Hello all.

Ok, please bare with me while I describe below and cry at the same time.

I have a 2002 V8 5.4L F-150.

Earlier on this year, in February, I had my check engine light come on. Please note that this was a very cold day. I am not from the states but it was -17C.

Now I went and got the codes pulled and it was showing system too lean. The guy at O'REilly's said that the F-150's around this age were notorious for doing that in cold weather. He said not to worry about it and do just clear the code, so I did so.

Now 9 months later and the check engine light came on again, when it has been a cold day, showing system too lean.

This time the engine would die on me if I was in Park on a cold morning. The rev counter would go between around 700RPM and 1200RPM constantly.

I took it to a garage and they found that the fuel filter was 90% clogged and the PCV valve was also split and letting in air. They replaced these and things were all good for about another week.

Now this is where I am at. The engine light came on again, system too lean, and I took it back to a garage and told them about the work that had been done about 1 week ago.

The truck has died on me before when in park at a drive-thru or something and sometimes it will 'lunge' when I accelerate.

The work that has been done recently is the following:
- Remove and replace Idle Control Valve
- Clean TBI
- Tested DPFE & EGR Valve
- Clean Mass Airflow Sensor
- Replace TBI Gasket

After all of this I still have the same problem. The garage told me the next thing they will try if this doesn't work is to replace the MAF sensor. I have ordered one online and I will be replacing this myself.

So my question is, does anyone have any ideas on what I can do to get this resolved?

Thank you very much.

 

It might be the MAF, but it's more likely a vacuum leak somewhere. Most common is the PCV elbow behind the intake.

 

I had that replaced like 1 month ago. I have gone along and looked for anymore leaks but I can't find any. When I have some time off (hopefully black Friday if I can get out of work early) I am going to have another good look. I did replace the air filter about 3 months ago but I have double checked that everything is sealed tight together again.

 

If you had a tuner, it would tell the duty cycle of your Idle Air Controller.
If it has a maxes out percentage, you have an air leak.

Use carb cleaner or starting ether. Spray spots around the top of the motor to see if it picks up on idle.

Check the fuel rail pressure. The regulator could be broken allowing too much fuel to return to tank.

Check the idle voltage on your throttle position sensor too. you need .90-.99 volts.

Get back to us asap. and we can go from there.

Miz

 

Don't waste your time, the computer is almost always too fast for you to detect anything audibly. You need to use a scan tool or similar to watch either the short term fuel trims or the actual upstream O2 sensor voltages to see the effect of the additional flammable. This is the BEST way to find those sneaky vacuum leaks.

"Lean" codes are caused by a mismatch in the air/fuel mixture as detected and controlled by the computer. The problem is either insufficient fuel (low pressure/volume) or air that's getting into the system but being reported by the MAF sensor. Intake vacuum leaks account for over 90% of these faults. A dirty MAF sensor a few more percentage points, especially if an oiled filter is used. The rest will be caused by fuel deliver problems.

IAC duty cycle can be read with any capable scan tool. I can read it with my smartphone and a $10 ebay adapter, if I choose. IAC valves don't cause "lean" codes anyway, they usually manifest as either idle speed issues or cold weather stalling at startup (winter "morning sickness").

The TPS cannot cause a "lean" code as the PCM always checks it at power on. That old "just under 1V" TPS reading is irrelevant on the more modern systems.

 

I appreciate everyone getting back to me on this. I didn't see these replies until after I replaced the MAF sensor. I replaced sensor and still the same thing. When I get some time off I will be checking for vacuum leaks.

Again, I appreciate your help with this guys but this is just frustrating. Do you have a link to the adapter from eBay that you have? I would like to get one that someone else approves that already has one!

 

Just keep in mind - a lean code means that either you don't have enough fuel, or air is entering the intake system somewhere after the MAF. It can also be caused by an exhaust leak before the front O2 sensor.

 

I had a 4.2 V6 do the same thing I finally found the rubber seals under intake manifold had hardened up and were sucking air in causing lean codes.

 

Did emission testing for 20+ years on those fords was the upper clam shell gasket. There was a TSB a shop we did testing for told me about. Mainly at cold start up they would leak. Remedy is to replace gasket and NEW bolts as well. The new bolts have shorter shoulders and tighten up more.

 

If you don't find any vacuum hose leaks, my vote is intake manifold is leaking from either a crack in the intake or just a vacuum leak through the intake manifold gaskets.

 

Also, I would recheck the pcv. Sometimes the connection on the back of the intake gets too loose from the hose swelling and lets in air. If it slips on and off really easy, change it.

 

Have you ever replaced your fuel filter?

A buddy of mine was having lean issues and I asked the same question, he said never have. After he replaced it his codes have not come back.