensors on these cars.

1. On the water pump housing, below the alternator. This is the sensor the ECU uses to determine engine temperature. It radically effects the air/fuel mixture.

2. On the rear iron, below the oil temp sender, is the 2nd temp sensor. It just runs the temp gauge you see on the dash.

3. At the lower driver side corner of the rad is the temperature switch. It's only function is the 3000 RPM startup.

The factory service manual (see FAQ) contains test procedures for all of these sensors.

 

No check engine lights. What is the sensor on the very top of the radiator?

Thanks for the locations Aaron Cake. I was having trouble trying to figure out about the one on the pump housing. The only sensor I could find was the 2nd temp sensor.

Would watching the fan and when it is on be a clue to the problem because I'm pretty sure mine is always on... I think... That's something I will have to check next time I start my car cold.

*edit* It does warm up to normal operating tempature however.

 

Coolant Level Sensor I believe.

 

You are correct.

 

Thank you very much sir, I just needed to know which was the little devil I was looking for this time. My luck, I'll go out there, find that it's unplugged, and magically be at 15mpg city...

 

just that post deserves an archieve....

 

Aaron, for #2 on your list, does that also report to the ECU and allow it to run rich if cold?

What I don't understand is why the hell the ecu throws more fuel at the engine when its cold, if anything it would want to do this when its extremley hot, running it rich, so it would cool down slightly.

 

Hey, how do you check the temp sensor behind the water pump on an s5 without pulling the UIM?

 

no. number 1 does that.

air is denser when cold, so a stoichiometric mixture requires more fuel. A lot more. I add 64% at 20*F with my microtech.

pat