General consensus seems to be that the NGK BPR6ES are the best and these are what I have always used. The reason that I ask is I am getting plug fouling and thinking about a hotter plug. Here is the background
- moved to Denver a year ago and since them have had rough running: poor low RPM, light load acceleration, some intake backfiring

Thinking it might be the high altitude have done the following
- Set fuel pressure in the rail to the lowest range of the spec 28.5 psi
- checked the MAP sensor. Zero diaphragm leaks and passes the electrical tests
- Just cleaned and oiled the air filters to make sure no restriction there
- Checked both the coolant and air temp sensors

Grant Francis has provided most on this forum great advice and it looks like he runs a hotter plug NGK BP5EY.

Have others tried running hotter plugs in the pre HE engines?

 

Mine has run BP5EY for just over 640000kms. Never used the "R" spec plugs in any of them, resistor HT leads are good enough. The "ES" was dropped down here for teh "EY", which has the split centre electrode.

OK, it soots up at times, our 50KPH speeds in the suburbs are to blame.

Quick blast on the highway, all sweet again.

I also run Injector Cleaner on a monthly basis in all the Jags, it just helps, in my opinion.

The MAF might want a SMALL adjustment, via the hex adjuster under the Black end cap. The threads of that adjuster are COARSE, so a little bit, makes a huge difference.

Timing could do with a tickle, drive timing is the best for these.

I set the FPRs by ear, you can hear the changes in the idle "sweetness" after the number I have done, just like the mixture screw on a carby engine. One of mine is sweet at 31psi, the other is sweet at 29psi, dunno, both are female, never get a straight answer.

Hotter plug, MAYBE, never tried. That poses an issue on sustained long/hard runs, of which I have many.

 

Thanks for the great response Grant. Do see any issue using BR5ES which is one stage hotter than what I have in there now.

BTW. I previously used your tune by ear technique to get the V12 singing so it is already pretty advanced versus stock. It was running well until the move so something has broken or the altitude is causing it to run richer

 

Almost sound to me like it's running lean, have you verified the fuel rail pressure? Any vacuum leaks?

 

Thanks for the response Jagboi64. Fuel rail pressure is verified and I have a gauge in the car for continuous monitoring. The black spark plugs (with no oil smell) led me to thinking running rich. Plus get a little soot deposited on the ground under the exhaust pipes when warming up in place for a while. Interested what leads you to thinking lean. The backfiring?

 

on vacuum leaks. With these engines it’s impossible to say for certain but I am 90% + certain there are no leaks. Recently had a project that caused me to remove and reseal intakes, injectors and replace all vacuum hoses. Have also recently checked the overrun valves to make sure they aren’t leaking.

 

probably a yypo, but BR5ES is a flat nose plug, and not good in the V12, either spec. I know the books list them, utI have used the "P"P spec plugs forever, and that stopped the sooting. Basically putting the spark out in the mixture, as appose to up inside the plug core.

Heat range "5" is fine.

Its probably home sick more than broken, HA.

Only other thought, on coffee 1, so who knows. The Coolant Temp Sensor may be getting flaky. NOT a real issue with the PreHE, more of a major pan with the HE, but worth a check/swap out.

I removed those silly over run valves on all the V12 engines. They were/are a pain, and I notice no ill events on over run on any of them.

Have you adjusted the fuel pot on the side of the ECU?. It ONLY affects Idle Mixture AT operating Temp, but maybe worth a click or 2??

 

Thanks. I did mean BPR5ES. Will try those this weekend. I tested the coolant temp sensor across the temp range and it had the right values.

I plan to keep the overrun valves as I am collecting parts for a manual transmission conversion

 

That and the stumble and apparent lack of power.

What is the ignition system? The original Opus system wasn't great, you could be having an intermittent lack of spark.

 

Agreed that the Opus ignition system was poor. I upgraded to the ReOpus ignition some years back and don’t believe that is giving me problems. I did suspect it a while ago and sent the unit back for testing. It was fine and the problem at that time was a flakey FI relay. Also recently replaced the plug wires and the coil, rotor and distributor cap are relatively new.

Thanks for the ideas