Stutter - even worse after fuel pump replacement

[InvalidUserID]

Hi all,

This is on my girlfriend's 2001 Mustang (V6). She mentioned that it recently developed a stutter during acceleration. Sure enough when I drove it, under normal acceleration it would stutter a little, like a misfire but no CEL. Since we were heading up to her father's weekend place, he said to bring it up and he'd look at it during the weekend.

He hooked up a fuel pressure gauge and said when the car was shut off, the pump would lose pressure. Thought it was odd as it was only two years old (Airtex) so he replaced it with a Motorcraft one. Unrelated but he also replaced the A/C compressor which took up more of his time. By the time it was time to head back, we restarted and the idle was still a little off and there was slightly more hesitation under acceleration. I knew it was still there because just shifting into reverse without gas, you could feel it hesitate and jolt.

So it's at his place until this weekend when we can investigate more. Plugs looked good and are only about 15-20K old, as well as the fuel filter and plug wires which were all changed at the same time.

Where would you guys start to look?

 

[Clevy]

Catalytic convertor

 

[Olas]

Compression? Timing? Does it stumble under acceleration every single time or is it gear/road speed/throttle position dependant?
Id check for codes and vac. leaks first as easy ones to rule out.

 

[InvalidUserID]

No codes before or after the fuel pump change.

Before the fuel pump change I only noticed slight hesitation under moderate acceleration (getting up to 40 mph quickly from a stop). Idle and light acceleration were fine, nothing noticeable.

After the fuel pump change, I really only drove it around the block a few times and noticed more/harder hesitation on moderate acceleration and when I initially threw it into reverse. Idle and light acceleration felt normal.

 

[Olas]

Visually check the plugs are sparking and injectors are squirting after you check for vac leaks.

 

[Powerglide]

Don't you mean SPUTTER? Never heard a car stutter.

 

[Trav]

How does the pressure look now?
Did he replace the whole module or just the pump mounted to it? Fuel pressure regulator checks out ok?

 

[Roadkingnc]

Plugs wires and coil will fix it, and don't go cheap. Get oem if you can, the coils are junk on those, usually #2 misfiring

 

[OVERKILL]

Probably a coil. Our Expedition at one point developed a problem where it would "buck" under acceleration, never threw a CEL for it, #7 coil had decided to take a dive under load, replaced it and we were golden.

You'll need a scanner that has access to mode 6 and check the misfire counts for the cylinders. One will probably have a lot more than the others, in our case it had 131 or something whilst all the others were basically zero.

 

[JimPghPA]

I am thinking sparkplugs, and fuel.

How old are the sparkplugs (how many miles are on them)?

And how old is the fuel, if it is a low use car, starting with a full tank, the second half of that full tank may be in the car too long, and may have gone bad.

With a low use car you want to put enough fuel in the car to last a month or so, so do not fill it up all the way, but think about how long it will be when the vehicle will require fuel again.

Also if it is a low use car and you want to fill it up all the way, you might consider using Sta-Bil fuel treatment. Put the Sta-Bil fuel treatment in the tank just before you fill it up.

 

[Brybo86]

Overkills advice sounds the most plausible to me

 

[OneEyeJack]

Keep us updated.

 

[InvalidUserID]

Spark plugs have less than 20k on them and looked good when we pulled them. Didn't check coils, will do this weekend.

Hesitation was present on previous tank of gas and a full refill did nothing.

Appreciate the comments, I'll post an update when we get back up there.

 

[chrisri]

I would say bad coil but does your car use MAF sensor?Symptoms look like bad MAF.

 

[Powerglide]

Porky Pig stuttered.

 

[Tzu]

I was thinking the same thing. I am a GM guy, but our Impala gave us the same symptoms you describe, and I thought the hesitation, bucking was from poor fuel pressure (replaced 14 yr. old pump with new and still acted up). Turned out to be a MAF sensor that set no code. Try unplugging it and then see how it drives. If it drives much better, there you go. If not, that was my only guess. Good luck.
Originally Posted By: chrisri
I would say bad coil but does your car use MAF sensor?Symptoms look like bad MAF.

 

[InvalidUserID]

He ended up taking it to a mechanic and they checked the basics (plugs, wires, MAF, vacuum lines, etc) and found it was a slightly clogged cat.