Hello,

First time posting. I would go to a mechanic but I'm low on cash right now and wondering if someone could help me pinpoint a problem or the problems. I don't know much about engines etc but here is what is going on.

It started a few weeks ago, idling at a high rate until the truck was warm. Everything seemed to start up fine. A week ago the truck started having trouble taking gas when accelerated to around 1500 rpms, but it never shut off. . Then it started to have trouble starting when the engine was cold, it would take 2 or 3 attempts and idle at a high rate. Now it seems to start randomly, cold or warm varying back and forth. When it starts right up and idles, you can push the rpms to 1200-1500 and it dies. If you are moving and it hits 1200-1500 rpms, it will die while moving.

Thank you for reading and responding, and you may have to dumb it down pretty simple for me to understand you.

 

Welcome to the forum

I have a 1994 Ranger 4x4 with a 4.0l engine

A little confused with your post

It should idle at 1,000-1,200 when cold, that is normal
It will start to drop down as engine warms up, and be 625rpm with manual trans and 750 with automatic, when fully warmed up

First thing I would do is to check battery voltage with engine off and then with engine running, low voltage causes lots of issues
Engine off battery should show, 12.3 to 12.8volts
New battery is 12.8v
5 year old battery 12.3v <<< time to shop for battery sale

Start engine, should show 14.4v at least, 14.4-14.9v
If not alternator is failing/failed.

The idle is computer controlled but computer uses the IAC Valve on upper intake
Good read here on how to clean an IAC Valve: How to: IAC valve cleaning thread (w/pics) | Ford Explorer and Ford Ranger Forums - Serious Explorations

Vacuum leaks, also cause problems, after engine is warmed up, unplug the 2 wires on the IAC Valve, idle should drop to 500, or engine may even stall, either is good, no leaks
If idle doesn't change then there is a leak, you just have to start checking hoses

The MAF(mass air flow) sensor needs to be clean every few years, especially on the 4.0ls
How-to is here: Ford Ranger Mass Air Flow Cleaning, Removal and Installation

MAF is on the air cleaner housing connected to the BIG air tube going over to the upper engine, 4 wires connected, 1995 and up have 6 wires
Also check air filter, and engine NEEDS good air flow

Fuel filter is located in the Frame of the truck under the drivers seat area, not IN the cab, under the cab
This should be changed every 5 years or so, $12
If filter is clogged up then engine will starve for gasoline, so limited RPMs

And it could be the Fuel Pump in the gas tank is starting to fail, usually it will just quit one day, no start until it is replaced.
But it could start to lose volume, so it is still running just not pumping the fuel volume needed by the engine


Clogged exhaust system, any engine is basically an air pump, if you block the output then you stop the input, so engine can only REV so high and then can't suck in any more fuel.
You can use a Vacuum gauge to test for this, and other things
Or just use you hand or rubber mallet on COLD exhaust and bang on the Cats and Muffler to see if you hear rattling.
If you have a friend that can help, start the engine and put hand over tail pipe while friend REVs engine, you should feel if exhaust is clogged