Plug gap surprise
#1
Plug gap surprise
So my V12 has been feeling not quite right for some time. There was a roughness about the engine. Both at idle and throughout the rev range
Checked everything I could think of. I also had a persistent FF44 error code. Replaced the O2 sensor in the A bank, but it reappeared shortly.
Last week, I pulled the old plugs as a last resort. One spark plug was gapped at 0.015, the other at 0.040
Regapped them and took it out for a test. The difference was astounding. The engine is so much smoother. And the idle is very stable.
I have never seen an engine so sensitive to plug gap
Checked everything I could think of. I also had a persistent FF44 error code. Replaced the O2 sensor in the A bank, but it reappeared shortly.
Last week, I pulled the old plugs as a last resort. One spark plug was gapped at 0.015, the other at 0.040
Regapped them and took it out for a test. The difference was astounding. The engine is so much smoother. And the idle is very stable.
I have never seen an engine so sensitive to plug gap
Last edited by scottpeterd; 11-09-2021 at 08:12 PM.
The following 2 users liked this post by scottpeterd:
Doug (11-09-2021),
Greg in France (11-10-2021)
#2
The following users liked this post:
JagGuardian (11-11-2021)
#3
A simple way to check the tune of your V12 is buy one of those $25 infrared thermometer’s point it at each cylinder’s exhaust manifold. If they are all the same. Then all 12 are firing properly and everything is as it should be .
If one or more is cooler then you need to check the plugs and or the injectors. I have a cheap pen like device that set on a spark plugs wire tells me if it’s getting a good spark.
I also have a cheap stereoscope to set on each injector to listen to it firing.
It takes me about 10 minutes to check everything.
If one or more is cooler then you need to check the plugs and or the injectors. I have a cheap pen like device that set on a spark plugs wire tells me if it’s getting a good spark.
I also have a cheap stereoscope to set on each injector to listen to it firing.
It takes me about 10 minutes to check everything.
The following 3 users liked this post by Mguar:
#4
Your right about the IR. I have one on my sailboat, where I use it to monitor coolant flow during engine checks.
I do use a stethescope for the injectors. That is how I found (with my noid) my injector harness was bad.
I also have one of the spark pens. I also found a defective lead in a new set of plug wires.
These procedures should be part of checking my tuneups.
I do use a stethescope for the injectors. That is how I found (with my noid) my injector harness was bad.
I also have one of the spark pens. I also found a defective lead in a new set of plug wires.
These procedures should be part of checking my tuneups.
#5
I've often speculated that there is no such thing as a "Marelli Failure", ie it isn't a failure of the Marelli system or parts. The real culprit is incorrectly gapped plugs which create the conditions of failure. Akin to how a light switch is burned up by poor connections and high resistance, and we never refer to that as a "switch failure".
Cheers
Cheers
The following users liked this post:
JagGuardian (11-11-2021)
#6
Your right about the IR. I have one on my sailboat, where I use it to monitor coolant flow during engine checks.
I do use a stethescope for the injectors. That is how I found (with my noid) my injector harness was bad.
I also have one of the spark pens. I also found a defective lead in a new set of plug wires.
These procedures should be part of checking my tuneups.
I do use a stethescope for the injectors. That is how I found (with my noid) my injector harness was bad.
I also have one of the spark pens. I also found a defective lead in a new set of plug wires.
These procedures should be part of checking my tuneups.
The following users liked this post:
JagGuardian (11-11-2021)
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