I have a 1993 4.0 ford ranger that was said to be good after getting a new clutch installed took it home no problem got home and tried to start it again and realized that it would just crank but not start. I had a extra inertia switch lying around from a old pickup same model and everything and swapped it out and still nothing. Ran a test and got code 121,522,542 i replaced fuel pump and also realized someone had ran a new power wire from fuse box under hood to pump which had pump running all the time when turning key instead of the few seconds. I got that fixed but still same issue. It will start perfectly fine on a cold start but after pickup has been running and shut off and trying to turn back on it will just crank. I soon found that popping the inertia switch and turning it on and right away popping inertia switch back in will help truck turn on but at a high idle. Has anyone dealt with this and can give me some info?

 

Welcome to the forum

121 (O,R,M) Throttle Position (TP) sensor out of range - TPS
522 (O) Park/Neutral Position (PNP) or Clutch Pedal Position (CPP) circuit fault - PNP
542 (O,M) Fuel pump open, bad ground or always on - - Power / Fuel Pump Circuits

Manual or automatic?
None of these point to, or would cause, a hard warm start

Because its a 1993 model computer I would pull out the computer and have a look inside at the circuit board, and plan on replacing the 3 capacitors regardless
They are blue or black, and will leak after 20+ years causing odd codes and no starts
Blue ones seen here: Ford EEC-IV

Locations can change even in the same years
Each will have a specific uF value, you must match that, and each will have a voltage value, like 30v, you can use a higher voltage value but NOT lower
So 16uF 30v Cap can be replaced with a 16uF 50v Cap
Each also has a + and - side which must be installed the same way, these types of Caps have a stripe on the side denoting "-" side
Take pictures before doing any desoldering
Its a $5 fix that needs to be done even if its not the current problem, because it will be a problem down the road

I had to do this to my 1994 4.0l going on 2 years ago, had on going issue similar to yours, but not exactly the same, since changing the Caps its been trouble free
Except for new O2 sensors over the years all sensors and even the fuel pump is original
O2 sensors are the only sensors that wear out, 100k miles or 12 years is their limit

This applies to all 1986 to 1994 Ford EEC-IV computers, in 1995 a newer computer was used, EEC-V and didn't have changeable Caps so you have to swap whole computer $$$

Also just a heads up
1993 4.0l has 2 O2 sensors, one on each exhaust pipe by manifold
The plugins for these are universal, so no left or right designation
If they are reversed there WILL BE running issues after warm up, when the O2 sensors are used, they are not used on cold start
I had a shop do my clutch, they reversed these
There is only 1 wire color difference in the 4 wires
Grey/blue passenger side
red/black drivers side

 

And by chance would you happen to know why popping off the inertia switch, turning engine over, and then popping back on helps it start but at a high idle after a warm start?

 

No, there would be no reason for that
Long shot would be Computer issue, it monitors the inertia switch, and runs the fuel pump..............but as said long shot
Open the computer and have a look at the circuit board, especially the 3 barrel capacitors, common issue on the 1990-1994 4.0l Rangers, had to swap out the 3 capacitors on my 1994 2 years ago