I have a 98 5.7 and chased the same stinking random misfires. After a grand later going through all the possible issues in the forums I went to firestone. My distributor ended up being off by a tooth.....check the simple stuff and that 100 dollar diagnostic at Firestone could save you hundreds and a ton of headaches lol.
99 Tahoe misfiring issue
- Thread starter Dualstroke
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Dualstroke
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Thanks for all the replies guys. I ended up pulling off the upper plenum and accessing the spider. This truck is deffinately loading up with fuel big time. It was pretty caked with carbon. I ended up replacing the regulator on the spider along with new upper plenum gaskets and the fuel line o rings. I cleaned the throttle body really well as it was caked. There is a small plunger looking sensor on the throttle body in the corner of the tb. That was caked and stuck so I freed it up with lots of cleaning. I am assuming this piece has something to do with choke???? I got everything back together and took it for a test drive. It seems a lot less hesitant under power but its still not right. Very rough at idle still and still a little under powered. I am certain it is a fuel issue dumping to much fuel in the plenum. What is left besides injectors? I am going to try a new choke??? Assembly and some sea foam in the next few days.
You can buy choke cleaner to put in the fuel tank but that stuff is a waste of money and time. Choke cleaner is Naphtha and Alcohol. Fuel already has Alcohol why would you need more. You can buy a whole gallon of Naphtha at Lowes or Home Depot or any paint store or any hardware store $10 per gallon. If you insist on using cleaner drive your vehicle until the engine dies from lack of gas. Pour the 1 gallon can of naphtha in the fuel tank and drive another 10 miles. I tried this and did not help.
Have you checked the engine temperature sensor and the air temperature
sensor? I think you said you already changed the cooling system thermostat.
Old parts give the computer false readings. I replaced my engine temperature sensor and my gas mileage went up 1 mpg. I replaced my air temperature sensor and gas mileage went up another 1 mpg. I changed my cooling system thermostat gas mileage went up 3 mpg. I replaced my spark plugs and wires gas miles increased 4 mpg engine started running smooth again.
Next I replaced the air temperature sensor with a 1000 ohm resistor gas mileage went up another 2 mpg.
Anything you can do to your engine to make it run hotter or make the computer think it is running hotter will give you better gas mileage.
If 1 or more of the oxygen sensors in the exhaust system are bag it will give the computer false readings and the engine will burn more fuel or less fuel.
Check the voltage across the oxygen sensor. Buy a new sensor replace the old one then take another voltage reading. If voltage is the same your old sensor is good.
Here is a photo of the wire that plugs into my 1997 Chevy Tahoe temperature sensor. See the 1000 ohm resistor in the plug. This tricks the computer into thinking the engine is sucking in 180 degree air so the computer tells the engine to burn less fuel. You can buy a 1000 ohm resistor at Radio Shack or Ebay for 5 cents. This is not something you should do to your engine if it is already burning the correct amount of fuel. I increased my gas miles another 2 mpg buy using this resistor.
Check the mass air flow sensor. If it tells the computer your engine is sucking in too much air the computer will make the engine burn more fuel in an attempt to get 14.7 to 1 the air/fuel mixture it wants.
Have you checked the engine temperature sensor and the air temperature
sensor? I think you said you already changed the cooling system thermostat.
Old parts give the computer false readings. I replaced my engine temperature sensor and my gas mileage went up 1 mpg. I replaced my air temperature sensor and gas mileage went up another 1 mpg. I changed my cooling system thermostat gas mileage went up 3 mpg. I replaced my spark plugs and wires gas miles increased 4 mpg engine started running smooth again.
Next I replaced the air temperature sensor with a 1000 ohm resistor gas mileage went up another 2 mpg.
Anything you can do to your engine to make it run hotter or make the computer think it is running hotter will give you better gas mileage.
If 1 or more of the oxygen sensors in the exhaust system are bag it will give the computer false readings and the engine will burn more fuel or less fuel.
Check the voltage across the oxygen sensor. Buy a new sensor replace the old one then take another voltage reading. If voltage is the same your old sensor is good.
Here is a photo of the wire that plugs into my 1997 Chevy Tahoe temperature sensor. See the 1000 ohm resistor in the plug. This tricks the computer into thinking the engine is sucking in 180 degree air so the computer tells the engine to burn less fuel. You can buy a 1000 ohm resistor at Radio Shack or Ebay for 5 cents. This is not something you should do to your engine if it is already burning the correct amount of fuel. I increased my gas miles another 2 mpg buy using this resistor.
Check the mass air flow sensor. If it tells the computer your engine is sucking in too much air the computer will make the engine burn more fuel in an attempt to get 14.7 to 1 the air/fuel mixture it wants.
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You can buy choke cleaner to put in the fuel tank but that stuff is a waste of money and time. Choke cleaner is Naphtha and Alcohol. Fuel already has Alcohol why would you need more. You can buy a whole gallon of Naphtha at Lowes or Home Depot or any paint store or any hardware store $10 per gallon. If you insist on using cleaner drive your vehicle until the engine dies from lack of gas. Pour the 1 gallon can of naphtha in the fuel tank and drive another 10 miles. I tried this and did not help.
