Topic: What would cause 1 spark plug to oil foul?? Viper Engine #3

So, the third installment of "How many viper engines have we ruined" is up and trying to figure out what happened here.

We have one spark plug that keeps oil fouling (#10)...and it's doing it pretty bad.

We changed the valve seals, and it's still happening....the only other thing I can think of is a cracked pistons or oil ring issue?

Anybody have any idea of what it could be???

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Re: What would cause 1 spark plug to oil foul?? Viper Engine #3

Bad rings or bad valve guides come to mind

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Re: What would cause 1 spark plug to oil foul?? Viper Engine #3

Type44 wrote:

Bad rings or bad valve guides come to mind

/agree

Did you compression test the offending cylinder?

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4 (edited by darkostoj 2020-05-18 05:08 PM)

Re: What would cause 1 spark plug to oil foul?? Viper Engine #3

chaase wrote:
Type44 wrote:

Bad rings or bad valve guides come to mind

/agree

Did you compression test the offending cylinder?

We did. Came back fine.

The compression test wouldn't show anything in regards to the oil ring correct?  From what I know, it only measures the compression rings.

Also, all the other plugs are perfect...super strange.

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Re: What would cause 1 spark plug to oil foul?? Viper Engine #3

darkostoj wrote:
chaase wrote:
Type44 wrote:

Bad rings or bad valve guides come to mind

/agree

Did you compression test the offending cylinder?

We did. Came back fine.

The compression test wouldn't show anything in regards to the oil ring correct?  From what I know, it only measures the compression rings.

Also, all the other plugs are perfect...super strange.

PCV system problems can cause it as well but I would expect that to affect all of the cylinders. I would check the valve stem seals next.

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6 (edited by darkostoj 2020-05-18 05:20 PM)

Re: What would cause 1 spark plug to oil foul?? Viper Engine #3

chaase wrote:
darkostoj wrote:
chaase wrote:

/agree

Did you compression test the offending cylinder?

We did. Came back fine.

The compression test wouldn't show anything in regards to the oil ring correct?  From what I know, it only measures the compression rings.

Also, all the other plugs are perfect...super strange.

PCV system problems can cause it as well but I would expect that to affect all of the cylinders. I would check the valve stem seals next.

Changed valve stem seals on problem cylinder with no change.

We are running the same PCV setup as the last motors (none/open hose to puke tank) and this is the first engine where we have seen an issue

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Re: What would cause 1 spark plug to oil foul?? Viper Engine #3

darkostoj wrote:
chaase wrote:
Type44 wrote:

Bad rings or bad valve guides come to mind

/agree

Did you compression test the offending cylinder?

We did. Came back fine.


The compression test wouldn't show anything in regards to the oil ring correct?  From what I know, it only measures the compression rings.

Also, all the other plugs are perfect...super strange.

Yes, bad oil ring likely would not show up on compression test.  Wonder if you could do a smoke test by putting that cylinder at TDC then forcing smoke into the spark plug hole.  With valve cover off see if smoke shows up around the valve or thru crankcase.  Since this is Lemons, I'd consider putting one of those anti-fouler deals on that cylinder and calling it good.


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Re: What would cause 1 spark plug to oil foul?? Viper Engine #3

One of my Benz DOHC sixes had this exact symptom, it turned out to be a hosed intake valve guide (2v engine, like the Viper is)... would dump oil into the chamber on every intake stroke, basically blowing out the fire and making a dead miss, which is a lot harder to feel with 10 cylinders rather than 6. Compression would check out OK as long as the valve would seat. I don’t think it’s PCV related, I could be convinced the oil ring is bad. Usually, I’d think some degree of damage to the bore would occur, which would show up in poor sealing of the compression rings? So, I’m back to the hosed valve guide theory...

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Re: What would cause 1 spark plug to oil foul?? Viper Engine #3

You got plenty of cylinders Send It!

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Re: What would cause 1 spark plug to oil foul?? Viper Engine #3

darkostoj wrote:
chaase wrote:
darkostoj wrote:

We did. Came back fine.

The compression test wouldn't show anything in regards to the oil ring correct?  From what I know, it only measures the compression rings.

Also, all the other plugs are perfect...super strange.

PCV system problems can cause it as well but I would expect that to affect all of the cylinders. I would check the valve stem seals next.

