Need help with 4.6 check engine codes

Wild Horses · Jan 14, 2014

I just bought a 98 GT 4.6. It runs good and feels pretty strong. It has a ton of bolt ons and I'm leaning towards this being the source of my problem. The current mods are as follows.

-BBK CAI
-MAF (not sure what size but aftermarket)
-Trick Flow 75mm throttle body w/plenum combo
-BBK Piggy back style under-drive pulleys.
-BBK Shorty headers
-BBK Cat-Less H-Pipe (has all sensors)
-Little single chamber flow masters

Thats about it.

Now the problem I'm having is at WOT at mid range rpms. It fells like a miss but random. Just a tiny loss of power for a split second a few times each gear. My gut feeling is it's starving for fuel.

So I figured I'd take advantage of free code reading and printout at auto zone and this is what we got.

Code P1443- evap can purge valve fault
P0171- fuel bank one lean or rich condition
P0174- fuel bank two lean or rich condition
P0420- catalyst efficiency low-bank

Alright, so I'm pretty sure I have a fuel problem most likely lean. Each code print out gives a brief description but I need some help understanding what the hell they are talking about. If she was carbed I'd tune her up and be good to go. I'm sure this problem is caused by the mods. Is all of this because there's probably no custom tune on the computer? What else can I do? Fuel pump? Injectors?

Not sure where to start. Any help is greatly appreciated.

Ferocious · Jan 14, 2014

P0171 & P0174 are usually due to a vacuum leak somewhere in the system. I had those codes come up a while back after swapping my intake manifold.
Try spraying carb or brake cleaner near the vacuum lines and listen for a change in idle. I would also clean the MAF, TB, and the plenum while you're in there.
You can also change the fuel filter if it's clogged up or clean the injectors. All of those will cause a lean/rich code.

P0420 may possible be a clogged catalytic converter.

Wild Horses · Jan 14, 2014

I'll check for a leak. It really doesn't act like it has one but it's definitely possible.
I'm planning on cleaning everything when I put my BBK 78mm on tomorrow. I hope I fix something.

P0420 is more than likely because there are no cats. I didn't really mean to post that one. It has the BBK off road H. I love not having emissions in my county.

Ferocious · Jan 14, 2014

Whoops, didn't read your mod list. Disregard my last statement lol.

Wild Horses · Jan 14, 2014

Hah yea I figured you missed it.

My father an ASE mechanic of 35 years came by the house today and as soon as I started the car up he says "you know that thing has a miss, right?" Me- "yea when it's wide open". Him- "No it's missing right now, how the f*** do you not hear it?" That went on for a bit and now I'm getting ready to check the cylinders by grounding plug wires at the coil to find the cylinder. It stopped missing after the car warmed up but still did it under load mid rpm and up. I guess I just didn't notice because it was only doing it on cold starts.

I'm going to check the cylinder misfire and swap from my trick flow TB/plenum to my bbk one piece while checking for vacume leaks or the other way around. Maybe I'll find something.

Wild Horses · Jan 15, 2014

I got my BBK 78mm on tonight. Discovered 2 vacuum leaks while swapping parts from the trick flow plenum. First was the lack of any gasket between the IACV and the plenum. The second was a torn up EGR gasket that wasn't replaced when the trick flow plenum was installed. I was quite amazed that someone wouldn't even bother putting new gaskets in. I mean the IACV was just clean metal to metal and I guess when the car heated up the metal would create somewhat of seal.

The car runs much better but is still a little off. I have some header gasket leaks and a couple at the H pipe I need to take care of so I can hear the motor before anything else. I'm pretty sure she needs plugs. May get some msd coils and a fuel filter for it tomorrow.

Forgot to mention I disconnected the batt for 15 mins and I haven't had a CEL come on yet. I drove it for about an hour afterwards.

chris91 · Jan 15, 2014

It usually takes a while for the CEL to come back on. Sometimes a couple days. The ecu does a full system sweep. Not sure but it might be throwing those PO174 AND PO174 due to the lack of cats. Pick you up a set of MIL Eliminators. The mods you have don't require a tune.

SVTstang96 · Jan 15, 2014

chris91 said:
It usually takes a while for the CEL to come back on. Sometimes a couple days. The ecu does a full system sweep. Not sure but it might be throwing those PO174 AND PO174 due to the lack of cats. Pick you up a set of MIL Eliminators. The mods you have don't require a tune.

What he said.... MIL eliminators are where you want to start first. this will trick the o2 sensors into thinking its running well, and adjusting the air/fuel curve to where it should. This will give you a good baseline to start diagnosing the other codes. LMR or AmericanMuscle sells these, but if I am correct there is a write up on here where you can make your own fairly cheap. I would check out the how-to section before spending $40-$60 on some fancy wires.... Illl check there also and if I see the thread I will send it your way

Wild Horses · Jan 15, 2014

Awesome. Thanks for the info. I see bungs with sensors in them on the h pipe but I'm guessing whatever it is isn't right because it's throwing those codes. It also has some header gasket leaks I'm dreading getting to. I've heard they could be an issue because it's before any sensors. Ill do some research on MIL eliminators and I'm kinda on a budget so that link to make your own would be a great help.

chris91 · Jan 15, 2014

They may still be there but they aren't working like they should. They are used to getting a certain amount of airflow. When you pull those cats, the airflow is increased greatly so the sensors don't know what to do.

Wild Horses · Jan 17, 2014

I'm still getting a miss under load. Now it seems like when I'm at a lower RPM and hit the gas more than a 1/4 way down. The car starts falling on its face. I can't afford these mil eliminators yet. I've got to get rear tires on this thing for inspection. Found out the car has 10.5" rear wheels after I bought 245s for all 4. There were no lips on the rear wheels so I assumed they were all 9" wide. I can't return the tires I got and now I need 2 - 275/40/17s. The stupid little crap that the previous owner doesn't tell you can really screw you up.

Addermk2 · Jan 17, 2014

Wild Horses said:
I'm still getting a miss under load. Now it seems like when I'm at a lower RPM and hit the gas more than a 1/4 way down. The car starts falling on its face. I can't afford these mil eliminators yet. I've got to get rear tires on this thing for inspection. Found out the car has 10.5" rear wheels after I bought 245s for all 4. There were no lips on the rear wheels so I assumed they were all 9" wide. I can't return the tires I got and now I need 2 - 275/40/17s. The stupid little crap that the previous owner doesn't tell you can really screw you up.

you need to get yourself some type of scanner that will allow you to look at your fuel trims. you might want to consider one of the Bluetooth obd2 connectors that can interface with your cell phone. there is an app available for Android phones called torque

you need to look at your short term and long term fuel trim. if you're feeling is correct and nothing is out of spec then you are due for a tune up.

Wild Horses · Jan 17, 2014

Well I just made my own MIL eliminators thismorning and I'm pretty sure they're doing their job. I built them and soldered them up just like the pics in the how to. 5 bucks worth of caps and resistors and 20 mins worth of work. It seems to idle much smoother. I'm gonna go ahead and start with basic tune up stuff as the post above says. I'll grab a fuel filter and some NGK plugs tonight. The ford racing wires on it look pretty new. It's at 97k miles so I'm thinking a full 100k service is what I'm going to end up with.