Post transmission swap engine trouble...

[Emsant50]

So I replaced the M5OD transmission in my 94 xlt. Did the master and slave as well. Did it twice actually because I'm an idiot and didn't r+r the slave the first time. Drove it to work this morning and for the first few miles it was fine. Then the throttle response got bad. Low power. Pedal to the firewall and no change. So I took it easy to work and it would randomly pin me back and start running normally. When it did, as long as I didn't let off the pedal it would stay. Otherwise it ran like garbage. Didn't have enough power to climb hills. I did start to smell gas after a while. I know I messed with the o2 sensor harness and unplugged two spark plug wires to get at the top bolts out of the tranny. I reconnected all of it after but I wonder of that affected it. If anyone has had a similar issue and has any guiding points id love to hear them. Thanks.

 

[gmanpaint]

Man, all that work, and then this happens. Bummer.

I would just start going over everything with a fine tooth comb. Get under it, trace the harness to make sure the O2 sensors are plugged in right, check the vac lines, check for a blown intake gasket, make sure all the pug wires are in proper firing order, and boots are tight, check the coil pack connectors, the Maf, basically every connector on the engine harness you can find.

Weird things happen on these older rigs when wrenching on them. Fuel pump might have decided to say, you know what? I'm tired, and I'm out of here!

More than likely, it's something simple from the trans work, and you just haven't seen it yet. Keep looking, grab a good flashlight, a friend, have a sammich or two, kick the tires, and it will eventually tell you I'm sorry, this is what's wrong.

 

[boominXplorer]

Make sure you didn't flip flop the o2 sensor wiring side to side. Also check for pinched wires. Do you have any codes?

 

[TxCowgirlInCo]

Also it sounds remote and not hugely likely, but since the Bellhousing was down, did you replace your clutch, pressure plate, flywheel? If not, did you use any shims at the engine backing plate when mounting the Bellhousing back up? Most likely something did get knocked loose or something, but anytime I hear major drivability issues after messing around in the trans clutch is the first thought everytime. I had a clutch that intermittently would alternate btwn slipping and dragging/ binding up bc of a Bellhousing misalignment. Good luck!

 

[410Fortune]

could be a bad fuel pump from sitting? Sounds fuel related?
Check psi at the rail if all else checks out with the wiring

 

[Emsant50]

Fortune you are right. It was bad gas. When I put gas in after I finished, I put in 93 because the station was out of 87. The 4.0s don't like that octane I guess. Once I burned through it and put in 87 I was good to go. Couple months later still running smooth as.silk.