5.3 hesitation, stumble, lean and random misfire codes, worse when cold.

Discussion in 'Chevy Suburban Forum (GMC Yukon XL)' started by kleake, Aug 12, 2011.

  1. kleake

    kleake New Member

    This is kinda long winded, but I am at a loss as to what is the problem is...

    I have a 2000 suburban with the 5.3. For the last several years it has been randomly giving bank 0 lean, bank 1 lean, and random misfire codes. It is MUCH worse when cold, especially on startup, but it is getting to the point it does it even when hot. Normally once warmed up it runs pretty good, although when pulling my camper and trying to back into a space it will stuble and cut out as I am trying to accelerate. It basically hesitates to the point it won't hardly move at times. Over the years I have changed spark plugs, fuel pressure regulator, fuel pump, MAP sensor, MAF sensor, throttle position sensor, and tested EGR by completely blocking it off. I have also checked for vacuum leaks by disconnecting hoses and capping them temporarily. I was completely at a loss, and heard about intake leaks or cracks so yesterday I put on a new intake gasket and inspected the intake pretty closely. This still did not solve, nor even change the issue. I have even sprayed carb cleaner and such all over the intake while its running, and there is no change in the way it acts while spraying it. I don't remember what the fuel pressure is at, but it was within spec when I checked it last. I can unplug the regulator to up the pressure and it helps a tiny bit at idle, but never fixes it. What else could I be missing? The IAC was also taken out, cleaned and checked to make sure it is working, and it is, but I haven't replaced it. 02 sensors are within normal reading as well. It basically has the symptoms and such of a vacuum leak, but I don't hear one, nor can I find one. No other codes have ever been set, and none ever show up. It is definitely a random misfire at idle as it sounds like it has a cam in it, but uner heavy acceleration while backing the trailer, or holding the brake, it seems to be more of a steady misfire when it does it. And, it doesn't do it all the time, but under the right conditions, and the right throttle it will. And only at low rpm, never anything above about 2500rpm. Any other idea's what this could be?
  2. billnorman

    billnorman Rockstar 100 Posts

    Find a mechanic with the clip on spark plug spark checker that counts misfires. it will help you find a coil pak or wire that is breaking down. It counts the # of times each plug fires in a given amount of time. You haven't changed 02 sensors, have you checked them all? i don't know how many you have. Once in a while, everybody has to seek professional advice and actually PAY for help. It's a rotten pill, but take it with a full glass of water. If you don't want to pay, start with the basics, compression, fuel, spark, timing. good lluck.
  3. kleake

    kleake New Member

    I have not checked the 02 sensors other than just looking at the data they are sending the computer. It "appears" to be acting normal, but when it is cold, the computer isn't even looking at the o2 sensors if I understand correctly. I would consider the coils, but I would think it is unlikely that they all would be breaking down at the same time. This is truly a random misfire. Also as it stumbles sometimes, it will catch itself and rev to 1500rpm, then taper back down to 6-700 before it starts the rough idle again.
  4. janikphoto

    janikphoto Rockstar 3 Years 100 Posts

    Not saying this is your problem, but I'll share a previous and similar problem with you. A 1998 Explorer we used to have developed a tiny leak in a gasket somewhere on the intake side of the engine and it would be much more noticeable on cold days. It let the engine suck in extra air and the engine would run more rough and throw codes. Ford actually had a recall on it, but we didn't know until we were well past the cutoff.

    Anyway, don't be surprised if you find your problem at a gasket like with our explorer, or something similar.
  5. kleake

    kleake New Member

    I just replaced the intake gaskets last week. The originals had lost their "thickness" in the seals, but didn't appear to be leaking. I inspected the intake for leaks but couldn't find anything. There was no change in the way it ran with the new gaskets either. I double checked my fuel pressure last night and it is 50-52 at idle, and jumps to 60 at WOT or when I unplug the regulator. There is no change in rough idle when I unplug it.

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