Hi i am new to the forums and have been having a difficult time with my 1993 F150 XLT 5.0L v8. The problem started after i got the truck from a friend who had it sitting in his garage. The problem began when the truck had no power and spewed smoke whenever you would strain the engine going up a small hill or something similar. The first thing i did was change the wires and plugs, after that didn't make a difference i pulled the codes and changed the egr position sensor and the egr valve. After that I changed the vacuum lines, and that didn't help, so i checked the plugs and noticed the #8 plug (drivers side far rear) had the electrode exploded and fused with the ground strap , so i replaced it and it didn't make a difference. After some thinking I decided to change the distributor hall effect sensor, the ignition module, and the fuel pressure regulator, which ended up not helping, also when i was timing it I noticed it didnt have the SPOUT plug, so i jumped it with a wire (made no difference). Recently the charcoal canister started flooding with gas so i plugged the hose that was causing the problem (probably flooded the charcoal canister because i deleted the rear tank and just plugged all the hoses, but I don't know), and as the tittle says when you turn the defroster on at idle, will either kill the engine or drop the rpms really low and if you leave it on the engine won't start until you turn it off. So now i'm at a loss and am here to hopefully get some much needed help, if anyone has any info please chime in as I would really appreciate it.

Ps. I am thinking of swapping the tad/tab valve behind the engine any info on weather that is a possibility would be very much appreciated, as the vac hoses leading to the TAD and TAB vac solenoids were completely sucked shut when i used standard vac hose so I recently replaced it with rigid pvc water tubing.

PPs. The engine has a majority of the spark plugs reading very lean, but fuel pressure is spot on.

 

unplug the AC clutch and see if that cures the issue...

 

Your having a spark issue if some sort....have you checked the alternator to see what voltage and amperage it's putting out...or it could just be a bad coil,ignition module,it has something to do with spark your engine runs at idle....and when you turn the defrosted on it idled real low or dies....when you turn the defrosted on the fan miter starts running and uses amperage from the alternator or battery..if the alternator is bad..do you have to jump it to get it started again....the voltage regulator could be bad.something us causing a drain on the voltage and the the ignition doesn't get enough power when you turn on the defrosted...and it running bad and not having any power,all point to an ignition problem..take the alternator to a parts shop and have it tested....if it's good,start checking the wiring and start with the positive and negative right at the battery..if it sat for a yr either cable could be corroded inside the black or red coating where you wouldn't notice it so peak them back a little bit and see what there...also could be a mouse or rat chewed some wiring if it sat a yr.....good luck to you sir...go back to the basics an engine needs two things to run...fuel and spark...your not getting one if them...and I'd bet it's the spark....I'll pray for you..your gonna need it...I wish you the best..you'll find it....