I'm going to try to explain this without sounding too stupid. I bought a 99 Lightning wrecked its all fixed and looks great, but it does'nt run well. The engine compartment appeared stock when I bought this thing but after looking closer and finding things, number one the lower blower pulley is 8.75 inches in diameter I think from looking on here that stock should be 7.5? The second thing I found is from the factory airbox the hard tube where the MAF sensor is located is a larger diameter then the box opening and has been sealed to the factory box but it is not the factory setup. The problem I am having is if you roll into the throttle slow its not terrible but if you go to WOT fast it bucks like a mule and sounds like it is running on 6 cylinders. (starving for fuel?). There is nothing unhooked or wires cut. It has the stock exhaust. I unplugged all of the COP's one by one with the engine running and they all had the same effect a slight miss until plugged back in. I have driven these before and this thing just isn't right. Now for what I have been trying to ask what can I do to get this thing running reliably without spending a fortune will it require a computer chip or reprogram and if so what do you recommend. Any and all help would be greatly appreciated. Sorry this is so long winded hopefully someone can understand my ramblings. Thanks in advance, Roger

 

With out a MIL it's going to be tough to diagnois. First thing, I would check for vacume leaks, it's possible a hose was broken or damaged during the wreck. Next i'd take a look at the fuel pressure, to be sure the feed and return lines were flowing and that the pump is building sufficient pressure. After that, it's time to hit up the forums for a stock MAF and pulley on the cheap.

 

Change the fuel filter if it hasn't been changed recently. What you are describing is a symptom of a fuel system that can't keep up when suddenly placed under load. The most common cause of that is the fuel filter. I change mine every year regardless of mileage, which is typically under 2k per year. You need a special tool to do the filter; you can get it at any parts store.

 

Yeah, I agree it seems to be fuel related. I checked the vac lines and grounds even under the dash to see if someone unplugged something and that all seems to be in order. I changed the fuel filter this afternoon and it seems to be a little better ( the other one was in need of a change for sure it was plugged ) I also filled up with 93 octane and put a can of injector cleaner in the tank. The last trip I took down the road it runs real nice until the boost get to 10 or above and then it starts stuttering (you can feel it in your seat) if you give it a second it will start pulling again but you can still feel the miss until you get back down to mid boost levels. It almost feels like a bent driveshaft if you know what I mean, but you can here the miss in the exhaust note.

 

The fuel pump resistor/relay might also be stuck in the low flow mode so it doesn't kick the fuel pump to highspeed.

 

Mine did the exact same thing recently, turned out to be two bad coils. They supplied enough spark at light throttle/low boost levels but at WOT it would buck like crazy.
Greg

 

Could be the low/high resistor for the fuel. It's located up behind the front bumper. Looks like a white ceramic piece. This kicks the fuel pumps on high when you go into boost.

 

Thanks for all the input I really appreciate it. I got it fixed today. Turns out it was a bad coil front left side it would only act up once in a while and more so the hotter the engine got. It says alot for these engines that it would run as well as it did on 7 cylinders. Thanks again, Roger

 

Glad I could help.
Greg