4.0 ohv engine choking

[1994fordranger]

engine is choking on my 4.0 ohv, will be driving and the rpm's will suddenly just drop by a few hundred rpms, feel as if i tap the brakes for a split second, it randomly does it, will keep doing it and if i dont keep revving the engine it will stall, i have so far cleaned the maf, replaced the TPS and changed the fuel pump and fuel filter, any ideas?

 

[RonD]

MAF is the most common issue for that type of thing on the 4.0l
Yes, TPS would be suspect as well
Fuel pressure after those

You seem to have covered the bases

I would check the voltage at the MAF as well, info is here:
http://www.therangerstation.com/tech_library/CleanMAF.html

Does the CEL(check engine light) come on when you first turn on the key?
So you know that part of the computer is working
And do you get a CEL when stumbling happens?

The Fuel Pump relay on the Rangers can be an issue, usually they just stop working, but it could become intermittent.
Computer grounds this relay to send power to Fuel Pump, and it goes on and off according to Speed, RPM and TPS

There are 3 relays in a row EEC Relay, Fuel Pump relay and WOT(wide open throttle) Relay.

The EEC relay powers the computer(EEC) and most other 12volt engine systems when key is on, it also powers the Fuel Pump Relay.


Inside the cab in the passenger foot well is the inertia switch, 12volts IN(from Fuel Pump relay) and 12 volts OUT(to Fuel Pump)
In case of an accident inertia switch cuts power to the fuel pump.
Anyway if you were to hook up a 12v test light to the inertia switch, you could watch when the computer was turning fuel pump on and off, while you are driving.
So if it starts to stumble you could see if light was still off and its starving for fuel.

There are a few other things, like the coil pack or the CKP(crank position) sensor.
CKP sensor rarely fails, and usually it's an all or nothing failure, so a no start not a stumbling, but it's wiring runs from the front crank pulley up and over the top of the lower intake and into the main harness, so a wire issue could be intermittent.
CKP sensor tells computer the crank is turning so start spark and fuel, it also IDs #1 cylinder for timing

Coil pack losing it's 12v would shut the engine down like a switch was thrown, but not sure it would come back up, so.........

Computer issue.............well it does happen, really no way to test these.
I would try to read the codes, even if CEL is not on the computer will still have "history" codes, or at least respond to a scanner, or the "jumper method"

 

[1994fordranger]

people have told me to check engine light, no the check engine light doesnt come on instantly it takes a few minutes of running before it pops on, where do i plug in a computer to check it? i dont know where the plug is, but i will definantely try that thanks for all the help it is appreciated, this truck has been giving me way too many problems i just wanna get past them and move on

 

[RonD]

OBD I port on the '94 should be in the engine compartment between Power Box and Firewall, so drivers side.