2004 Expedition Needs Expedited

Okay the post title doesn't really mean anything other than I thought it sounded cool. 2004 Ford Expedition with a customer described "hesitation on accel and decel". Intermittent as well. I'm suspecting a miss and since the check engine light is on I'll start with checking stored codes. Since I only have the customer description of the problem so far I'll run the full scan. Full scan will check all the computers for stored codes and not just the engine computer.
I've ended up with 1 PCM fault, 3 DSM faults and 1 HEC fault. PCM is the Powertrain Control Module. DSM is Driver's Seat Module. HEC is Hybrid Electrical Cluster.  I can ignore the seat module codes. They indicate a problem with the passenger side mirror and that isn't the complaint I'm after. The cluster has one code for a data link fault but it isn't a current problem. I'm going for P0171 "system too lean bank 1".

 On these vehicles it is pretty common for the PCV vacuum hose to be rotted and leaking. It is a fairly easy check. I did find a bad PCV hose. Replaced with 3/8 hose and an elbow.

Vacuum leak fixed. But is a vacuum leak what set the lean code? It is most likely but to be even more sure I could look at the freeze frame for the P0171. If the code set at low speed or at idle then it was probably the vacuum leak.

I have a vacuum leak indicated in freeze frame. I found and repaired a vacuum leak. Just have to tie up some loose ends before we are finished. Remember that the complaint could have been caused by a misfire and I haven't driven the truck. I need to drive the truck to verify no more running problem with accel/decel.

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The truck ran fine. There were no misfire codes stored and the truck did not misfire on the test drive BUT (big but) there is another place to check for misfires that may have been noticed by the engine computer. Those would be logged in the mode 6 test results TID 53. When I checked the mode 6 logs I found a very low number of misfire counts for cylinder #7. Given that the truck didn't misfire on the test drive and that the counts were low I decided to clear the KAM (keep alive memory) and let the system start over on the mode 6 tests. Yes, it is a judgement call.

Vacuum leak found and repaired. Codes cleared and KAM reset.
Ready to hit the road!

Thanks for reading!

Kenny

kenny@ggauto.repair