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Discussion Starter · #1 ·
I have a 2004 Taurus SE w/ a Vulcan engine( w 100k miles and health problems).
From all my research p0171 and p0174 are fairly common on the Duratec, but i cant find a lot of infos on Vulcans with this problem. My car was running like a real piece of crap last winter, turns out i drove it with lean codes for tooooo long. The first thing i did was change all four o2 sensors, with no luck. Next i changed the spark plugs and wires figuring that 100k was probably about time. No luck from that either! Next was the PCV valve, still no luck. It really started misfiring, so i took in into the shop and they said i had fried my cats, so i replaced all 3 cats and cleaned out the exhaust. Good results it ran about 50% better than it did previously, (and sounded better too!) but still wasnt quite firing perfectly.
I took it into a muffler shop to check my exhaust out and make sure i hadnt screwed anything up and they did a diagnostic with a smoke machine and discovered i had a cracked intake manifold. I replaced that piece as well, reluctantly, but it really made a big difference and gave me another 45% increase in performance... that puts me at 95%! :)
so its running quite well now but i am still getting a CEL and it is throwing codes P0171 AND P0174, which the guy suggested could be related to the MAF sensor or the IAC. I had pulled the MAF previously and it looks fine, there is no gunk on it, i cleaned it with MAF cleaner just to be sure but didnt notice a change. The IAC looks fine too, no gunk, it moves freely.
I guess my initial question is, can i take my car somewhere to test the MAF sensor?? I believe that previously a mechanic told me he had taken the MAF "out of the loop" and it hadnt made a difference, but he told me some other wacky stuff too so im reluctant to rely on his word.
My next question would be, If the MAF is truly fine, what could my next step be? Could driving on a lean condition have gunked up some other part that i havent yet cleaned or replaced?? Thanks for any suggestions, and for reading this lengthy post. Frustrating!
 

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Check the o-ring seal around the idle air control valve, it's the round part mounted on the upper plastic intake on the pass side, near the firewall, and has a connector with 2 wires going to it. There's a long post about this on the topic finder, ('04+ Vulcan engine, poor start, poor acceleration). You can use a oil filter gasket to replace that seal. You can check if it's leaking by spraying starting fluid on it while the engine is at idle, but do this when the engine is cold and not hot, and wipe off excess with a rag. If it's leaking, the idle should change when it sucks in the starting fluid, you could probably hear it hissing if it's really leaking. Another thing to check is the pcv valve and hose for cracks/breaks.
 

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When you cleaned the maf sensor, did you spray the 2 small fine filament wires with crc mass air flow cleaner (gray can)? Po171-174 is telling you eng. has vacuum leak(s) affecting both banks. Check what austex04 suggested above for starters.
 

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So what would affect both banks, all vacuum leaks will affect both banks, as will any leaks where the upper manifold meets the lower manifold. The lower manifold can leak too, and can affect bot banks, but will affect one more strongly than the other, and may sometimes only set one code. There are also gaskets between the manifold and throttle body, and between the IAC and throttle body, and between the EGR and manifold, and any leaks at any of these locations can cause a problem.

They can check with a smoke machine again. May reveal something that did not show up the first time.

I have seen vacuum reservours crack open, and a ruptured diaphragm in the power brakes can cause a lean code.
 

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Did you use the Motorcaft PCV designed for you engine or some cheap no name junk from the discount parts store? What shape was the PCV hose in?
 

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Discussion Starter · #7 ·
97LX makin me feel bad... haha. The Intake mani was actually cracked and my cats WERE totally destroyed, charcoal rattling around inside, so i dont feel like the work i have done was for nothing, each part ive replaced has needed replacing.
Jeff K, i got the exact piece, the ONLY $20 PCV valve in existence(sigh). So no worries there.
Sheila, i am sure i sprayed some filaments with MAF cleaner, i basicaly got everything i could see well hosed down.. did i fry something?
and Khan, thanks for the suggestions, i will run through the whole intake and check gaskets again, i think im going to end up having them run another diag. with the smoke, that seems like my best bet.
Could this be a fuel pressure problem? correct me if im wrong but lean is too much air, too little fuel, so could the problem be the inverse, fuel pump problems? or would that trigger a diff code.
Thanks everyone for your input, this site alone has saved me at least $1000 during this whole process!!!
 

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It can absolutely be a fuel pump problem. Can be measured in two ways with a scan tool.

If your LTFT is higher at idle, then drops to a lower value as the throttle is opened, that points to a vacuum leak. If while driving the vehicle, the LTFT increased as speed and load increases, the fuel delivery may be to blame.
 

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More idle Air control motor data

First post;
since you all helped me get to the solution, thought i would share.

Po300 171 174 trouble codes here on my recently purchased 2004 sable/vulcan 80k miles. Other symptoms similar to others above.

A smoke test showed a competeley broken Idle air control motor leaking smoke everywhere.

new IAC motor fixed problem.

now on to the rear spring suspension problem, SAS.

D in Colorado
 

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I would try the smoke test again. The EVAPS sytem can also cause the 171 and 174 codes. If the smoke test determines that you have no leaks then back to a fuel delivery problem. Easy to check fuel pressure. Pull vacuum line off fuel pressure regulator and look and smell for fuel. When did you change your fuel filter?

Ed
 

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Discussion Starter · #11 ·
no leaks after all. im still, STILL having fuel issues. haha ive spent another grand or so on it, i believe checking valves is my next step, then fuel injectors.
 

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It can absolutely be a fuel pump problem. Can be measured in two ways with a scan tool.

If your LTFT is higher at idle, then drops to a lower value as the throttle is opened, that points to a vacuum leak. If while driving the vehicle, the LTFT increased as speed and load increases, the fuel delivery may be to blame.
I'm with Khan, look at fuel pressure on a scan tool. Should be around 40ish idling, without too much variation under throttle. There's no pressure regulator to check, so don't worry about that. If fuel pressure is good, there may still be a vacuum leak somewhere. They don't always show up on a smoke machine. Sometimes you need to spray something flammable around all the gaskets while watching short term trims on a scan tool.

Was the replacement intake new or used? If used then the IMTV/IMRC o-ring around the back of the intake could be leaking.

I doubt this is an engine mechanical problem or an injector issue, because the odds of having bad injectors or valves on both banks are very low. Also a problem bad enough in one cylinder to cause a lean code would also be setting a misfire code.

Post LTFTs at idle after checking fuel pressure.
 

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Discussion Starter · #13 ·
new intake. was shiny and clean. will check fuel pressure first, before i do anything else. new fuel pump was also put in... but perhaps something in the line from fuel tank to engine
 
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