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i have checked all the plugs this morning and there all fireing, not one plug is dead,
Did you check they where firing at idle and you say it misses at speed?
I have had plugs fail at anything above idle.
I would still like to know why Matt said pulling the codes was a waste as it would give all kinds of codes?
You have had the truck for 15 years, it comes from the factory with a feed back system, read a computer runs the show, I have not seen where you changed it over to a non-feed back system so why no code pulling?
All it takes is 1 of the things Matt said would show up if codes where pulled to go bad to throw the computer into a fit and make the motor run bad.
If the computer is not getting a signal from a sensor it goes into "limp mode" to get you some place to get it fixed and I would say that's what you have and the codes can tell you that.
Now if you have done a swap to remove the feedback system and was posted sorry I missed it and we will need to go down a different path to fix this.
Other wise we need to see what the computer is see / saying to have a clue what maybe wrong.
Just my .02
Dave ----
Did you check they where firing at idle and you say it misses at speed?
I have had plugs fail at anything above idle.
I would still like to know why Matt said pulling the codes was a waste as it would give all kinds of codes?
You have had the truck for 15 years, it comes from the factory with a feed back system, read a computer runs the show, I have not seen where you changed it over to a non-feed back system so why no code pulling?
All it takes is 1 of the things Matt said would show up if codes where pulled to go bad to throw the computer into a fit and make the motor run bad.
If the computer is not getting a signal from a sensor it goes into "limp mode" to get you some place to get it fixed and I would say that's what you have and the codes can tell you that.
Now if you have done a swap to remove the feedback system and was posted sorry I missed it and we will need to go down a different path to fix this.
Other wise we need to see what the computer is see / saying to have a clue what maybe wrong.
Just my .02
Dave ----
Pulling the codes is a waste in this instance. The YFA feedback solenoid controls the air bleeds for the main and idle circuits, but during open loop operation (cold engine) the feedback solenoid does not operate and the O2 sensor is disabled and the system defaults full rich and has no impact on idle on a cold engine..
The only sensor the ECU uses to control the fuel air mix on the feedback carbs is the O2 Sensor all other sensors are for ignition control., since the feedback solenoid and O2 sensor are disabled in open loop operation the system defaults to full rich so even if there was an issue with the feedback solenoid (NFG or stuck) or the O2 sensor it would not show up at idle on a cold engine..
This is the built in safety if the O2 sensor goes for a dump the system defaults to full rich just like in SEFI set ups. Pulling the codes in this instance will tell you nothing.
This appears to be a carb issue with how it is running the fluctuating idle is dead give away as is the black smoke.
The OP will have to set the base timing to the factory setting, disconnect the air mix solenoid on the carb open the choke fully heat the engine up and try setting the Idle air mix screw. If this does not clear it up replace or rebuild the carb.
dont know how to pull codes on this truck,where is the computer? anyways,
just went out to put the mower up, and i let the truck idle, for about 15mins, came back to the truck and it was idling still like crap, not 1 min later it started to clear up at idle, was idleing like it should be, so i gave it a little rev and it died, started right back up came to a good idle, gave it a rev again, it wanted to die, so i had to feather the throttle once it got passed the dead spot it rev smooth and clear,,
dont know how to pull codes on this truck,where is the computer? anyways,
just went out to put the mower up, and i let the truck idle, for about 15mins, came back to the truck and it was idling still like crap, not 1 min later it started to clear up at idle, was idleing like it should be, so i gave it a little rev and it died, started right back up came to a good idle, gave it a rev again, it wanted to die, so i had to feather the throttle once it got passed the dead spot it rev smooth and clear,,
Pulling the codes is a waste in this instance. The YFA feedback solenoid controls the air bleeds for the main and idle circuits, but during open loop operation (cold engine) the feedback solenoid does not operate and the O2 sensor is disabled and the system defaults full rich and has no impact on idle on a cold engine..
The only sensor the ECU uses to control the fuel air mix on the feedback carbs is the O2 Sensor all other sensors are for ignition control., since the feedback solenoid and O2 sensor are disabled in open loop operation the system defaults to full rich so even if there was an issue with the feedback solenoid (NFG or stuck) or the O2 sensor it would not show up at idle on a cold engine..
This is the built in safety if the O2 sensor goes for a dump the system defaults to full rich just like in SEFI set ups. Pulling the codes in this instance will tell you nothing.
This appears to be a carb issue with how it is running the fluctuating idle is dead give away as is the black smoke.
The OP will have to set the base timing to the factory setting, disconnect the air mix solenoid on the carb open the choke fully heat the engine up and try setting the Idle air mix screw. If this does not clear it up replace or rebuild the carb.
Ok now I see why you said about the codes.
So this whole time it has been a cold motor stuck in open loop and why it runs rich?
It is hard to believe he has not run it long enough to get it out of open loop to then check codes to get some hint what maybe going on?
I would also guess the ECM has to be looking at the engine temp thru a temp sensor to know when to go into closed loop.
If this sensor was bad, ECM never went to closed loop, it run rich long enough, plugs could become fouled and not fire right and the miss fire even with newish plugs.
Dave ----
Ok now I see why you said about the codes.
So this whole time it has been a cold motor stuck in open loop and why it runs rich?
It is hard to believe he has not run it long enough to get it out of open loop to then check codes to get some hint what maybe going on?
I would also guess the ECM has to be looking at the engine temp thru a temp sensor to know when to go into closed loop.
If this sensor was bad, ECM never went to closed loop, it run rich long enough, plugs could become fouled and not fire right and the miss fire even with newish plugs.
Dave ----
Yes it uses the ECT to go closed loop. It should not be running so rich to foul the plugs even in open loop.
Someone else is also having issues with a scanner and was asked if both plugs were plugged into the scanner.
Large red one and a single wire with gray plug, both need to be plugged in they say.
Dave ----
You need to use both connectors to get the codes. I had a 86 4.9 with the exact same symptoms. Turned out the carb was shot and fuel filter clogged. Plugs were fouled from rich carb
as well.
