MOST FOUL RESISTANT PLUGS

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j.johnson23
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MOST FOUL RESISTANT PLUGS

Post by j.johnson23 » Sun Nov 10, 2019 8:09 pm

Hi all, I am having problems with plug fouling on a RV8.
It seems only to be a problem if the car is not used for a couple of months, normally no problem at all.
Have tried NGK bp6es and they were fine in Sept when car last used, this is the 2nd set as the first were fouled up in March after leaving it for 3 months.
The fouling appears to be soot and if brushed with acetone the plugs will fire on my test rig (will not fire until cleaned), have never reused them in the car though.
3.9 WITH 14CUX system no cats and 35dm8 distributor (GM hei based ignition system), changed distributor and hei module last time as well as leads and coil (Bosch)before realizing the plugs were fouled.
I have fitted a fuel pressure gauge in the supply line and it shows 35 psi on switching on ign, it holds pressure for about a minute when ign is turned off so I assume the injectors are not leaking. Rovergauge shows no faults and a tester I made shows injectors are firing.
Has anyone else had this problem?
On the test rig (made using the old hei,coil & distributor) the hei will make a spark on a plug that has had the electrode cut off and will jump a 20mm gap between ht lead and earth so it is a good unit.
Sorry for the long post.



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stevieturbo
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Re: MOST FOUL RESISTANT PLUGS

Post by stevieturbo » Mon Nov 11, 2019 7:10 pm

Ensure the ignition system is up to par.

And equally important, ensure tuning is correct. If it's too rich, too often, it will foul even with hotter plugs.

You could try 5's, but the plugs are probably not the problem.
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DaveEFI
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Re: MOST FOUL RESISTANT PLUGS

Post by DaveEFI » Tue Nov 12, 2019 9:55 am

Have you checked you have the full 12v getting to the ignition system? Easy way to check is to connect a DVM set to volts to battery positive and coil positive. With the engine running, this will measure any voltage drop in the circuit directly under the normal load on that circuit. Should be no more than 0.5v And do the same with the ignition ground.
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j.johnson23
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Re: MOST FOUL RESISTANT PLUGS

Post by j.johnson23 » Fri Nov 15, 2019 7:03 pm

Full 12v as it is supplied by a dedicated relay,have checked connections,the test rig won't give a spark till the residue is wire brushed off.
The problem is after the car has been left for a month or two,no problem at all if used regular,if the mixture was wrong I would have this problem all the time.
If the injectors were leaking it would not hold pressure after pump is turned off,the residue on plugs is dry so not oil and there is no smoke on start up.
I have a spare set of injectors so will try them and see how it goes,i'm wondering if the spray pattern is bad due to clogging/carbon build up.
Will let you know my findings as I progress.

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Re: MOST FOUL RESISTANT PLUGS

Post by garrycol » Sat Nov 16, 2019 12:31 am

I have a similar problem in another vehicle - in my case the carb is running a bit rich and over a couple of days carbon builds up on the spark plugs with a commensurate reduction in performance until the engine will not run - there is no spark at the spark plugs so mimicking an ignition problem which I though the issue was at first. I replaced the entire ignition system but the problem persisted so looked at mixture.

Cleaning the plugs and the engine fires straight away and runs fine but again slowly deteriorates until the engine stops again.

In my case I rebuilt the carb and all I can assume was the accelerator pump was leaking fuel into the carb making it run rich.

So in your case all I can assume something similar in your engine but in your injection - either too much fuel per squirt or fuel is dribbling in from other injectors (I know you checked for this). However as has been suggested and I did in my engine, you need to ensure your ignition system is all good, no low 12v etc then look at the mixture issue.

Oh I also went one heat range higher to help burn off the carbon and went to long tip plugs to get the ignition point lower down in the combustion chamber - didn't fix the problem but did help.

Garry

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