TRACKMAN2

scince i put motor 7.5 together my self i cant seem to get it to run right.. it idels like a champ but when i try to give it gas under load. it stutters pops and losses power.. if you push the clutch in it revs quickly and seem to be fine you let out the clutch and accelerate it breaks up again.. oil pressure rises but just slightly when i rev it a vaccume test says no blow-by..vaccum is a little low steady at 15 then drops and goes to about 23 at 3000 rpm... ran fine on the dyno before valve swpring failed..installed new edelbrock preformer heads.. checked all plugs wires there all right.. im thinking fuel issue seems like timing mabe im new to this self building..header leak was fixed ran it with both o2s unpluged ran better. but i didnt try it under load knock sencor is unpluged Tunner says its not needed on a racecar.. idle air unpluged.(wrong plug on harness) tunner says its not needed either..going to check the fuel press tomarowalso the kill switch kills every thing including the ecm but tunner says it will only loose learned info not nedded on a racecar...banghead:

383vett

Heck, with all the sensors unplugged that your tuner says are not needed, the car is probably running in limp home mode.

JackDidley

O2s unplugged, you are in open loop. Datalog is your friend.

TRACKMAN2

the guy is pcms for less one of the most respected tunners in the bizz should i believe him???

TRACKMAN2

whats that mean???? im a building contractor.....

JackDidley

Datalog, as in scan. I prefer TTS Datamaster on a laptop. You can download it and use it 20 times, free. You can get a cable from Moates.net. Datalog and learn what the motor is doing.

Midnight 85

Did you close (extend) the IAC before you unplugged it?

TRACKMAN2

i didnt do anything just bolted it on

Midnight 85

If the pintle on the IAC is retracted then it is allowing a lot of air into the engine even with the throttle blades closed, then when you open the throttle blades you may have to much air entering the engine.

staugur

WTF!!!!! I just read in another post you were a professional engine builder and here you are soliciting advice.On the other post you were giving it!

TRACKMAN2

dude im a professional builder as in contractor i build houses and stuff...this is my 1st engine build but i have been through 7 engine builds never repeat never claimed to be an engine builder..

87 vette 81 big girl

I don't care what you do for a living.

You are a home mechanic & C4 driving enthusiast.

You are OK.

Any chance you have a vacuum leak anywhere of some sort ?

From you description at the top of the page,
Has me wondering if you do.
May be obscure.
Lower intake gasket leaking,
From inside of the engine valley.
Blocked off from observing eyes by the front & rear china walls.

BR

TRACKMAN2

mabe your on to somthing i did have the thing all upsidedown shaking it vigorously to get all the crap out of the intake mabee somthing moved ill check that

TRACKMAN2

thanks man!! i checked with a guage pluged into the intake how would i check 4 this

87 vette 81 big girl

What was inside of the intake ?

broken piston & valves ?

87 vette 81 big girl

Chuck may be onto something too.

Junk blocking the IAC.

Easier checking the IAC 1st.

TRACKMAN2

all of the above ther was chunks of metal and alluminum in there i spent about an hour cleaning and blowing it out

Midnight 85

You could shake it until the cows come home, it won't change the position of the IAC. You say the connector on your car does not fit the IAC? I don't know what connector you are looking at so maybe you could post a pic of the IAC and the connector. Once we figure out how to get power to the IAC then you can close (extend) it.
If the IAC is retracted you will not get a good vacuum reading anyway so let's take this one step at a time.

87 vette 81 big girl

At engine idle speeds,

Vacuum gauge readings will swing slowly say from 15 inches steady to then maybe 9 inches & then back to 15 inches, and then maybe as high as 18 inches.

Bigger the camshaft profile in duration,
less intake manifold present of course.

A vacuum gauge reading at engine idle speeds that vary + or - 5 inches from baseline points to a major engine induction vacuum leak.
Lower intake gaskets often slipped or failed on generation 1 sbc's motors.

TRACKMAN2

when i checked it it held steady +/- 1 mark for about 5 min...then i shut her down