mustangdannyjr

I am new here. I have a 1991 Mustang GT 5 speed I just bought. It has some performance upgrades (BBK Cold Air Induction), MSD Ignition, and sounds like it has a performance cam as well. I have been having an issue of hesitation upon acceleration and occasional backfiring under power. I have noticed that the Temp seems to be really low (@150) and I would think it would be higher. I was told that temp could be a culprit. Any help would be appreciated.
Thanks,

86 5.0L

might be that the previous owner installed a thermostat lower then 180*, anything lower then that, will force the ECU to run in "warm-up" mode or open loop(I think its open) which means the ECU is dumping extra fuel into the engine to warm up, bubt it never does.

mustangdannyjr

So should I change the Thermostat and why would he do that?

86 5.0L

its an old school 'trick' to make your carbed engine run cooler, thus more HP, somehow people still don't know the intricate workings of the SEFI 5.0

mustangdannyjr

I knew it worked for Carburetors. I am new in the game on SEFI. What temp should I go back with? Thanks for your advice BTW.

mustangdannyjr

While I am asking about the hesitation problem, any ideas why my dash lights do not work with the headlamps on but will when I rotate the switch and turn the dome light on?

dreamer1uk

Hey,

Go with the OEM temp thermostat.
Is the CEL on?
Its deffinately running too rich as stated above if its backfiring. You could ohm the injectors as well as completeing a fuel system leakage test
Do you know if you have the right injectors installed for the engine setup you have?

mustangdannyjr

I feel stupid, but what is the CEL? I do not know all the mods that have been done to the car as I bought from a car lot. I am going to try and track down the original owner before me to see if he can update me. I will probably start with a new Tstat and take it into get the fuel system leakage test done if that doesn't cure it. Since it has been modified, will I need to take it to a "speed" repair shop or can I take it to a standard ASE certified garage to have this done?

mustangdannyjr

Duh. Check engine Light. No it isn't on.