Jump to content

P0300 and P0332 code help - Chevy Suburban

cbarn

Recommended Posts

cbarn Enthusiast

cbarn

Posted
Posted

I have a 2004 Chevy Suburban 1500 with the 5.3L V8, about 180,000 miles. Several few weeks ago it started running rough at idle especially after warmup ... RPM will vary between 300-600, sometimes threatens to stall but hasn't actually done so. No apparent loss of power or change to fuel economy, and it runs perfectly at speed. After this started it began throwing code P0300 (multiple misfires) and lit the warning light - however, it will sometimes clear the light on its own, and if I clear it myself with the code reader it may remain off for several days.

 

Yesterday the warning light came on, and when I checked codes this morning I had an additional code P0332 (knock sensor). Cleared the light and it remained off through this morning's 60 mile drive. I've read other threads regarding P0332 and with the age of the car it could certainly be a failed sensor, but given the weeks of P0300 cropping up it seems (to me anyway) that the sensor may just be doing its job and that I should clear up the misfire issue before worrying too much about P0332.

 

I haven't had a chance to experiment myself or get it to someone with a better reader, so I don't know if this is a spark plug issue, vacuum leak, sensor issue, etc. yet - I'm quite willing to have a mechanic do the diagnostics but would like to have an idea which direction to point him rather than have it turn into a massive fishing expedition.

 

Any suggestions or recommendations for what to check (or warnings that I'm not treating this with sufficient urgency!) would be appreciated!

txab Senior Enthusiast

txab

Posted
Posted

If you have to "point" your mechanic in the right direction, he's not much of a mechanic.

 

I'd check intake and intake gaskets for leaks. Clean the MAF and throttle body

Gregs Enthusiast

Gregs

Posted
Posted

First clean the Maf sensor with Maf cleaner (Not carb clean or anything else). If that doesn't fix it then I woul dbe putting my money on leaking intake gaskets, which is a good thing because you have to take the intake off to replace the knock sensors anyways. For the knock sensors replace them both and also replace the knock sensor harness and use RTV silicon to make a "dam" around the knock sensor's holes so you don't have to worry about getting in them. FYI water in the knock sensor's holes are the main reason they go bad.

cbarn Enthusiast

cbarn

Posted
  • Author
Posted

Thanks for the help fellas ... I've cleaned the MAF sensor and throttle body with the appropriate cleaners and while that seems to have made a slight improvement it's still noticably rough at idle - hasn't thrown a code yet but I'm pretty sure it will by the end of the weekend. Gregs & txab, I think you're right, probably an intake leak ... is there an easy way to test that here at home, or is it an "only the technician will do it right" job?

 

I'm no technician (or mechanic) but I'm handy enough with a toolbox - I can change my own oil, do my own brakes, and I managed to keep a '75 MGB running OK back in the early 90's (granted, when something went wrong with that it was usually blatantly obvious what had broken). I'd like to do more of the maintenance on the Suburban myself - I've read the procedures for replacing the knock sensors and intake gaskets and I'm confident I can do that myself without screwing it up, but want to be fairly sure that's actually the problem before investing that time & effort. :-)

txab Senior Enthusiast

txab

Posted
Posted

One way to check intake gaskets is to spray something like carb cleaner around the area where the intake an heads meet. See if there is a change in the engine sound/speed.

 

When, if ever, have the plugs/wires been replaced?

Gregs Enthusiast

Gregs

Posted
Posted

i would also try spraying the carb clean around the intake gaskets and look for rpm changes. Another thing i just remembered and its really common, bad fuel pressure regulator. To test this you can turn the ignition key on for a few seconds to get rail pressure up then pull the vacuum line to it and see if it has fuel in it. If there is fuel then the diaphram is leaking. I've had ones that would only leak when the engine was cold and would seal up as it got hotter. If you have access to a scantool you can watch your long term fuel trims and see if they are out of whack.

  • 2 weeks later...
cbarn Enthusiast

cbarn

Posted
  • Author
Posted

I've tried spraying carb cleaner around the intake gaskets and didn't notice an RPM change, but I'm also not convinced I did a thorough enough job so I'll try it again this weekend. Also trying to get my hands on a better scanner so I can see the fuel trims, and as it's been a LONG time since plugs were replaced I'll do that and check their condition to see if there are signs any particular cylinders are worse than the others.

