1998 Mustang GT hesitation

RAU03MACH

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there are a few here that have pretty good ideas try to help
got to have that patience.
 
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1998Mustang

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Its hard bro . Ive not given up after replacing my fuel pump, fuel filter , TPS, MAF , sparkplugs and soon my fuel pressure regulator.
 
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1998Mustang

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thats why the good lord gave us hands to tear shit apart and trouble shoot
I had to tear out my fuel pressure regulator shit was stuck in there. That gave me a little hope ngl. Plus i don't think its actuating properly
 

RAU03MACH

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i might go as far as timing is a bit off sounds
fuel will Couse a bunch of problems also
 

Mustang5L5

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Plug a scanner in that can read live data. Take a look at the fuel trims. Are they pegged rich at all? What are your short terms and long terms? Add your STFT and LTFT on bank 1 up. Do the same for bank 2. Are they under 10% each side?

What is your MAF flow in Grams/s at idle? Should be roughly the displacement of the engine once warmed up and in a stable idle. So 4.6-5.2 grams/s at idle.

Take a look at the upstream O2's. Are they switching properly? Do they vary between 0.1V and 0.8V up and down in a consistent manner at idle? Do they both switch the same?

Hesitation could be attributed to running rich. I'd plug a fuel pressure tester into the rail and actually verify fuel pressure first before just replacing parts. But, when you say it sounds like a 2-step, that could also be a misfire as well as 2-steps generally cut ignition to achieve that affect.

1998 was a transition year in which later models got the PWM fuel pump modules. I beleive those report fuel data in the live data, including fuel pressure. You might be able to start the car up, look at the live data and see what the fuel pressure is. Go for a drive, record the live data, see if the fuel pressure remains consistent.

Not saying looking through the live data will solve the problem, but it may provide some clues. I prefer this approach before firing off the parts cannon.
 
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1998Mustang

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Plug a scanner in that can read live data. Take a look at the fuel trims. Are they pegged rich at all? What are your short terms and long terms? Add your STFT and LTFT on bank 1 up. Do the same for bank 2. Are they under 10% each side?

Take a look at the upstream O2's. Are they switching properly? Do they vary between 0.1V and 0.8V up and down in a consistent manner at idle? Do they both switch the same?

Hesitation could be attributed to running rich. I'd plug a fuel pressure tester into the rail and actually verify fuel pressure first before just replacing parts. But, when you say it sounds like a 2-step, that could also be a misfire as well as 2-steps generally cut ignition to achieve that affect.
Fuel pressure when i tested it was ass, O2 seemed good, fuel trims where weirder. STFT was like 99.2% and it wasn’t moving. LTFT i forget but it seemed normal, i might of been the other way around
 

Mustang5L5

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You sure it was 99%? I thought they maxed out at 25%. Might want to double check that but I would think the LT would have added fuel as well. If it's dumping fuel on one bank that would certainly give you a hesitation.

If it happens at higher RPM however, i think it might be ignition related. I don't think 1998 has misfire detection like the 99-04 cars do in it's live data stream.
 
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1998Mustang

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You sure it was 99%? I thought they maxed out at 25%. Might want to double check that but I would think the LT would have added fuel as well. If it's dumping fuel on one bank that would certainly give you a hesitation.

If it happens at higher RPM however, i think it might be ignition related. I don't think 1998 has misfire detection like the 99-04 cars do in it's live data stream.
It was 99% ik that i read that 99.2 or whatever is when its not in use, and its really any rpm. When i get off work im putting in the new fuel pressu Regulator and seeing what happens
 
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1998Mustang

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You sure it was 99%? I thought they maxed out at 25%. Might want to double check that but I would think the LT would have added fuel as well. If it's dumping fuel on one bank that would certainly give you a hesitation.

If it happens at higher RPM however, i think it might be ignition related. I don't think 1998 has misfire detection like the 99-04 cars do in it's live data stream.
Taking my car up to manassas for it to be
Diagnosed as the fuel pressure regulator didnt fix it, ill update when its back
 

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