Since you indicate the P0171 is the first code, only focus on that one. Following codes, pending or displayed, generally are resultant of the primary problem.
Any vacuum leak will set the P0171 so inspect by looking at all vacuum lines, either a rub through where a line touches something or a crack at one of the attachment nipples......any line originating from the intake side is suspect.
You are going to have to try harder to figure out if the check valve is still in the manifold and based on the model year and mileage and the high failure rate of the earlier design, I would not be shocked if it is the main culprit.
You indicate a cam cover (pcv) replacement has occurred and the newer covers have a more robust diaphragm but it still will fail if under constant vacuum from a failed check valve......just not as catastrophically.......visualize a small tear causing a small vacuum leak as opposed to a full, end to end tear causing a massive vacuum leak.
FWIW, the new manifolds have a metal ring attached internally to keep the check valve in position.......the original design just had the plastic kind of melted around the valve and as it got brittle over time (and heat) the edges created from the melting process broke off, allowing the plastic valve to go.........well, no one knows where it ended up but I believe ingested, burned up, blown out......whatever, it disappeared.
Anyways, diagnosis from afar, if no vacuum lines are damaged, a manifold and cam cover are likely the issue.
Rob
Any vacuum leak will set the P0171 so inspect by looking at all vacuum lines, either a rub through where a line touches something or a crack at one of the attachment nipples......any line originating from the intake side is suspect.
You are going to have to try harder to figure out if the check valve is still in the manifold and based on the model year and mileage and the high failure rate of the earlier design, I would not be shocked if it is the main culprit.
You indicate a cam cover (pcv) replacement has occurred and the newer covers have a more robust diaphragm but it still will fail if under constant vacuum from a failed check valve......just not as catastrophically.......visualize a small tear causing a small vacuum leak as opposed to a full, end to end tear causing a massive vacuum leak.
FWIW, the new manifolds have a metal ring attached internally to keep the check valve in position.......the original design just had the plastic kind of melted around the valve and as it got brittle over time (and heat) the edges created from the melting process broke off, allowing the plastic valve to go.........well, no one knows where it ended up but I believe ingested, burned up, blown out......whatever, it disappeared.
Anyways, diagnosis from afar, if no vacuum lines are damaged, a manifold and cam cover are likely the issue.
Rob
