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I got a 1998 Mustang and when I got it it w
as sputtering at higher RPMs. I replaced the spark plugs and the fuel pump and it ran great and only sputtered around the 6k rpm mark. The plugs looked like it was running rich after I pulled them and referenced them to pictures. It ran good for about a week but it is now sputtering horribly at all RPMs. The car has been run on nitrous.here is the as with most all th mods -the nitrous which was a 125 wet shot: 1998 Ford Mustang. The body has 145,000 miles. The body is in perfect condition, meaning no body damage, and not even a single dent, but does need some paint work, as it is faded out in some spots and has some cracked paint on the front of the hood (very minor). The motor ha s a complete PI swap (heads, intake, etc), has a Magnaflow magnapak exhaust, upgraded Mass air flow sensor, injectors, and recent centerforce clutch, full suspension (high dollar) - coilovers in the front and the rear is set up with frame and sub frame connectors. It has a sct chip with 4 tunes. Have most receipts from work done. Even window tint receipts. It has been Dyno'd it made 340hp 411tq with sheets to prove it. Has a leather interior, with minor crackage on the driver seat, but besides that the interior is very clean. No cracked dash or none of that.
What do y'all think is the problem? Thanks.
 

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Have you tuned the ECM's fuel and timing curves..?
If you have a really hot plug in it with a lot of timing, the Nitrous will melt the insulator of the spark plug. If so, lucky it did rather than detonate and melt pistons. Try a 1 step colder plug.

Always read fuel enrichment on the base ring and detonation on the porcelain.
 

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Likely it's all the modifications. You have so many things done it could be a combination of the mods and your driving techniques. It might want you to drive it harder to keeps the plugs clean, who knows. If you want a fast car it's best to buy one thats fast without all the changes. Ford spent 100 million dollars on engineering to design that car. Then aftermarket guys played mix and match with chips etc. I would guess that the car is running rich due to the chips etc. That's fouling out the plugs and causing them to misfire.

1. Get an exhaust gas analysis done to see if it's running rich etc. Check the air filter and fuel filter too.

2. Check the ignition system to make sure that each plug has 50k or more volts depending on the specs. Weak spark means fouling plugs.

3. Check the fuel filter and fill the car with 91 to 93 octane fuel.

4. Buy a Porsche 911 like I did and stay away from American heavy metal. Lol

Good luck!!!
 

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May not have a clear answer but have you checked the fuel filters? I ask because you didn't mention it. I had a vehicle that I had many upgrades done to and had nothing but problems in the long run! Nitro is bad... Had some buddies that had it professionaly installed and they started having problems too. And the bad thing is that "IF" you have the dealers warranty, it will void it. Point is, sometimes too many upgrades will ruin your engine in time. Good luck...
 
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