97 silverado L31 cylinder 3 issues p0303

hello

i have a 97 Z71 with the L31 that has 260000 miles on it. it is giving the p0303 code, it has been doing it for a year or so and getting steadily worse. i put the mfi octopus fuel injecter in around 6 months ago and put a new ac delco distributer in around the same time and the 303 code was still there and still intermittent, when it is actually happening the truck smokes (it smells like fuel) at idle and runs rough. yesterday i decided to put a new ac delco cap and rotor in, new spark plugs (tr 55) , fuel filter and ac delco plug wires. well now it is code 303 all the time , running rough and smoking like crazy, i pulled the number 3 plug wire off and it was no difference. i used a cheap spark plug checker light to confirm spark and it was lighting up as i assume it should .

the old plugs looked good except for number 3 , it had a coat of oil on it. i dont have a real scanner just a cheap obd2 reader that displays on the 7 inch radio display that lets me read and clear codes and little else. also i will try to get me hands on a camera that will let me see inside of the spark plug hole to check for damage.

does anybody have a idea of what the problem is? should i take it to a shop with a scanner and one of those little cameras to look thru the spark plug hole?

i will try to add the pictures i have of the stuff im talkin about.

thanks for your time
dave

Without the data stream, hard to determine. With all the parts you've thrown at it, you could have gotten a legitimate scanner to diagnose the problem properly. In most states you can borrow one from a local parts shop and get access to the O2 sensor data, that's where you'll want to look.

Out of curiosity, does it run fine when it first starts up, for about 30 seconds, then start ******** the bed, or it runs like crap from the start?

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Do a compression test. Unless you feel like it's good. Only reason I'm recommending it is because my original motor #3 died. Had the flashing cel.. ran decent but going up to speed or maintaining cruising would shake and run rough. Turn out had fluid leaking to #3 some guys didnt notice it at slower speeds.. wasnt unless you got on it a little. Or hold the brake and press the gas...

RawbDidIt said:

Without the data stream, hard to determine. With all the parts you've thrown at it, you could have gotten a legitimate scanner to diagnose the problem properly. In most states you can borrow one from a local parts shop and get access to the O2 sensor data, that's where you'll want to look.

Out of curiosity, does it run fine when it first starts up, for about 30 seconds, then start ******** the bed, or it runs like crap from the start?

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it runs fine for the first 30 seconds.
what is a relatively cheap scanner that will do what needs to done to diagnose this problem?

thanks

SUBURBAN5 said:

Do a compression test. Unless you feel like it's good. Only reason I'm recommending it is because my original motor #3 died. Had the flashing cel.. ran decent but going up to speed or maintaining cruising would shake and run rough. Turn out had fluid leaking to #3 some guys didnt notice it at slower speeds.. wasnt unless you got on it a little. Or hold the brake and press the gas...

Click to expand...

i have a compression tester and can check it against the number 1 cylinder tomorrow,
thanks

Unssafe said:

i have a compression tester and can check it against the number 1 cylinder tomorrow,
thanks

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If it runs fine in open loop (before the O2 sensors heat up and the engine starts adjusting fuel based on their inputs) but has issues in closed loop, it's fuel/air related. A compression test may help isolate the cause, especially if you can track down where the leak is coming from. Sounds like a blown gasket, most likely your head gasket. You pulled the plugs and there was oil on number 3? This also points to head gasket. The plugs for 1, 5, and 7, did they look yellow, like they'd been running lean?

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Unssafe said:

https://photos.google.com/photo/AF1QipOK8X0WH7hRcGmdNSv7vDU__OcfuEEohsOEOJhv

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This link is broken, can you load it directly to the site? Easy from the phone using the tapatalk app

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Here are the relevant pictures

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RawbDidIt said:

This link is broken, can you load it directly to the site? Easy from the phone using the tapatalk app

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Click to expand...

thanks

i downloaded tapatalk

i will do a compression test tommorow , thanks for the info on the head gasket.