Engine misfire

Brad Kermes · May 22, 2016

Hey guys first post on the forum and I'm hoping I can get some info back.

A couple months ago my truck threw the god awful "reduced engine power" warning. It went away after a day however now I still have a CEL on and occasionally it will flash at me. (Typically when I step on the throttle.) The truck also has a rough idle which explains the misfire code.

I attached a photo of the codes it is throwing. I'm thinking I have an issue with the throttle body however I am a little stuck. I checked my wires that connect to the TB and everything seems fine. I am going to check for any loose grounds tomorrow.

What do you guys think? I really don't want to buy a new TB just to try it out and start wasting money.

Any help is appreciated.

anumber1 · May 22, 2016

Don't know what year or motor you are dealing with. Possibly spark plugs or wires if you are up over 100k miles. Possibly a bad throttle body.

Need more info.

Brad Kermes · May 22, 2016

Oops thought my display listed everything, my bad.

04 silverado 5.3l with 180,000 roughly. I'm gonna change the spark plugs tomorrow for the hell of it, definitely can't hurt, but the throttle body codes is what has me worried. Do you know how I can test it? I've found a lot of info about the mechanical TB's however mine is electronic and I am a little stumped on how to go about it with a multimeter.

Thanks for the quick response.

anumber1 · May 22, 2016

With that many miles, definitely plugs if you do not know when or if they were ever done.

Next check should be fuel pressure. 55 to 60 or so, key on, engine off and it should hold that pressure for at least 10 mins or so.

Pull the vacuum line off of the fuel pressure regulator. If there is gas there, the regulator needs replacing.

Clean the engine to battery ground and the chassis ground, hopefully that may help with the throttle body.

Cleaning it with some throttle body cleaner is advisable also.

It is not uncommon for the throttle body to fail however.

There is not much else you can test regarding the throttle body without a high end scan tool or a tech2

Brad Kermes · May 22, 2016

Yea I will do a fuel pressure test tomorrow as well. Earlier when I was inspecting the TB I noticed it has a decent amount of gunk built up in it, I'm assuming that means unburned fuel so maybe I do have a dead spark plug or a bad coil pack.

I found some information earlier about testing the throttle position sensor. They said at idle the sensor should be receiving 0.5V (from the PCM I believe?) and at WOT it should be receiving 5V. I was wondering if that is where my issue is because that sounds like it could possibly relate to the P0220 code. Not sure.

Brad Kermes · May 22, 2016

Where abouts is the fuel pressure regulator located? Mine doesn't seem to be anywhere on the fuel rails.... I read that some trucks have the regulator located in the fuel tank along with the fuel pump. Does anyone have any input On this? As stated earlier truck is a 2004 silv with 5.3l

I also tested all coils earlier today and they all work. (Putting some new spark plugs in later tn)

I tested the Throttle body /Tps as well and all voltage /resistance is within range which is making me think my problem is fuel related

Found a good article on testing the throttle body....

http://easyautodiagnostics.com/gm/4.8L-5.3L-6.0L/p0120-tp-sensor-tests-1

I'm gonna check fuel pressure tonight but the regulator has me stumped...