Strange Problem

1999 Expedition 5.4L Eddie Bauer, 145,000 miles

I have been having the P0171 and P0174 codes for while now. I checked and cleaned the MAF with MAF cleaner, replaced the PCV valve and one hose that appeared frayed but the codes come back. Overall the truck worked OK although the fuel efficiency was lower. I was just waiting for available time to get it checked by a mechanic since my knowledge is limited.

A few days ago, the truck started idling slower and some times it would die at a traffic light but started right back up with no problems. Sometime I would just give it a little gas when stopped at a light and the truck would do OK.

Yesterday it died at a traffic light and when I restarted , put it on gear and gave it gas the truck would shake and fishtail when moving forward. Weirdest thing. I was not too far from home so I limped it there at 10 MPH.

Today I run my Acton Code reader and found the following codes:

P0442 - Evaporative emission system leak detected - pending
P0174 - Bank 3 system too lean - confirmed
P0171 - Bank 2 system too lean - confirmed
P1151 - Heated Oxygen Sensor Bank 2 Sensor 1 switch point indicates lean - confirmed
P1131 - Lack of heated oxygen sensor (bank 1 sensor1) switch, indicated lean - confirmed

My limited research indicates it could be a bad purge valve or a faulty PCM.
Would any of these codes cause the truck to shake and fishtail when moving forward othre than very slowly?
Would a faulty PCM cause this or am I looking at a drive train issue?

The front brake pads and rotors were replaced about 500 miles ago but do not seem to be the issue. would seized brake cause this issue? There does not appear to be any smell so nothing seem to be binding, as far as I can tell. When idling in park the engine is a little rough and sputters some but not terribly so,

Really weird issue. any help you can provide would be greatly appreciated as I need to decide if the repairs are worth it for a truck this old but in otherwise pretty good shape.

You might try looking for a vacuum leak first. Trace the PCV hose around to the back of the intake; there's a rubber elbow on the end that often cracks/ dry rots. Next look at the right side of the throttle body extension, there are two hoses. They can be old and rotten/ loose where they push on to the throttle body extension. Maybe wrap with a zip tie if they're loose, see if there's improvement then replace if needed. The evap purge solenoid is mounted on the firewall next to the brake booster. There's a hose from there to the intake downstream of the throttle body. That hose was rotten on my '01 with 5.4. Inspect every connection between the MAF and intake manifold, including if the big plastic intake pipes are properly assembled, not broken, and throttle body is securely attached and gasket is intact. Make sure the IAC valve is clean, tight and the gasket is intact. Also check the intake manifold, you can do this by spraying carb cleaner on a cool running engine and listen for rpm changes.

You can look at LTFT live data on your code reader as you fix leaks or replace components to see if the numbers converge on zero. High numbers mean the computer is detecting a lean condition and is adding fuel. If it gets up around 20% it will show an error code and check engine light will come on. If you fix a vacuum leak you should see LTFT go down. 6% or lower isn't too bad. The number itself means the computer is adding that percent much more fuel to compensate for the lean condition. The numbers come from a table created by the ecu as it learns, you can make it forget the table and start fresh by disconnecting the battery for a couple hours. You would then see the ecu create a table with new LTFT numbers learned since.

It may be a fuel problem, check fuel pressure, replace fuel filter, could also be fuel pump going out.

Upstream O2 sensors could be bad. You can spray some carb cleaner into the engine while it's running and look for voltage rise, like from 0.7-ish volts to 1v.

Look for exhaust leaks upstream of the O2 sensors.

It could be combo of any/ all the above. One fix might make the codes go away, but there may still be problems. Use LTFT to see how close to zero you can get under different driving conditions (not just idle).

Could also be stuck-open egr valve but not as likely.

