My '98 GT vert auto has developed an acceleration quirk that is driving me crazy trying to figure out. At 1/2 to 2/3 throttle the car accelerates fine in all gears. In any gear, at any time, if I try to give it 3/4 to full throttle, the engine all of a sudden bogs way down, won't take gas and I get some kind of flutter effect in my exhaust note. Very strange. If I didn't know better, I would say my cats are stuffed. But why the good acceleration at lesser throttle settings? Wouldn't stuffed cats effect all acceleration across the board? Need to put an end to this once and for all! Any suggestions?

 

Under full throttle the tranny isn't kicking down? Something definitely isn't right. CEL on? My guess would be a faulty TPS or the like.

 

check the fuel filter

 

also check for coolant along your intake manifold. Thats how mine started doing right after the crack in my intake got big enough to allow coolant to seep out.

 

I have this same problem... i have tried and tried and tried... NOTHING. I have replaced everything possible. And it still occurs. Im pretty sure every Mustang from 96-04 has this problem. I have heard from people with 98's, 97's, 02' 03's. Still nothing. I have tried for a long time to find out what is was and still cant figure it out. But i do know if you get a dyno tuned chip it takes care of it alot.

 

The fuel filter has less than 3,000 miles on it and I am not trying to kick down the tranny but rather keeping it in a lower gear all the way until manually shifting when needed. It seems to happen most around 4,000 to 4,500 rpm. Could my rev limiter somehow be reading my rpm's wrong and prematurely shutting me down? If so, what sensor actually reads the rpm's to let the rev limiter know when to shut things down?

 

If you still havent got it after a YEAR (LOL, J/K) Try this:
-K&N Air filter
-Lucas fuel system treatment
-check fuel system pressure

Good Luck!

 

To check and see if your cats are clogged, run the car for about 30 mins. after reaching normal operating temperature (should be done at night or when its dark out) check under the car and look at the cats, if theyre red or look illuminated due to excessive heat, then theyre clogged

hope it helps!

 

Good trick on the cats, looking at them after dark. I had an ignition problem on an old '68 302 2+2 and couldn't figure out the problem until one night I decided to lift the hood. I couldn't believe my eyes....all over the distributor cap were electrical fingers running back and forth. The problem was a cracked distributor cap. Put a new cap on and all my problems stopped. Also had a high rpm breakdown on another older Mustang and fixed it by putting on a new coil. I don't suppose some of my current problems could be due to bad coils? I did replace them with Accel Super Coils (2 on a '98) about a year ago. I wonder if those coils could be acting up? I have heard some bad stories about a few of the aftermarket coil manufacturers. Thanks for the tip on the cats.

 

could be a vacuum leak?....