Hello, I have browsed the forums and couldn't find a issue similar to mine so I made an account and am now posting. I have a 2002 firehawk. It has a built motor. When I bought the car it had a running bad issue that I determined was the fuel pump. I replaced it and it ran a little bit better. The issue I am having now is that it will randomly bog down and misfire and be down on power , then it will clear up. But when it clears up the throttle response is not crisp like it should be. Like when you jab the gas quick there is a delay before the engine tachs up. I put a scan tool on it and the computer thinks it is running lean so it is dumping fuel even thought it doesn't need it. Like dumping so much that it will burn your eyes sometimes. It has a MAF code but I have put 3 on there with no change. The alternator overcharges for a while and then it will come down. Put new 02 sensors on it with no change. New map sensor no change. Verified no vacuum leaks. I also added a ground to check if it was a ground issue. With no change. Also at about 4300 it has a misfire all the way to redline. On the scan tool both o2 sensors are stuck lean with short term fuel trims at 25 percent. Which is making it run incredibly rich. Sorry for the screen door post. Any help would be appreciated.

 

If it has a maf code and you've replaced it multiple times with no change it could be SD tuned.

 

with the maf unplugged it loads up really bad and becomes undrivable. I should also mention that for the first few minutes on cold start she runs fine. Once it goes into closed loop is when the problems start.

 

Unplug the O2, Voltage should now read around .447MV on a scan tool, If still stuck low....Short to ground in the harness or a bad PCM.

 

I checked voltage on them today. And the voltage is within spec. It sat around .445. I wonder if a coil going out would cause these symptoms

 

Have you have a good tuner look into what's really hapening Big Joe?

 

that is my next step as soon as my tax check comes in. I am just trying to make sure it isn't anything I have overlooked before I take it to them
the closest one is about an hour from me

 

Also in addition to my previous comment the car ran fine. The tune or nothing mechanical has been changed. That is one reason it is stumping me

 

It is showing lean because of the misfires.
An O2 sensor reads O2 content not fuel, too much fuel causes misfires and that puts unburned O2 in the exhaust.
The ECU thinks its lean because it is using the tables to squirt a measured amount of fuel and seeing high O2 levels.
Unless the injectors are oversized. Then it is squirting way too much fuel and causing the misfires which in turn cause high O2 levels.
Check the part # on the injectors and make sure they are the correct stock size unless it has been retuned for them.
The ecu has to know what size the injectors are for open loop operation.
Check fuel pressure too. If the fuel pressure is high the ecm cannot measure the fuel accurately.

After that Start with ignition (plugs & wires)(stock plugs and stock wires, nothing exotic)
You can burn the carbon off a plug with propane torch and a glove. But don't bother if you have some whacky plugs in it. STOCK PLUGS
Use your scanner to get into the data stream and do a sanity check on the sensors, sensors can be bad but not out of range to set a code.

Running that rich it will have gas in the oil as well, which will ruin bearings, lifters and such, will also mess up the way it runs as the gas gets drawn into the motor through the PCV in vapor form when the motor warms up (can also make it smoke).

I hope you are not buying MAFs, at the most you should swap a known good one and if that does not fix or change it put the old one back on.
Do not use a parts cannon to fix stuff, some times swapping parts is unavoidable but only after you have made sure other causes are not to blame.

If it has been retuned go back to the tuner and find out what he did, or find a reliable tuner that will guarantee his work.