Ok so i have a 355 tpi no check engine light comes on when the motor is running. Another thing to is i have a high idle running around 1000-1100rpm at idlewhen i put it in drive it idles/runs around 500-700rpm at a stop so thats somewhat right what could cause horrible mpg so far i changed out fuel filter, spark plugs, accel wires, an cap an rotor also do have a cam 208 intake, 218 exhaust with a 407 lift the heads on the 355 are gm cast iron 194 intake opened up to 202. I am running egr an cold start do these play a major role in mpg ????

 

how bad is the mpg?

 

70 miles to a full tank

 

4.8 mpg??? It better be a dual Demon carb'd Pro Stock Big Block!

 

Holy crap thats not even close to right...

 

Could be a bunch of different things. Leaking 9th injector, stuck FPR, leaking FPR diaphram, Leaking injectors... That's all I can think of right now. What do the plugs look like?

 

Yeai know its terrible what are causes you guys think it could be ??? I was thinking i got a vac leak someone just havent tested to see yet i know tpi motors are known for the runners an the corners of base intake gaskets let go But the funny thing is i have no engine light coming on all injectors read 16.7 ohms. An fuel pressure holds a solid 42 at idle an jumps to 47 when under load all of the emission stuff has been ripped out expect egr an solenoid all vac lines are good no cracks or breaks

 

Fuel pressure sounds a bit high. Should be 43 at idle with vacuum unplugged and around 35psi with vacuum plugged in. Basically the max pressure you should ever see out of it is 43PSI.

 

Ok so i tryed a different fuel pressure guage an it reads 40 psi at start up an it runs jumps to 43 when under a load. I also did the whole fpr test with the vac line off an no gas came out of the line so it tells me that it is good i have no idea what i could be im very stumped

 

It needs to be computer tuned.

 

does the check engine light work right? without cranking the motor, turn
the key on, does the CEL flash on & off then come back on?
have you tried to pull codes?
no doubt something is bad wrong.
tuning the computer would help, but the cam isn't that big.
if the basics aren't right, tuning alone won't solve the problem.

 

and therein lies its downfall