Cylinder 8 misfire help please!!!
Hello everyone, I am new here and was hoping I could get your help with a Ram I am trying to help a friend fix.
It is a 1998 Ram 1500, with the 5.9. I am getting a cylinder 8 misfire code, and a definite miss in the motor. I have already checked spark, replaced spark plug, checked injector wiring, etc... It still misses. Someone told me today it probably has a cracked head at the exhaust seats, could this really be? Any help or ideas would be greatly appreciated.
By the way, this seems like a great forum! Thanks fellas.
It is a 1998 Ram 1500, with the 5.9. I am getting a cylinder 8 misfire code, and a definite miss in the motor. I have already checked spark, replaced spark plug, checked injector wiring, etc... It still misses. Someone told me today it probably has a cracked head at the exhaust seats, could this really be? Any help or ideas would be greatly appreciated.
By the way, this seems like a great forum! Thanks fellas.
TO TEST:
Warm the motor.
Pull the plug
Perform Compression Test
Results: if there's <90 on the guage, that means there's not enough compression to ignite the mixture thus causing the misfire condition.
There's several things that would cause that such as blown rings however, it is highly noted about the cracked valve seat as was in my case. You may also find a spent valve spring or cracked valve due to an overheat condition due to a blocked CAT. In that situation, the heat backs up into the rear of the motor and takes out CYL No 8 by overheating the valvetrain components and the CYL itself. Then, when it thermal cycles (super hot and cools over time), the valve or head will crack due to thermal stresses over time.
Now, one SIMPLE thing that can ALSO cause the same exact symptoms is called induction crossfire. Due to cheap ignition wiring (that is not routed per Dodge TSB which, it states to keep No 8 and No 6 away from one another by at least a minimum distance of 1 inch to prevent induction), one wire ARCS over to another thus firing off the plug prematurely. Good wires will not do this and, good wires need NOT be routed to the TSB.
If you want the best wires money can buy: go here and get a set from: www.magnecor.com You will not have to deal with that bogus workaround for a design flaw and lousy ignition wires ever again. I run these in standard configuration and, I've been across country twice on them and up to elevations of 7000 ft under full load / towing and no issues when strung neatly next to one another. It's rock solid. In my case, I got exactly what I paid for- the best damn ignition wire set ever made-bar none. I've used lots of wire sets too including those junk MSD super deals- garbage in my experience.
The TSB is here: http://dodgeram.info/tsb/1998/18-48-98/18-48-98-v8.htm
Now, before you proceed any further and start changing anything, the root problem must be determined by first ruling out certain things and conducting some tests such as compression test.
If the compression tests show low compression on Cyl No 8, the problem is rooted at the head or CYL level. If the compression reads fine, the problem may simply be at the ignition level which is either going to be coil, cap, ignition wire, plug or head ground issue.
If all that checks out, you now looking at the EFI system. In particular, the fuel injector is to be checked last and, you don't have to pull it to test it. Also, you can damage them if you don't know how to properly pull them / insert them.
TO TEST:
-using a long prybar or screwdriver, simply press the blade to the injector body at the mating seam and the handle to your ear.
-listen for steady clicking sound. If you hear that, it's working at least. (electrically speaking that is and mechanically too) SO, you can rule out a NON-power condition at the wire harness. But, you can simply check that as well with a NOID light to see it flashing while operational. Even though you won't know the voltage amount, it's just a dummy check to verify it's getting some power at least.
I would also check the resistance of the injector and note whether or not it meets OEM spec which is around 12-15 OHMs if memory serves me correct.
However, even though you can hear it mechanically, it may be partially clogged thus not able to inject the full amount of fuel into the combustion chamber thus causing a lean mix that will not burn thus causing a misfire condition.
In that case, the injector should be tested. It is to be removed by rocking side to side and gently pulling up- NEVER TWIST injectors when removing or inserting for it ruins and cuts the O-RINGS thus creating a fuel and or vacuum leak. You should actually remove the entire set and have them tested on a machine as well as professionally cleaned. However, you can also take a cheaper approach and run a good EFI cleaner in one tank of fuel and run the tank through them in one shot in attempt to clean the injectors without having to remove them. However, I prefer to test them vs not knowing.
