ht4100

iTrader: (2)

My friend/mechanic is having a problem maintaining fuel pressure on my 86 Z28. The car has just had a TPI 383 swapped in with 24lb ford injectors, chip adjusted for injectors, and a holley AFPR. The car will have enough pressure when you turn the key but then drops off to way lower than what it should be. Any ideas? I think it might be something with the AFPR.

Supervisor42

If the stock TPI ECM is being used, it will run the pump for about 2 seconds at key on, to prime the fuel system and turn it back off if there is no signal from the distributor. If the pressure regulator or injectors do not hold this fuel "tight" then the pressure will bleed off if the engine is not started. This is normal. If the fuel system doesn't have the right pressure idling or during WOT, then worry about it.

jocool

If you have a fuel pressure gauge hooked to the shrader valve and you are turning the key forward engine not cranking and you get fuel pressure anywhere around 40 psi and then it rapidly falls off then you are right to suspect the afpr. I would try squeezing off the return line(the smaller line that goes back to the tank) while watching the gauge and see what happens.

jocool

Supervisor42 is right. They key word is if the fuel pressure falls of Rapidly causing a no run condition then I would try what I stated earlier.

ht4100

iTrader: (2)

Jocool: it doesn't run

jocool

Sorry I didn't get back sooner I've been very busy. There are a few things that could cause your fuel pressure to fall off. It could be faulty injectors(not seated and allowing fuel to dump into engine)but I doubt it. It could be that silly thing in the fuel tank that the pump hooks (most guys replace this with a short fuel hose and clamps) to that is bleeding off. Could be a leak in the fuel line. Or for whatever reason I suppose it could just be bleeding off through the pump(maybe a weak or bad pump). However most likely it is you afpr, if you squeeze off the return line to the tank and this helps maintain fuel pressure then I would say you have eliminated all the other things in question which only leaves the regulator. One more thing to check the vacuum hose that goes from the intake to the top of the regulator pull it off and prime the pump(turn key forward) see if fuel comes out of the vacuum hose attached to the regulator. Sometimes the diaphram fails and allows fuel to go through the top of the regulator and into the engine however if this was happening I think your car would get plenty of fuel and your car would run rich.