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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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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.
202mph standing mile
Rover SD1 VDP EFI
Tech Edge 2Y
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.
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.
Still worth a try in my opinion
So, rich mixture and cold engine may kill the plugs. In my opinion even if you clean a wet plug it may not work again. I may actually have this issue with my RV8. I ran the engine after rebuild for a short time and next time with did not want to start and when it did it ran on 4 cylinders. I have now replaced the plugs but did not have time to check if it helped. I´ll report back...
The AFM, TPS and coolant sensors are all fine and within the correct resistance parameters.
I have upgraded the dissy to new high output Bosch Scorcher (same as most historic racers use here) and MSD Blaster2 coil. I think the problem though is the 3.9 can run very rich on cold occasional start ups that only let the engine run for a short time, not long enough to get the engine properly warm enough to burn the deposits off the plugs. It doesn't seem to be a problem if I take the vehicle for a drive and it reaches operating temperature.
Will give the disconnect the battery for 30 seconds trick a go to see if it makes a difference.
Rover SD1 VDP EFI
Tech Edge 2Y