The other day I got the pleasure of working on a 2008 SuperDuty with a 6.4L under the hood. All I am told when I am handed the ticket is that the customer wants the exhaust leak fixed. Wonderful. When it is started cold, you can hear the leak as well as see smoke coming from back by the firewall. A quick peek through the fender opening reveals a exhaust manifold leaking but the rear pipes are also suspected. In our shop, we pretty much pull the cab for a lot of different repairs. Its rather easy.
I get the cab off, see the exhaust manifold leak but rear pipes look good. I replace the exhaust manifold gasket, torque all the pipes down to spec, and reinstall the cab. I start it up and do not hear a leak, so I take off on a test drive. The truck falls flat on its face whenever half throttle or more - so I wonder, what did I do?
The truck comes back into the shop, and I run IDS on it and get the dreaded P0088 code for excessive fuel pressure. Ford has a TSB referencing this code so I follow the repair procedures (a reflash of the PCM) then retest drive but experience the same results. Sounds like the truck is going to need a new high pressure fuel pump.
We end of talking to the customer and find out that falling on its face was the issue all along. He just assumed, and heard from other mechanic buddies, that an exhaust leak can cause that particular issue. His exhaust leak did need to be repaired, but he could have saved valuable money in the long run. In reality, this is a life lesson for both the dealership and the customer. The customer should learn to have diagnostics performed to verify the cause, and the dealer should learn that the customer isn't always right.