Performance issue 4.2L V6
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Mountain Pass
Joined: Nov 2001
Posts: 222
Likes: 5
From: NE PA
Performance issue 4.2L V6
2003 4.2 V6 seems to bog down when coming to a stop and sometimes sputter. Check engine code was "lean" bank 1 and 2. Unplugged Mass Air Flow sensor and had no effect on idle speed.
-Replaced MAF sensor and the truck would barely run. Smelled like it was running rich and starving for air. Unplugged the new sensor and ran as it did before changing the sensor.
-Checked for air intake and vacuum leaks. Air filter is brand new
Any other ideas would be appreciated.
-Replaced MAF sensor and the truck would barely run. Smelled like it was running rich and starving for air. Unplugged the new sensor and ran as it did before changing the sensor.
-Checked for air intake and vacuum leaks. Air filter is brand new
Any other ideas would be appreciated.
Tuned
Joined: Jul 2019
Posts: 311
Likes: 19
Best would be to smoke test it. Otherwise a scan tool that can see the short and long term fuel trims. There’s some really good post here in this forum that will show you how to replace the intake gaskets and isolator bolts. Get a repair manual so that you tighten all the right bolts on the correct sequence and torque specs
More Turbo
Joined: Sep 2017
Posts: 574
Likes: 146
These codes are not easy to track down as many things can cause them.
Was the new MAF sensor from Motorcraft or a cheapy online purchase ? I went through a similar problem and replaced my MAF with a cheapy only to still have the same lean codes. When i replaced it with a Motorcraft sensor - problem solved.
Check your freeze frame data as to the speedometer speed when the codes were activated. If the speed was near zero, then you probably have vacuum leak. If it was while you were on the road you may have a sensor problem.
Vacuum leaks can be in many places. Check the simple things first. The last resort should be the manifold gasket and isolator bolts. I also recommend a smoke test.
Was the new MAF sensor from Motorcraft or a cheapy online purchase ? I went through a similar problem and replaced my MAF with a cheapy only to still have the same lean codes. When i replaced it with a Motorcraft sensor - problem solved.
Check your freeze frame data as to the speedometer speed when the codes were activated. If the speed was near zero, then you probably have vacuum leak. If it was while you were on the road you may have a sensor problem.
Vacuum leaks can be in many places. Check the simple things first. The last resort should be the manifold gasket and isolator bolts. I also recommend a smoke test.
Lead Driver
Joined: Sep 2006
Posts: 7,907
Likes: 143
You got all the right suggestions.
The stall is from being too rich, a normal reaction to a large vacuum leak.
The system tries to correct it and over does it.
This is because the OX sensors detect to much Ox n the exhaust that signals the fuel tables to go rich.
The fault begins as Lean then turns to over Rich. from the loop action.
A Scanner to look at the Long Term Trims will show them to be 25% shifted positive as proof.
Plus you have codes 171 and 174 due to the shifted Trims. The codes telling you Lean is the tipoff to the vacuum leak, not excessive fuel, in the end.
Trying to spray find a leak may not work well because the motor is already too rich, if flammable spray is used.
Only if the leak is sealed enough would the Idle tend return toward normal.
Good luck.
The stall is from being too rich, a normal reaction to a large vacuum leak.
The system tries to correct it and over does it.
This is because the OX sensors detect to much Ox n the exhaust that signals the fuel tables to go rich.
The fault begins as Lean then turns to over Rich. from the loop action.
A Scanner to look at the Long Term Trims will show them to be 25% shifted positive as proof.
Plus you have codes 171 and 174 due to the shifted Trims. The codes telling you Lean is the tipoff to the vacuum leak, not excessive fuel, in the end.
Trying to spray find a leak may not work well because the motor is already too rich, if flammable spray is used.
Only if the leak is sealed enough would the Idle tend return toward normal.
Good luck.
Mountain Pass
Joined: Apr 2017
Posts: 170
Likes: 9
The intake manifold isolator bolts are notorious for shrinking over time and leaking. If yours have not been replaced then they need it and it's really not that hard to replace them.
Look at the PCV hoses coming off the top of the valve cover for leaks. Check the vacuum line to the brake booster and remember that a bad booster Can cause a leak too. Follow all the little vacuum lines and looks them over for cracks and leaks. The o-rings around the injectors could also be leaking, but it's not too likely.
Look at the PCV hoses coming off the top of the valve cover for leaks. Check the vacuum line to the brake booster and remember that a bad booster Can cause a leak too. Follow all the little vacuum lines and looks them over for cracks and leaks. The o-rings around the injectors could also be leaking, but it's not too likely.
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Mountain Pass
Joined: Nov 2001
Posts: 222
Likes: 5
From: NE PA
Very late update: Replaced upper intake manifold gaskets and isolator bolts and problem solved. Thanks for everyone's advice. Unfortunately had to take it somewhere because I could not get my large hands in to reach the back bolts, lol.
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