Can a single cylinder be rich with MFI?

[Fastissimo]

I should start by saying I'm definitely new to the MFI world. I've noticed a bit of exhaust backfires until the car is fully warmed up and decided to change to plugs yesterday. Plugs 1,2,4, and 5 look pretty good. 6 maybe a bit rich. 3 very rich. Is it possible for a single cylinder to be rich with MFI? If adjustable, can each cylinder be adjusted independently?

[edmayo]

Yes, bad injector or fuel valve in pump can affect one cylinder, what new plug did you put in? the BPR7ES ? Put a couple hundred miles on them and then see what they look like.

[Fastissimo]

Yes, bad injector or fuel valve in pump can affect one cylinder, what new plug did you put in? the BPR7ES ? Put a couple hundred miles on them and then see what they look like.

Yes, the BPR7EIX on the photos were on the engine when I bought the car. I just replaced plugs with BPR7ES (at 0.028), wires, rotor, cap, points. I'll follow your advice and drive it for a couple hundred miles and see if anything has changed. Is there a way to lean the mixture on a single cylinder throughout the range (idle - WOT)? The reality is that I don't know when it's rich and without checking I'm just guessing. Thanks!

[BartdeBruijn]

Single cilinder adjustments are performed during pump calibration by adjusting the clamp that holds the specific piston.
First step in MFI adjustment/calibration is to get equal fuel quantities over all the 6 cilinders at a given rpms(2000 pump) and load condition(full throttle). If you are into this doing yourself here is a link as I did it myself (pump rebuild and calibration) there are also links of others who did it before!
https://www.early911sregistry.org/fo...tup-and-tuning

Regards,
Bart

[Fastissimo]

Thanks Bart!

[werinhari]

Hi,

great looking spark plugs! Have only seldom seen such overall pattern on older cars.
If I were you I'd check/correct ignition cable, valve clearance, injection nozzle and adjustment of bypass air on cyl. 3 (alignment of all cylinders !) at first step.
If everything is perfect move on to the specific pump output, not vice versa.

Good luck!

Best, Wolfgang

[Fastissimo]

Thank you Wolfgang. I just replaced the plugs and wires. Valve clearance was set about 300 miles ago. I will look at the injectors and bypass air. Any tips on adjusting the bypass air? Thanks!
Oscar