so i put on a straight pipe so my truck could sound cool. now it runs like crap. It runs fine when its cool but after it warms up it runs really rough up until 3000 rpms it shifts late. IVe had people tell me that it could be a bad fuel injector, spark plug, or ignition coil. Ive had people say that the motor doesnt have enough backpressure. I have no check engine light on and someone put a code scanner up to the computer and no codes were being activated or triped. I dont want to weld the muffler back on but i cant even tow anything without any low end torque. Ive already reset the computer and that didnt help. ONe other point of interest the check engine light did flash for about 20 seconds the day i had it done but then it stoped and hasnt sprung up since. Please help me i have no clue i dont want to put the muffler back on if its not the problem and i dont want to have some other place hook it up to diagnostics for 70 bucks to find nothing wrong. What do yall think

ben

 

it really sounds to me like its your cop boots letting water down onto the plug making it miss.and that's not a hard job if you haven't tried it yet you just have to take your time and do it right. mine did the same thing last time mine was missin the mil blinked for a while and then went off for a week and finally came back on after i drove the ***** out of it to make it come on.it won't cost you anything to check it so you might as well try.another thing to check is the cop.if you have a ohm meter check across the terminals it should be around 5-10 ohms i think

 

usually when the CEL flashes it means a miss. Now that it is not flashing and the truck runs like crap it could mean you have a bad plug or coil. My bet is a fowled plug.

the straight pipe is irrelevant.

good luck-

 

What engine do you have? I'm thinking the muffler shop messed something up and the O2 sensor is misreading once it kicks in. The O2 sensor is bypassed untill the exhaust reaches a certain temp, in which that point it does its job. As far as the bad plug/coil or the other problems mentioned, it would seem like if that were the case it would do the same during cold engine temp situations. Give some more info on your truck, and how your exhaust was reworked. Did you cut your cats off?

 

Its a 1998 5.4 with auto tranny overdrive thats the only mod i have is the strait pipe. The cats are still on. I didnt think there were any sensors hooked up to the muffler. But if it was an engine problem any type of sensor or emissions thing wouldnt that trip the check engine light.

ben

 

p.s. way fast i have no idea what a cop boot is. I know engines but i dont know any of this modern stuff. I didnt weld the muffler my self a shop did it.

 

p.s.s. the muffler shop welded on a pipe that is smaller then the exhaust that is on it right now. just one size but as far as i know it should be alright.

ben

 

for everyone who is trying to help me i do appreciate it. I just wish i didnt half to do this now. Dont have alot of money to throw around right now.

ben

 

I'm not sure how the exhaust set up on a 99 is, but im sure its similar to my 98. From the factory the exhaust went came together downstream from the cats at a Y pipe. Was that Y pipe messed with or left? I ask because the O2 sensor on the passenger side was really close to that Y pipe, close enough that my muffler shop wouldnt remove it back in '99. You say the exhaust has a smaller pipe, how much smaller? I'm thinking taking it to a shop and have a professional scan the engine is going to be your best bet. If you take it to them when its acting up, then it'll definitely return some sort of problem.

 

its weird but its almost like its getting better. It doesnt shake as bad as it used to be. Its about a foot to a foot and ahalf after the y pipe. Like i said it was arleady on a code scanner and nothing came up. I supost i could change out the sensor on the exhaust or maybe just start replacing sensors and filters.

ben

 

When was the last time you replaced the fuel filter?? If you don't know, then it should be replaced anyway..... How's the air filter?

A "COP" is the Coil On Plug design of these new engines. Your 5.4 has a coil pack on top of each spark plug... No distributor... Really, a cool setup, but a PITA to replace if it's one of the rear ones.... When you have a miss or a sensor is going out, you will get a flashing CEL 99% of the time and the code will point you directly to the offending one.

I'd start with the above, as they are not that much $$. COP's run about $50.00 each and the O2 sensors are about the same... Fuel filter is about $15.00 and the same for the air filter...

Good luck!

Mitch