Hot Rod Forum banner

400 tbi problems

2K views 5 replies 2 participants last post by  joe_padavano 
#1 ·
I have put the top end from a 350 tbi onto a 400 sbc. After some wiring issues I have the thing running now. But it runs better with the wire connector for the map sensor unplugged. I'm running an inline fuel pump rated at 18 psi. With the map sensor plugged in the engine lopes and won't idle or stay at one consistent speed. However it runs nearly perfect without it plugged in. When the map sensor is unplugged the computer makes the mixture rich right? Is it possible that since it is a 400 instead of 350 that it's not getting enough fuel? I have tried multiple map sensors and triple checked the wiring. The sensors are working fine and the engine is making 20 inches of vacuum.
 
#4 ·
You've increased displacement by about 15%. Assuming you have the stock 55 lb/hr injectors (orange/black color code, P/N 5235206), you need to upgrade to the "cop car" injectors for the 350 that are 65 lb/hr (yellow/brown color code, P/N 17084327 or 17112412). That's just over a 15% increase in flow rate, so all else being the same (including the PROM), those should get you close.
 
#6 ·
So if I can use those injectors without changing the ECM?
They'd probably get you close enough.

What about tweaking the fuel pressure regulator?
Actually, if you can get enough flow through the stock injectors by raising the pressure, yes that also works. The whole issue is to get enough fuel into the engine to match the larger displacement. There are three ways to do that: Increase the amount of time the injector is open (that's a PROM change), increase the flow rate of the injector, or increase the fuel pressure. I don't know what the flow rates of TBI injectors are at higher than stock fuel pressure, but I'm sure that info is available. There's also a limit to how high you can to with those injectors. I think its around 16 psi or so.
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top