I just dropped in a new 383 into my 1988 iroc. My question is do i need to get a new prom burned to get this thing to crank. We have gotten it to run by playing with the timing but it never seems to wanna crank back up after it is turned off. Idle is very rough to begin with when it does turnover, but then it evens out after 2-3min of holding the throttle down. Compression is 10.5:1 and we have tried every combination of timing we can think of. Anything would be helpful. Thank you.

 

Something else is wrong. It should idle and rev with no load just fine. I'd recheck all your connections (electrical and vacuum). Make sure your firing order is right too.

 

whats the specs of the motor? still fuel injected but what intake setup is on it?

any work done to the ecm/prom at all? Stock computer wont run that motor more than likely if it has any sort of heads/cam setup on it thats far from stock

 

lol its the stock computer. The heads are off the late 70's, The heads are 1.94/1.6 valve size,The specs on the cam are 290/300 adv duration, 222/230 @.050, .468/.480 with 1.5 rockers, 110lsa.... It has 1.6 rockers so the lift is actually .499/.512 at the valve. Firing order hasn't been changed and electrical/vacuum lines all seem to be fine. Its just real funny on how it wants to respond. The first successful time was set to stock specs. I had to hold down the throttle to keep it from dieing, but then after it warmed up i drove it around the block with almost no power, and it felt like i had no power brakes (weak idle). The distributer would not tighten so had to remove to get the hold down back on. Then it would not crank again. Tonight after trying to repeat the process we got it to run after advancing the timing 10-12 degrees. Strong idle but this time when i turned the car off it would not crank again. Wouldn't even begin to. Tested and its firing and i am getting fuel so i have no clue what this computer is doing. I am using AutoXray 6000 to try and help but without it cranking i'm not sure how accurate the information is. Thanks for the help.

 

How did you get the 383? Crate motor, bare block DIY built, or shop rebuilt stock engine to 383 specs? is it still a TPI?

Are you using the Instruction Manual directions to set the timing?

I would suggest investing in a mini-high torque starter.

 

My 383 did run on the stock prom and I changed much more including much larger head specs. Runs much better on the "custom" prom.
Part of the problem is with the prom but you have something else causing the base problem.

 

It is still the stock tpi intake, but the block itself is a crate motor (ZZ4 crate motor). With 30lb injectors, holley fuel pump, new distributer, 8mm wires, 48psi fuel pressure and new champion plugs. So i hoped i could rule out electrical and fuel problems based on my tests, and narrow it down to timing or air intake. The scan tool says it running lean though?

 

With a stock prom and those injectors you should be running rich.

 

Thats part of his problem. Holding the gas pedal down to keep it alive means its too rich. You need to get that car tuned asap.

You'll have to set base timing to whatever you want it to be, doesnt matter with EFI since you can change timing in the prom to what you want. 6 degrees base is stock but some motors wont run on that. Mine didnt, i went as low as 10 degrees before it started getting pretty choppy on the idle so i left it at 10, did the prom for 10 base and added idle timing to 26-28 degrees i think it was to get it to smooth out.

I never tried to run my 383 on stock prom. I dont think it would work well. The very least you'll have to change injector constant and idle speed and go from there. Set timing. Reset the IAC to the new idle speed and then play with fueling at idle thru MAF table 1, if your still MAF.


And when you say wont crank, you mean it physically isnt turning over at all? Or does it turn over and not fire again?

If its not turning over at all, check your starter and engine grounds. you may need a new starter to turn it but my 11 to 1 motor turns over no problem with stock LT1 starter