Diagnostic questian
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Diagnostic questian
My 2003 f150 4.6l has a code for low cumbustion bank one and bank 2. I have tested for a vacuum leak made sure the air filter and maf are clean. It randomly hesitates and looses speed when driving. My fuel pressure is at 30psi when idleing and 40psi when driving but drops to 30psi when it hesitates. I've been told by some it could be an o2 sensor and by others to change the fuel pump. Since a fuel pump is so expensive I want to be sure before I get one. Any other ideas? Thanks! I have enjoyed this site for awhile but this is my first post so if I'm doing it wrong, feel free to let me know! Happy new year!
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IMHO, although you have some initial quick info (diagnostics), it's time to really do true diagnostics on each system and if that proves out fine, then it's time for a compression test....heck, you could just have a bad/clogged injector
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I tried using injecter cleaner when it first came on, I don't know if that would be enough asumimg it might still be an injecter cleaner. Is there any brands of compression testers that you would recommend or that I should stay away from? It needs to be affordable on a low budget.
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Clarifying my question
Okay, just wanted to rephrase my question so it is more clear. I was told by a Mechanic that it is probably the fuel pump going out slowly but could be an O2 sensor or exhast leak right before the pre-catalytic converter. He used his scanner but compression combustion and everything else was fine at the time. He thinks it is the fuel pump because it is inttermittent and the pressure drop to 30 psi when it happens. He lives several hours away so my work schedule won't let me get there to have him test the sensor or for an exhast leak. I want to get another opinion that agrees or disagrees with him before I spend all that money and time replacing it if it isn't the issue.
My question is:
does it sound like the fuel pump or one of the these other components?
I will be doing several cross country trips this year but have a limited budget and want to make sure it is reliable as I can get it.
My question is:
does it sound like the fuel pump or one of the these other components?
I will be doing several cross country trips this year but have a limited budget and want to make sure it is reliable as I can get it.
Last edited by Banjo picker1; Jan 3, 2017 at 04:36 PM. Reason: Asding missing info
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From: Thousand Oaks, CA
Codes P0171 & P0174 are defined as "System Too Lean Bank 1 and Bank 2.
Adding the word "combustion" just confuses any discussion.
Fuel pressure above 30psi is still good.
If the engine hesitates from a vacuum leak the fuel pressure could drop back to idle levels.
The most common cause of codes P0171/P0174 are a vacuum leak.
Carefully inspect all the vacuum lines, in particular the PCV line, for any leaks, soft spots, cracks, etc.
A vacuum leak may be caused by a crack in the intake manifold or bad intake gasket which is a bit harder to locate.
An exhaust leak will usually cause only one of the codes to be set.
I had a loose passenger side manifold/pipe connection that set P0171 and never set P0174.
When both codes are set the vacuum leak would be from the exhaust manifold forward to the throttle body.
The way the intake manifold criss-crosses over to both banks 1 & 2 is why both codes will get set.
An exhaust leak will only affect one bank.
A bad/clogged fuel injector would only affect one cylinder on one bank.
Has the MAF ever been cleaned?
How many miles on the engine?
Adding the word "combustion" just confuses any discussion.
Fuel pressure above 30psi is still good.
If the engine hesitates from a vacuum leak the fuel pressure could drop back to idle levels.
The most common cause of codes P0171/P0174 are a vacuum leak.
Carefully inspect all the vacuum lines, in particular the PCV line, for any leaks, soft spots, cracks, etc.
A vacuum leak may be caused by a crack in the intake manifold or bad intake gasket which is a bit harder to locate.
An exhaust leak will usually cause only one of the codes to be set.
I had a loose passenger side manifold/pipe connection that set P0171 and never set P0174.
When both codes are set the vacuum leak would be from the exhaust manifold forward to the throttle body.
The way the intake manifold criss-crosses over to both banks 1 & 2 is why both codes will get set.
An exhaust leak will only affect one bank.
A bad/clogged fuel injector would only affect one cylinder on one bank.
Has the MAF ever been cleaned?
How many miles on the engine?
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My Mechanic friend has a smoke vacuum leak tester and we confirmed that it does not have a vacuum leak. Yes the maf has been cleaned. The engine has 236,000 miles. I'm not sure of the fuel pressure drop is a symptom or a cause. Because it drops in speed when it happens, it can be dangerous on faster or mountain roads. Also, I don't want to risk breaking down 1500 miles from home! 
Last edited by Banjo picker1; Jan 3, 2017 at 09:48 PM. Reason: Need to add more info
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From: Thousand Oaks, CA
Now that we know it's had a smoke test that would rule out a vacuum leak.
Have you checked the air intake boot between the MAF and throttle body for leaks?
I don't think the smoke vacuum leak tester checks that.
Here's a good article - P0171 and P0174 - OBD-II Trouble Codes
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I did check the air intake boot and it's fine. Great article though! Does the '03 f150 have pcv software that needs updating? I replaced the fuel filter about 6 months ago and in not so sure that an injecter on each side are both randomly clogging at the same time.
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Something else I just thought of, and I'm not sure of it's related or just part of the cold winters here in SC. (i moved here from Texas earlier this year.) about 1 in every 15 times or so, it has a harder time starting. The battery is only a year old.
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That code combo is almost always caused by one of the two following conditions:
1: Over-aired - Excess air is entering the system that the MAF is not measuring or the MAF is not correctly measuring the air that does come in. Probably accounts for >90% of these faults.
2: Under-fueled. The fuel delivery system is unable to supply the proper amount of fuel that the engine's management system is demanding.
You need to look at the freeze frame data for when the code(s) were set to see what the operating conditions were. If they were set at or near idle speed, it's #1 above. If they were set during heavy load conditions, towing uphill for example, then it's likely #2 applies.
Your mechanic should have known to check this data before embarking on a smoke test.
Insufficient description.
30 psi fuel pressure is within (barely) the specification for that engine. Again, it depends on the load so check the data above.
1: Over-aired - Excess air is entering the system that the MAF is not measuring or the MAF is not correctly measuring the air that does come in. Probably accounts for >90% of these faults.
2: Under-fueled. The fuel delivery system is unable to supply the proper amount of fuel that the engine's management system is demanding.
You need to look at the freeze frame data for when the code(s) were set to see what the operating conditions were. If they were set at or near idle speed, it's #1 above. If they were set during heavy load conditions, towing uphill for example, then it's likely #2 applies.
Your mechanic should have known to check this data before embarking on a smoke test.
about 1 in every 15 times or so, it has a harder time starting. The battery is only a year old.
30 psi fuel pressure is within (barely) the specification for that engine. Again, it depends on the load so check the data above.
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I know the light on the dash came on while driving. I live in the mountain foothills. He is acctually a doctor that has been doing Mechanic side work for the past 12 years just because He loves it. He said it's usually caused by a vacuum leak or dirty MAF and hasn't seen anything like what's going on with my truck. He said that 30 psi fuel pressure going uphill and losing power is probably an indicator of the fuel pump dying. Since I can't afford to take it to an actual Mechanic shop, I'm just getting other's opinions and ideas. When he put his anaylizer on it showed the maf reading correctly but since the problem is inttermittent and we couldn't get it happen in the short time is was able to be there, could it possibly going in and out?
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