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Car Experts Needed

Twista

Twista

Diamond Member
If you have a car that doesnt crank on the 1st try after sitting overnight what would you fix?

I have a 97 GT Mustang with pretty much stock everything becept air filter and exhaust. It seems after the car sits for along time it has a HARD time cranking back up. The 1st crank never fires up and the 2nd crank the stang fires up. I had a buddy look @ my car and he hooked up some guage thing to this fuel thing ontop of the injector rail. He told me to fire up the car to see what my fuel pressue was. On start up it @ 28 PSI which he said is low. He said my car should atleast be @ 34ish on start up. (or he might said 40ish.. i cant remember)


Now heres another problem. He said when the car is turned off the pressue is suppose to be stable and steady. However, on my car my fuel pressuse droped down from 28 to 15 within 10min. Now we believe when its having a hard time cranking in the morning because by than my fuel pressue has dropped down to 0.


What do you think it is? Fuel pump? We just changed the fuel filter and that didnt fix the problem.



leaky injectors
or
leaking fuel pressure regulator -cheap fix
or
fuel pump
or
something else? (explain pls)
 
sounds like a fuel pump to me...

after it sits for awhile, try turning your key the the last position before it cranks.. let the pump run for a few seconds then try cranking it.
 
If you have proper fuel pressure when the engine is running, it's not the pump.

Either the injectors themselves are leaking down or fuel is being allowed to drain back into the tank through the return line without being checked properly.

ZV
 
Originally posted by: Zenmervolt
If you have proper fuel pressure when the engine is running, it's not the pump.

Either the injectors themselves are leaking down or fuel is being allowed to drain back into the tank through the return line without being checked properly.

ZV
Click to expand...



Its not proper though. It should be way above 28 PSI on idle. ;[

I asked my buddy and he said it wasnt the injector since he was just looking @ the car. He thinks its the fuel pump.
 
It's the pump, probably. The pump has a check valve that holds a bit of pressure in the fuel line, so you won't have to crank the car forever to get it to start.

The injectors COULD be the problem, but usually this symptom is the fuel pump.

 
28psi isn't that low during idle. It's unlikely that the pump is causing the problems, but rather low fuel pressure is caused by the same thing that is causing you to lose pressure when the engine is off. It's possible, although unlikely, that the pump check valve is gummed up and not closing. I say it's unlikely for two reasons - these check valves are very basic and very reliable, tey are just a ball and spring valve and also because fuel doesn't sit in them, it is always moving through them so it's unlikely that it has been gummed up by the fuel.

The first thing to check is look at the exhaust when the engine fires up first thing in the morning. If you have a puff of black smoke, then the fuel is making its way into the cylinders, ergo you have leaky injectors. If there is no black smoke, the fuel is going somewhere else. Check all of your fuel lines for fuel stains. Look around the injectors, fuel rail and all the joins in the line for stains. If nothing is found, then you consider the pump.
 
I think, but am not 100% sure, that the fuel pressure regulator has a check valve to keep the pressure in the system when turned off. There should also be a check ball valve in the fuel pump. It sounds like one of these is failing. Instead of cranking on the first turn of the key simply turn the key to the on position, then off, and then crank. That should get enough pressure to start. It is a hassle but it will make it start. The problem is going to be in determining which valve is letting the pressure bleed. Test the pressure in the system while running, if within spec it will tell you that the pressure regulator is keeping the correct pressure and that the pump is functioning properly....but will not tell you which vavle is leaking. This is a toughie to figure which part is bad.
 
the fuel pressure regulator does hold the fuel pressure up after shutting off the engine but it doesn't hold it forever. Bleeding down some over 10mins probably isn't a problem. When the one on my van was dead my fuel pressure while running was 80+psi when it should have been around 40psi and when you shut the car off it dropped to 0 right then. A doubt a leaky fuel injector could use enough gas even if the injector was running wide open to drop the fuel pressue any while running. The fuel pump should be more then able to make up for it to keep the fuel pressure normal. Low fuel pressure while running sounds like a pump problem to me. Changing the fuel filter first wouldn't hurt though.
 
Did you check the fuel pressure with the vacuum line attached or not? If its attached, you'll have more vacuum, opening the FPR, causing lower fuel pressure. You should be checking the pressure with the line disconnected (in case you didn't already know that).

Mark
 
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