Check Engine Codes (P0171 & P0174)

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Jason Barnes

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I have read most of the other posts pertaining to these codes (171 / 174). I have a new pcv valve and elbows including the hard plastic. My check engine light stays off as long as I don't try to pass someone. As soon my truck goes into the "passing gear" the check engine light comes on and stays on until I pull the battery cable off.



My ST is a 2002 model made in December 2001.



Any ideas?
 
I would check the intake duct that goes from the Mass airflow sensor to the intake manifold. Sounds like you got a small leak in either the pipe itself or the clamps are not tight enough.





Tom
 
Check the maf for contamination and if so clean it. If the maf is clean and assuming it is ok sounds to me like you need to have the fuel pressure and volume chaecked next.
 
I just cleaned the MAF but I am not sure if it fixed it yet or not. That is what I did the last time the check engine light was on before I reset it.



I am basically posting these messages to see if anybody else has had this same problem when they push the pedal to the floor or if their check engine light just comes under normal driving conditions.
 
I had this happen when my fuel pump started to go out. Does it happen as soon as you start driving or after a little while of driving?
 
You know how sometimes you have a problem with a vehicle and take it to a mechanic and you can't recreate the problem for the mechanic.



Well this problem is just the opposite; as soon as I punch it the check engine light will come on. No matter if I just started it or if I've been driving for 3 hours.
 
CHECK YOUR INTAKE TUBE BETWEEN THE MAS AND INTAKE MANIFOLD.



When you get on it, the engine flexes under the hood. If there is a crack in the hose, it will open up during that flexing and lets unmetered air enter the engine causing a lean condition.



It is free to check and pretty simple to identify.





Tom
 
Vaccum line. CoastieJoe usually posts this one... I would have to agree with Caymen, if the elbows are not on right, they will flex under load and give you the same problems....
 
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Ok on having replaced the elbows. So that leaves checking on what Caymen mentioned. Either that, or a vacumm leak elsewhere. Problem is, vacumm leaks ARE hard to find sometimes.



I had that problem with the intake pipe Caymen is talking about a couple of months ago. Somehow, I didn't get the pipe back into the air intake duct after I checked the air filter. Rough idle and missing/stumbling on acceleration. Didn't get a trouble code, but it was probably only a matter of time. I pulled over after having it just about stall at 35 mph, and double checked under the hood and found the line was not connected to the air intake duct. Reconnected it and all was good again.
 
I have taken the intake duct off completely and looked for cracks and I even bent it different ways to see if there is a crack in one of the grooves, but there wasn't.
 
Jason,



Did you every figure out the root cause of your P0171 issue? My 2001 ST is throwing the same code. Just installed a new MAF, but the issue did not go away. The elbow that everyone seems to talk about is fine on my Sport Trac. I plan to replace the fuel filter tomorrow, but frankly I doubt that will fix the issue. Seems like folks replace the PCV valve as well for this issue, but I am not crazy about diving into that unless I am sure that is it. How did you fix your issue?



Thanks,

Tim
 
Tim,



the PCV valve is not a hard operation. Its quick and cheap too. If you think that will help you should definitely do it.
 
I did get it fixed, or at least for the past 4-5 months it's been fixed. There is another rubber elbow that was bad. This one is on the passenger side valve cover near the front of the truck. It connects to a plastic tube that connects to the air intake tube. I couldn't find an exact replacement elbow, so I bought a small 90 degree molded heater hose and shortened the straight ends to make it fit. I also used radiator hose clamps for extra insurance, but be careful and don't make the same mistake I did by leaving the clamp's excess on the same side as the upper radiator hose. Needless to say the clamp rubbed a hole in the radiator hose and I had to replace the radiator hose.
 

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