lack of acceleration

[chris90deville]

I am having another problem with my 90 deville 4.5 My acceleration is horrible. for example when i am on the highway to get my car to speed up i have to floor the gas all the way down then start letting up off of it slowly and the then car goes. My gas milage is horrible! my average is 11.5 my mpg guage reads between 0 and 4 when i floor it and about 8 when im cruising unless im going over 40 at a constant speed then it reads 12-18. The car got way better gas milage when i bought it. I have a friend with an 89 deville he gets 26 on the highway. What could my problem be??? I have new plugs, wires, fuel filter, tps, Ecu, new ground wires,o2 sensor and a new idle control motor. Any ideas???, suggestions???

[maxwedge]

Have the cat checked for back pressure readings at the o2 port, may be clogged, if ok check fuel pressure or do that first.

[chris90deville]

I will check fuel pressure im sure its not the cat. I had to put my car in the shop when the ecu went out about a month ago to figure out what the heck was wrong with it. I paid 160 for them to tell me it was the injector drivers in the ecu and in the process they cut my exhaust before the cat im sure to see if that was the problem then they said it was already like that when i brought it to them and tried to charge me 5 hundred to replace the ecu. I replaced the ecu myself for 20.00 at the junk yard. I reported them to the BBB. I am now running a flex pipe from the back of the motor down to the cat. Fuel pressure was my first guess just wanted to get some more opinions. What does a bad ignition control module act like what about pick up coil? I just hit 170,000 miles i heard of these going 250,000 miles if you take care of them before you need a rebuild, true??? how much should a rebuild cost? what parts should i buy in the way of performance when i do get a rebuild to make my lac faster?? i dont know what performance parts are available for these 4.5s all comments are appreciated, thanks

[maxwedge]

There are no effective performance parts for that car. Usually a bad ign part of any kind will cause stalling or no start or severe misfire under load.