GNJ

Cleaned the spark plugs. Changed the coolant sensors in both motors after the scan showed the coolant temp was 85*
if anyone can help with this - Its still loading up and fouling plugs
I put the scan tool on after a brief run to warm up the engines - Here are the values at idle:

Port Engine
Coolant temp 142*
Manifold air temp 119*
TPS Volts .72
Throttle Pct 1.9
Map Volts 4.09-4.15
Manifold Pressure 25.7
Barametric Pressure 30.4
Battery Volts 12.9-13.0
Spark Advance 12-27 (jumps all around)
IAC Position 140
Base IAC 140
IAC follower 0
Inj Pulse Width 4.9-5.1
Fuel Flow Rate 3.10-3.33

Starboard Engine
Coolant temp 134*
Manifold air temp 117*
TPS Volts .92
Throttle Pct 7.4
Map Volts 3.88-3.94
Manifold Pressure 24.1-25.4
Barametric Pressure 30.0
Battery Volts 14.2-14.3
Spark Advance 13 (steady)
IAC Position 150
Base IAC 140
IAC follower 20
Inj Pulse Width 4.1-4.2
Fuel Flow Rate 2.68-2.85

SB

Do those NGK plugs have gaskets on them ? Sure looks like it. GM cast iron heads use tapered seat plugs. Factory plug is AC Delco MR43T.
Those NGK's also look like they have more threads than the standard Delco plug. Almost looks like plugs you got where like the ones for the 525EFI which uses the NGK BPR6ES that has longer reach threads and a gasket because of the engine having the Edelbrock/Mercruiser aluminum heads.

Here is a pic of factory plug for the 500EFI - AC Delco MR43T - notice amt of threads and also notice tapered seat:


Here is a pic of factory plug for the 525EFI - NGK BPR6ES - notice amt of threads and also notice gasketed seat

SB

Okay, was able to enlarge your pics and you definitely appear to have wrong plugs if you still have the OEM 500EFI heads on your motor. The plugs you have in them appear to have too long of a reach (too many threads) and they are gasketed.

So, it appears that NGK Br6fs is also listed in some 500 efi manuals. Therefore, AC Delco MR43T or NGK BR6FS are the correct plugs.

Edited in my disclaimer: I can not see the NGK # on your plugs. What I have wrote I believe to be true. Please double check my info if you are going to use it. LOL.

Pic of BR6FS for comparison

GNJ

SB - I have Dart 308 Iron Eagles and they call for 3/4" long gasketed plugs. The motors have about 80 hrs on them since rebuilding and were working fine up to this point.

SB

Okay good !

What a waste of about 1/2 hr of seemingly good detective work on my side. LMAO.

Edit in: Since on the subect, any cam change and ignition 'upgrades' also ?

GNJ

Thanks SB - It has the 741 cam, AZM throttle bodies, ECM's remapped by Precision Marine, but I don't think those are factors since it was all running correctly for 1-1/2 years

SB

Good stuff.

I understand, but helps with things like MAP readings.

So, no ignition modifications ? ALL OE parts other than plugs ?

GNJ

Yeah, Stock 500EFI ignition components

Sydwayz

Distributor caps and rotors both in good clean shape, with no corrosion or moisture?

mike tkach

i,m not saying this is the case but often ignition problems cause issue,s that get blamed on the fuel system.if the ignition system is weak the fuel can,t get burnt so people blame the fuel system.