Tech / General EngineIs your car making a strange sound or won't start? Thinking of adding power with a new combination? Need other technical information or engine specific advice? Don't see another board for your problem? Post it here!
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TBI-->Carb fuel psi is dying out once engine is running?
I have the mallory three port regulator I adjust the pressure to 5.5 when the pump primes right when the key is turned to the "ON" position. Then start the motor and psi gradually drops to zero and engine dies. I have the regulator first in line then the in line filter. For those of you who have switched did you have to rewire anything to the pump??
Drove the car around. First time did ok. second time the car stalled like it ran out of pressure again. Could the pump be getting too hot since it is pump 13 psi and only 5 is getting through? I figured that the return line should keep the pump cool. Should I skip the relay?
Do you still have the stock oil pressure switch for the fuel pump hooked up? that sounds like what's wrong... the relay only powers the pump during startup, then after the engine starts, the pump gets its power through that OP switch. It's a safety feature so that if the engine stops running the pump shuts off.
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"So many Mustangs, so little time..." ICON Motorsports
[This message has been edited by RB83L69 (edited October 21, 2001).]
Yes the stock op switch is connected. My other theory is that the pump is made for higher psi but not volume. The stock pump can supply tbi just fine at 13psi but not a carb on a 400hp motor at 5psi due to volume problems??? So pump is overheating and shutting off because it can not keep up???I propose to buy a holley blue in line pump already set at 7 psi and 97gph should do the trick??? Anyone??
Before buying a bunch of high-dollar stuff you probably don't need, I'd suggest checking to see if you have 12V at the pump. Start with the basics, don't outsmart yourself. As I am fond of quoting, from an ancient Greek philosopher from days long before FI or even carbs (!), "The simplest explanation that fits all the facts is usually the right one". Exhaust the simple first, then move on to complicated theories.
Volume requirements are essentially identical between FI and carb; fuel burns at about a 14.7:1 ratio by weight with the air it burns with, no matter how the fuel gets introduced into the air. TBI vs. carb, or the engine's displacement, are irrelevant in determining the engine's fuel requirements: 14.7 grams of air require 1 gram of fuel more or less, period.
Now if you were having a high-RPM, high-load lean condition, then yes, it would be time to suspect the pump. But you're not going to exceed your pump's capacity at idle no matter how many HP you think your motor might have, with any kind of motor you're going to be able to jam into one of these chassis.
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"So many Mustangs, so little time..." ICON Motorsports
If you can get it to cut off sitting still in your garage or whatever, immediately go and check if the pump if still getting power. My guess is something to do with the oil pressure junk. Just wire up the pump to be on when the key is on, circumventing the switch and see if the problem goes away.
I wired mine to run when the the key is on. With the key on but without the engine cranked you can hear the pump running, so there's no doubt. I had TPI though, don't know if the TBI pump is weaker though. I suppose that the pump itself could be the problem but I kinda doubt it...
I assume you are running a return line from the regulator into your tank... If not, you are "dead-heading" the pump, which is a big NO NO... The TBI pump is more than enough to feed the carb if regulated and lined properly. Pump will last much longer than if running OEM TBI, actually, as it doen;t have to work hard any more.
Hey Josh,
Go around the oil pressure switch. I know you wern't really wanting to do this, but at least you will be able to drive the car. I was wrong on the tan wire on mine being the power to the pump, it is a gray wire. Did you try the things I sent to you at work? If you are still having problems, let me know, maybe we could set up a time to meet, and we can look into it.
