Engine shuddering under acceleration; code P0171, P0174
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Engine shuddering under acceleration; code P0171, P0174
'03 Expedition Eddie Bauer, 4.6L V8
My Expedition is running extremely rough at idle and under acceleration. The problem is much better at cruising speed, but still somewhat noticable. Code reader shows codes P0171 and P 0174 (Lean condition, left and right bank). I tried cleaning the MAF, the problem seemed to go away for a quick loop around the block, but the next time I drove it, problem was back. Help!
My Expedition is running extremely rough at idle and under acceleration. The problem is much better at cruising speed, but still somewhat noticable. Code reader shows codes P0171 and P 0174 (Lean condition, left and right bank). I tried cleaning the MAF, the problem seemed to go away for a quick loop around the block, but the next time I drove it, problem was back. Help!
Laughing Gas
Joined: Jun 2003
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From: Chino, California
I don't know where it would be on a 4.6. Usually they are located on the valve cover (passenger side) and a hose runs to the air intake before the TB or air cleaner.
I'm pretty sure I am correct on this.
I'm pretty sure I am correct on this.
Last edited by pops_91710; Oct 1, 2007 at 08:45 PM.
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Laughing Gas
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Hotshot
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From: St Louis
You have a massive vacuum leak.
Your problem most likely isn't the PCV valve, it's that the stupid hose elbows on the line to it are crap. The one all the way in the back facing the firewall is the most common one to fail.
FWIW, you're not running lean, you're running rich. Your fuel mileage is probably poorer than normal.
Steve
Your problem most likely isn't the PCV valve, it's that the stupid hose elbows on the line to it are crap. The one all the way in the back facing the firewall is the most common one to fail.
FWIW, you're not running lean, you're running rich. Your fuel mileage is probably poorer than normal.
Steve
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I found a small vacuum hose on the passenger side of the engine that was knocked off. I put it back on, and cleared the CEL with the programmer. Now the engine doesn't shudder like it did, but still surges while at idle. No CEL, but haven't driven it much. I did notice that there's a (vacuum?) hose that goes from a point above the brake master cylinder to the throttle body, that the top layer flakes off it when you touch it. I can't really tell if it's leaking though. Would a leak here or in some other vacuum hose cause surging? If not, then what? Also, how can you even tell if a hose is leaking?
Laughing Gas
Joined: Jun 2003
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From: Chino, California
Get a small bottle of propane and put a small torch tip on. Open it then wave it around suspect areas. If the engine speeds up, it's sucking raw air. I learned this trick from a Ford assembly plant emissions trouble shooter.
Project, no one said the PCV valve was leaking, just said it was the hoses for it.I directed him to the valve which would undoubtedly lead him to the hoses.
Project, no one said the PCV valve was leaking, just said it was the hoses for it.I directed him to the valve which would undoubtedly lead him to the hoses.
Last edited by pops_91710; Oct 2, 2007 at 09:34 PM.
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Found it!
The rubber elbow all the way at the back of the throttle body was rotted, collapsed and had a small hole. I replaced it with a short length of 5/8" marine fuel hose, and the surging went away. I still have a slight "miss" under acceleration, but the truck idles fine now. Thanks for all the tips, probably would have spent a grand at the dealer, but through here, figured it out for almost nothing.
The rubber elbow all the way at the back of the throttle body was rotted, collapsed and had a small hole. I replaced it with a short length of 5/8" marine fuel hose, and the surging went away. I still have a slight "miss" under acceleration, but the truck idles fine now. Thanks for all the tips, probably would have spent a grand at the dealer, but through here, figured it out for almost nothing.
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