I have a 1989 F150 XLT Lariat with a 351w EFI. I currently have a C6 3AT transmission in it. I want to replace it with something a little better. I have been reading up and someone said a E4OD was a good replacement, especially being a successor to the C6 and having overdrive. Would the E4 be a plug n' play or would I have to make any modificatioons? Thx.

 

I would leave the C6 in there. The C6 is not electronically controlled like the E4OD. The C6 is hydraulically controlled. .If you are seeking better mileage, you are better off getting something newer. Your 89 with a 5.8 is not going to get decent mileage no matter what you do to it. It's a project not easily done and that would not be worth doing.

 

Finding a donor truck would be ideal. For an E4od swap, you'll need a new ecu and harness, along with the wiring behind the dash for the overdrive cutoff switch. I would assume you'll need a trans cross member and driveshaft as well. But the electrical will be the hard part for this swap. An AOD might be a better option since it has an overdrive gear, but is not computer controlled, the harness for the MLPS/neutral safety switch/reverse light switch is different, but that would be the only real important wiring issue. But ford didn't put AODs behind a 5.8l in any trucks from the factory, and there might be a reason for that. I also have not seen an AOD in a 4x4 configuration before.