Check engine light issues!
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Check engine light issues!
Here goes, I have a 1999 F-150 with a 5.4L V8, about 90,000 miles on it. I have had p0171 and p0174 codes for a while now and just recently had p1451 come up. After some research I have figured out that I must have a vacuum leak somewhere but can't find it in the engine compartment. I had a mechanic do a smoke test and he was stumped. I replaced the fuel pump about 1.5 years ago and have been fighting with the light since. Could the 3 codes be related and have something to do with the fuel tank? I attached a couple screenshots I took while connected to a Bluetooth code checker, hopefully it worked.
Last edited by BigJoeRN; Aug 15, 2016 at 09:49 PM. Reason: Added an attachment
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Joined: Sep 2013
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From: Edmonton, AB
The codes for p0171 & p0174 are indicating a lean condition. this could do with the MAF sensor, a vacuum leak or low fuel volume delivery. Lets start with having you check and clean the MAF sensor ( that stands for Mass Air Flow Sensor )
If the MAF sensor is dirty or gummed up that can lead to the above two codes being thrown. So let's get you to look at the MAF and see how it is, if there is any dust or it looks gummed up give it a good cleaning, and then put it back in.
Then lets check for Vacuum leaks. Check ever line and the little elbows and tees, all it takes is a hole or wear in the line or a cracked tee or fitting to be leaking and it will throw a code. You also need to follow the vacuum lines to the various connection points and make sure they are all good and connected, if one is off, then you will trigger a codes or codes.
The MAF sensor is located in the air inlet tube ahead of the throttle body, so lets get that out clean it up and put it back in. Also check your air filter and see if it is clean or dirty. It may not be catching all the debris and is plugged up, lets make sure that is clean.
I know you said a mechanic looked at the vacuum lines but I would go thru and check this again it doesn't take much to have a vacuum leak happen. and this is all part of the process of elimination make sure to follow the lines and see they are all connected especially behind the IAC that one is notorious for coming off and for cracking
fp1451 is an EVAP code os it is saying there is a fault somewhere on the circuit I would go under neath the bed of the truck , if you have a spare tire underneath, take it off and then look at the evap canister, there is some wiring that goes to it, check the conditioning of that wiring and make sure nothing is broken or come or is grounding out. It could be the solenoid, but I would check that wiring to the canister first and then look at the solenoid. It could be that solenoid needs to be replaced.
Try these steps and let see what you find out
If the MAF sensor is dirty or gummed up that can lead to the above two codes being thrown. So let's get you to look at the MAF and see how it is, if there is any dust or it looks gummed up give it a good cleaning, and then put it back in.
Then lets check for Vacuum leaks. Check ever line and the little elbows and tees, all it takes is a hole or wear in the line or a cracked tee or fitting to be leaking and it will throw a code. You also need to follow the vacuum lines to the various connection points and make sure they are all good and connected, if one is off, then you will trigger a codes or codes.
The MAF sensor is located in the air inlet tube ahead of the throttle body, so lets get that out clean it up and put it back in. Also check your air filter and see if it is clean or dirty. It may not be catching all the debris and is plugged up, lets make sure that is clean.
I know you said a mechanic looked at the vacuum lines but I would go thru and check this again it doesn't take much to have a vacuum leak happen. and this is all part of the process of elimination make sure to follow the lines and see they are all connected especially behind the IAC that one is notorious for coming off and for cracking
fp1451 is an EVAP code os it is saying there is a fault somewhere on the circuit I would go under neath the bed of the truck , if you have a spare tire underneath, take it off and then look at the evap canister, there is some wiring that goes to it, check the conditioning of that wiring and make sure nothing is broken or come or is grounding out. It could be the solenoid, but I would check that wiring to the canister first and then look at the solenoid. It could be that solenoid needs to be replaced.
Try these steps and let see what you find out
Thread Starter
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New User
Joined: Aug 2016
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The codes for p0171 & p0174 are indicating a lean condition. this could do with the MAF sensor, a vacuum leak or low fuel volume delivery. Lets start with having you check and clean the MAF sensor ( that stands for Mass Air Flow Sensor )
If the MAF sensor is dirty or gummed up that can lead to the above two codes being thrown. So let's get you to look at the MAF and see how it is, if there is any dust or it looks gummed up give it a good cleaning, and then put it back in.
