Diagnosis is a challenge for any shop. Sometimes things can get even more complicated by a previous repair, or a part that has been recently replaced. This case involves both of these scenarios. After all, we really want to believe that a new part is a good one, right?
The 2005 Ford Freestar arrived to my bay with 120k miles on the odometer and a complaint of intermittent neutraling and shifting issues with the transmission. A quick pre-road test inspection revealed brown and varnished transmission fluid. Although there was no check engine light on, there was a code stored in memory, P0340. This code is for a camshaft position sensor fault. I wasn't too concerned with the code itself; the customer had reported that this sensor had been previously replaced by another shop, so it was possible that the technician had forgotten to clear the codes after the repairs. A visual inspection revealed a very new-looking cam sensor.
I cleared the codes and set out for a litt le windshield time. I noted that the transmission had a delayed engagement when cold. It also had a ?are on the 1-2 shift. The check engine light did not illuminate at all, and when I got back to the shop I retested for codes and there were none. Based upon the lack of any indication that this could be an electrical issue, and the ? uid condition, I recommended we replace the transmission with one of our remanufactured units.
The reman unit was installed, so I set out for a post-install road test. I went two or three miles to get to the interstate with no issues at all, and the transmission was operating perfectly. As I traveled down the on ramp and merged onto the interstate, I got up to cruising speed and still had no issues at all. As I accelerated up an incline in the roadway and as the transmission downshifted to accommodate the hill, the van suddenly nose-dived and lost power. I also heard a strange chirping noise from under the hood when this occurred.
After this initial power loss, operation returned to normal. However, I was able to replicate this condition on an intermittent basis over the next eight miles of driving. Within that time, I got it to occur about four more times. In the course of doing this, the check engine light illuminated. I again retested for codes and had found that the P0340 had indeed returned, so I went back to the shop to perform further testing.
As the van idled in the bay with the hood open, nothing seemed out of thee ordinary. If I accelerated the engine the chirping that I had heard on the road returned intermittently. I had an assistant take over the accelerator duties while I poked around the cam sensor with a stethoscope. Sure enough, the noise was being generated by the cam sensor.
I pulled the cam sensor o? of the drive housing to inspect it. There was no sign of internal damage to the sensor. I decided to then pull the drive housing (synchronizer per Ford nomenclature) from the engine so I could inspect it more closely. I brought cylinder #1 to TDC, marked the housing and pulled the synchronizer for inspection.
Inspection revealed a very worn synchronizer shaft and housing. This was allowing the shaft to have lateral movement that was creating internal contact and causing the squeaking noise. After researching this further, I actually found out that this is a relatively common issue for Ford. Also, a genuine Ford cam sensor comes as a synchronizer assembly, with both the sensor and the housing. What usually happens is that the shaft wears and allows the ?window? to contact the sensor causing noise, and ultimately, breakage. The previous technician had only addressed the failed sensor without addressing the root cause: the synchronizer.
This case just goes to show that just because the part is new, it doesn't mean that it's good. Fortunately we were able to make a happy customer at the end of the story, which is what's most important anyway.