Remember: Tops leak fuel, lowers leak air so, what can happen is that the lower O-RING becomes dried out and shrinks up thus causing a gross vac leak. This allows way too much air into the chamber thus leaning out the mix thus, it doesn't burn etc etc etc. Same as above just a different failure mechanism.
SO, what I am doing here is routing you from start to finish on how to trouble shoot this starting from the simplest things to the more complex system level. Starting at the ignition system and working outward to the plug to the injector and then working your way into the head / valvetrain to find the root cause for failure.
Now, since I already know the history with these lousy, poorly cast / designed Magnum heads, I immediately run a compression test first vs going through all the wires. If it passes test- I simply start at the ignition system and work outward and rewire to the TSB and retest after rewire and continue on the path depending on the outcome. If it does not pass, it's time to check the valvetrain components and rings at the piston level. I have 240K and my rings are solid so, chances are, it's the head- especially when I hear / read about CYL No 8- it's a dead ringer for first prize for a head failure and / or ignition wire issue.
CM
Last edited by cmckenna; May 21, 2010 at 12:33 PM. Reason: Clarification & Typo
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Yeah, Dodge Magnum heads SUCK and are notorious for that. Mine was also shot.
TO TEST:
Warm the motor.
Pull the plug
Perform Compression Test
Results: if there's <90 on the guage, that means there's not enough compression to ignite the mixture thus causing the misfire condition.
There's several things that would cause that such as blown rings however, it is highly noted about the cracked valve seat as was in my case. You may also find a spent valve spring or cracked valve due to an overheat condition due to a blocked CAT. In that situation, the heat backs up into the rear of the motor and takes out CYL No 8 by overheating the valvetrain components and the CYL itself. Then, when it thermal cycles (super hot and cools over time), the valve or head will crack due to thermal stresses over time.
Now, one SIMPLE thing that can ALSO cause the same exact symptoms is called induction crossfire. Due to cheap ignition wiring (that is not routed per Dodge TSB which, it states to keep No 8 and No 6 away from one another by at least a minimum distance of 1 inch to prevent induction), one wire ARCS over to another thus firing off the plug prematurely. Good wires will not do this and, good wires need NOT be routed to the TSB.
If you want the best wires money can buy: go here and get a set from: www.magnecor.com You will not have to deal with that bogus workaround for a design flaw and lousy ignition wires ever again. I run these in standard configuration and, I've been across country twice on them and up to elevations of 7000 ft under full load / towing and no issues when strung neatly next to one another. It's rock solid. In my case, I got exactly what I paid for- the best damn ignition wire set ever made-bar none. I've used lots of wire sets too including those junk MSD super deals- garbage in my experience.
The TSB is here: http://dodgeram.info/tsb/1998/18-48-98/18-48-98-v8.htm
Now, before you proceed any further and start changing anything, the root problem must be determined by first ruling out certain things and conducting some tests such as compression test.
If the compression tests show low compression on Cyl No 8, the problem is rooted at the head or CYL level. If the compression reads fine, the problem may simply be at the ignition level which is either going to be coil, cap, ignition wire, plug or head ground issue.
If all that checks out, you now looking at the EFI system. In particular, the fuel injector is to be checked last and, you don't have to pull it to test it. Also, you can damage them if you don't know how to properly pull them / insert them.
TO TEST:
-using a long prybar or screwdriver, simply press the blade to the injector body at the mating seam and the handle to your ear.
-listen for steady clicking sound. If you hear that, it's working at least. (electrically speaking that is and mechanically too) SO, you can rule out a NON-power condition at the wire harness. But, you can simply check that as well with a NOID light to see it flashing while operational. Even though you won't know the voltage amount, it's just a dummy check to verify it's getting some power at least.
I would also check the resistance of the injector and note whether or not it meets OEM spec which is around 12-15 OHMs if memory serves me correct.
