02dkbluegt

About 2 weeks ago I got the notorious P0171 and P0174 codes. I assumed the MAF was dirty so I cleaned that with the right cleaner and also changed my fuel filter and cleaned my air filter while I was at it.

Now about 250 miles later the same two codes popped up. The car runs completely fine. What do I check next? Vacuum leaks? I've read some about the EGR valve going bad, how would I check that?

vanquish

Are you running the stock tune? What do you have done to your car?

02dkbluegt

I'm running a 93 octane tune from a Sniper Tuner, really no mods that could effect the fuel system other than that... K&N drop in, some transmission work, weld in flows. That's it.

vanquish

I would consider taking a couple minutes and make a fresh 93 octane sniper tune without touching any of the trims for fuel/spark and run that to see if the codes go away

tbirdscwd

check your fuel rail pressure in recon....it might be fuel pump time. I got the same codes when my pump was going out but the pressure wasn't low enough to trip the low rail pressure codes I guess. Shouldn't get lower than 39psi

HaneyMotorsport.Com

You cleaned the K&N.... did you over oil it? MAF may need a recleaning.

02dkbluegt

My sniper tune is just the 93 octane base tune, nothing else was modified (fuel trim, spark advance, etc.). I'll have to throw a new 93 tune on there and take a ride with recon and see how the fuel pressure looks.

Before I replaced the fuel filter I checked the fuel pressure and it seemed very jumpy, it still averaged at 40psi but after the filter change it was much smoother (right around 39-41psi).

I did oil the K&N filter the same day I cleaned the MAF, I guess I should clean it again to make sure no oil got sucked onto it.

Thanks for the help guys, I'll let you know what I find.

cliffyk

The fuel rail pressure will change quite a bit, as the electronically controlled returnless system adjusts the rail pressure to maintain a 40psi pressue drop across the injectors.

When manifold vacuum is high, typically 18 to 20inHg (negative 8.8 to 9.8psi) at idle and cruising, the rail pressue will be around 30 to 31psi, at WOT when manifold vaccum is low (2inHG, 1psi) the rail pressue will be 39psi or so.

Davojan59

its gotta be a vacuum leak somewhere...

02dkbluegt

I just re-cleaned the MAF, cleared the codes (P1130, P1150)...oddly these were different from the original codes I cleared yesterday. I rode around town for about 15 minutes, rode it easy for a bit, romped on it a few times and no check engine light.

This morning it took only about 3 minutes of cruising to school to get it to throw the light (the P1130, P1150 codes).

Hopefully this means it was just oil from the K&N on the MAF causing the problem, it was the first time I've cleaned one so maybe I put a little too much oil on it.

I logged the car with Recon during the whole test drive and the fuel pressure looks like it was acting normal. Here's a graph of it while cruising and accelerating.