joemilli

Hey everybody this is my first time posting...I have a 1996 GT with 82,000 miles, I just bought the car2 months ago. From what i saw and was told, the car came with 3:55 gears, a Dynomax catback exhaust, Eibach springs, and i was told it had a chip of some sort (which I don't think is true because the speedometer is off). Fist thing I did was oil change and new Autolite plugs. After a few week of having the car I had a FordRacing king cobra clutch installed, i installed a BBK CAI, & I decided to try the new Mac Prochamber H-pipe which installedabout10 days ago. I also replaced the passanger side front(upstream)O2 sensor w/ a new Bosch sensor (the old one crapped out on me).

When i first bought the car it ran fine. I noticed though that when i pushed the car,Ifelt some hesitation, or a very slight skip in the acceleration. When i got around 3900 - 5200 rpm. It didn't seem that that bad &I figured the guy had the car sitting for about3 months before i bought it, so maybe it would take some time before it ran completely smooth again. Next I had the FR clutch installed at a local shop, and about a week later I installed the Mac Prochamber.After the install i left the back (downstream) O2sensorsunplugged, I was told this wouldn'taffect the car's Air / Fuel delivery.For the first week i didn't run it hard at all, I wanted everything to break in nice and smooth. But after that week it was time to have some fun so I took it out to some new streets their building, buncha of 1/4 mile straight aways with no people or houses, out in the middle of nowhere..anyways i started getting on it and i started in 1st got it up to 5600....power shifted to 2nd and floored it and i felt alot of hesitation and the car was bogging down ..and also I heard what sounded like an exhaust leak, a deep sputtering, coming from near the motor..this same thing happens every time every time i go WOT or close to WOT .. Weird thing is I'll start the car in the morning it runs good, the hesitation isn't so apparent, it warms up a little i hit it and more hesitation and bogging and that sputtering sound. Keep in mind I onnly hear that sputtering when i try to accelerate fast, when i run it through the gears nice and easy it runsgood.
I threw the car back up on jackstand and cheacked for exhaust leaks but found none. I then took it to a local shop had them throw it on a lift and had the mechanic check for leaks he found none...he didn't drive the car at all but just had it turned on while it was on the lift..So im pretty confident the car doen't have any exhaust leaks. I was hoping someone could tell me what would be causing this problem. could it be the downstream O2's being unplugged, a bad fuel injector, could it be running lean somehow?? I'm not getting any OBD codes axcept for the expected downstream O2 sensor codes. Someone PLEASE help me!!!!!!!

ajmodelski

Does it bog down only when you are driving? IF you rev the engine when you are just sitting still, does it do anything different? IF it doesn't have any problems reving when you are in neutral but bogs down when you have it in gear, and only when the car is warm, It is probably your plug wires and/or plugs.

cahtr6

sounds like a popped plug as in the spark plug blew out of the cylinder head (common on 4.6) check all your plus and plugwires to see if one is loose.

AmericanRicer87

I had the popped plug, i have had my coil on plugs go out and cause this, i ha my egr blocked off not knowing better and had it running a little lean and had low power. I have had 02 sensors go out and through a light, I really wanna say i'd look for spark probems, try a fuel filter too even air filter.

4.698GT

Is the prochamber the off road varient without cats? If so, your gonna need some MILs. Without the car will go into limp mode and run like ultra poo

contentsunderpressur

How long did the car sit up? If it sat a long time you may need to run a few tanks of gas through it to clean it out. If you can rev it up with no problems in neutral but it misses while under a load then it's a spark problem for sure. The two down stream o2 sensors do not affect drivability so no worries there. All the mil eliminators do is turn the check engine light off. The car makes adjustments from the readings it gets from the two upstream sensors so your good there as long as there operating like there supposed to. The 96-98 gts are bad about burning up coil packs too. I'm guessing that it didn't throw any more codes than the downstream o2 sensors so it's a good possibility it's bad gas or a stopped up fuel filter.

SmallFeesh

No way... when you blow a spark plug it is loud as ****!

Replace the fuel filter, check the Air filter, MAF, etc. What kind of gas do you run?? Ford spec for 99-04 is Regular 87... check the owners manual... i am unsure on the older 4.6's... your fuel system could be fouled as well... but I would replace the fuel filter first... I remember now you said you instaled a CAI, so air filter is pretty much out of the question. Could be ignition as well....

BTW... don't mess with the font and boldness... just makes it harder to read! We are all used to the plain ol' stock font!

Chris98Gt

Did you gap your plugs right? My car had the same symptoms when I had way too much gap in the plugs.

joemilli

Thanks to everybody that posted...I'm gonna check the plugs out today. i gapped them before i put them in so i dont think gapping is the issue, but ill recheck them anyway, better 2 b safe then sorr, right? And yes the car sounds good when I rev it in neutral, the problem is only when the car is under load. How would I check to see if one or more ofthe coil packs has gone bad?? Also what's a good way to test the plug wires to see if those are functioning properly?? I occasionaly run 91 octane could this actually hurt performance?? If so I'll go back to 87 w/ no complaints..

and last but not least the mil debate. I have seen a debate over this. Will the downstream (back) O2 sensors being unplugged hurt the performance of my car in any way?? I have an off-road (no cats) Mac prochamber, no Mils. I heard mils crap out and I'm just saving my cash for a tuner. alotta people sayit does others say it doen't can I get a finalanswer on this PLEASE!!!

Anywaysi want to say thanks again for the help, i really appreciate it guys.

on a side note: don't post if you dont know what the hell your talking about, it does no good to anyone if you give out wrong or incorrect info to someone,, it's frustrating and just waste everybodies time..= ) thanks again everyone...

SmallFeesh

Ford states in the 99-04 manual:

"Your vehicle is designed to use"regular" unleaded gasoline with an (R=M)/2 octane rating of 87. We do not recomend the use of gasolines labeld as "regular" that are sold with octane ratings of 86 or lower in high altitude areas."

"Premium unleaded gasoline is not recomended because it may cause these problems to become more pronounced"(starting, rough idle or hesitation driveability problems during cold start)

"It should not be necessary to add any aftermarket products to your fuel tank if you continue to use high quallity fuel of the recommended octane rating. Aftermarket products could cause damage to the fuel system."

It really depends on what the previous owner used alot... and if he had a tune or not... IE: if he had it tuned for 91 it would run like crap on regular... if it has had no tune then follow what ford says in your manual! Have you changed your fuel filteryet? Being the car was sitting for awile, and that is an item commonly overlooked, I would DEFINATLEY change it regardless if it needs it or not!

Propper gapping on the plugs is also a possibillity... I don't know alot about the coil packs on these cars so I can't help you there... but I did notice you mentioned you changed the spark plugs... did you change the wires as well?? changing plugs does diddly if the wires are bad!