However, even though you can hear it mechanically, it may be partially clogged thus not able to inject the full amount of fuel into the combustion chamber thus causing a lean mix that will not burn thus causing a misfire condition.
In that case, the injector should be tested. It is to be removed by rocking side to side and gently pulling up- NEVER TWIST injectors when removing or inserting for it ruins and cuts the O-RINGS thus creating a fuel and or vacuum leak. You should actually remove the entire set and have them tested on a machine as well as professionally cleaned. However, you can also take a cheaper approach and run a good EFI cleaner in one tank of fuel and run the tank through them in one shot in attempt to clean the injectors without having to remove them. However, I prefer to test them vs not knowing.
Remember: Tops leak fuel, lowers leak air so, what can happen is that the lower O-RING becomes dried out and shrinks up thus causing a gross vac leak. This allows way too much air into the chamber thus leaning out the mix thus, it doesn't burn etc etc etc. Same as above just a different failure mechanism.
SO, what I am doing here is routing you from start to finish on how to trouble shoot this starting from the simplest things to the more complex system level. Starting at the ignition system and working outward to the plug to the injector and then working your way into the head / valvetrain to find the root cause for failure.
Now, since I already know the history with these lousy, poorly cast / designed Magnum heads, I immediately run a compression test first vs going through all the wires. If it passes test- I simply start at the ignition system and work outward and rewire to the TSB and retest after rewire and continue on the path depending on the outcome. If it does not pass, it's time to check the valvetrain components and rings at the piston level. I have 240K and my rings are solid so, chances are, it's the head- especially when I hear / read about CYL No 8- it's a dead ringer for first prize for a head failure and / or ignition wire issue.
CM
TO TEST:
Warm the motor.
Pull the plug
Perform Compression Test
Results: if there's <90 on the guage, that means there's not enough compression to ignite the mixture thus causing the misfire condition.
There's several things that would cause that such as blown rings however, it is highly noted about the cracked valve seat as was in my case. You may also find a spent valve spring or cracked valve due to an overheat condition due to a blocked CAT. In that situation, the heat backs up into the rear of the motor and takes out CYL No 8 by overheating the valvetrain components and the CYL itself. Then, when it thermal cycles (super hot and cools over time), the valve or head will crack due to thermal stresses over time.
Now, one SIMPLE thing that can ALSO cause the same exact symptoms is called induction crossfire. Due to cheap ignition wiring (that is not routed per Dodge TSB which, it states to keep No 8 and No 6 away from one another by at least a minimum distance of 1 inch to prevent induction), one wire ARCS over to another thus firing off the plug prematurely. Good wires will not do this and, good wires need NOT be routed to the TSB.
If you want the best wires money can buy: go here and get a set from: www.magnecor.com You will not have to deal with that bogus workaround for a design flaw and lousy ignition wires ever again. I run these in standard configuration and, I've been across country twice on them and up to elevations of 7000 ft under full load / towing and no issues when strung neatly next to one another. It's rock solid. In my case, I got exactly what I paid for- the best damn ignition wire set ever made-bar none. I've used lots of wire sets too including those junk MSD super deals- garbage in my experience.
The TSB is here: http://dodgeram.info/tsb/1998/18-48-98/18-48-98-v8.htm
Now, before you proceed any further and start changing anything, the root problem must be determined by first ruling out certain things and conducting some tests such as compression test.
If the compression tests show low compression on Cyl No 8, the problem is rooted at the head or CYL level. If the compression reads fine, the problem may simply be at the ignition level which is either going to be coil, cap, ignition wire, plug or head ground issue.
If all that checks out, you now looking at the EFI system. In particular, the fuel injector is to be checked last and, you don't have to pull it to test it. Also, you can damage them if you don't know how to properly pull them / insert them.
TO TEST:
-using a long prybar or screwdriver, simply press the blade to the injector body at the mating seam and the handle to your ear.
-listen for steady clicking sound. If you hear that, it's working at least. (electrically speaking that is and mechanically too) SO, you can rule out a NON-power condition at the wire harness. But, you can simply check that as well with a NOID light to see it flashing while operational. Even though you won't know the voltage amount, it's just a dummy check to verify it's getting some power at least.
