Spark plug foul up

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martingmc86

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I have an 86 GMC Sierra 5.0 with a MSD atomic 1 EFI have had an issue with my spark plugs, getting folded up after a couple hundred miles to get cover in black and truck runs like **** first, I thought it was my carburetor so I decided to swap it out to an MSD atomic one EFI and it runs great but after a couple hundred miles like I’ve said the spark plugs foul and goes back to **** what can it be? I rebuild the distributor and put new pick up coil new capacitor, spark plug module new rotor plugs and new cables and still does the same thing my distributor does not have a vacuum advance it is a ESC ELECTRONIC SPARK CONTROL came out of California, so it had smog regulations
 
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First you have to determine if it is too much oil or gas. Plenty of youtube vids can help you.
 
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See if your timing actually advances,no advance will foul plugs. Monitor O2 sensor voltage with a multimeter,postcresults. O2 sensor has to be hot to work so monitor hot.
 
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Ricko1966 said:
See if your timing actually advances,no advance will foul plugs. Monitor O2 sensor voltage with a multimeter,postcresults. O2 sensor has to be hot to work so monitor hot.
Click to expand...
Ok it’s a single wire o2 sensor so I’m guessing positive to wire and ground to ground and should I be shecking volt or ohms
 
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martingmc86 said:
Ok it’s a single wire o2 sensor so I’m guessing positive to wire and ground to ground and should I be shecking volt or ohms
Click to expand...
Positive lead lead of a meter to single wire on O2 sensor ground lead of meter to ground,looking for volts .1 is lean .5 is stoich .9 is rich. you can run a wire into the car so you can monitor daily as you drive. Piggy back your wire at the O2 meaning leave it in the system just monitor it.Didnt you have something going on where you need 2x O2 sensors. 1 for OE computer 1 fir aftermarket EFI ?
 
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Ricko1966 said:
Positive lead lead of a meter to single wire on O2 sensor ground lead of meter to ground,looking for volts .1 is lean .5 is stoich .9 is rich. you can run a wire into the car so you can monitor daily as you drive. Piggy back your wire at the O2 meaning leave it in the system just monitor it.Didnt you have something going on where you need 2x O2 sensors. 1 for OE computer 1 fir aftermarket EFI ?
Click to expand...
Yes, that is correct. I have two oxygen sensors one is for my EFI and one is for my trucks ESC I added back my original oxygen sensor and didn’t notice a difference thing that sucks right now is that my truck runs like **** but if I clean or put new spark plugs run it will a couple hundred miles really good then my spark plugs foul up and goes back to running bad and my truck runs like **** again lol
 
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Monitor the o2 sensor voltage,post back
 
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Ricko1966 said:
Positive lead lead of a meter to single wire on O2 sensor ground lead of meter to ground,looking for volts .1 is lean .5 is stoich .9 is rich. you can run a wire into the car so you can monitor daily as you drive. Piggy back your wire at the O2 meaning leave it in the system just monitor it.Didnt you have something going on where you need 2x O2 sensors. 1 for OE computer 1 fir aftermarket EFI ?
Click to expand...

Question on this: Does the O2 sensor generate the voltage (using a thermocouple-type device) or does the ECU provide a specific voltage to the wire going to the O2 sensor (voltage changes based on resistance inside the sensor)? Doesn't change the way the voltage is monitored, just wondering what the actual process is.
 
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YakkoWarner said:
Question on this: Does the O2 sensor generate the voltage (using a thermocouple-type device) or does the ECU provide a specific voltage to the wire going to the O2 sensor (voltage changes based on resistance inside the sensor)? Doesn't change the way the voltage is monitored, just wondering what the actual process is.
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O2 sensor produces voltage. That's what the ecu reads it evaluates the voltage and determines add or subtract fuel
 
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martingmc86 said:
I have an 86 GMC Sierra 5.0 with a MSD atomic 1 EFI have had an issue with my spark plugs, getting folded up after a couple hundred miles to get cover in black and truck runs like **** first, I thought it was my carburetor so I decided to swap it out to an MSD atomic one EFI and it runs great but after a couple hundred miles like I’ve said the spark plugs foul and goes back to **** what can it be? I rebuild the distributor and put new pick up coil new capacitor, spark plug module new rotor plugs and new cables and still does the same thing my distributor does not have a vacuum advance it is a ESC ELECTRONIC SPARK CONTROL came out of California, so it had smog regulations
Click to expand...
Sounds like either bad rings or bad valve guides with missing seals. Maybe both. You can try one heat range hotter, that might do the trick until you rebuild the engine.

J. B.

J. B.
 
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martingmc86 said:
Ok so I got some readings at idle.41 and at 25mph I got a reading of .73
Click to expand...

O2 voltage should be constantly varying back and forth between 0.1v and 0.9v as the computer constantly adjusts fuel. high volts is rich and it pulls fuel (fuel trims will be below 128). low voltage is lean and it adds fuel (fuel trims will be above 128). ideal AFR is around 0.5v, but it will never sit around 0.5v for long.

are you having oil consumption?

might post some pics of the plugs after theys are fouled.
 
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martingmc86

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gmbellew said:
O2 voltage should be constantly varying back and forth between 0.1v and 0.9v as the computer constantly adjusts fuel. high volts is rich and it pulls fuel (fuel trims will be below 128). low voltage is lean and it adds fuel (fuel trims will be above 128). ideal AFR is around 0.5v, but it will never sit around 0.5v for long.

are you having oil consumption?

might post some pics of the plugs after theys are fouled.
Click to expand...
My bad the reading was .4 at idle and .6 at 30 mph
 
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martingmc86

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v8 5.0
gmbellew said:
O2 voltage should be constantly varying back and forth between 0.1v and 0.9v as the computer constantly adjusts fuel. high volts is rich and it pulls fuel (fuel trims will be below 128). low voltage is lean and it adds fuel (fuel trims will be above 128). ideal AFR is around 0.5v, but it will never sit around 0.5v for long.

are you having oil consumption?

might post some pics of the plugs after theys are fouled.
Click to expand...
Yes I’ll post pics in a bit
 
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