Lester

Just fired up my 2 502 MPI motors after building them over the winter. Cams, headers ,MSDs, fuel regs, and remapped ECUs. When throttling up tp 2000 rpm or more and then cutting the throttles back to idle both motors stall. Is this the IAC valve dynamics changed with the new ECMs? More fuel pressure needed ( I'm at 42 psi now)?......any ideas? I do not have a scan tool, yet.

Breathe Later

IAC is not able to let enough air in to control idle. You've got to open the secondary throttle blade slightly with the set screw (the primary blade opening controls idle speed). Without a scan tool, you can't see the IAC position so just try a small adjustment at a time. The cam affected the idle slightly and the IAC motor needs to be able to respond by opening and closing to allow air flow past the throttle blades. If it's all the way open and still there's not enough air, the engine will stall when you chop the throttle. You can see the same effect by removing the flame arrester and manually opening the secondary blade with your finger. Also, make sure your base timing is at 8 degrees.

Lester

Thanx Breathe, I gave it it's first hard water test yesterday. Adjusted base timing to 10 degrees per the programer's recomendation. I tried a slight throttle plate adjustment but now the motors both want to wander at idle and they are slow to return to 800 rpm they will hang around 1200 for awhile then drop, this isn't doing my drives any good. After base timing adjustment the stalling thing seems less of an issue. going to try returning the secondary throttle plate back to where it was to try and stabilize the idle. Another question is I'm running 40, and 41 lbs at idle on fuel press, brought the motors up to 4000 under a load, press dropped on both motors to around 36 or 37. I have not installed the adjustable regs yet like Teague and others say you need to but what my gages are telling me is that the stock pumps will not maintain the recommended 42-44. In theory if I'm dropping to 36 now and have 40 at idle than new regs won't solve that. Any advice?

ST31

Lester,

I had both of my motors rebuilt in much the same way as you over the winter and am having some of the same issues. When I put the motors into either forward or reverse they have a tendancy to stall. They are trying to work through the problem now by reconfiguring the ecus. I will let you know what happens.

Lester

Thanx ST, I'm ordering a Scan tool tomorrow and will look forward to your input as well