Check Engine Light Mystery With My 2003 Chevrolet Silverado

[darkyellowsky]

Alright, I apologize for the long explanation in advance, but really want to get some ideas on what is going on.

 

I have 2003 Silverado, 4.3L, automatic transmission, with about 115,000 miles on it. I bought it brand new in late 2002.

 

About 4 months ago I was driving from home in Phoenix to San Diego. It is a drive I have taken often. About half way through the trip my check engine light starts flashing. It flashed for about 2 min and then went away and I forgot about it. Then 3 months ago I was taking long drive from San Diego to Barstow and again the check engine light starts flashing, but this time it stays on permanently for about an hour then went away. Same thing happened when I was driving back to San Diego. It went away after a short time and again didn't think much of it again. Now last month I was driving home from San Diego and again I go the flashing check engine light, but it went away. When I got to AZ I did some research and learned that a flashing check engine light means there is a reoccurring misfire. I told my Dad (who is pretty knowledgeable with vehicles, especially Chevys) about it and thought it was no more than a fuel filter problem. The next day I was driving to my girlfriends house, who lives about 30 min away, and the check engine came on permanently. I took it into a mechanic. They did a code check and that showed a "300," random misfire. They continued a diagnostic and found that there were issues with the cap and/or rotor, which I had changed out about a year and half ago when I did a tune-up. I took the vehicle home and switched out the cap and rotor. The Cap did have a decent amount of wear on the posts. The following day I noticed my vehicle was running smoother. That night again driving to my gf house I got a solid check engine light again. I took it to Autozone and they did a code check. Again I got a "300." Within 12 hours the check engine light went away, but I checked all the plugs and wires, all were still in really good condition. Two days later I got a check engine light flashing and then solid. I took it back to the mechanic the next day, and by that time the check engine light went away. He did another code check and again a "300." He cleared the code. And yes, you guessed it, three days later I get another check engine light on. I take it back to the mechanic and again they are getting a "300." This time the mechanic spent a half a day trying to figure out why there was a random misfire. He could not find anything. My Dad talked to mechanic and the mechanic recommended that I try changing the coil. If that doesn't work he told me that it might be best to wait to were it happens more frequently, thus making it more obvious. The next day we changed out the coil, and we also noticed that a clip on wiring harness which looks to be connected to the computer chip had been busted off. My Dad secured the wiring harness to ensure a bad connection was not causing these check engine lights from appearing.

 

Two days later I am driving back to San Diego and half way there the check engine light starts flashing, then stays permanently on through the rest of the drive. BUT I did notice that when I was going down hill, at which I take my foot of the gas pedal, the check engine light would start flashing as soon as I tapped the peddle slightly, once I started driving on flat rode and accelerate, the check engine light stops flashing and stays on solid. This happened about 6 or 7 times an only when I was going downhill. I tested it going up hill, but was not getting the same results. The check engine light stayed on until the following morning and then went away.

 

So here are facts:

1. I am either getting a flashing check engine light or a solid with a "300" code.

2. I am only getting these after a longer drive, making me believe that heat is partially the cause of the malfunction.

3. I was getting a check engine flashing when I was going downhill when I was not in full acceleration.

4. Check engine light goes away after about 12 hours, usually sitting overnight.

5. I did a tune-up at about 90,000 miles with AC Delco parts.

6. Changed out the cap and rotor, plugs and wires are still in good condition.

7. I changed out the coil

8. Changed out the fuel filter.

9. About 2 1/2 years ago I had to change out the fuel pump

10. About the same time I also had the catalytic converter replaced because the old one was bad.

 

Now, I have done research on the internet, to include this forum and every time read about a similar issue someone is saying that there is a different cause. I have read that if this continues a random misfire could f' up my pistons. I don't know how true that is, but I need to keep this truck for about another year at least, so I need to get this issue (if there is one) fixed.

 

Thanks for the help in advance.

[markw8]

Now I never did have a flashing cel for more than a year I had an intermitant solid light. The light was on from minutes to days. This was on a 6.0. I finally had it scanned on the way to deal to trade. It was a oxygen sensor.

 

Mark

[blacksierra01]

I had the somewhat same problem on my 01 4.3l. Replaced plugs, wires, cap, rotor and still got the misfire code. I put a full bottle of injector cleaner into a half tank of fule and went for a good long hard run and its never given me the misfire code again.