SureTrack Community Fix: Leaning RV

Real Fixes from ShopKey’s SureTrack® expert information resource are documented issues from actual shop repair orders and community discussions. Read on to see how SureTrack can help you correct issues that are not easily diagnosed using OEM information alone. SureTrack is currently available free with the purchase of a current Snap-on® diagnostic software version or in our ShopKey Pro product.

Typically when your RV is leaning it’s because you didn’t get a flat campsite, but when it’s the fuel system leaning, that causes other issues. SureTrack community member Z_Sled had a 2011 Ford E350 Super Duty RV in the shop that had problems with a rough idle and stalling. They posed the question to the community, and with the help of fellow community member runtherack and others, they were able to resolve the issue quickly.

The following Community Fix summarizes the interaction between members of the community that led to the solution.

2011 Ford RV Cutaway E350 Super Duty 6.8L

Rough idle and stalling with lean codes, replaced MAF sensor.

Customer states that RV has rough idle and stalls sometimes.

Diagnostic Steps Performed/Parts Replaced
Checked for codes and found P0171, P0174 and P0300. 50% short term fuel trims, idles good at 50% then it starts to lean out to below 0%. At 30% starts to run rough then at 10% and less hardly keeps running and may stall. Sometimes it will richen up fuel trims before stalling but usually quits. Timing is all over 5 to 30 degrees. If you drive down the highway runs great, good power.
Fuel pressure is ok. Replaced exhaust manifold gaskets and studs because of leaks. Unplugged EVAP purge vacuum hose on manifold and plugged port, no change. Unplugged upstream 02 sensors and MAF sensor, no change.

When fuel trims are falling off I added fuel through vacuum port and idle smooths out. 02 sensors either go rich or start switching till fuel is removed. Unplugged EVAP purge solenoid hose of manifold, and plugged port, ran at idle and no change. Listened for vacuum leak at intake manifold and could not hear a leak. sprayed a fuel source around intake, watched 02 sensors, no increase in 02 voltage. Is there a MAP sensor? Cant find it on manifold or in engine wiring diagrams. Starting to suspect PCM. What else am I missing?

Best Answer from Community Member runtherack
Verify there are no vacuum leaks. What are the fuel trims and MAF sensor readings at 2000 RPMs?

Faulty MAF sensor.

MAF sensor fixed it. Warmed up engine, held throttle WOT till it governed around 3800RPM. Held it for a minute, Only had MAF sensor data pid up on scanner. After about a minute the g/s dropped to 40. Lesson learned was don’t test by what freeze frame tells you. P0171, P0174 and P0300 was setting at idle and when I was driving MAF sensor looked good. In-bay test solved it.

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About the Author

Nick Taylor

Nick Taylor is the SureTrack Community Administrator and a Senior Applications Specialist at Mitchell 1 with over 25 years of experience with electronic repair data systems. Nick previously worked in the automotive dismantling and engine rebuilding industries.