prob with my 86

[ponyboy86]

I have a 1986 gt that has the following mods.

gt40 upper and lower
f-cam
off road x-pipe
flows
msd ignition
mass air conversion
cold air intake

The problem that i am having is it is running extremely rich and gettin about 120-140 miles per tank of gas, and most of the time the idle will fluctuate up and down. In wide open throttle is is great, but i can not figure out what the problem is. I have put a new coil on, a new iac valve, checked the wires and plugs. The only thing that i can think of is maybe the o2 sensors are bad, or maybe the egr is bad. I resest the tps to the specs that it is supposed to be (.98-.99) and that helped the idle a LITTLE but i cant afford the gas that i am having to put in it all the time. Do you think that it could be the egr or the o2 sensors, or could it be something else? Really need to get this solved. I was told by one person to put an adjustable fuel reg on it but i was told by someone else that it would not solve anything. I have the stock injectors as well. Thanks in advance.
Cody

[Mike Croke]

You have either:

- vacuum leak

- bad or not functioning MAF sensor

- bad fuel pressure regulator.

Check for vacuum leaks first because that's free. Get a spray bottle of water or a can of carb cleaner and spray everywhere while the engine idles. If you get a sudden change in idle (better or worse), you'll have found it.

Test the fuel pressure. When the regulator fails, it can bump the pressure to 80-90psi which is double the normal range. There is a schrader valve like a tire valve located on the fuel line next to the alternator.

[v8only]

hmm, gas milage close to 150 really isn't too bad if you do a lot of street driving. how much street driving do you do??

[MY4IDGT]

No expert, but I would pull an O2 sensor and see what color it is. I could be wrong, but if it is functioning correctly, it should be a grey/tan color. If it is black, it is malfunctioning.

Of course, if I'm wrong, I expect everyone to tell me so

[rbohm]

first off you are going to have to change the o2 sensors anyway as they are likely ruined by the constant rich mixture. first check the fuel pressure, a bad regulator, or a glogged return line will cause too much fuel to be pushed past the injectors. test the map sensor to make sure it is operating in its proper range, the ford shop manual will have the test procedure, and the specs. look for vacuum leaks, bad solenoids in the electrical system(these solenoids are vacuum triggered). look for bad connections, bad wires, bad grounds, and perhaps even a bad computer(though not likely).

[ponyboy86]

thanks for all the help, i will get around to checking all these soon, although i have no earthly idea where the map sensor is. By the way what does it do? i thought that they got rid of that when they switched over to the mass air flow cars, and if so, mine has been converted to mass air so would it still be used? also one other thing that i forgot to mention was i have a 70 mm accufab tb.

[rbohm]

the map sensor measures manifold air pressure, and yes it should have been change to a bap, barometric air pressure, sensor. i have found them in different places on different cars. for instance, my 84 tbird had the map sensor under the coolant overflow reservour.

[86gt]

I had a friend that put a 70mm tb on his engine and it ran like yours did. He put a 65mm on it and it fixed the problem. He had the same mods as you did. Funny to believe it helped.