 

I'll wind up replacing the intake gaskets anyway since the knock sensors need their service, but I'd like to make sure I'm not missing something else that I could be fixing at the same time - don't want to take it all apart more than once!

Archived

This topic is now archived and is closed to further replies.

Go to topic listing

  • Latest Articles

  • Posts

    • Atlas
      AC diagnostic on a neo-classic Camaro

      By Atlas · Posted

      tldr; Shade tree mechanic stumped by variable displacement AC compressor.   Not Silverado related, but for my 2000 Camaro SS. I've never really used the AC since acquiring the car a good handful of years ago. I plan to take it on a trip this summer so I wanted to make sure the AC was in good shape. On an 73 degree day in the shop with the car idling I set the AC on "Max", temp set to cold, and fan on hi. The compressor turned on and air turned nice and cold.   I let it run for several minutes but noticed the compressor never cycled off. The engine was up to temperature enough that it began cycling the cooling fans on high. I had a set of manifold gauges hooked up and it was consistently at about 25 psi on the low side and between 200 and 225 psi (warm engine) on the high side. Per temperature charts, the low side is low (should be 30-35) and the high side is a little high (up to 170 per chart). I read the low pressure as potentially being under-charged underscored by a continually running compressor This was also underscored by temp readings of mid-20 degrees at the vents. Not just cold, freezing cold. Switching off the AC but leaving the HVAC fan on high produced a deluge of condensation underneath the vehicle. I was getting ice buildup on the evap core most likely.   The low reading (25psi) concerned me that the compressor wasn't switching off so I swapped out the pressure switch. No change in behavior, still ran constantly.   The AC clutch works fine as it engages/disengages with the HVAC switch on command. The compressor relay is good as I swapped it with two different known good relays just to be sure. Having eliminated that, and the pressure switch, I added refrigerant, thinking the constant run and low "low" pressure were signs of a slight undercharge. Makes sense, the car is 26 years old and it doesn't appear the AC system has ever been touched.   Adding some R134a didn't meaningfully change the low side pressure. And that's when a lightbulb flashed upstairs. While I consider the car "old", it's possibly "new" enough to have a variable displacement compressor. Did some reading and sure enough. Dangit. I don't work on these for this reason.   Adding refrigerant means the compressor will just compensate and won't really change pressures until it's severely overcharged or undercharged. But at least I wasn't getting ice/frost anymore, but instead high 30 degree temps out of the vents. That's more normal, but with variable displacement now I have no idea where my charge level is at. It's probably overcharged now. The high side even with the engine radiating serious heat was never really over about 225.   The static pressure at room temperature is dead on, before and after the charge. Both high/low equalize after some rest.   I'm thinking I'll need to take it to a shop. I want the proper charge level so I'm not working the compressor too hard. The only way to get an accurate charge is to evacuate and then re-charge with the exact amount specified for the system -- at least that's what I'm reading.   Anyone here with modern automotive AC knowledge?  
    • Byrds8
      Ac not keeping up

      By Byrds8 · Posted

      Mine is in the shop for the AC now. While it did get cold after a bit, it would take a while to even start to cool the air at all. Turns out the compressor was bad and cycling. 
    • KARNUT
      Ac not keeping up

      By KARNUT · Posted

      I call B.S. when I first moved to Texas my first house would only cool to 80 with the Texas heat. The AC tech said it was normal at 100 degrees outside. I remodeled the house put in a new AC. I could hang meat. My cars may need recirculating to start. Once moving it switches to regular AC and I could hang meat. Living in Texas no one would put up with only 20 degrees difference. 
    • Silverado4x4
      Ac not keeping up

      By Silverado4x4 · Posted

      AC in home or auto only cool down 15-25 degrees from outside temp, but what will help is to put the ac in recirc mode this will recirc the Inside cabin air rather then trying to cool down the outside hot air, I always have mine in recirc mode.
    • Mrob7
      1965 GMC 1000 series floor shifter

      By Mrob7 · Posted

      Found the fix for this.  Untightan the bolt just below top linkage on the steering column, turn assembly left to reduce space between the two linkage rods at the steering column, tighten bolt.  Made a big improvement.

  • GM-Trucks.com Clubs

  • Popular Contributors

×
×
  • Create New...