so my 1993 f150 v8 5.8L doesn't start every once i a while. it's not all the time, but probably 50 percent of the time. the engine cranks fine so i don't think it's the starter and it has the dual fuel tanks so i don't think it's a fuel pump issue since neither tank works. any suggestions as to what the problem could be? thanks

 

Have you checked for fuel delivery and spark when the engine won't start?

 

no, how would i go about doing that?

 

For spark, you can remove one plug at a time and reconnect the plug wire to it and let the bottom of the plug rest against something metal. Turn the engin over and see if the plug is sparking.

For fuel, the "simplest" way is to pull the wire from the coil to the distributor and turn the engine over. Then, remove the plugs one at a time to see if they are still wet with fuel.

 

have you been in deep mud or water? i did that once and dirty water plugged the exhaust up to the first converter

 

A good way to check if that is an issue is to disconnect the exhaust from the catalytic converter back.

 

no, i haven't been in anything deep, i did take it off roading last weekend but the problem was going on before that. it's a pretty strange problem, sometimes it starts fine, other times it doesn't start at all. i replaced the ignition coil one day when it wouldn't start and after i did that it started fine for a couple days, and then it wouldn't start again so i figured i would check the plugs and wires that i replaced like a month or so ago. one of the wires wasn't on all the way so i fixed that and i pulled one of the plugs that i had had an issue getting in right and the gap had gotten much smaller than i set it to so i fixed the gap and put it back in right and it started up fine. then like 2 days later it wouldn't start again but i didn't have time to work on it, but then a couple of days later my dad decided to drive it and it started fine. i don't really know what the issue is... my thought is that the fact that the spark plug gap would change might be a clue, any ideas as to why this would happen?

 

Was the gap getting smaller? Are you sure you have the correct plugs in the engine?

 

well i got the plugs from advance auto, they are autolite i think, the guy said they were the oem part. do you think the battery could be causing the issue? i know that normally if the battery isn't working the engine won't crank at all but when i drive i have noticed that the battery gauge will fluctuate a lot and i didn't think this was normal...

 

Well theres a few things ide check electricly first, and then fuel and so on.
Do you have a DMM (Multimeter)? check for static charge on the battery. if it is less than 12.45V than you have a low battery for some reason. If you have one, or know someone who does use a VAT to check your alternator draw, starter draw, and battery output. If you cant get ahold of one than take it to your favorite shop, or dealer and they most likely will have one. Ide bet that it is a bad ground though. most of the time on older well used trucks the ground to the block gets corroded, or comes loose thus only allows starting when its just right, or moved, or even if it is wet or humid at the time!