This is my 1st time posting on Ranger forums, thanks to everyone a head of time. Heres my ordeal. Im working on my dads 1998 Ranger with a 2.5 L 4 cyl 2wd. He started getting a light miss on the highway a few weeks back so I check it out for him. I sprayed some water on the plugs and wires found the the #4 spark plug boot had a hole in it and was arcing bad. I picked up some plugs and wires from autozone, the plugs are Autolite Plantinums "AP104" the plug wires are Bosch. I installed them last night and wow, ran horrible, I though maybe i cross a wire or something but firing order is dead on. I re did everything I did, I took the Upper plenum back off inspected the plugs all looked fine, I set the spark plug gap to .045 as specs said to set between .042-.046. To extra care to make sure every vacuum line was put back on in the right spot reinstalled everything same deal. Its driveable and once you get it going down the road it feels fine, doesnt feel like its missing at all. But it stalls out on take off sometimes and just shakes a misses real bad under heavy load. Anybody got any ideas where to start?

 

The ignition coil may be getting weak.
Try gapping the plugs down to 42 to see if it improves before throwing money at it.

 

did you use a rubber isolated socket to install them? if you are CERTAIN the firing order is correct, ohm out all the wires, and then remove all the plugs and find the one that the porcelain is cracked

 

^ good catch

 

i know those plugs arent fun to remove but its worth a shot...alot of 2.3/2.5 4.6/5.4 2 valve motors came in with customer installed cracked plugs

 

Good idea on checking the Ohms on the wires, slipped my mind! I did use a rubber insulated spark plug socket to.. I guess Ill do it one more time just to cover everything!

 

Well guys, I figured it out. I called a good buddy who is a Ford Tech and he asked me what diagram I was using to figure out the firing order and I told him its from Mitchell, basically an online manual for every car made, its a program I used to use when working a small garage. He said dont trust it, clean off your coil packs, there numbered if they are original and make sure there are routed by accordingly. Sure enough, the diagram i was using was wrong. It had number 3 and number 1 crossed up on the front coil! I feel stupid, but im glad thats all it was!! Thank you all for your insight!!!!!

 

That is the reason for changing spark plugs and wires one at a time. That way you never mix it up. Hey, I've had it happen to me before. Plus with 8 spark plugs and wires it can get crazy, but doing it one at a time its virtually impossible to mix it up.

 

before removing wires i use a permanent marker and write right side 1-4, left side 1-4 on the coil pack