I would also check the resistance of the injector and note whether or not it meets OEM spec which is around 12-15 OHMs if memory serves me correct.
However, even though you can hear it mechanically, it may be partially clogged thus not able to inject the full amount of fuel into the combustion chamber thus causing a lean mix that will not burn thus causing a misfire condition.
In that case, the injector should be tested. It is to be removed by rocking side to side and gently pulling up- NEVER TWIST injectors when removing or inserting for it ruins and cuts the O-RINGS thus creating a fuel and or vacuum leak. You should actually remove the entire set and have them tested on a machine as well as professionally cleaned. However, you can also take a cheaper approach and run a good EFI cleaner in one tank of fuel and run the tank through them in one shot in attempt to clean the injectors without having to remove them. However, I prefer to test them vs not knowing.
Remember: Tops leak fuel, lowers leak air so, what can happen is that the lower O-RING becomes dried out and shrinks up thus causing a gross vac leak. This allows way too much air into the chamber thus leaning out the mix thus, it doesn't burn etc etc etc. Same as above just a different failure mechanism.
SO, what I am doing here is routing you from start to finish on how to trouble shoot this starting from the simplest things to the more complex system level. Starting at the ignition system and working outward to the plug to the injector and then working your way into the head / valvetrain to find the root cause for failure.
Now, since I already know the history with these lousy, poorly cast / designed Magnum heads, I immediately run a compression test first vs going through all the wires. If it passes test- I simply start at the ignition system and work outward and rewire to the TSB and retest after rewire and continue on the path depending on the outcome. If it does not pass, it's time to check the valvetrain components and rings at the piston level. I have 240K and my rings are solid so, chances are, it's the head- especially when I hear / read about CYL No 8- it's a dead ringer for first prize for a head failure and / or ignition wire issue.
CM
The #8 cylinder only has 90 PSi compression
The rest tested out at 130-150 PSI. So definitely major problems with the #8 hole. The new spark plug is actually letting it run on all 8 cylinders now, according to my computer, but barely. I also checked for a faulty plenum gasket. I jacked the rear of the truck up, opened the throttle plates and peaked down inside. There was hardly any oil at all in there, so that isn't the problem. As bad of condition as that spark plug is in, I am thinking major issues. What do you guys think? By the way, thanks for all the input!
Last edited by fummins; May 22, 2010 at 02:37 AM.
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Joined: Apr 2010
Posts: 5,011
Likes: 6
From: Meeker, CO
There should be NO oil in there. A blown plenum gasket, though, will not cause low compression, so this is really a moot point.
Good luck with it.
Good luck with it.
It's either one or two areas: head or rings and, if she's not burning oil, chances are, you've either got a cracked head (dry crack) between the valve seat and plug hole or, you've got a cracked valve or, you've got a bad / weak spring. In all cases, the valve is not fully seating into the seat thus the low compression.
When you tested it, did you note whether it HOLDS that 90psi or not. If it's not holding, your looking at a valve that is not seating. If there's metal deposits on the plug, that's a sure sign of wear. Metal is being sucked into the combustion chamber and, again, it's most likely rooted at the head level- particularly, a bad intake / exhaust valves that may be chipped is the root cause for that debris that is seen.
You can remove the valve cover and take a peak and see if there's visual indication of a problem in that area such as a gross failure of the rocker arm, pushrod, springs etc.
What I was hoping for was a weak spring as that's not too bad to fix and, the head doesn't have to be pulled in order to do so. But, after reading about metal debris- that's a tell tale sign of a chipped, cracked valve.
If you have the skills, tear into it, if not, have a pro investigate and fix it for you.
CM
When you tested it, did you note whether it HOLDS that 90psi or not. If it's not holding, your looking at a valve that is not seating. If there's metal deposits on the plug, that's a sure sign of wear. Metal is being sucked into the combustion chamber and, again, it's most likely rooted at the head level- particularly, a bad intake / exhaust valves that may be chipped is the root cause for that debris that is seen.
