Backfire issue plz help
Lead Driver
Joined: Aug 2003
Posts: 7,592
Likes: 10
From: **** hole San Jose ca.
Ok like other post say could be any of the issues.
Old trucks that have been used for towing or camper with out the gas lead additive soon will burn the exhaust valve seats that cause it to backfire popping through the carb and loose power when pushing the throttle down a little to much, like passing or going up hill. And only keeps getting worse as you drive the vehicle. If the stock heads have not had the harden seats installed. Or a set of D2TA or D4 heads have not been swapped out.
I'd do the basic tune up test. 1st thing do a good compression test, a dry & then a wet one= wet means squirt a few pumps of oil in each cylinder and see how much the psi comes up from the dry test run. Recorded each test. This is like the doctor checking your blood psi. Low cylinder compression.
Also check the plugs color if wet & oily with high cylinder psi cold be a bad intake gasket with a bluish tail pipe smoke plus using a lot of oil. When adding a few squirts of oil in the cylinder does is seals the rings and tell you what the condition is. Then if compression is still way low you know it's do to the valves condition. If all say above 125-155. But if 160+ psi and wet not. #2. think is use a vacuum gauge hooked in to intake manifold and watch meter movement if you don't have the vac.movement chart look on the net. This give you more needed info on the engines condition. #3 Check points gap & condition replaces as needed. also look for any loose wires broken or or frayed wires inside the distributor also check inside the dist-cap for any cracks and arcing or carbon build up. Pull each wire out of dist cap and check for any corrosion down inside the holes. Replace as needed. set point at .017 if you have the single port vacuum advance. And 0.21 with with double port vac. advance once this is done set timing to about 6 BFTC if you don't have a book. Spark plug wire can only be checked with a ohm meter to weed out the bad one's. This is all the basic things when doing a tuneup. Recheck order of spark plug wires all coil wires..orich
Old trucks that have been used for towing or camper with out the gas lead additive soon will burn the exhaust valve seats that cause it to backfire popping through the carb and loose power when pushing the throttle down a little to much, like passing or going up hill. And only keeps getting worse as you drive the vehicle. If the stock heads have not had the harden seats installed. Or a set of D2TA or D4 heads have not been swapped out.
I'd do the basic tune up test. 1st thing do a good compression test, a dry & then a wet one= wet means squirt a few pumps of oil in each cylinder and see how much the psi comes up from the dry test run. Recorded each test. This is like the doctor checking your blood psi. Low cylinder compression.
Also check the plugs color if wet & oily with high cylinder psi cold be a bad intake gasket with a bluish tail pipe smoke plus using a lot of oil. When adding a few squirts of oil in the cylinder does is seals the rings and tell you what the condition is. Then if compression is still way low you know it's do to the valves condition. If all say above 125-155. But if 160+ psi and wet not. #2. think is use a vacuum gauge hooked in to intake manifold and watch meter movement if you don't have the vac.movement chart look on the net. This give you more needed info on the engines condition. #3 Check points gap & condition replaces as needed. also look for any loose wires broken or or frayed wires inside the distributor also check inside the dist-cap for any cracks and arcing or carbon build up. Pull each wire out of dist cap and check for any corrosion down inside the holes. Replace as needed. set point at .017 if you have the single port vacuum advance. And 0.21 with with double port vac. advance once this is done set timing to about 6 BFTC if you don't have a book. Spark plug wire can only be checked with a ohm meter to weed out the bad one's. This is all the basic things when doing a tuneup. Recheck order of spark plug wires all coil wires..orich
Freshman User
Joined: Apr 2012
Posts: 44
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Well, the backfire tru the carb issue was found and fixed. It was bad points. Now with good points i've notice that the knockin sound persisted and i thought this was part of the ignition problem, but no.
I took off all sp wires one by one starting from cyl. #1, doing that the engine hesitates a little, until i got #7...nothing happens, then #8....same thing, no hesitation from the engine.
Took apart spark plugs #7 and #8 and they look that they were not firing. They have carbon deposit from unburned gas and the threads have oil.
Do you think i might get a broken piston rings or could it something else?
Thank you.
I took off all sp wires one by one starting from cyl. #1, doing that the engine hesitates a little, until i got #7...nothing happens, then #8....same thing, no hesitation from the engine.
Took apart spark plugs #7 and #8 and they look that they were not firing. They have carbon deposit from unburned gas and the threads have oil.
Do you think i might get a broken piston rings or could it something else?
Thank you.
