1990MellowYellow

OK so here is the story on my 1990 Mustang Lx 5.0 i picked up just the other day. It sat for 2-3 years with out being driven. It runs pretty good it can be driven. So I changed the plugs with some motocraft plugs I just did some 8mm wires for now cause i'm short on money only 21 yrs old. I changed the oil, did a new oil filter. I took off the dizzy cap and cleaned up the rotor might need new rotor and cap soon. Ran better for just cruising but as soon as i wanna go over 3k rpm under load it just sputters. sputters alot under load and backfires. I'm stumped on what else to do. I was gonna do the fuel filter next. Any other ideas?

dawson1112

Sitting for that long , I would change the fuel filter , run some kind of fuel system cleaner through it for the next few tanks of gas. Probly at with time you may need to change the fuel filter again. Fuel evaporates over years of sitting and leaves a sticky brown tarnish.

1990MellowYellow

I just ran to the auto part store. Bought a fuel filter, dizzy cap and rotor, and some mystery oil to throw in the gas tank. I will throw some mystery oil in and some 93 octane. How long do you think it will take to clear up?

1990MellowYellow

It just missfires and sputters after 3200 rpm so im hoping this will fix the problem.

1990MellowYellow

So I changed the fuel filter the dizzy cap and rotor. It still is sputtering and backfiring after 3k rpm. i am kinda stumped on what else to do any ideas?

nitrous_bob

i hate to ask a dumb question...but......

have you double checked all wires are "snapped" on all the way ? firing order is correct ?
wires arent touching headers or crossed and causing mis fire ?

if it ran good before you gave it a tuneup...YOU did something. and mystery oil wont fix it

did you use platinum plugs ?

if yes...throw them away and start over with coppers

if none of that applies....gap your plugs down to .042" and see what happens

you might be pleasantly surprised, and put timing at 12* BTDC with SPOUT out

Maxwelhse

Here's another goofy question... Did you pump all of that old gas out before you started hanging new parts?

1990MellowYellow

I am not positive the firing order is correct i didnt change the order i just changed the wires and plugs. But one of the wires do keep slowly coming off. and they aren't touching the headers i made sure because the old ones were hitting them. It ran good for sitting so long but has had this misfire, and sputter under load. It had autolite platinums i threw those out and threw in some copper motocraft plugs. I heard 12 degrees for timing as well that was going to be the next thing on the list. I did not pump out all the old gas it was pretty much empty so i threw 93 octane and ran the old fuel out.

1990MellowYellow

Hey everyone i figured out my issue the rotor that was in it was the wrong size so i wasnt getting enough spark replaced cap and rotor and ripped sideways thru first and 2nd up my street