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cylinder 4 and 6 have excess fuel/carbon

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Old 05-23-2019, 03:48 PM
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Default cylinder 4 and 6 have excess fuel/carbon

i have a 95 blazer 4d 4wd and i recently changed plugs, wires, pickup unit, dist. rotor, dist. cap, map sensor, coil, fuel tank, fuel pump, and fuel lines .

the engine ran smooth for about 300 miles then developed a rich condition in cylinders 4 and 6. there was carbon build up on cylinder 4 plug and the spark plug from cylinder 6 was covered in fuel.it also has carbon build up in the exhaust and smells odd. it has to build itself up before it will start but it doesn't roll over hard, and has a miss when idling but at highway speeds it has no problems running and there is no power loss or acceleration problems. i cant read codes because i cant find a scanner but the light is on. is there anyone who might have had this problem and knows what could be causing it? thanks in advance.
 

Last edited by Theblazomatic2; 05-23-2019 at 03:51 PM.
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Old 05-23-2019, 06:32 PM
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I would suggest considering the possibility that the fuel injection spider or hoses are leaking under the upper intake manifold plenum. If you take off the upper intake manifold and notice areas, especially around the #2 and #6 intake ports, that are cleaner than others, then it is likely that those are the locations where fuel has been leaking and dissolving the accumulated oil film that gets into the intake.
 
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Old 05-24-2019, 06:47 AM
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Originally Posted by christine_208 View Post
I would suggest considering the possibility that the fuel injection spider or hoses are leaking under the upper intake manifold plenum. If you take off the upper intake manifold and notice areas, especially around the #2 and #6 intake ports, that are cleaner than others, then it is likely that those are the locations where fuel has been leaking and dissolving the accumulated oil film that gets into the intake.
do you think there is any other possibilities? id like to avoid taking off the intake if its possible. just looking at all the options before i start spending money. thanks for the reply
 
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Old 05-24-2019, 10:37 AM
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Originally Posted by Theblazomatic2 View Post
do you think there is any other possibilities? id like to avoid taking off the intake if its possible. just looking at all the options before i start spending money. thanks for the reply
I would argue that carbon build-up and the gas-soaked spark plug is pretty good evidence for leaking gas and causing an over-rich condition. Fortunately, it is not so much hard to take off the upper intake manifold but rather I would say it is more in the annoying category. Now, removing the lower intake manifold (LIM) is hard. Although, our Blazers can suffer from the LIM gaskets failing and dumping coolant into the lifter valley so it is worth considering doing. (There are lots of threads on the LIM gasket replacement.)

Try to get to an auto-parts store where they can read the codes for you. I would not be surprised if you got an O2 sensor error too. I had this happen on a 92 when my fuel injection system leaked and caused carbon buildup on the O2 sensor (in addition to the other things mentioned above.)

Furthermore, I'm pretty sure excessive gasoline leaking down the cylinder walls can dilute the oil and reducing the lubrication. If your oil smells like gas, that is another clue that you have a gas leak.

Edit: Oh and that a leak has develop suddenly is consistent with the failure mechanism being a burst connection or tubing.
 
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Old 05-27-2019, 07:40 AM
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alright so update. i havent done anything to the vehicle except drive it. the issue is intermittent sometimes it runs normal. other times it runs like a dog. im not sure why.
 
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Old 05-30-2019, 06:44 PM
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Originally Posted by christine_208 View Post
I would argue that carbon build-up and the gas-soaked spark plug is pretty good evidence for leaking gas and causing an over-rich condition. Fortunately, it is not so much hard to take off the upper intake manifold but rather I would say it is more in the annoying category. Now, removing the lower intake manifold (LIM) is hard. Although, our Blazers can suffer from the LIM gaskets failing and dumping coolant into the lifter valley so it is worth considering doing. (There are lots of threads on the LIM gasket replacement.)

Try to get to an auto-parts store where they can read the codes for you. I would not be surprised if you got an O2 sensor error too. I had this happen on a 92 when my fuel injection system leaked and caused carbon buildup on the O2 sensor (in addition to the other things mentioned above.)

Furthermore, I'm pretty sure excessive gasoline leaking down the cylinder walls can dilute the oil and reducing the lubrication. If your oil smells like gas, that is another clue that you have a gas leak.

Edit: Oh and that a leak has develop suddenly is consistent with the failure mechanism being a burst connection or tubing.
I think you are right here. i started checking all of the different sensors tps, iac, irv,
and distributor and others and when i pulled the intake running valve off and looked into the intake there was fuel everywhere inside the intake. so now i need to figure out what all tools i need for the job and what parts are mandatory for replacement when this service is done. any help with that info would be appreciated.

 

Last edited by Theblazomatic2; 05-30-2019 at 06:56 PM.
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Old 05-30-2019, 09:18 PM
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Originally Posted by Theblazomatic2 View Post
I think you are right here. i started checking all of the different sensors tps, iac, irv,
and distributor and others and when i pulled the intake running valve off and looked into the intake there was fuel everywhere inside the intake. so now i need to figure out what all tools i need for the job and what parts are mandatory for replacement when this service is done. any help with that info would be appreciated.

Ah, you have one of the engines with the cool intake manifold. I had one in my '92. What happened on mine was that the plastic tubes between where the gas lines penetrated the back of the intake and the fuel injectors split. That was over 10 years ago so my memory is not great but I don't remember it being very hard to do, only a bit annoying to get everything off and out of the way.
 
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