2005 GMC misfire

[jayroge25]

So I have a 2005 Sierra 1500 5.3. Has 230,xxx miles and a few different issues that have me stumped. First off I am not able to link to the odbii to pull any cel's. Powers scan tool on but will not link. Have tried different scan tools and made sure cigarette lighters all work.

 

Second I'm having a really bad misfire mainly at idle. With occasional power loss on acceleration. I have replaced all plugs, wires, coils, and injectors. Also replaced cats and oxygen sensors. I know the passenger bank is running extremely rich, can smell it clearly and can foul clean plugs out immediately. All 4 on the passenger side will be black. 

 

Any help will be greatly appreciated cuz I am stumped.  Thanks guys/girls

[carkhz316]

Well, without being able to read any codes or live data, you're kind of just going blind. You're going to have to get that straightened out first before you throw any more parts at it.

[jayroge25]

22 minutes ago, carkhz316 said:

Well, without being able to read any codes or live data, you're kind of just going blind. You're going to have to get that straightened out first before you throw any more parts at it.

Right, that's why I was hoping for help with problem 1-A first lol

[carkhz316]

I understand, but live data would definitely help you pinpoint the rich condition (ie, and O2 sensor) and whatnot. So to the first part: can you check for power at the OBD 2 port? Barring that, it sounds like you have a loss of communications to the ECM via the purple wire at the OBD port.

[jayroge25]

12 minutes ago, carkhz316 said:

I understand, but live data would definitely help you pinpoint the rich condition (ie, and O2 sensor) and whatnot. So to the first part: can you check for power at the OBD 2 port? Barring that, it sounds like you have a loss of communications to the ECM via the purple wire at the OBD port.

I am assuming I have power to the port. It turns on my scanner which is powered by the port. Does that purple wire run all the way back to the ecm? If I was going to trace it for breaks or shorts?

[Jsdirt]

More than likely the CAN bus line or lines are down. Common with the crap wiring they use today, and at that mileage level, it's pretty much a given.

 

Looking at the data link connector with the widest part at the top, the #2 pin from the left is the J1850 bus +. Should be a square wave signal on that line. #4 is chassis ground, #5 is signal ground for most sensors, 6 is CAN high (best way to test this is with a scope - a multimeter is far too slow to pickup the rapid signal changes),  (second row now - starts with pin 9) 10 is ground for the J1850 bus, 14 is CAN low, and 16 is battery positive (4A max current available here).

 

 Using an ohm meter from pin 6 to pin 14 should give you 60 Ohms.

 

Here's a great article to get you familiarized with the systems:   https://www.motor.com/magazine-summary/communication-is-key-serial-bus-diagnosis/

[jayroge25]

I appreciate it! So last night I was able to intermittently connect my scanner. Some light love taps on the pcm, which is obviously concerning in its self. I was able to pull some codes P0300 random/multiple miss, and p0449 vent canister solenoid. I erased them to get a good base line and they came right back but I think I want to drive it some more get some more cycles on it to see if anything else comes up. I cant see the vent solenoid causing a multiple miss maybe the purge if it is stuck open but I could be wrong. Wouldn't be the first or the last time haha

[txab]

Remove the plugs from ECM and re-seat them

[Jsdirt]

If the purge solenoid is stuck open, it's the same as a vacuum leak (once all the fumes are purged out of the charcoal canister), and can definitely cause a 0300.

[jayroge25]

1 minute ago, Jsdirt said:

If the purge solenoid is stuck open, it's the same as a vacuum leak (once all the fumes are purged out of the charcoal canister), and can definitely cause a 0300.

Any way to test it?

[Jsdirt]

Pull the hose off both sides of it, and see if you can move air through it. Plug it in, and cycle it with a scan tool to make sure it allows air to move when its supposed to, then stops the flow when it's supposed to.

[mjm-1957]

P0449 is the vent solenoid not the purge solenoid. Take the wire connector out and connect a test light across the connector and cycle the vent solenoid on and off with your scan tool. If the test light goes on and off you have power and ground and the solenoid is bad, very common problem on that truck.