check engine light go away!

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  #1  
Old 03-03-03, 07:35 PM
Timorama
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Question check engine light go away!

My 'check engine' light is on. I have a '96 1/2 ton chevy extra cab p/u with a 5.7l, 4l60 trans, A/C, 2wd, pwr everything, etc,etc. The codes I have pulled are:P0430, and P0420. The printout says that the "catalyst system efficiency for bank 1 and bank 2 is below the thresholds for the current operating conditions. Bank 1 identifies the location of cylinder #1, while bank#2 identifies the cylinders on the opposite bank." I changed the plugs with Autolite platinum plugs, as well as the cap and rotor. Fuel pressure is good, the engine runs and tows fine, gas mileage hasn't changed since the light appeared. connections to the oxygen sensors are tight and clean. It seems that one code might indicate a downstream oxygen sensor, or maybe a catalytic convertor, but having both codes has me stumped. I'm not doing or driving differently than I ever have. Short of changing all oxygen sensors and cat convertors I'm not sure where to look next. I don't have access to any OBD2 software short of taking the truck to a shop, but I'd rather fix it myself. Any ideas?
 
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  #2  
Old 03-03-03, 08:22 PM
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i would suggest taking to a shop where they have the tools such as a scanner to determine both the upstream and downstream o2 sensor readings to determine whether you have bad convertors or defective o2 sensors, generally it is a bad cat causing these codes, if you just recently purchased this vehicle their is a possibility someone may of hollowed the cats out which would cause these codes to set.
 
  #3  
Old 03-04-03, 03:51 AM
Joe_F
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I agree with BeJay. You must have the proper tools to do the job, and that includes a scantool. Without it you are guessing.

You don't mention mileage, but changing the O2 sensors is probably a good idea.
 
  #4  
Old 03-04-03, 07:58 AM
short_circutz
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I agree with the other posts......however ....there is one thing I would do first....why did you install autolite plugs in a GM?? The only plugs I've found that work well in a GM are AC plugs....scrap the Autolite plugs and install a nice normal set of AC plugs. They are what GM's are happiest running with.....
 
  #5  
Old 03-04-03, 09:07 AM
Joe_F
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Thumbs up

I agree. Regular stock Delco replacements are all that is required.
 
  #6  
Old 03-04-03, 11:15 PM
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The delco parts are fine, but there are also many aftermarket parts that work very well. The Bosch Platinum plugs are a good example of this. In a stock motor the delco parts are fine, but they can be much improved on. I can almost promise you its an OBD II issure. Are there any other problems with the truck? If there are no other problems I would be careful about getting it fixed. It’s just a light. Have you tried to reset you computer yet? That might be a good place to start
 
  #7  
Old 03-05-03, 08:45 AM
AVGJOE35
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If truck is running fine poke out the light with an awl or cover it with black tape.
 
  #8  
Old 03-05-03, 09:24 AM
Joe_F
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Which accomplishes zip. Just because it "runs good" doesn't mean there isn't a problem.

The check engine light is a warning sign that should not be ignored.
 
  #9  
Old 03-05-03, 09:43 AM
AVGJOE35
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Sorry Joe just kidding about the awl and tape. Humor.
 
  #10  
Old 03-05-03, 04:49 PM
Timorama
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The truck has about 120,000 miles on it, so it probably would be a good 'preventative maintenance' thing to do(changing o2 sensors). I did reset the computer when I cleaned the battery cables(more preventative maintenance). The cats shouldn't be hollowed, It did pass emissions, and that was about 9 months before the light came on. I considered that the autolite plugs might not be firing as efficiently as the delco platinums that I replaced and maybe loaded up the cats, but gas mileage hasn't suffered and there is no 'rotten egg' smell from a rich mixture. (Not that it always smells but I did consider it). The cap and rotor are delco parts. I didn't put delco platinum plugs in because I about fell over when I was told they were about $11 apiece! If I got really ambitious I could backprobe the o2 sensors with my DVOM; the downstream o2's should read fairly high(lean), correct? Oh yea, there isn't anything else wrong with the truck, except the plastic bedliner which I would like to scrap for a sprayed in one.
 
