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Discussion Starter #1
Hi All,
05 taurus, vulcan, 150k worry free miles. Just installed new coil, wires and plugs and things are running well. The other day, the CEL popped on. I got home, read the codes and I had P0171 and P0174, lean bank 1 and 2. Now, I'm assuming I either have an abundence of air or a lack of fuel, right? I am going to check my vacuum hoses for leaks (I read about some elbow by the PCV). Is there anything else I should check? I would think if it was low fuel pressure or injector issue I would have gotten a code associated with that, right? I'm actually surprised I got a lean code instead of an emission or vac leak code (which I've gotten in the past on different vehicles).

Anyway, I cleared the codes after recording what they were to see if this was a hiccup or an actual issue. So far I have about 100 miles on it since the codes first appeared and no re-occurance. If I cannot find any vacuum leaks should I just wait and see if it surfaces again or should I take it in to a shop and they can do the smoke test?
 

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P0171 and P0174 codes mean that both banks are lean, and very often they are lean due to vacuum leaks allowing unmetered air to enter the engine. Try to spray a little bit of brake cleaner near the intake gaskets and vacuum lines and listen for a change in idle speed. You could also try to clean the MAF with mass air flow cleaner and see if that helps.
 

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Discussion Starter #3
Thanks. I actually recently (like last 4000 mi) cleaned my MAF. I've been doing alot of research and think I'll look at the PCV elbow and other lines - hopefully its obvious. I've never had much luck in spraying cleaners looking for leaks. Look at the vacuum line routing on this car, there are quite a few sources that tap into the intake after the MAF... Lets just hope its not the intake gaskets!
 

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You could also test the fuel pressure to make sure it is not low. Too much air or too little fuel will cause both banks to be lean. Another thing to check would be 02 sensor function to make sure they are both switching properly. If that all checks out, then you have even more evidence supporting a vacuum leak as the cause.
 

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171 / 174 are virtually always due to a vac leak, and not failed O2 sensors. Since you have both 171 and 174, the vac leak affects both banks. Very common vac leak is the runner control valve gasket. Cheap and easy to replace.
 

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Follow the hose from the brake booster to the vacuum distribution box on the firewall. Check it for cracks and related hosed that connect to it.
I know of one case where a member had a bad booster and got both codes. To check it, pump the brake pedal a few times with the engine off. Press it down, start the engine and it should rise against your foot.
 

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Discussion Starter #8
Thank you guys for your responses. I was sitting at work yesterday researching vacuum leaks, EGR valves, PCV valves, common failures, etc etc. I was all prepared to do a vac leak test when I got home. Because I am impatient, I popped the hood before I left for home. Didn't see anything obvious, until I walked around the driver side and noticed whats in the attached photo.... Guess I found my leak! So... I'll be the first to admit, I did have my intake off when I was putting new plugs and coil on, but that was 5k miles ago... So, this thing either popped off OR its been off for 5k miles and the improvments that came with new plugs and a coil masked the vacuum leak. Anyway, I plugged it back in, and immediately I noticed it started better (I actually didn't realize it was starting a little hard until I had this plugged back in) and I got a few extra MPG's. I normally run about 30, but it dropped to 28, and I figured the onset of winter will hurt the MPG a bit. On the way home I was getting 30 again. So, like I said, I'm not sure if it popped off on its own or I left it off - but 5k miles seems to be a really long time for the CEL to come on...

Thanks for everyones help! At worst the car is running well again and I know am more knowledgeable about future vacuum leaks.
 

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Thank you guys for your responses. I was sitting at work yesterday researching vacuum leaks, EGR valves, PCV valves, common failures, etc etc. I was all prepared to do a vac leak test when I got home. Because I am impatient, I popped the hood before I left for home. Didn't see anything obvious, until I walked around the driver side and noticed whats in the attached photo.... Guess I found my leak! So... I'll be the first to admit, I did have my intake off when I was putting new plugs and coil on, but that was 5k miles ago... So, this thing either popped off OR its been off for 5k miles and the improvments that came with new plugs and a coil masked the vacuum leak. Anyway, I plugged it back in, and immediately I noticed it started better (I actually didn't realize it was starting a little hard until I had this plugged back in) and I got a few extra MPG's. I normally run about 30, but it dropped to 28, and I figured the onset of winter will hurt the MPG a bit. On the way home I was getting 30 again. So, like I said, I'm not sure if it popped off on its own or I left it off - but 5k miles seems to be a really long time for the CEL to come on...

Thanks for everyones help! At worst the car is running well again and I know am more knowledgeable about future vacuum leaks.
Good catch. That hose off is a double negative. Unmetered air enters the accordion, Unmetered air also enters the hose to the valve cover. Pull one off idling car and watch it get unhappy.
Also, unfiltered air entering the intake.
-chart-
 

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Discussion Starter #11
So, would you guys agree it should throw a code sooner than 5K miles if I did in fact leave it off?

Its not like the car didn't have a chance to throw it - I drive 88 mi/day minimum for work, 1 hr commute either way.
 

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Could have just fallen off recently if it wasnt fully secured when you reassembled it originally.

A leak that big will throw lean codes pretty quickly.
 

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171 / 174 are virtually always due to a vac leak, and not failed O2 sensors. Since you have both 171 and 174, the vac leak affects both banks. Very common vac leak is the runner control valve gasket. Cheap and easy to replace.
my egr valve sounds like its hissing , ruff idle, car wont take off fast at all but cleans up a tad at 65 but loses momentiom going up a hill wont keep 65 up hill. plz help
 

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You can perform the egr "suck" test: remove the vacuum line from the egr valve and replace with ~12" piece of scrap vac. hose. With the car idling, suck on the open end of the sampling hose opening the egr pintle/diaphragm allowing egr flow. Engine should bog down or die due to the fact that there should be no egr flow at idle or wot. Are you getting any p0420/430 codes?
 
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