lazyboi808

Hey guys. I noticed when we were dynoing her and just driving her around she seems to misfirer at WOT in 3rd through 6th. When we tossed her on the dyno she ran good until upper rpms we noticed she's hitting 10.5 afr at WOT in upper range. Would that cause it? Or spark plugs bad? I have msd coil pack on her now could that be it? I can go like 75@ throttle and no misfirer but any more she does. All help would be great and one more thing. I'm debating another tune. Mail order from Texasspeed. That's were the motor is from and was tuned for nitrious but never used. All help would be great guys. Thanks again. Aloha!

NBM-LS1

iTrader: (7)

Thats a pretty rich air fuel ratio. You normally want to shoot anywhere from 12.9-13.4:1 on your afr for best performance. I think thats correct?

Your tune may be off.

Correct me if Im wrong guys.

travismcgillsdaddy

you made need to regap the sparkplugs. i had a similar problem with one of my old mustangs.

lazyboi808

You guys think I should try a mail order tune from texasspeed or vengence? Or replace the plugs? I don't have anyone to tune my car or I would get the hptuners system. I also noticed when I just replaced my o2 sensors I only have two. I thought I'm spoused to have four? Maybe when it was tuned with efilive before they deleted them? Lol thanks guys an is hptuner easy to tune yourself?

LS6427

iTrader: (2)

Things that cause misfires:

Clogged fuel injectors
Leaky fuel injectors
Spark plug wire(s) touching any part of the metal exhaust manifolds, or even banging up against them while driving/shifting/accelerating.
Bad plugs
Improperly gapped plugs (N/A .050 Nitrous .035-.040)
Spark plug wire not snapped all the way into place on the coil and/or the boot
Bent valve
Worn cam lobe(s)......(I think......)
Fuel pump not being able to maintain pressure in the upper rpm's
Bad gas
Dirty MAF.....because the MAF comes into play when you go WOT
Bad 02 sensor(s) or bad wiring/plugs

Start there.............

Since it doesn't happen until the higher rpm's....I'd go with one of the bold selections above.

.

lazyboi808

Thanks bro, yea i just changed the 2 o2 sensors and put a walboro fuel pump with 42lbs green top injectors, and fast fuel lines and steel braided lines..so Im pretty sure its not the fuel, im goin to chech the wires and plugs next. i really feel that the tune is whats causing it, when we dynoed her she spun 494rwhp at 10.5 afr at wot, and it was smooth but would misfire at upper rpms. i think if i was able to pull fuel and adjust the timing a bit, it will fix it, the motor was built an bought from texasspeed, less then 10k miles. but the plugs were never changed since then. being its a 98 im limited to tuning managment ive learned. you think a mail order tune from texas or vengence would help?