blake96

So i just replaced my fuel pump as preventative maintenance on my 92 sc400 and now it takes double the time to start. Airtex OEM fit). What could it be?

bigwhite

Just put a new Airtex in my 93, and did the fuel pump ecu bypass and it starts in 80% less time. Aside from the bypass, tune-up and ECU is about all thats left.

t2d2

iTrader: (8)

I've tried pretty much everything to address the long-crank starts on mine. Plugs, wires, caps & rotors, checked coils, fuel filter, swapped in a used fuel pump, fuel injectors, fuel pressure regulator, charcoal canister, ECU capacitors, vacuum lines... None of it has consistently helped. For some reason, fuel pressure drops when the car is shut off, but every hunch has proven to be a dead end.

The two things that have worked consistently are:

1) A quick bump of the starter, wait a second, then turn the key again.

2) Fuel pump ECU bypass. Wait a couple seconds with key in the "On" position, then crank it. I've only done it by jumpering the pins in the diagnostics box at this point, not the permanent bypass.

Both methods bring the fuel pressure back up to where it should be. It may just be an unsolvable mystery what's allowing it to drop... I've exhausted all the likely culprits.

bigwhite

Do you have air pressure blowing out the gas cap when you refill at the gas station?

t2d2

iTrader: (8)

Me or the OP?

Yes, I have what seems like excessive pressure (but no consensus that I could find about how much pressure is ideal) when opening the gas cap, to the point that gas will pour up and out of the spout when fairly full. That's why I looked into the charcoal canister, in case the venting system wasn't working properly. I haven't figured out how to disconnect that line at the tank end, though, and see if air will blow through.

bigwhite

The OP seems to have a worse case.

t2d2

iTrader: (8)

I doubt that. If I don't employ one of the two workarounds, mine will crank for 3-4 seconds before starting. That's definitely more than double normal, which is what the OP stated.

bigwhite

So do either one of you have pressure blowing out of the gas cap when you refill?

t2d2

iTrader: (8)

I can't speak for blake96, but I already answered that in post #5.

bigwhite

Must have overlooked #5, just wanted to make sure you had pressure on the system. I know there were some faulty gas caps.

blake96

Sorry about the late response... I am now thinking that the fuel lines i reconnected to the fuel pump aren't clamped down tight enough ant the pressure leaks out into the tank. There is obvious built up pressure wher I remove the gas cap.... only thing I can think of.

t2d2

iTrader: (8)

Interesting theory, let us know if it pans out! I've looked into related aspects (the pump's pressure relief valve and return/tank venting), but hadn't considered the hose to the pump itself being suspect. It doesn't take much to make an old hose leak if the clamp isn't put back exactly where it was before... I just had that happen last week with the upper radiator hose, in fact.

I had the long-crank problem prior to first swapping pumps, but maybe the hose was already fading or a previous owner had also fiddled with it and didn't get the clamp right. It's about as plausible as any remaining options.