  #11  
Old 03-05-03, 05:21 PM
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i would just stick with whatever plugs you have in it now the a/c platinums are high priced but you should be able to find them for around 5-6 $ each.
if you do decide to read the millivolts the o2 senors are putting out usually anything below 400 is considered lean and anything above 400 is considered rich the higher the voltage indicates a rich condition. and on a fully warmed up vehicle the downstream o2 sensor should not be reading high they should always read low, the upstream o2s should be constantly cycling low and high voltages as the computer enrichens or leans out the mixture based on their readings.
 
  #12  
Old 03-05-03, 05:39 PM
Timorama
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Low voltage-lean. I should've remembered that. I think I worked too hard today and my brain is tired. Thanks!
 
  #13  
Old 03-05-03, 05:40 PM
Joe_F
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Agree. 120k on original O2 sensors is WAY too long. Should have been changed a while ago. Cheap enough. Use a scanner to clear the trouble codes.

Stick with the OEM plugs. GM cars run best with Delco plugs.
 
  #14  
Old 03-06-03, 12:13 AM
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I worked in a few high volume service departments for several different care manufactures. Their were a lot of things that were in common with all different care makers. One of the was the “ghost light” AKA the check engine light, that was on for no reason. Most of the time we would pull a code and fix the things that code indicated, then reset and try again. Nope, still the light we would do this until we would get down to a generic trouble code. At this point we would try swapping in a new computer and the light would go away. If the O2 sensors do not fix it would not kill myself trying to fix and OBD II thing. You could run down to the Chevrolet place and have them put it on there machine and see what they come up with. But the bottom line in a lot of these “ghost light” situations is it take a computer swap to fix it. I have even heard other technicians talk about snipping the wire to the light to fix it, at the request of there bosses. I have never worked for any place like that but it dose happen. My friend has a 96 Chevrolet Blazer that has a check engine light on sense 98 and its running just fine. His warranty was out because of excessive mileage. I told him I would do it after hours for cost of parts. Me and another technician, worked on it for 2 weeks replacing about 500 bucks worth of parts. Keep in mind we had access to dealership diagnostics and factory repair information and we still could not get it. We dropped in a new computer and still no luck. So we went back to the original computer and replace the wiring harness and it fixed it. But he did not want to spend the money for a new wiring harness. And I could not advise my friend that it would be a good idea to replace it for the price they were asking. So we put the old harness back in. The truck has worked fine every sense. Well except for the fuel pump going out, but I don’t see how that could be related. The story I have gotten from many of the automakers I have worked for it that if a reading changes by just a little, you get a check engine light, that means as little as 1-3ohm’s or 1.5mA change in the reading will result in a false positive result. And while I am ranting DECLO parts are good but they are a compromise between price and quality for there intend market, that is stock replacement. I have seen a dyno proven gain in emissions and performance just by a change to an after market plugs. The motors were stock GM and Ford motors and both showed a similar gain over factory plugs. Yes they do cost more, so you have to ask your self if its important enough for your application to spend the extra money. And just in case you are wondering what the plugs were they were Bosch Platinum2. Another question is if what if it is running rich or lean what are you going to do about it? Are you really going to spend the money to fix it? Have the computer re curved? Change out all of your sensors so the computer gets the right info? You have to know where you are going to draw the line. Ok I doubt any one would still be reading so I will close my rant by saying that always consider cost:benefit ratio for any money spent on a repair or upgrade.
 
  #15  
Old 03-06-03, 03:44 AM
Joe_F
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You will not see the benefit of changing plugs alone. If so, just drop in Delco Rapidfires and be done with it . Cheaper than Bosch Platnum and they are OEM .

As for the OBDII scenario, the OEM's are still working out some bugs in some models and such, but most times if you use proper diagnostic procedure you'll find the problem. Membership to IATN in your friend's scenario would have been the way I would have gone. Someone has seen your problem before!
 
  #16  
Old 03-06-03, 11:09 PM
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Actually I am a member of iATN. As well as the other technician that was working with me. We are both certified in GM light and heavy line products. And I was working for a GM dealership at the time we had lots of opinions and 99% were the same that is was a an output change in the wiring harness. And well all agree that we would not worry about it on our own personal vehicles I think we did follow proper diagnostic procedure maybe not what they teach in books but an abridged version that we use everyday. OBD II has been a pain in the butt every sense it came out in 96, you think in seven years they could figure it out. All we did was add plugs to the motors that were running in spec on a dynamometer, the gains were seen at the higher air flows in the mid range of the RPM band. Bosch plugs made a HP and Lbs gain over OEM premium plugs.
 
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