Fuel Pump Boost Assist Switch Issue

[Mike S]

I think I have tracked my lean condition under more than 10-11 PSI of boost to an electrical issue with the fuel pump boost assist switch or what ever it is called. The fuel pressure gauge will only register ~52psi even though my boost pressure is 15-17psi. My wide band sensor and knock sensor shows that the engine goes dangerously lean under full throttle.

Here is what I have done so far:

replaced the fuel pump with HP 255LPH unit
replaced the fuel filter
verify in static condition that the fuel pump is capable of producing >70psi to the fuel rail
replaced the AFPR hoses to eliminate boost leaks at ~12psi of pressure from my mightyvac
added clamps to all hoses to insure seal under boost pressure up to 30 psi
had to add thread sealant to Kirban AFPR set screw to stop pressure leak.
verified I had same voltage at fuel pump as battery using fuel pump tester jumper
verified i had no leaks with 30psi to boost switch
Test drive with fuel pump tester jumpered and fuel pressure acted as it should until my MBC came apart and the guts ended up on the road.


What is the boost pressure required to activate this switch?

Would unplugging it and making a jumper for the connector be enough or does there need to be some additional resistance in the jumper to raise the voltage at the fuel pump? If a resistor is needed, how much?

Any suggestions are appreciated

[Mike S]

16 views and no input?

[MikeFleming]

You will be safe to bypass/jump that switch - no resistor needed. Then full voltage will always go to the in-tank pump.

[JTurbo]

I have mine bypassed on the black SVO. I left the controller in the circuit (in case I go back to stock), but just installed a jumper wire within the connector.....

[Mike S]

OK. I just jumper it out.

[Mike S]

So after trying many different things, isolating all boost leak, jumping everything that could be jumped, installing my new PIMP ecm, I have finally found the source of the issue reported above that the AFR would go lean above 5K rpm.

The PIMP ECM aloud me to to rev to 6.4K fuel cut without going lean. In going thru the auto tune process, I disconnected the manual boost controller to only allow 10psi of boost in my 3rd and 4th gear pulls to red line. During these runs, I noticed that above 5K rpm at WOT, the boost would begin to creep all the way to 18psi. Further attempts to determine if there was a boost leak revealed that the culprit was the waste gate actuator. The waste gate was functioning to a point, but above 5Krpm, ~12psi of boost, the seem around the waste gate actuator housing was leaking. This small leak essentially was acting as a bleed valve and thus the over boost condition.

The stock ECM could not react quickly enough to compensate for the added boost and thus the lean condition. Just thought everyone would like to know.

By the way, the PIMP is Da'bomb.

[Raven855]

Sorry Mike, I some how missed your post.

The switch is normally open at idle and closes when vaccum gets below 5 in/hg. Its purpose is to cut out a resistor in the fuel pump circuit to allow the fuel pump to operate at full output under heavy part throttle acceleration and WOT. Otherwise the pump runs at a lower speed to reduce the noise of the pump but has the predictable side effect of not providing full output. that switch was only used on 85.5-86 SVOs

When using auto tune I like to richen the cells and let autotune lean the mixture out. Its safer that way. And check your plugs for color and proper heat range.