My car is only getting 20-21 MPG with just an intake and straight pipes, plus it doesn't feel like its got the same power as in months past? Is this a rich condition that can be fixed with a hand held programmer or is there something else that can cause it? Oh yeah, it hasn't been tuned yet, but can just an intake cause a 10-12 MPG drop? Thoughts?

 

Mine actually improved a bit when I added an intake and exhaust, but it took a few days to settle in... a bit later on, the fuel mileage went down similar to yours', so I changed the plugs and wires, and it was like a new car again...I didn't have a lot of mileage, but they were 6 years old! How old are yours' and what's the mileage? Check your connections between the air intake and maf btw to make sure there's no leaks too...

 

Suggest you check your MAF and see if it might be dirty and benefit from a cleaning of the specific spray cleaner designed and sold for this purpose. Also you might want to check for proper installation function of oxygen sensors, in addition to suggestion for a good tune up.

 

also check for a dirty air filter.

 

Thanks guys, I've got a feeling that the plugs may be the issue considering its got 75K on it, they're probably the originals? I bought the car with 65K on it and haven't changed them, planning on picking up some MAF cleaner as well, thanks again!

 

I'll add one more to the mix of good suggestions already given, run a bottle or two of Techron fuel system cleaner. Your problem can be caused by dirty injectors too. Less likely, but could be part of the problem might be an exhaust restriction. Cats starting to go bad...

 

did you change fuels?

Most fuels are now 10% EtoH wich has hurt millage

 

Make sure you hooked the IAT back up when you put the CAI on.

Have you checked for codes?

 

All are very good recommendations!

If you have never read your oun DTCs;

READING YOUR Engine Diagnostic Trouble Codes (DTC)

This procedure should be carried out any time you experience a problem with your C5. Most inexpensive store bought aftermarket code readers will ONLY read power train DTC’s. Reading the DTC’s with the C5 built in code reader will allow you to read ALL the modules in the vehicle.

The Diagnostic Display Mode is entered with the following procedure:
1) Turn on the ignition but don't start the engine.
2) Press the RESET button to turn off any warning messages. (i.e. door open, trunk open ect)
3) Press and hold the OPTIONS button
4) While holding OPTIONS, press FUEL button four times within a 10 -second period.

Initially, the on-board diagnostics go into an Automatic Mode which will cycle through each module and shows diagnostic codes in a pre-set sequence: PCM - TCS - RTD - BCM - IPC - RADIO - HVAC - LDCM - RDCM - SCM - RFA. All codes will be displayed for each module. ( i.e. PCM = 4 codes) If none are present in a given module, you will see No More Codes on the display.

There are two types of diagnostic codes, Current and History designated with a letter suffix, “C” or “H”. A current code indicates a malfunction is present in the module displaying data. A history code indicates a problem existed sometime in the last 40 or 50 ignition cycles. When not accompanied by a current code of the same number, it's potential evidence of a previous problem, now resolved, that was not removed by clearing the codes. More likely it's an indication of an intermittent malfunction.

Intermittent codes are the most challenging of the diagnostics. An intermittent code may have happened once, may have happened more than once but is inconsistent or may be happening on a regular basis but not at the time the codes are displayed. History codes can also be caused by a current malfunction in a system that is not operating at the time codes are displayed. An example is the rear window defogger which doesn't operate until the Body Control Module detects engine rpm. For history codes set by a module that does not operate with the key on and engine off, a special diagnostic tool called a Scan Tester is necessary to properly diagnose the malfunction.

Once the system has displayed all modules, it goes into the manual mode which allows selection of each module using combinations of Driver Information Center buttons. Manual mode can also be entered during the automatic sequence by pressing any button except E/M. Once the display shows Manual Diagnostics, select a module by pressing the OPTIONS button to go forward or the TRIP button to go back. Once a module is selected, a code is displayed, and if more than one are present; press GAGES to go forward or FUEL to go back.
To exit the diagnostic mode at any time, press E/M. If you want to erase codes in a given module, press RESET To reset the codes once in manual mode, press and hold RESET until it displays NO CODES Press OPTIONS to go to the next module. Repeat the steps until you have reset the codes in all the computer modules.
NOTE!! Only reset the codes IF you want to - it is NOT necessary to do this. Clearing a code does not repair a problem. You are simply erasing the evidence of it in the module's memory. If you clear the code/s, and extinguish the Check Engine Light, your emissions status ready will NOT allow you to pass an emissions test until you have completed the required driving cycles. There are a few body module DTC’s that if set will prevent the module from operating properly. Once the DTC is cleared, the module will return to full function. This is not true for power train DTCs.

If you have never read and cleared your codes, there will probably be a lot of old history DTCs. It is recommended that you clear your codes and see if any come back during a driving cycle. Those are the ones that you need to concentrate on diagnosing.

Once you have the codes, the next question is: What to do with the information?
First, consult the factory service manual. Any serious C5 Do-It-Yourself owner should invest in the Corvette Service Manual of the appropriate model year. The Service Manual is really a requirement if you want to understand and work on your C5.

These are some very good C5 Diagnostic Trouble Code (DTC) explanation web sites!!! They also explain how to read the DTCs

Here are some very good sites that explain what DTC mean:

http://www.gearchatter.com/viewtopic11755.php

http://www.obd-codes.com/trouble_cod...d-ii-codes.php

Make sure to include the H or C suffix when you post your DTCs!!

 

I'd also recommend checking proper function of the oxgen sensors. Mine went out and the computer did not pick up a code. I only new about it when the car would not pass inspection. The sensors were flashing on / off so quick the computer did not pick up the error. Replaced the sensors, fuel mileage went back up, and the car ran smoother. Looking back on the problem I noticed different smell to the exhaust during cold start which is not present now so that might be a indicator too. Hope this helps....

FSTFRC

 

hey guys im getting very low mpg as well like 17 city 18.5 hwy i have cleaned the maf changed the plugs and wires whats next? 2002 z06 with 32k

all my friends talk about getting 20 city and 30+hwy i want that !

 

wheres this intake air temp sensor

and i have no current codes only history codes related to my window failing

 

What type of MODs do you have?

What type of air filter do you you have and is it clean???

Does the car idle good??

Are you POSITIVE that the connections between the MAF and the throttle body are AIR TIGHT? check each joint 100% and make sure that there are NOT any gaps to let un-metered air into the intake tract. Spray some Carb Cleaner arround the joints and if the idle is effected, thats your leak.

Please answer those questions.

The IAT sensor is on the drivers side of the air bridge on early C5's and it is inside the MAF on later C5's. On your 2002, its inside the MAF. You only have ONE plug to worry about and if the MAF is working the IAT should be also.

 

I have a haltech venom the filter is clean the intake cuplers are sealed tight and my maf and iat are one unit and recently cleaned (few days ago) and plugged in tight. And it idles good

 

Anyone with a EFI Live or HP Tuners can data log your car and see whats going on. You just need to find someone in your area that has the software and a laptop and will do it for you. Data Logging doesn't require a license and it will tell you a LOT.

You need to see what the O2 sensors are doing and what the LTFT are doing. That will tell you what the fueling system is doing efficiency wise. Otherwise its just a guess,,,and there will be LOTs of them. You didny by chance remove the screen in the MAF did you??????

BC

 

LTFT ? long term fuel trim right

 

CORRECT!!