(1) carbon fouled plug/Neg LTFT bank 2

Bank 1 LTFT are consistently 0.8 as was bank 2 until I parked the car for 3 months.

Now, bank 2 LTFT is -4.7 certainly well within parameters, but suggests rich condition.

Pulled plugs and 5,6, and 8 look great, but #7 electrode has dry black soot. That eliminates MAF, fuel regulator, and air filter

First thought was bad plug, but new plugs reveal same results.

car is 97 5.2 with COP conversion so I swapped coils and nothing changed. Its been 3 years/8k miles since original injectors were cleaned.

Is my next task to pull injector?

 

What drives the ignition coils? Are the sparks sequential or do they fire in pairs like in the original ignition concept? Can you show a diagram of how this conversion is wired.

 

A special amplifier is used. Fired in pairs…

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Diagram shows coil wires are shared between 2 cylinders; does this mean firing is wasted spark like original set up?

Since 7 is shared with 6, can I assume the issue is not the MSD controller? (#6 spark plug looks fine)

 

Yes.

Splice issue? Check for continuity between output 1 and #7 COP and volts on #7.

 

Will a continuity check between #6 and #7 coils reveal any info?

 

Yes, that should also check the splices.

 

If the wiring is good, I would next check compression of #7.

 

You could also try swapping injectors side to side and see if the problem moves.

 

Good idea; is there any way to remove injectors without removing the plenum air boxes?

 

I agree with the "injector" being suspect.

Coils and plug wires age well when not in use.
Injectors not so much.

 

Wire checks show continuity, so (I believe) I can put MSD, wires, connectors, coils, and plugs in rearview mirror.

Compression test is never a bad idea, but I loaned my tester out to a friend. Less than 12k ago a very complete valve job
was done with ALL valves/guides and necessary parts replaced. I think we can all agree that -4.7 LTFT is not a concern. ?????
But, I always prefer to be proactive; the fact is, plug is carbon fouled. (dry soot, no oil.....no wetness)

I think #7 injector is not closing properly. Can't remember how much of a pain it is to remove the plenums?
Should I roll the dice and get a new injector rather than move around and do twice the work?

I have already gone thru a bottle of Techron and after some spirited highway driving trim readings were slightly better. only to return
after stop and go traffic.

My next test is to install a new plug, drive hard, and check at 50, 100, 200 miles etc and see how soon the electrode gets dirty.

I should mention that the car starts and drives perfectly. If I hadn't done a random OBD scan I would have no idea that there was an issue
No codes to report, only fuel trim neg on bank 2.

 

Not sure, but the bolts to remove the fuel rails are on the outside of the TB's so there should be?

 

I think the injectors need clearance to be removed and the plenum is in the way?

 

Did you try searching the forum?

 

Yes, but it's not very clear.(as in this thread) Will report back when I get to that point.

https://www.ferrarichat.com/forum/threads/355-fuel-injector-removal.185592/

 

The second paragraph indicates that it is the injector.

I generally recommend removing and trying to clean the injector before buying the replacement, but your second paragraph leaves me without great hope it will clean up to a useable state.

 

Not familiar with Techron, but assuming it's somewhat similar to Seafoam - which is what I usually add to clear minor things like that up. Any car I have that's been sitting I pour a bottle of that in and it usually clears up any slightly rough running.

 

Techron is a popular fuel injector cleaner/additive. I have found it to work well.

Mitch, do you think there are some crusties on the injector that won't clean up? If, there was an engine issue, rings/valve seals etc. .
would the LTFT not fluctuate?

After only 50 miles new plug shows dry black on electrode. However, driving hard brought LTFT to -2.3 after the drive.

Could use some schooling: when driving above 4500 rpm, LTFT would immediately drop to -0.8? I thought only STFT
had quick response? Is this another indicator that my general engine health is good?

 

I believe fuel trim has a multiple mappings depending on RPM. I.e. it's not a single trim it's dependent on rpm. And at open throttle that all goes out the window flipping to open loop mapping.

Unfortunately removing and reinstalling the plenum is quite a tedious job filled with ample new vocabulary. It would be worth it to put a compression tester on there for the simple reason of it takes so little effort to at least eliminate a variable before going full open heart surgery.

 

I might have made some progress.....or not....???

More high speed driving (about 50 additional miles) and I am reading more positive STFT which is countering the negative LTFT. Seems like ST and LT are having a battle, if that makes any sense? (Last week, most of the STFT were negative.) Really want to drive longer, but the congestion is awful.

If a spark plug is fouled due to an injector issue, and then the injector issue is resolved, does the fouled plug make it difficult for proper spark? Should a fouled plug be discarded?

 

I would clean it but only discard if you see wear or it's not firing - ie if you move it to another cylinder and it fouls it's probably a bad plug.