stumbling hesitation possible misfire

[jklolkik]

I have a 93 with the 4.0 ohv with the 98tm casting heads(swapped heads a couple years ago) it was running fine then one day it was blowing smoke sputtering and died. Refused to start so towed it home. Got it home and replaced the head gaskets, lower and upper intake gaskets. Took it for a drive did fine till it got to operating temp. Starting having a stumbling almost misfire only at operating temp and at partial throttle. At wide open throttle it does not do it.

The fuel pump and fuel filter have been changed as I had alot of water in the tank causing a no run issue.

Can anyone offer any insite as to what could be causing this?

 

[RonD]

You have the O2 sensor plug-ins reversed

CEL(check engine light) should come on as well, with BOTH Lean and Rich codes

3 wire colors are the same on both 4 wire O2 plug ins
passenger side(bank1) should have a grey/blue wire
drivers side(bank2) a red/black wire

Thats the only difference in the 2 plugs

This happened on my 1994 4.0l a few years back
Ran fine until warmed up, because O2 sensors are not used until they are warmed up
Ran fine a WOT(wide open throttle) because computer ignores O2s at WOT, fuel economy is out, full power is what WOT means
Ran like crap after warm up and anything below WOT

My O2s plugs were reversed, easy to do, near each other on main wiring harness behind engine on firewall

So check that out first


Next check the Fuel Pressure Regulator(FPR) under back of alternator on lower intake
It has a Fuel line(return) AND a vacuum hose, check that hose for gasoline, replace FPR if hose has gasoline in it, its flooding out the engine
Cold engine doesn't mind a bit of extra fuel, neither does WOT

 

[jklolkik]

thanks Ron I will check it in the morning. thing that also stumps me is the o2 and and a couple of other plugs one being the camshaft position sensor? just behind the intake manifold was not plugged in along with the crankshaft position sensor? before i did the head gasket change. also the o2 sensors have had the same plug plugged in the entire time i have owned the truck although 1 was unplugged and it ran fine. But I will check the o2 plugs in the morning.

I also have a bunch of plugs and wires I could not find on the diagrams would you be able to help with that?

 

[RonD]

4.0l Cam sensor was only used on 1995 and up Ranger unless it was a Calif sold vehicle
But if you have the 3 wire plug in for it then it may have been a Calif vehicle, or engine was swapped

Engine wouldn't start without Crank sensor, would be the same as having an older engine with distributor unplugged

One O2 unplugged would have solved the Reversed O2 plugs issue as computer would only have one feedback sensor so would run both banks of the engine air/fuel mixed based on that, no conflicting signals, but CEL would be on the whole time

1993/1994 used the same wiring diagram/colors

Other wiring thats unplugged can be for Options that your Ranger doesn't have, in engine bay that can be for cruise or fog lights or AC
Also there may be a 3 wire plug at back of engine for automatic trans that would be unplugged if you have a Manual trans

 

[jklolkik]

Ok thank you. I just took my truck out for a drive after plugging the o2 sensors into the correct plugs and it did not have any stumbling. Now just need to figure out the other connectors so I can trim them or atleast label them