You can remove the valve cover and take a peak and see if there's visual indication of a problem in that area such as a gross failure of the rocker arm, pushrod, springs etc.
What I was hoping for was a weak spring as that's not too bad to fix and, the head doesn't have to be pulled in order to do so. But, after reading about metal debris- that's a tell tale sign of a chipped, cracked valve.
If you have the skills, tear into it, if not, have a pro investigate and fix it for you.
CM
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From: Idaho
It's either one or two areas: head or rings and, if she's not burning oil, chances are, you've either got a cracked head (dry crack) between the valve seat and plug hole or, you've got a cracked valve or, you've got a bad / weak spring. In all cases, the valve is not fully seating into the seat thus the low compression.
When you tested it, did you note whether it HOLDS that 90psi or not. If it's not holding, your looking at a valve that is not seating. If there's metal deposits on the plug, that's a sure sign of wear. Metal is being sucked into the combustion chamber and, again, it's most likely rooted at the head level- particularly, a bad intake / exhaust valves that may be chipped is the root cause for that debris that is seen.
You can remove the valve cover and take a peak and see if there's visual indication of a problem in that area such as a gross failure of the rocker arm, pushrod, springs etc.
What I was hoping for was a weak spring as that's not too bad to fix and, the head doesn't have to be pulled in order to do so. But, after reading about metal debris- that's a tell tale sign of a chipped, cracked valve.
If you have the skills, tear into it, if not, have a pro investigate and fix it for you.
CM
When you tested it, did you note whether it HOLDS that 90psi or not. If it's not holding, your looking at a valve that is not seating. If there's metal deposits on the plug, that's a sure sign of wear. Metal is being sucked into the combustion chamber and, again, it's most likely rooted at the head level- particularly, a bad intake / exhaust valves that may be chipped is the root cause for that debris that is seen.
You can remove the valve cover and take a peak and see if there's visual indication of a problem in that area such as a gross failure of the rocker arm, pushrod, springs etc.
What I was hoping for was a weak spring as that's not too bad to fix and, the head doesn't have to be pulled in order to do so. But, after reading about metal debris- that's a tell tale sign of a chipped, cracked valve.
If you have the skills, tear into it, if not, have a pro investigate and fix it for you.
CM
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From: Central Oklahoma
No, a little oil is acceptable.
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There was almost nothing in there at all. It was actually very clean down inside, and even after I jacked it up there was no oil puddle whatsoever. I feel bad for her. No job, the economy hasn't really picked up much, and now a broken truck that she really likes a lot, and can't afford to fix.
So what would happen if she just keeps driving it the way it is? Will it get worse? Like I said, it is firing on #8 now, but it is right at the point where if it loses any additional compression, it will start missing again. I wonder how long the new spark plug will last before it fouls up again.
So what would happen if she just keeps driving it the way it is? Will it get worse? Like I said, it is firing on #8 now, but it is right at the point where if it loses any additional compression, it will start missing again. I wonder how long the new spark plug will last before it fouls up again.
There was almost nothing in there at all. It was actually very clean down inside, and even after I jacked it up there was no oil puddle whatsoever. I feel bad for her. No job, the economy hasn't really picked up much, and now a broken truck that she really likes a lot, and can't afford to fix.
So what would happen if she just keeps driving it the way it is? Will it get worse? Like I said, it is firing on #8 now, but it is right at the point where if it loses any additional compression, it will start missing again. I wonder how long the new spark plug will last before it fouls up again.
So what would happen if she just keeps driving it the way it is? Will it get worse? Like I said, it is firing on #8 now, but it is right at the point where if it loses any additional compression, it will start missing again. I wonder how long the new spark plug will last before it fouls up again.
CM
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I've know many who drive on what is called a dead cylinder. It will still run and, as long as you keep changing the plug out, you can still run it- UNLESS- the valve is chipping away due to becoming brittle from thermal hardening this can cause major damage when and if the valve chip jams the valve in the open position. The piston may smack the valve (if it's a large chip wedging it open far enough into the combustion zone and then your talking a bent valve and possibly damage to the connecting rod as well.
CM
CM