Fuel pressure increase when in open loop due to CEL

[dfib]

I am try to trouble shoot a misfire (cylinder 6) on a 2008 Yukon xl 5.3l with AFM DOD. One question I have that I noticed is the fuel pressure goes from 43.5 psi in closed loop to 58 psi as soon as the CEL has come on and goes to open loop. As soon as I clear the code and it goes back to closed loop the pressure drops back to 43.5 psi plus or minus 1/2 psi.

Is this supposed to happen?

I will make another thread with questions about the misfiring after I am done troubleshooting it if I can’t figure it out.

 

[TSOL]

Yes. Mine does that exact same thing. I have 43 PSI closed loop, 58 PSI open loop. I have 2013 Chevy Suburban 5.3L V8.

Misfires are typically due to spark plugs as far as I've seen. They have plenty of other causes, but these are by far the most common and a great starting point. Have you checked yours in a while? Also make sure your wire is properly seated. If it looks properly seated, change the wires with another plug and see if it moves. Repeat with the other ignition components until you've ruled ignition out.

 

[dfib]

I appreciate the response about the fuel pressure. I have been troubleshooting. This is my old car that I bought with 3 miles on it and gave it to my son at about 200,000 miles. He took it to a mechanic a month ago, cause it was misfiring and the mechanic said the motors blown you need a new one and want to charge him $9k to $10k for it. I told him if you’re driving it it’s not blown, bring it back to me and I will look at it and try and fix it to sell it. He has bought a new car since.

Things I have done so far.

Swapped spark plug still misfired
Swap wires still misfired
Swap coil packs to misfired
Took all the valve cover off and rockers seem to be tight.
Ran seafoam through the vacuum line and now it’s not misfiring all the time.
Did a compression test. First result 30 psi, second result 120 psi, third result 20 psi fourth result 125 psi all on the same cylinder. I checked the sale next to it and it was close to the 120 psi.
My next step is to take the valve cover off crank the motor and make sure all the rockers are moving. Hindsight I should’ve did this when I had the valve cover off the first time.
If that doesn’t show any results, I’m gonna swap fuel injectors because my long-term fuel trim on that bank is -20%.

At this point I am thinking one of my valves is not seating tightly.