Motor drops power

[Aaron285]

I have a 91 ranger 4.0 that was fully rebuilt, some of the wiring and exhaust O2 sensors are not plugged in. The truck starts and idles perfect, but when driving from 2nd when into 3rd gear sounds like it drops 2 cylinders or runs like I'm going 30 in 6 th gear. What could cause this issue? Again, everything on the truck is either rebuilt or new. Except some wires are not connected. Truck was driven 1 mile to get fitted for exhaust, that is how I found out this issue. Truck still has no lights, bumpers, Etc.

 

[alwaysFlOoReD]

I'm not sure what the computer will do with no o2 sensors. Perhaps default to rich? Could be causing your problem.

 

[Aaron285]

I replaced/ installed 4 wire O2 sensor on the passenger side screwed into Y pipe. Am I missing another sensor?? The headers and Y pipe if have are aftermarket and have 3 locations on them for O2 sensors. 1st location is off driver side header, 2nd is driver side start of Y pipe and the last location is the one I mentioned I installed/ replaced sensors. Other locations are capped off. Not sure how many it had stock. And cannot find another plug for a 2nd sensor coming off harness but I could be not seeing it.

 

[Roert42]

I'm not sure what the computer will do with no o2 sensors. Perhaps default to rich? Could be causing your problem.

Definitely the O2 sensors that are causing this. I drove my mustang around a bit w/o o2 sensors when I did the exhaust and it did the same thing.

Idled fine then ran super bad when you tried to accelerate.

 

[Aaron285]

I can't find the wires/ plug on a wiring diagram fro the 2nd sensor. anyone have any pics of the sensor locations on the pipes and where the plug wires trace back in the wiring harness???

 

[Roert42]

I can't find the wires/ plug on a wiring diagram fro the 2nd sensor. anyone have any pics of the sensor locations on the pipes and where the plug wires trace back in the wiring harness???

I was just looking at a schematic for a '91 ranger custom w/4.0, looks like there is only one sensor that I can find. However, there is a 10a fuse for the sensor, located in position 18.

Maybe check that.

 

[Aaron285]

Fuse is good.

 

[Aaron285]

Can you post that schematic?

 

[gaz]

Aaron:

If you plugged in your sole O² sensor, then reset your computer.

1) unplug your negative battery cable for 20 minutes
2) reconnect your negative battery cable
3) start your engine

 

[Aaron285]

The battery cables are removed every time the truck is not driven due to a short somewhere that kills the battery. Ill try what you said. But it seams to be something different. maybe vacuum problem?? The motor/ truck idles good on start up, then out of the drive way all is good thru 1st gear, and 2nd is good till about 3500 RPMs then it seams to loose all power and runs rough, into 3rd it feels like its funning on 3 cylinders. I was in 3rd running rough and let of the gas for about 2-3 sec and then re applied the pedal and it ran smooth for about 2-3 seconds then immediately back to no power. and then at lights the idle seams very low and like it may stall. but doesn't.

 

[bobbywalter]

Sounds like a possible maf issue or intake leak.

False air somewhere making for load table issue unless your fuel is laying down on volume...or both. All the PCV in place?...big vacuum lines ect?

1st thing...get all sensors hooked up

 

[bobbywalter]

This assumes good injectors plugs and wires.

 

[Roert42]

I can't post the whole schematic, only individual pages. Pennsylvania Library has access to MotorSelectline, like an alldata type website. Might check on your library's website.

 

[Roert42]

These seem to be the pages that are related to the engine sensors

 

[bobbywalter]

I can't see those. But there are many changes for the 4.0...


The earlier even had baro sensors that sometimes are mistaken for map...and no hi speed data link can in the OBD1 plug critter.

Aerostars had weird stuff to.

If you have a later pcm looking for cmp on a older setup this can pull timing too.

So maybe a mis match that way.

Wiring and sensors and codes need to be knowns.