SpartanSV

Hello everyone. I have a 98 5.4 scab flareside with 190k. I'm getting lean codes for both banks (P0171, P0174). Long-term fuel trims at idle are about -15% on both banks. When maintaining highway speeds or accelerating from a stop they are maxed at +25%. STFT's are also all over the place in the same directions. MAF is showing 50 cfm at idle, about 150 cfm at 1500 rpm. Fuel pressure is 30 at idle and 40 at WOT. Intake air temps seem accurate.

Would anyone like to take a stab at a diagnosis?

I'm confident I know the issue but won't mention it yet to avoid skewing opinions.

white89gt

The PCV elbow on the back of the throttle body is probably leaking.

SpartanSV

Thanks for the response, but that's been checked. It also would be showing lean at idle instead of rich if the issue were a vacuum leak.

Jbrew

Pumps going south If 30 is accurate.

SpartanSV

Pressure is accurate. Checked with 2 different testers. 29 on one 31 on the other at idle. I thought bottom of spec was 28 at idle, and was thinking the fault to be with the injectors. With the trim fluctuations I'm seeing I was expecting something more than a pump at the edge of spec. I drove extensively with a gauge hooked up and never saw it fall below 28. It holds steady at 40psi at WOT.

white89gt

Your codes you list are lean codes. Not rich codes.

SpartanSV

Correct. The codes say it is running lean for a long enough time to trigger a code. Watching fuel trims tells the whole story. Fuel trims are showing rich at idle and lean only under load. A vacuum leak would show lean at idle as well.

Jbrew

Deleted. - in denial, why do these guys even ask? Sparty, - make sure come back and post when the pump goes out, like I said it was going to

white89gt

Are your fuel pressure numbers with the vacuum disconnected?

SpartanSV

Vacuum line to the regulator was connected if that's what you're asking.