Posting Guru
Joined: Jun 1999
Posts: 1,083
Likes: 1
Plug a good plug into those wires one at a time and test for spark...no spark = bad wire...clean and test 7 & 8 plugs on a known good wire...no spark = bad plug. Do a compreesion test, dry and wet, to test engine and rings...all 8 numbers should be within 10-15% of each other. Does the knock increase with rpm? If your lucky, it's a sloppy fuel pump arm or a pulley noise...if not, keep feeding it oil, baby it, and drive it until it dies...meanwhile lookin for another engine to drop in or rebuild.
Freshman User
Joined: Apr 2012
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tmcalavy: do you think a sloppy fuel pump arm or a bad pulley has anything to do with no firing at cyl. #7 and #8?
I also changed sparks plugs on cyl #7 and #8 for another ones brand new and also changed the s.p. wires and the symptoms of no firing continues on those cylinders only.
Orich:
Also I have noticed that there's no oil in the coolant, nor in the engine cap that suggest me there's a leaking gasket.
Besides doing a compression test (I don't have the gauge or tool to do it and order one from the states could take weeks to arrive here, remember i'm stuck in the caribbean) ...what other methods can i use to diagnose for a bad intake gasket?
Thanks for your replies....
I also changed sparks plugs on cyl #7 and #8 for another ones brand new and also changed the s.p. wires and the symptoms of no firing continues on those cylinders only.
Orich:
Also I have noticed that there's no oil in the coolant, nor in the engine cap that suggest me there's a leaking gasket.
Besides doing a compression test (I don't have the gauge or tool to do it and order one from the states could take weeks to arrive here, remember i'm stuck in the caribbean) ...what other methods can i use to diagnose for a bad intake gasket?
Thanks for your replies....
Senior User
Joined: Aug 2008
Posts: 484
Likes: 0
From: pahrump nv
To test a bAd intake gasket leaking into crank case plug the pcv valve and see if there is vacuum at the oil fill cap you place your hand over it or listen for it also plug the dip stick tube that's how I always find intake leaks...engine must be running
Lead Driver
Joined: Aug 2003
Posts: 7,592
Likes: 10
From: **** hole San Jose ca.
One tip off is oil turns black soon after oil change. Also using a lot oil. Maybe smoking from left if you have dual pipes, more blow by noticed now then before. with leaking intake gasket. If you pull intake inspect gasket for a blackish burnt oily area at all port areas of intake gaskets will indicate leaking sucking oil into intake cylinder..
orich
orich
Freshman User
Joined: Apr 2012
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Thought it may be a broken piston ring on those cylinders, but it seems not. anyway tomorrow i'll try to take apart the intake manifold and check the gasket as Orich says.
I hope this is not to difficult for me being a doctor, but if i do some surgeries in a person, in an old truck must be easier, not? (at least the truck won't die from my mistake...hope so)
I hope this is not to difficult for me being a doctor, but if i do some surgeries in a person, in an old truck must be easier, not? (at least the truck won't die from my mistake...hope so)
Lead Driver
Joined: Aug 2003
Posts: 7,592
Likes: 10
From: **** hole San Jose ca.
A good back is needed for lifting that 78lb. intake off & on but is even harder putting it back on unless your standing over the motor. You may need a back surgery aftertha ... Hope you have manual Don't mix up push rods, even end for ends can matter And rocker arms .. orich
Freshman User
Joined: Apr 2012
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Orich and tmcalavy:
When I connect the #8 sparkplug wire to cyl. #8 the knocking sound starts, when is unplugged, there's no knocking sound, so obviously i have something serious in these cylinders. Cyl. #7 doesn't do anything, so plugged or unplugged the engine acts like if it doesn't exist. Same for #8 but the difference is that when this cylinder is plugged some knocking sound can be hear.
So,
I disconnected the PCV hose and suddenly the sound disappears but the engine shakes like crazy. Also, I've noticed that some bluish smog came tru the PCV inlet (left side valve cover cap), don't know what that mean and if this is expected or not. Also the same blue smog came from the other valve cover, the right side.
Haven't tried to disassembly the intake manifold since it's too heavy for me alone...for now.
Any coments?
When I connect the #8 sparkplug wire to cyl. #8 the knocking sound starts, when is unplugged, there's no knocking sound, so obviously i have something serious in these cylinders. Cyl. #7 doesn't do anything, so plugged or unplugged the engine acts like if it doesn't exist. Same for #8 but the difference is that when this cylinder is plugged some knocking sound can be hear.
So,
I disconnected the PCV hose and suddenly the sound disappears but the engine shakes like crazy. Also, I've noticed that some bluish smog came tru the PCV inlet (left side valve cover cap), don't know what that mean and if this is expected or not. Also the same blue smog came from the other valve cover, the right side.
Haven't tried to disassembly the intake manifold since it's too heavy for me alone...for now.
Any coments?