Then lets check for Vacuum leaks. Check ever line and the little elbows and tees, all it takes is a hole or wear in the line or a cracked tee or fitting to be leaking and it will throw a code. You also need to follow the vacuum lines to the various connection points and make sure they are all good and connected, if one is off, then you will trigger a codes or codes.
The MAF sensor is located in the air inlet tube ahead of the throttle body, so lets get that out clean it up and put it back in. Also check your air filter and see if it is clean or dirty. It may not be catching all the debris and is plugged up, lets make sure that is clean.
I know you said a mechanic looked at the vacuum lines but I would go thru and check this again it doesn't take much to have a vacuum leak happen. and this is all part of the process of elimination make sure to follow the lines and see they are all connected especially behind the IAC that one is notorious for coming off and for cracking
fp1451 is an EVAP code os it is saying there is a fault somewhere on the circuit I would go under neath the bed of the truck , if you have a spare tire underneath, take it off and then look at the evap canister, there is some wiring that goes to it, check the conditioning of that wiring and make sure nothing is broken or come or is grounding out. It could be the solenoid, but I would check that wiring to the canister first and then look at the solenoid. It could be that solenoid needs to be replaced.
Try these steps and let see what you find out
If the MAF sensor is dirty or gummed up that can lead to the above two codes being thrown. So let's get you to look at the MAF and see how it is, if there is any dust or it looks gummed up give it a good cleaning, and then put it back in.
Then lets check for Vacuum leaks. Check ever line and the little elbows and tees, all it takes is a hole or wear in the line or a cracked tee or fitting to be leaking and it will throw a code. You also need to follow the vacuum lines to the various connection points and make sure they are all good and connected, if one is off, then you will trigger a codes or codes.
The MAF sensor is located in the air inlet tube ahead of the throttle body, so lets get that out clean it up and put it back in. Also check your air filter and see if it is clean or dirty. It may not be catching all the debris and is plugged up, lets make sure that is clean.
I know you said a mechanic looked at the vacuum lines but I would go thru and check this again it doesn't take much to have a vacuum leak happen. and this is all part of the process of elimination make sure to follow the lines and see they are all connected especially behind the IAC that one is notorious for coming off and for cracking
fp1451 is an EVAP code os it is saying there is a fault somewhere on the circuit I would go under neath the bed of the truck , if you have a spare tire underneath, take it off and then look at the evap canister, there is some wiring that goes to it, check the conditioning of that wiring and make sure nothing is broken or come or is grounding out. It could be the solenoid, but I would check that wiring to the canister first and then look at the solenoid. It could be that solenoid needs to be replaced.
Try these steps and let see what you find out
I still need to crawl under it to take a look at the solenoid and wiring. I will take a peek and see what I find.
Hotshot
Joined: Jan 2004
Posts: 19,762
Likes: 1,079
From: St Louis
A gas cap cannot cause "lean" codes or any other of your reported symptoms.
The P1451 is a separate issue, follow the previous instructions to get started on that one, Pocketlint's directions are spot-on.
The "lean" codes are from the engine being either "under fueled" or "over aired".
The first would be to an insufficient fuel supply that is not delivering adequate fuel at adequate pressure in order to satisfy the requirements of the system. You can use a fuel pressure gauge to test for this condition.
The second is usually due to excessive air entering the intake after the MAF or the MAF itself is mis-reporting the mass of the intake air charge. This could be due to defective, dirty, (or incorrect) MAF sensor or it's due to an air leak that's behind the MAF. Just because the mechanic couldn't find anything doesn't mean that a leak does not exist.
The P1451 is a separate issue, follow the previous instructions to get started on that one, Pocketlint's directions are spot-on.
The "lean" codes are from the engine being either "under fueled" or "over aired".
The first would be to an insufficient fuel supply that is not delivering adequate fuel at adequate pressure in order to satisfy the requirements of the system. You can use a fuel pressure gauge to test for this condition.
The second is usually due to excessive air entering the intake after the MAF or the MAF itself is mis-reporting the mass of the intake air charge. This could be due to defective, dirty, (or incorrect) MAF sensor or it's due to an air leak that's behind the MAF. Just because the mechanic couldn't find anything doesn't mean that a leak does not exist.
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