some days ago I posted a thread about rich codes and few live data from my scanner.
I replaced the MFA sensor and the mileage/gallon improved yet I was still getting the engine light on and the Long trim data showed -17 on both banks with rich combustion.
I decided to replace the spark plugs and here came the surprise.
first of all the sparkplugs were Denso iridium, which I had no ideea that STR runs on this plugs.
Secondly 2 spark plugs one on each bank missed the iridium tip. How that happened? no clue...
anyways I replaced them with NGK iridium and voila,problem solved.
Engine light off permanently. now that data from the scanner shows Long trim at -3,-4 on both banks.
I hope this info is usefull for people with same problem.
it s not that of a bad ideea that if you have rich codes on both banks to clean or replace the MFA sensor and put a new set of sparkplugs.

 

It would help if you give car details (see my sig) - hardly any above.

I've never seen such a problem posted before. Even -ve trims are very rare for STRs.

 

I bought the car from a dealer . I believe they tried to just sell the car. didn t look like they care too much about customer care either.
it was weird though the coding sequence. Always rich on both banks, around -17,-20% on both trims.
When I took the sparkplugs out, all were Denso with iridium head without platinum . and all looked that they were too hot for this engine.Except those 2 missing the iridium tip.
It also looked like the guy tried to readjust the distance cause the top electrode was bent in unusual angle.I had before another Jaguar S type V8 normally aspirated and not even a single problem in 7 years. So I was expecting the same from this new one.
Indeed I think Jags are really good cars, they just need ,like anything else,proper care as dictated by the maintenance manual.