Mechanics

ROUGH RUNNING, LACK OF POWER

2004 Ford F-150 • V8 2WD Automatic • 117,000 miles

I have changed the plugs, replaced one bank of fuel injectors, truck still runs rough, does not have power going up hills. Compression check shows all cylinders are in good condition. Mileage 117000
AD
Avatar
Jimdebruyn
February 15, 2011.




First is there a check engine light? If so, the first thing would be to have the computer scanned for codes. If not: Do a cylinder drop test. (Remove one plug wire at a time with engine running) You should notice a drop in rpm. If not, that cylinder wasn't firing. You'll then have to determine if it's the coil/wire or injector.

Also, I need to know what caused you to replace one bank of injectors? What about fuel pressure from pump? Fuel filter? Air filter? Check all vacuum lines and fittings?

Ernest Clark
Feb 15, 2011.
Mechanic read the codes, that was why he changed the plugs, he did a cylinder drop test and found the problems with the injectors. He has replaced fuel filter, air filter and Oxygen sensors. He says the fuel pump has adequate pressure.

Tiny
Jimdebruyn
Feb 15, 2011.
It doesn't sound like that mechanic really knew what he was doing. If there was a code in the computer, that would've pointed him in a certain direction. And he's supposed to test components before replacing them. To do otherwise leaves the same problem you started with, correct?

If you can tell me what the code/codes where and if you still have the check engine light on, this will allow me to give you accurate advice. If I guess at your problem that won't help you at all and only cause you to spend more time and money.

Ernest Clark
Feb 15, 2011.
Previous codes were as follows: PO309, PO356, PO316, PO308, PO306, PO305, 90304, PO300, PO174, PO171. Now the only code it is throwing is the PO171 and the check engine light is still on. He has now traced it to the possibility that it is the fuel regulator.

Tiny
Jimdebruyn
Feb 16, 2011.
A P0171 lean code for bank 1 is the cylinder bank on the RIGHT (passenger) side of the engine on Ford vehicles with a V6 or V8 engine and rear-wheel drive.

A P0174 lean code for bank 2 is the cylinder bank on the LEFT (driver) side of the engine on Ford vehicles with a transverse-mounted V6 engine and front-wheel drive. This code is not set on four cylinder engines (no bank 2).

WHAT A LEAN CODE MEANS

A lean fuel condition may exist if the engine is sucking in too much air and/or the fuel system is not delivering enough fuel. If bad enough, a lean fuel condition may cause lean misfire, a rough idle, hesitation or stumble when accelerating, and/or poor engine performance.
Unmetered air can enter the engine through a vacuum leak, a dirty airflow sensor that is not reading airflow accurately, an EGR valve is not closing and is leaking exhaust into the intake manifold, an EGR valve that is allowing too much flow (because the EGR differential pressure sensor that monitors EGR flow is faulty and is under-reporting EGR flow).

If the problem is not enough fuel, the underling cause may be a weak fuel pump, restricted fuel filter, leaky fuel pressure regulator or dirty fuel injectors.

DIRTY MAF SENSOR

One of the most common causes of Ford P0171 and P0174 lean codes is a dirty mass airflow (MAF) sensor. The MAF sensor is located in the air inlet tube
just ahead of the throttle body. The MAF sensor should be protected from outside dust and debris by the air filter, but sometimes the air filter doesn't fit real tight inside the housing and allows unfiltered air into the engine. Dirt can stick to the MAF sensor wire and form a coating that slows the response of the sensor to changes in airflow. The MAF sensor can also be contaminated by fuel vapors that back up through the intake manifold and throttle body when the engine is shut off. The vapors can leave a waxy coating on the sensor wire. This causes the MAF sensor to under report airflow, which in turn misleads the powertrain control module (PCM) so it doesn't add enough fuel to maintain a properly balanced air/fuel ratio. As a result, the engine runs lean and sets a P0171 and/or P0174 code (see Ford TSB 98-23-10 for details).

If the MAF is dirty, the fix is easy enough: just clean or replace the MAF sensor. In many instances, the MAF sensor can be successfully cleaned by spraying the sensor element with electronics cleaner. Do not use any other type of cleaner as this may damage the sensor.

Disconnect the air inlet tube just ahead of the sensor, and then spray the electronics cleaner through the screen at the wire element in the center of the little MAF sensor. Let the cleaner soak in for several minutes, then give it another shot of cleaner. Let it sit another five minutes, then reconnect the air inlet tubing and start the engine.

If the lean codes keep coming back, the MAF sensor may have to be replaced if the engine does not have a vacuum leak or fuel delivery problem.

VACUUM LEAKS

Another common cause of Ford P0171 and P0174 ean codes is an engine vacuum leak. Ford TSB 04-17-4 details procedures for checking fuel trim and looking for vacuum leaks.

On 3.8L Fords with a split-plenum intake manifold, the port gaskets and isolator bolt assemblies for the upper plenum can deteriorate over time and leak air, often as a result of oil being sucked into the intake manifold through the PCV system. Also the vacuum hose that connects the fuel pressure regulator to the intake manifold can swell and leak vacuum where the hose connects to the manifold. Ford TSB 03-16-1 says the fix involves several steps: remove the upper manifold plenum and replace the original gaskets and bolts with revised ones, replace the front valve cover with a revised valve cover that reduces the amount of oil vapor sucked into the PCV system, inspect and replace the fuel pressure regulator hose, and finally, reflash the PCM so it is less sensitive to lean fuel conditions.

BAD DPFE SENSOR

Ford p0171 AND p0174 lean codes can also be set by a bad EGR differential pressure sensor. These sensors have a very high failure rate once a vehicle has more than about 60,000 miles on the odometer or is more than five or six years old.

The DPFE sensor is mounted on the engine, and is attached with two rubber hoses to the tube that routes exhaust gas to the EGR valve. The original equipment sensor has an rectangular aluminum housing about three inches long. Corrosion inside the sensor reduces its sensitivity to EGR flow, causing it to under-report EGR flow. The PCM responds by increasing EGR flow, which may keep the EGR valve open longer than usual creating a lean condition in the engine. Thus, a bad sensor may set a P0401 code (insufficient EGR flow), or it may not set an EGR code but a P0171 and/or P0174 lean code instead.

The cause of the P0401 code in most cases turns out to be a bad DPFE sensor, not an EGR valve problem or an EGR valve that is plugged up with carbon (though this can also set a P0401 code). An aftermarket replacement DPFE sensor costs less than $50 and usually gets rid of not only the P0401 code, but also the P0171 and P0174 codes, too.
AD

Ernest Clark
Feb 16, 2011.

AD