98 Expedition Shift Solenoid Issues After AC Service

[Fitz98]

Wife just took Expedition to mechanic for AC service.
98 Expedition, 5.4
After the service, she noticed the vehicle surging and "running rough"
Later the CEL came on. I believe PO750 code.
I called mechanic, he said all the AC work he did was up top and easily accessible, so likely a coincidence.
I cleared light and test drove and the problem was noticeable and CEL came back on.
I disconnected connection at shift mechanism at transmission and re-plugged. It looked clean and in good shape.
I moved around wires and pressed on connectors in the accumulator area on the firewall, cleared CEL and test drove.
Problem improved, but around 45 mph, the shift became erratic again and shortly after problems on lower shift range as well. No CEL yet, but definitely something is not right.
Where is the wiring harness connection for the shift solenoid?
It seems like the problem is in multiple ranges, so what would be the likelihood that the solenoid pack could be bad?
Any other diagnostic tips?

 

[OVERKILL]

Is the vehicle still surging and running rough? If so, that's not a shift solenoid problem, I'd try and remedy that first and see if it solves your other problem. Sounds like a vacuum leak or similar.

 

[Fla]

Yes, it sounds like there might be a vacuum leak but the generic code P0750 says that you have a bad solenoid "A". That is the generic meaning, I'm sure that a Ford manual will be more specific. I don't know about 2008 but my 2009 F150 5.4 does use a couple of electronically controlled solenoids inside of the transmission for shifting. But if this happened immediately after the service work then I will say that the mechanic very likely damaged a wire or a connector. Have you checked the fluid level in the tranny yet? That's a load of fun!

Unless you get an error code showing a misfire I would leave the coil packs alone! The computer is very good about picking up misfires so unless it is detecting any, leave well enough alone. If there are any misfires then the O2 sensors will also probably detect a problem.

 

[OVERKILL]

Unless you get an error code showing a misfire I would leave the coil packs alone! The computer is very good about picking up misfires so unless it is detecting any, leave well enough alone. If there are any misfires then the O2 sensors will also probably detect a problem.

This era of Ford are notoriously bad for NOT triggering a CEL for misfires. You need access to Mode $06 data to get the actual misfire counts, which could be extremely high.

But, if it wasn't misfiring before it went in, and now is, I'd suspect something to have happened during the service visit, hence the vacuum leak theory, or similar.

 

[2strokeNorthstar]

Check those old brittle plastic vacuum lines

 

[clinebarger]

10th gen & newer Ford trucks are notorious for the Trans Harness laying on the right exhaust manifold/pipe, Melting & causing shorts.

 

[Fitz98]

Thanks for the feedback.
It is definitely a shifting issue, the RPM's are clearly showing that as it is surging while randomly shifting back and forth between gears, but I wouldn't rule anything out...I am leaning towards electrical.
As a side note, I did take it for another drive with overdrive disengaged. That was better, but still not behaving as it should.
Also seemed to get worse over time...maybe temperature related...another argument for the electrical harness idea proposed by Clinebarger. Maybe it got pushed on to manifold during service?
I will have to explore...all a little tight back in there.
Its not just 1-2, it happens in 2-3 as well and is worse with OD on.

I checked fluids...all good, even checked for the strawberry milkshake in the coolant, but it is all good.

 

[Fitz98]

10th gen & newer Ford trucks are notorious for the Trans Harness laying on the right exhaust manifold/pipe, Melting & causing shorts.

You called it again!
This was the issue.
Problem Fixed... Thanks!

Problem fixed. Was definitely compromised insulation causing a short.
Used adhesive line heat shrink for insulation repair. I didn't think it would work, but for the wires that only had a little insulation burned on 1 side, I split the heat shrink up the middle, placed over the wire with the split away from the bad side and heated. At first it flattened out and then as the heat progressed, it wrapped itself around the wire and the adhesive bonded it. The seam was very small. I was surprised at this outcome. I thought the seam gap would be bigger and that it would not bond well, but the seam was hardly noticeable and the bond was great. I have a lot of confidence in this repair.
Adhesive Lined Heat Shrink
The other wires that had 360 degree burn on the insulation, I cut in an accessible location, slid adhesive lined heat shrink down for the repair, (I did a double layer on these repairs) then used adhesive lined marine heat shrink butt connectors for the splice with heat shrink over top.
New wire loom, reroute the wiring harness away from the manifold and then place this heat protective material over the loom to protect the loom from melting again and keep the wires cooler.
Heat Shield Wrap