Changed valve stem seals on problem cylinder with no change.

We are running the same PCV setup as the last motors (none/open hose to puke tank) and this is the first engine where we have seen an issue

May be bad guides.  The seals can only do so much if the guides are bad.  I typically do a "wiggle test" to check the guides.  Remove the spring, pull the valve out about 1/2" and wiggle the valve back and forth.  Should only have slight movement.

Running an open PCV setup can lead to oil consumption.  Pressure can build up in the crankcase and cause ring instability.  This would typically affect multiple cylinders, tho.

Re: What would cause 1 spark plug to oil foul?? Viper Engine #3

You might try a wet compression test on that cylinder to
see how much pressure increase there is. A significant increase
indicates a ring sealing problem. A scratch is more likely than
an oil ring problem.

A cheap, smart phone bore scope might help, too.
Check the intake valve for massive oil deposits.

One bad valve guide seems odd, but I suppose it could happen.

Post a pic of the fouled plug. Black and sooty is usually fuel. (Bad injector)
Black and wet is oil.

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Re: What would cause 1 spark plug to oil foul?? Viper Engine #3

This was at the last Lemons race.

So..do a compression test, then dump oil in the cylinder and do it again and see the difference?  Does this give us any idea of condition of bore/oil ring?  I was under the assumption that compression tests measure the top 2 rings compression rings...not the oil ring.

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13 (edited by derekste 2020-05-20 04:58 AM)

Re: What would cause 1 spark plug to oil foul?? Viper Engine #3

sorry if this is a dumb question but have you checked for a dead coil on that cylinder? looks just like my 5 cyl does with a bad coilpack on #2.

edit: a compression test measures the overall compression capabilities of the cylinder. if rings #1 & #2 are shot, a wet ring #3 is all you got left presumably

edit 2: re: the dead coil... it is still possible to get a regular looking spark at idle speeds and cylinder conditions and then have a shitty spark at higher RPM.

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Re: What would cause 1 spark plug to oil foul?? Viper Engine #3

derekste wrote:

sorry if this is a dumb question but have you checked for a dead coil on that cylinder? looks just like my 5 cyl does with a bad coilpack on #2.

edit: a compression test measures the overall compression capabilities of the cylinder. if rings #1 & #2 are shot, a wet ring #3 is all you got left presumably

edit 2: re: the dead coil... it is still possible to get a regular looking spark at idle speeds and cylinder conditions and then have a shitty spark at higher RPM.

I would assume it would run fine until it fouls? But yes a bad coil or wire would cause an issue.

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15 (edited by fleming95 2020-05-20 05:23 PM)

Re: What would cause 1 spark plug to oil foul?? Viper Engine #3

The fouled plug also looks groddy compared to the others in frame.  Looks like corrosion to me?

If those were new plugs at the start of the race does that mean something?

Re: What would cause 1 spark plug to oil foul?? Viper Engine #3

fleming95 wrote:

The fouled plug also looks groddy compared to the others in frame.  Looks like corrosion to me?

If those were new plugs at the start of the race does that mean something?

Those were the plugs that were in the engine from who knows where. After we put a fresh set in they didn't look as bad but the fouling was the same.

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Re: What would cause 1 spark plug to oil foul?? Viper Engine #3

darkostoj wrote:
fleming95 wrote:

The fouled plug also looks groddy compared to the others in frame.  Looks like corrosion to me?

If those were new plugs at the start of the race does that mean something?

Those were the plugs that were in the engine from who knows where. After we put a fresh set in they didn't look as bad but the fouling was the same.

not crazy up on V-10's but I know BB Mopars can suck oil thru the intake gasket and can foul one plug or more at a time. How does the intake lay on top of that? Isn't it a Magnum V8 with 2 extra cans?

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Re: What would cause 1 spark plug to oil foul?? Viper Engine #3

Mr.Yuck wrote:
darkostoj wrote:
fleming95 wrote:

The fouled plug also looks groddy compared to the others in frame.  Looks like corrosion to me?

If those were new plugs at the start of the race does that mean something?

Those were the plugs that were in the engine from who knows where. After we put a fresh set in they didn't look as bad but the fouling was the same.

not crazy up on V-10's but I know BB Mopars can suck oil thru the intake gasket and can foul one plug or more at a time. How does the intake lay on top of that? Isn't it a Magnum V8 with 2 extra cans?

