98 gt. Fuel problems! NEED HELP!!

stanglover0526 · Oct 29, 2010

I checked for vac leaks and that came up with nothing. I also noticed i can smell gas outside the car. Found it leaking where the filler neck hooks to the tank. Also the car seems to start easy when you turn the key and crank for a second then turn it off then it fires when you crank it again. Any ideas?

wmburns · Oct 29, 2010

As to why the car starts better when the key is cycled on/off/on prior to cranking, fuel pressure leak down. It improves starting because the fuel pump runs (primes) for a short period of time prior to starting. By cycling the key on/off/on this builds up the fuel pressure to normal levels.

Leaky fuel injector(s), bad fuel pressure regulator, or bad fuel pump check valve.

Since you have stated there aren't any vacuum leaks, then possible the lean DTC code could be a CLOGGED fuel injector. Consider using an injector cleaning/flow test service such as injectorrx.com. Once cleaned, the injectors are as good as new. Cleaning is cheaper than buying new. I have used their service and have had great luck with it.

The gas smell is from the gas tank grommet is a common problem as these cars age. Tons of write-ups available on how to drop the tank. Remember to completely cut away the old grommet or damage to the fuller neck WILL result.

stanglover0526 · Nov 4, 2010

ok i finally got time to put a feul pressure guage on it and with the key on engine off the fuel pressure was non existant. But if i cycled the key it would slowly build up then drop back down and wouldnt hold pressure. Then after i started the car the pressure was at about 28psi idling and when i blipped the throttle it only jumped to about 32psi. im not sure what the pressure is supposed to be on these cars, but this sounds low to me. Think its the fuel pump?

wmburns · Nov 4, 2010

Mustang fuel pressure is supposed to by 40 PSI (delta or intake referenced). However, you are using an external fuel pressure gauge that is Atmospheric referenced. Remember that the intake is under a vacuum at idle.

Atmospheric-gauge - intake-vacuum = 40 PSI delta.
40 PSI Delta - intake-vacuum = Atmospheric-gauge.

In otherwords, it's completely normal for the gauge FP to be lower at idle. If you do not understand the difference between delta and atmospheric pressures, then this will continue to elude.

Try this for a TEST. Disconnect and plug the fuel pressure sensor vacuum reference line. What is the fuel pressure now? Does it jump to 40 PSI? Note, never drive the car with this reference line disconnected.

Now the fact that FP is zero after a cold soak indicates fuel pressure leak down. This is either leaky fuel injectors, bad FP regulator, bad FP check valve, or bad/weak fuel pump.

Also, it would be handy to know what the intake vacuum is. It seems to me that the fuel pressure should have gone up more when the throttle was blipped. We need to know if there is something wrong with the motor itself that is causing very low intake vacuum.

Consider running a compression test.

stanglover0526 · Nov 4, 2010

hopefully i can do these test and figure it out this weekend.

stanglover0526 · Nov 6, 2010

Ok when plugged, the fuel pressure sensor vacuum reference line the fp jumped to roughly 38psi when the throttle was blipped the pressure dropped. I went ahead and replaced the fuel filter which was pretty clogged. When we were doing the filter we hooked a guage directly to the line from the pump and the results were the same as before. We checked the pump and when its keyed up the pump kicks on to prime ans builds pressure and when it shuts off the pressure immediatly drops back to 0psi. Im thinking bad pump?

wmburns · Nov 6, 2010

The fact that the FP drops with the reference line disconnected tells me there are some issue with fuel delivery.

The fact the the FP drops so quickly when turned off is also a problem. However, based on the information, IMO you can not make a conclusive diagnosis of a bad fuel pump. The leak down could be from an injector, FP sensor, or the FP check value.

But based on the possibility of a weak FP, this would seem to me to be a good place to start.

stanglover0526 · Nov 6, 2010

we unhooked the line from the pump and checked the pressure directly from the pump on that test. So to me it sounds like a bad pump as there is pressure leak down directly at the pump just the same as when there was from the check line.

wmburns · Nov 6, 2010

So you split the line and tested the pressure directly from the FP? Great idea!

I agree. It the FP leak down is the same coming directly from the FP, that sounds like a two for 1.

Note, the check valve is normally replaced with the FP as an assembly. So you will have to so something special should you decide to replace JUST the pump.

Note, you may find once the tank has been dropped, that the source of the leak could be a leak in one of the flexible hoses. Just no way of knowing until you tear into it.

stanglover0526 · Nov 6, 2010

What is the check Valve? I ordered the pump kit and not the whole assembly as it was $80 cheaper. Can i tell if the check valve is bad by looking at it?

wmburns · Nov 6, 2010

As I said before, the check valve is normally serviced with the FP as an assembly. I personally have no idea exactly were the check valve is. Nor do I know how to test it. Nor do I know how where to get replacement parts.

However, based upon your tests, you KNOW there's a problem. So unless you find a leak in a flexible hose, THEN the check value has to be bad.

If replacing just the pump, the you are own your own. Sorry.

stanglover0526 · Nov 6, 2010

I just called autozone and changed my order to the full assembly that way im not tracking down more problems. Ill put it in tomorrow and post up if it worked.

stanglover0526 · Nov 8, 2010

Well the fuel pump fixed the hard start problem and gave it some power back. But i cleared the codes and now it popped back up. Its the p1151 code and now a p1000 code.

wmburns · Nov 8, 2010

Ignore the P1000 it just means that not all readiness test are complete.

Regarding the P1151, do you have an exhaust leak around the EGR tube? Any exhaust leaks? Any vacuum leaks?

stanglover0526 · Nov 10, 2010

I think there might be a exhaust leak on the drivers side. Under full throttle i think i might be able to hear one. But only under hard acceleration. I have not been able to find any vac leaks. Its going to be stormy here so i wont be able to look under the car for a few days. Im not sure ill be able to hear the leak at idle. It seems if there even is one it is very minimal. Im going to switch the new 02 sensor i got with the old one on the other side to see if maybe the new one is for some reason defective.

stanglover0526 · Nov 24, 2010

Well this weekend i swtiched the sensors around from side to side to see if i got a bad 02 sensor and the code has not popped back up since. Seems to be getting better gas mileage too. Weird, but ill keep posted if it comes back on.

98 gt. Fuel problems! NEED HELP!!

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