miss at 4,000

S

stang_95gt

New Member

Aug 29, 2007

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Aug 29, 2007

#1

• Aug 29, 2007

• #1

I have a 95 gt. I've only had it maybe 4 months or so. About two weeks ago i started noticing a miss. When I first take off in the morning or after it has sat for a few hours it runs fine but seems to lack the power it use to have. After about twenty minutes of driving the problem starts. As soon as it touches 4,000 it misses out bad. Sometimes when i'm just cruising it'll jerk. I just recently put a new pump and filter on it. It has about 32 psi of fuel with the key on and it stays around there when running. If I unplug the vacum from the regulator it jumps to 40. From what i've read the fuel system is good. About two months ago I put motorcraft platinums, accel wires, msd cap and rotor, and a msd blaster coil and never had a problem with any of it. I tried swapping the coil with my old one just to see and made no difference. I also read that platinum plugs don't go well with these efi 5.0's. This is the first mustang i've owned. If anyone has any ideas let me know.

 

Dino Dino Bambino

15 Year Member

Jun 13, 2007

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Cyprus

Aug 29, 2007

#2

• Aug 29, 2007

• #2

It sounds to me that your new fuel pump could be a dud. The symptoms are typical early signs of fuel pump failure. It just hasn't become bad enough to affect the idle yet but it's only a matter of time before it craps the bed altogether.
I suggest you look into it further and if my diagnosis is correct, return the bad fuel pump to the vendor and insist on a free replacement.

 

HISSIN50

"How long does it take to get help in here?

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Nov 29, 1999

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Aug 29, 2007

#3

• Aug 29, 2007

• #3

You're right about the Plats. It's also possible you're TFI or PIP are on the outs.

If the miss started after the plugs, that's definitely the place to start.

Good luck.

 

S

stang_95gt

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Aug 29, 2007

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Aug 30, 2007

#4

• Aug 30, 2007

• #4

replaced the plugs today with standard motorcrafts and didn't make a difference. I also double checked vacum lines just incase. I though that i might have gotton a bad pump but i've got the same amount of pressure before and after the new one and it acts exactly the same. I saw somewhere its common for the stator or something to go out in the distributor. Can anyone tell me on these cars if you have your fuel psi gauge hooked up with the car running and you rev it up does the pressure go up your cars? on mine it either stays the same or goes down 1-2 psi.

 

HISSIN50

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Aug 31, 2007

#5

• Aug 31, 2007

• #5

The stators tend to either work or not work, rather than causing a conditional miss. The TFI would be more likely for such a miss IMHO.

With the fuel pressure, it should never go below 30 PSI. Ever. With light throttle application, the pressure can dip below your idle reading but then it should come back up (it can have a lag time). And if you rev it hard (WOT), it can drop a PSI or two but then it should soar back up to 38-39 PSI.

They key IMHO is that it never dips below 30 PSI and it is consistant (so the adaptive control can deal with it). If you have a means of seeing fuel pressure in real time, that helps. You obviously use a lot more fuel when under load than while revving the engine in the driveway.

Good luck.

 

S

stang_95gt

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Aug 29, 2007

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Aug 31, 2007

#6

• Aug 31, 2007

• #6

when i'm at wide open throttle my fuel pressure doesn't increase at all it stays right around 32psi. Another thing is that when reving it in nutrual it doesn't miss. just misses going down the road at higher rpms. whats the TFI you were talking about?

 

HISSIN50

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Aug 31, 2007

#7

• Aug 31, 2007

• #7

I see an issue with WOT FP not increasing.

The TFI is the ignition module. Given what you just said, it's not the first thing I'd contemplate as being bad (TFI's dont care if there's a load on the motor or not). For info's sake, it's the module in a metal heat sink mounted to the front of the passenger wheel well.

 

S

stang_95gt

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Aug 29, 2007

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Sep 1, 2007

#8

• Sep 1, 2007

• #8

does it sound like a regulator to you? like I said i've got a constant psi around 32, but if i unplug the vacum to the reg. it shoots up to 40. I tried running it without the reg pluged in to the vacum and pluged the vacum line but it did the same thing. however it took longer for the problem to occur and it wasn't as bad a miss.

 

S

stang_95gt

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Aug 29, 2007

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Sep 1, 2007

#9

• Sep 1, 2007

• #9

It does it when the car heats up like 20-30min of driving. I read that the PIP is known for this

 

HISSIN50

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Sep 1, 2007

#10

• Sep 1, 2007

• #10

It's unknown if the fuel pressure issue is related to the miss. It doesnt sound like it is, given the exact RPM and time interval it takes to occur.

To diagnose it further, it will have to act up further or you will need a way to datalog. It can even be something like another bad plug wire. Anything else from me is going to just be a guess.