4.698GT

So i got a check engine light. Went out to check with a scanner and got p0171 and p0174 plus a p15xx code that I can't remember. So I changed the rear two oxygen sensors since the two 170's codes are for system to lean. Codes went away and now they are back. What else could be causing this code? MAF?Injectors? Anyone with some insight, help me out. Thanks

blownbayou

You running an O/R midpipe????

What type of fuel are you running....Do a search if you are running 93 octane and you will be suprised with what you find.

Later

Rebornmust_owner

why would you change out the rear 02's for a lean codes? all the rear 02 are for is to monitor your cat efficientcy. they do nothing else.
Look for a vac leak or low fuel pressure (fuel pressure reg possibly)? Could be a number of things causing those codes. Throwing parts at it is a waste of $$.

cliffyk

Yup. P0171 and P0174 are lean codes (Bank 1 & 2), and it's the front sensors, an air leak after the MAF, bad fuel pressure, or any exhaust leak near the sensors,that would be the most likely cause--with both codes at the same time I'd check the intake for vacuum leaks or fuel system first.[/align][/align]P1504 through P1507 are IAC valve issues, that could account for lean operation as well though it is metered air...[/align]

4.698GT

So how you you check the fuel system on the returnless style cars? I figured the rear sensors would be causing the codes but I am now wrong.

skinnidaniel

On the returnless fuel system you have a few sensors. There is one on the line and there is one on the fuel rail. The best way to test this is with a manual gauge and you can connect that to your shrader valve on the fuel rail. You can buy a kit at any local auto parts store with a fuel gauge that has a shrader valve connetor. Look up the specs for what your pressure is supposed to be then set up your gauge and go for a ride making sure your pressure is within spec all the time. you can also find a long flat strech somewhere and run your car at WOT(wide open throttle) then cut it off at WOT and pull a plug and check the color. White means lean, Black means rich and brownish orangeish is perfect

skinnidaniel

Now getting the returnless sytem to work right if its acting up is a whole new story. The way it works is the pressure sensor on the fuel rail reads the pressure and shuts the fuel pump down according to the amount of fuel needed. A little to much electronics for me. I like the return system seemed to work just fine to me. The returnless is almost a lost cause if it goes hay wire in my opinion.

DEALBRk

How long have you had all your mods before this started???

sfi

My question to you is, did you replace you o2 with stock replacements from ford, or did you go the cheap route and get bosch form Murrays ??? I had the exact issue and I was warned that aftermarket o2 don't work. Also, the codes would be from the front o2's, why didn't you replace them first ??The o2 are about $100 a piece from Ford.

4.698GT

I used some Bosch O2s frommy jobbecause I have never had a problem with them. This check engine light just came on recently about 100 miles ago. I changed the rear 02s first because they are the ones that usually determine the air/fuel ratio by the amount of unburnt gas? correct?