engine revs/runs rough

[scoutbuff]

So I have a 88 Bronco ii. It has a newer motor with about 15k on it. Since the swap it has done a weird run/miss part way thru warm up. It feels like it not getting spark or something. It doesn't do it cold or completely warmed up. only about 1/4 way warmed up. If in a hurry to drive it can hardly get out of it's own way and barely accelerates. It has a complete tune up on it. to include plugs, wires, cap, rotor, fuel filter, oil change. Yet it doesn't change anything. At a loss and need some ideas.

 

[RonD]

Fuel injected engines can't use a Choke plate, no jets to suck extra fuel from, but a cold engine needs more fuel, richer air/fuel mix, to stay running.
So all fuel injected engines have an ECT sensor, engine coolant temp sensor.
This is similar to the 1 wire temp SENDER used on all water cooled engines to run a temp gauge, but the ECT is a 2 wire SENSOR only used by the computer.

Computer sends ECT sensor 5volts on 1 wire then gets back 4 to .5volts on the other.
3volts is cold, under 1 volt is warmed up
If your ECT sensor is reporting cold engine(3v), as it should, when engine is cold but then jumps to under 1volt before engine is warmed up then engine would struggle to stay running until it did warm up.
You can test these with a volt meter, but you can also buy a new one for $7, so.........