timing chain or CPI?

i have a friend of mine who has a 95 blazer with 198,000 miles on the motor and tranny. his motor runs bad at idle, he gets about 10 mpg thats city or highway. he has a strong smell of pure gas coming from his exhaust and sets the SES light every other day. i've told him that its the CPI and he thinks it might be the timing chain. could the timing chain be causeing this or the CPI? the truck has decent pick up but the fuel milage is bad. some how it passed emissions but it was very close. when i had mine done the CO2 output was 54 and his went up to 364. he's lucky they don't care about your CO2 output.

cpi injector/nut kit

EGR valve stuck open

already pulled the EGR. all is clean. i kinda thought it was the CPI. what would it be doing if it was the timing chain?

It's not the timing chain.

Just tell him to remove the upper plenum cover to winess the washed areas caused by the leaking fuel spraying everywhere.