Have you checked the engine temperature sensor and the air temperature
sensor? I think you said you already changed the cooling system thermostat.
Old parts give the computer false readings. I replaced my engine temperature sensor and my gas mileage went up 1 mpg. I replaced my air temperature sensor and gas mileage went up another 1 mpg. I changed my cooling system thermostat gas mileage went up 3 mpg. I replaced my spark plugs and wires gas miles increased 4 mpg engine started running smooth again.
Next I replaced the air temperature sensor with a 1000 ohm resistor gas mileage went up another 2 mpg.
Anything you can do to your engine to make it run hotter or make the computer think it is running hotter will give you better gas mileage.
If 1 or more of the oxygen sensors in the exhaust system are bag it will give the computer false readings and the engine will burn more fuel or less fuel.
Check the voltage across the oxygen sensor. Buy a new sensor replace the old one then take another voltage reading. If voltage is the same your old sensor is good.
Here is a photo of the wire that plugs into my 1997 Chevy Tahoe temperature sensor. See the 1000 ohm resistor in the plug. This tricks the computer into thinking the engine is sucking in 180 degree air so the computer tells the engine to burn less fuel. You can buy a 1000 ohm resistor at Radio Shack or Ebay for 5 cents. This is not something you should do to your engine if it is already burning the correct amount of fuel. I increased my gas miles another 2 mpg buy using this resistor.
Check the mass air flow sensor. If it tells the computer your engine is sucking in too much air the computer will make the engine burn more fuel in an attempt to get 14.7 to 1 the air/fuel mixture it wants.
So Gary, you did all that work to get a 9mpg increase? what were you getting before?
BTW 1000 ohms is about 118*F..... 380ohms is around 180*
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Dualstroke
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So I finally limped this truck up to my buddies house(3 1/2 hrs) to get it on his scanner and see what was going on. Intake gaskets needed to be replaced. We replaced the lower intake gaskets, top was done last week and also put a new distributor in while it was out. It is 95% better now. I have no misfiring going on under acceleration now and fuel mileage is a lot better. However, it is still acting up on idle and running rough at idle. It is now throwing the P0174 code now. Fuel pressure is good. I am thinking of replacing both 02 sensors on bank 2. My thinking is that the thing was spitting so much un burnt fuel and soot that they are clogged? I feel I am on the path to winning the battle!!! Lol FWIW: Also back a few posts ago I mentioned the piece in the tb that was dirty and cleaned. That piece is the iac or idle air control.
My son is an auto mechanic. He says the computer learns as the engine runs. It has a lot of bad information stormed in the computer from the bad gasket. You will need to drive it 150 miles before it learns to run better. Best thing to do is remove the battery cable for about 10 hours so the computer looses its memory. Start the engine it will run ruff for 60 seconds then start running better real quick. Within 5 minutes it will be running smooth. You will need to drive it 75 miles for the computer to learn all it needs to know to get good gas mileage.
ma87k5
Full Access Member
You will need a scanner to delete the codes on a OBD II computer. Disconnecting the battery will not clear the codes. It will shut the engine light off. Then drive for 100 miles with no codes and no engine light on for the computer to reset.
Dualstroke
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I did the intake gaskets on Saturday night. Then drove the truck home Sunday and put about 300 miles on it. I reset the codes when I got home. Light came on for the wife today. I scanned them and only p0174 showed up. I'm gonna go get both 02 sensors for the right bank and see how she does.
baby huey
New Member
I have been told that hard starting, rough idle, and misfiring codes is bad fuel injection poppet valves spider system. Mine will shake the whole dash and start flashing the Check Engine Light if ran under heavy load like towing or a large hill for very long.
Im replacing the whole spider assembly with:
http://www.amazon.com/ACDelco-217-3...80639274&sr=8-4&keywords=tahoe+fuel+injection
Probably will not do it for another couple months now as the weather is getting cooler and I need new tires and shocks first. It doesnt seem to do it as bad in cool weather. Luckily mine isnt bad enough yet that I cant drive 80MPH down the highway since I travel 200-300 miles a week.
Im replacing the whole spider assembly with:
http://www.amazon.com/ACDelco-217-3...80639274&sr=8-4&keywords=tahoe+fuel+injection
Probably will not do it for another couple months now as the weather is getting cooler and I need new tires and shocks first. It doesnt seem to do it as bad in cool weather. Luckily mine isnt bad enough yet that I cant drive 80MPH down the highway since I travel 200-300 miles a week.
P0174 is a System too Lean Bank 2. This means the O2's are picking up extra oxygen in the exhaust (wasnt mixed with fuel and burned). Bank 2 is passenger side, the sensor that helps meter out fuel would be the 1 before the CAT. The sensor after the cat just measures if the cat is working. I would put a scantool or a multimeter on it and see if it is switching, stuck, or having other issues.