I would check the catalytic converters if there still on there. Have an exhaust guy do a back pressure test

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Thank you for the replies. would any of these issues make the car shake ad rattle a lot and fishtail badly when driving forward at other than very slow speed? TIA

Fuel starvation can make your engine run quite rough. Electric fuel pumps can fail intermittently, so they might run quite well one moment then crappy the next. I'm not sure what you mean by fishtail... to me it means excess torque to the rear wheels creating loss of traction and oversteer. Like running across a patch of ice, or opening the throttle in low gear in a powerful car. Eliminate vacuum leaks and confirm good fuel delivery. Don't forget that fuel pump relay. You can switch it with the headlight or similar relay and see if it clears up some problems. Years ago I had a fuel pump relay going out on my '01 R6 sportbike that had it running like crap one moment, then like a ***** ape the next. I believe it was creating a voltage drop to the fuel pump, intermittently starving the carbs. Clogged cats should create a rich condition and general loss of power, which you don't have. Another thing you could check is make sure there are good grounds to the engine, and battery connections/ cables are good. Note all these last items are less likely culprits than more likely vacuum leaks, fuel filter/ pump, bad O2 sensor(s), or exhaust leak before upstream O2 sensors.

Jim Brown said:

I'm not sure what you mean by fishtail... to me it means excess torque to the rear wheels creating loss of traction and oversteer. Like running across a patch of ice, or opening the throttle in low gear in a powerful car..

Click to expand...

That describes it pretty well along with overall rattling.

Based on the P1131 and P1151 you might consider testing the upstream sensors. They're the ones that control fuel trim. There are various ways you can test them, easiest is with propane, disconnect the air intake at the air cleaner, leave the rest assembled. Put a long hose on the propane torch and introduce it into the intake past the MAF. With the engine running, observe live data O2 sensor voltage with your scanner. Voltage should be around 0.5-0.7. Introduce a little propane to create a rich condition. Voltage should rise above 0.8. Remove the propane and put the intake back together. Next pull a vacuum hose to create leak creating a lean condition while observing live data. Voltage should drop to as low as 0.1 then rise to above 0.5 as you stop the leak. If the upstream sensors don't respond like that then they should be replaced. O2 sensors should be replaced every 100k miles or so as normal maintenance. Supposedly their response time becomes slower as they age. This would naturally have an impact on fuel mileage. So the cost/ benefit might justify changing the sensors if they alternative is poor mileage resulting in higher fuel costs.

A lean air/ fuel mixture will cause engine knocking, like a rattle from the pistons. Lean mixture will also create somewhat more power than rich. Poorly running engine can also impact transmission behavior causing abnormal shifts. The fishtailing/ rattling may be just another symptom, I wouldn't key in on it.

Unless they're not happening at the same time, as in, the engine runs like crap and is rattling, then runs real well, then runs like crap again, then runs real well. Then check fuel pressure, maybe look at fuel pump relay/ fuel pump. Maybe intermittent power issues to ECU/ ignition/ injectors, like a bad ground, or test throttle position sensor. The list starts getting longer... it's best to start diagnosis at the source, methodically eliminate possible problems.

Finally, if both O2 sensors went bad, it may be important to ask why. What is the underlying cause? Google-fu leads us to the following:

"O2 sensor failures can be caused by various contaminants that enter the exhaust. These include silicates from internal engine coolant leaks (due to a leaky head gasket or a crack in a cylinder wall or combustion chamber) and phosphorus from excessive oil consumption (due to worn rings or valve guides)."

Are you losing coolant, or excessive oil? What do the plugs look like?

Do you have high LTFT at all rpms? Is it high at low rpms then goes down at higher rpm, or vice versa?

If LTFT is lower at low rpm then goes up at higher rpm it suggests fuel starvation.

Also when you're looking at the scanner make sure it's in closed loop.

I am placing my bet on vac lines causing at least half your problems.
I have a 01 5.4 with almost 300K on it and have the rough/shudder sometimes and then it throws the lean code. I will replace a line and the prob goes away for a while. I am just too lazy to tear into it and replace them all at once.
Don't know what the factory lines cost, but I would get a cheap micrometer from Harbor Freight, measure the inside diameter of the lines and start replacing them with generic hose from a parts store.
Good Luck
Rich

Rock Auto: https://www.rockauto.com/en/catalog...8,1362439,exhaust+&+emission,vacuum+hose,5024

Or get silicone hose which is more expensive but withstands heat much better