This engine has the oil valley separated from the intake gasket. So, no way for that to happen here.

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19 (edited by derekste 2020-05-21 05:15 AM)

Re: What would cause 1 spark plug to oil foul?? Viper Engine #3

Mr.Yuck wrote:

I would assume it would run fine until it fouls? But yes a bad coil or wire would cause an issue.

it kind of depends. my particular bad coil would idle fine and break up under load/boost. during my latest test drive, it failed completely and no longer sparks at idle. I put new plugs in and the one on the dead cylinder turned black (and was wet) right after cranking. there are spark testing tools you can use to induce a higher-ohm load on the coil (by increasing the arc gap) but by this point you already know.

did you smell that plug? does it smell like oil or gas? I always try to crank and pull the plugs asap so I can find the wet ones... makes it pretty easy to find out where you are missing spark.

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Re: What would cause 1 spark plug to oil foul?? Viper Engine #3

derekste wrote:
Mr.Yuck wrote:

I would assume it would run fine until it fouls? But yes a bad coil or wire would cause an issue.

it kind of depends. my particular bad coil would idle fine and break up under load/boost. during my latest test drive, it failed completely and no longer sparks at idle. I put new plugs in and the one on the dead cylinder turned black (and was wet) right after cranking. there are spark testing tools you can use to induce a higher-ohm load on the coil (by increasing the arc gap) but by this point you already know.

did you smell that plug? does it smell like oil or gas? I always try to crank and pull the plugs asap so I can find the wet ones... makes it pretty easy to find out where you are missing spark.

When we put a new plug in, the car runs great and feels like it has full power.  After about 10 minutes on track it starts to break up and power loss is really noticeable. 

I would think since it runs so good with a fresh plug, the coil is working properly, but when the plug fouls it starts to run badly.

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Re: What would cause 1 spark plug to oil foul?? Viper Engine #3

valve guides are fine.
it does not look like much of oil foul, but rich foul.
check your injector. Maybe move the injector over one spot and see.
Check your crank vents. But easier if you can look inside the intake, I use inspection camera, can go through throttle body. Also when pull the injector, can see through the hole.

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22

Re: What would cause 1 spark plug to oil foul?? Viper Engine #3

Is there a situation where #10 runs hotter than 1-9 in it's normal Viper configuration, so the ECU compensates with a richer mixture, but now that condition doesn't exist but the ECU is continuing to run #10 rich?

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23 (edited by fleming95 2020-05-22 04:07 PM)

Re: What would cause 1 spark plug to oil foul?? Viper Engine #3

Has the ECM been ruled out as a cause?

I'm assuming that the injectors are individually fired for this suggestion to make sense: what if the injector driver on #10 has a problem and goes full-on, flooding that cylinder?  I'd think that would wash down that cylinder and stink of fuel, so not likely, but?

If you run the car with no fuel or spark on #10 for a while, what does a clean plug then look like?

(I'm trying to think through a case where the plug fouls as a result of a problem that's causing the '...really noticeable power loss...' which sounds possibly like the result of more than one cylinder dropping power.)

Re: What would cause 1 spark plug to oil foul?? Viper Engine #3

fleming95 wrote:

Has the ECM been ruled out as a cause?

I'm assuming that the injectors are individually fired for this suggestion to make sense: what if the injector driver on #10 has a problem and goes full-on, flooding that cylinder?  I'd think that would wash down that cylinder and stink of fuel, so not likely, but?

If you run the car with no fuel or spark on #10 for a while, what does a clean plug then look like?

(I'm trying to think through a case where the plug fouls as a result of a problem that's causing the '...really noticeable power loss...' which sounds possibly like the result of more than one cylinder dropping power.)

When we were racing if we killed the master power and started the car back up it would run better. That leads me to believe the ECU is working properly.  The fouled plug would misfire and the computer would compensate for it.

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Re: What would cause 1 spark plug to oil foul?? Viper Engine #3

In the old days , when they started getting fouled, we just put in a "HOTTER" plug. or plugs.

If you were "oil burning", you should have a ton of black burnt stuff on your plug when you pull it out.
until the gap was almost closed up.

that has lots of "wet" stuff on it, not burned  dry hydrocarbon.

Its not "burning" the oil, like it should.

try this hack... look up the plug number , and find one that burns "hotter"

good luck!