1999 fltri engine light coming on doesnt seem to effect running stays on for about 8 seconds what may be cause

this could be just a loose or worn alternator belt, also could be alternator brushes about to fail, with a multi meter start engine and set meter to 20v DC and put relevant prongs to correct battery terminals it should read about 13v to 14v, 12v up over is ok but should be above 13 on tick over and not much or at all higher than 14v, keep meter on battery and rev engine to make sure the charge rate doesnt fall below 12/13volts when engine under strain as this will effect battery current while driving etc. especially at night when using lights, this might be ok now but it will get worse so dont neglect problem as you dont want to get stuck in middle of nowhere one night when out driving, car will slowly start to lose power as it can only run on battery for approx an houre, its running on battery not alternator everytime battery icon shows whilst engine is running and over time this will also effect battery condition.

The Fi light indicates that your Fuel injection system is working. If it's not working - the engine wouldn't run!
When I first started having the light come on it didn't seem to effect anything, it was only a couple of thousand miles later when the light would come on intermittantly and then the engine would cut out. I'd switch the ignition off and on again (while rolling) and it would run as if nothing wrong.

you have one that has a sensor on the dipstick for oil level,so it comes on then goes off to tel you the level is fine.mostly fitted to European cars.

When your air fuel mixture is out of adjustment it triggers the ECU to adjust your fuel mix . You are likely dealing with either a clogged O2 sensor or fouled throttle body at the end of the intake snorkel however I have not seen mine cause any issues with braking.
A code reader will need to be used to take an initial reading and to erase current fault codes , adjusting the engine back to default settings. This should erase the warning light and allow you to start fresh.
When my front O2 sensor failed the fuel ratio had adjusted to compensate for the mis read and I was running at almost 50% fuel to air instead of 7% range at idle. I watched the readouts as the ECU adjusted the fuel mixture back down within 2 minutes on my RX300 after changing the O2 Sensor and all has been well since. The reader will identify if your issue rests with any of the 3 sensors or in another area. Upgrading 1 sensor will change how the remaining old ones function as well

Code 16 indicates that the ECM has seen a battery voltage of less than 6.2 vdc or higher than 15.5 vdc. The most common cause of this is loose or dirty battery cables or shorted rectifier.
To access codes, turn the ignition switch on for about 3 seconds (one second after the fuel pump stops running) then turn the ignition switch off for three seconds. Repeat the above procedure. Then turn the ignition switch on again and about 8 seconds later the codes will start to flash through the check engine light.
If there are no codes present or there is a code and it does not appear again the code will clear its self in 50 start/run cycles. (Start/run cycle is defined as engine running for at least 30 seconds and off for at least 10 seconds.)

cause there is more than likely a code set in the vehicle. Check engine lights dont just come on cause they want to. Just because the light comes on doesnt mean there is something bad rong. My step dads truck has had the check engine light on for 3 years, its been cleared several times only to come back on again to... turns out it just has some stupid sensors bad but they dont affect the running condition of the vehicle. Take it to autozone, ask them to hook up scanner and go from there

I had that problem. It is a bad catalytic converter. If your car has less than 80000 miles it will be covered by your dealer.

thats sound normal..like i always say if it's not broke don't try to fix it..

You have 2 codes, 8 and 5, code 8 is the TDC sensor, this would cause a no start, the code 5 is for the MAP sensor, it may be disconnected or defective.