Nautry15

Morning! I'm having an issue with my 2004 Suburban, 5.3L.
Alright, so. The issue is a p0300 code for random misfire. 90% of the time it's random misfire, but occasionally it will throw p0302 for cyl.2 misfire. This is an intermittent problem. Sometimes i can drive for an hour before it starts, sometimes its at idle. I watch live stats with my scanner, and have discovered that the Bank 2 LTFT will start rising, and as soon as it hits +25%, the p0300 is thrown and I can feel the misfires and crappy performance. All other STFT and LTFT readings appear normal. Only B2 LTFT appears to be off, and its only off when the problems starts happening. After a while at 25% it starts going down to normal, the CEL will go away, and it will be running fine... until it happens again.

I have cleaned the MAF, checked spark, cables, and for vacuum leaks, im finding nothing. The MAF readings are normal, the MAP reading is normal. I used a timing gun on each cylinder while the issue was happening, and all 4 cylinders are indeed misfiring while it's happening. Once it's done, all back to normal. The 02 sensors appear to be functioning properly. Any help would be appreciated. Let me know if there is more information I can give you to assist. Thank you.

**update**
I just got a p0174 with the p0300 this time around. P0174 is bank 2 system too lean.

Another clue- after sitting here at watching stats while it cycles from normal running to crap running for an hour, i noticed in addition to +25% LTFT bank 2, CEL p0300 and p0174... bank 2 sensor 2 sticks at .06-.07, once it stops misfiring, every reading goes back to normal.

MyCamaros2Fast

You could always try cleaning all the O2 sensors. I had an issue in the past where the upstream was dirty and the downstream was clean/good, but it kept thinking it was an issue because the other was "good" even though the readings weren't matching.

Nautry15

I replaced bank 2 sensor 2, and still the same issue. I don't think it's an 02 sensor at this point. I'm thinking it may be an injector. But I'm not for sure. I checked fuel pressure and it's normal.

MyCamaros2Fast

Sorry if my msg was confusing. What I was trying to say is that if bank 2 sensor 1 is bad, then bank 2 sensor 2 may be thinking its not working and throws a code. I would look at that just in case to rule it out.

repairman54

Trims going positive it's a vacuum leak on that bank. Check what vacuum lines go to that side of the motor like the brake booster for example.
There is no cleaning O2 sensors, just replacement. Only GM sensors with any sensor as aftermarket stuff is not reliable.

|What are the Possible Causes of the P0174 CHEVROLET Code?

• Dirty or Restricted Air Filter
• Dirty or Faulty Mass Air Flow (MAF) Sensor
• Intake Air Leaks
• Exhaust Gas Leaks
• Fuel Contamination
• Faulty or Clogged Fuel Injectors
• Faulty Front Heated Oxygen Sensor
• Ignition Misfiring
• Low Fuel Pressure
• Positive Crankcase Ventilation (PCV) Hose Leaks

Nautry15

Gotcha! I will look closer for vacuum leaks for that bank. And I will try to swap the new 02 to b2s1. I've ruled out most of that list, but I'll try the things I haven't. Gonna check all of that this weekend. My only concern is p0174 is rarely thrown, always p0300. Either way, I'll be testing both of your recommendations, I appreciate the help. I'll give you an update this weekend!