Please help me out if you can. Car stumble, farts, and falls, then dies...

So first off it's not a Terminator, MY bad guys...I'm poor.

It's a Mach 1. Anyways started it up after a year and everything has been fine. Well actually at the start when you would start it you would have to use the gas pedal to keep it running until it cleared up and idled fine. That issue went away since I've been driving it weekly. Anyways today it was in stop and go traffic @ 96 degrees outside and after the traffic opened up around 2,000-2,500rpms it would start breaking up. Had a little power, enough to gain speed but got worse and worse. Pulled over and it died.

Got out, popped the hood and checked for leaks because it felt like a misfire. Started the car up immediately to check for leaks and no leaks as well as ran fine. Ok

Drove about a mile down the road and same thing. Pulled over and shut the car off. Sat for 5 minutes this time and started it up. This time I got 2 miles down the road and it did it again. Shut the car off while in neutral and rolling. Started it back up and the car drove fine. I got home shortly later.

What do you guys think it is? My opinion is a bad or going O2 sensor...?

If say check for codes then use something to log while driving. See if fuel pressure is erratic or what

I'm guessing a dying fuel pump. A neighbor had similar symptoms in her V6 until it finally died completely on the freeway.

01yellercobra said:

I'm guessing a dying fuel pump. A neighbor had similar symptoms in her V6 until it finally died completely on the freeway.

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Ironically its a brand new fuel pump. That's why the car didn't run for a while.

If it was something fuel related I think it would be more consistent and not go away immediately when I shut the car off and turn it back on. I have no way of checking codes or logging data. It was tuned back in 2008.

Here for videos of farting car

Stopsign32v said:

Ironically its a brand new fuel pump. That's why the car didn't run for a while.

If it was something fuel related I think it would be more consistent and not go away immediately when I shut the car off and turn it back on. I have no way of checking codes or logging data. It was tuned back in 2008.

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Just because it's new doesn't mean it's good. How was it tuned? Did you use a hand held device?

Stopsign32v said:

Ironically its a brand new fuel pump. That's why the car didn't run for a while.

If it was something fuel related I think it would be more consistent and not go away immediately when I shut the car off and turn it back on. I have no way of checking codes or logging data. It was tuned back in 2008.

Click to expand...

Did the issue start after you installed the new pump?

Stopsign32v said:

Ironically its a brand new fuel pump. That's why the car didn't run for a while.

If it was something fuel related I think it would be more consistent and not go away immediately when I shut the car off and turn it back on. I have no way of checking codes or logging data. It was tuned back in 2008.

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a blue tooth OBD2 and app on your phone is a lot cheaper than the parts cannon, not like you won't be able to keep using it for a long time

98 svt said:

Did the issue start after you installed the new pump?

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No, drove fine for probably 2 months. This is a new thing that happened yesterday after sitting in stop and go traffic to the point of you get to wondering how your cooling system is doing. 3/4 tank of gas too so the fuel pump didn't get hot.

Who did the fuel pump?


Being a miss and falls flat.

Fuel filter is another,,
Assuming it was done with pump,,
I know sometimes it's a pita to get off,,chance something like this happened? Looks clean on outside,,
Will not set engine light,

Coils getting weak.

Same thing. Intermittently and jerks when past 1/4 pedal.

Will not set engine light

Oem air inlet tube.
Rubber seal at throttle body,,
Soft? Ripped?

hotcobra03 said:

Who did the fuel pump?


Being a miss and falls flat.

Fuel filter is another,,
Assuming it was done with pump,,
I know sometimes it's a pita to get off,,chance something like this happened? Looks clean on outside,,
Will not set engine light,

Coils getting weak.

Same thing. Intermittently and jerks when past 1/4 pedal.

Will not set engine light

Oem air inlet tube.
Rubber seal at throttle body,,
Soft? Ripped?

Click to expand...

So I installed the fuel pump, it is pretty straight forward and it either is done right or it isn't. The car has ran great since then and WOT shifts 2-3 send the car sideways. Power all the way to redline.

The problem happened after the car got very hot and would stumble and got worse and worse until it died. Sounded like it was dumping way too much fuel in. Immediately turned the car off and back on without waiting and while still rolling and clean power anywhere from 1/4 throttle to roughly 3/4 throttle. I didn't think it was smart to hammer it, long story short the car felt normal and sounded normal. Then it came back. Turn off and back on and we are good to go.

That doesn't sound like something mechanical to me like a fuel pump or filter.

A month later and the car drives like normal and hasn't done it since. But I also haven't been in heavy traffic. Good gas mileage, good throttle response, no hesitation, hazes the tires into 3rd....Any ideas what would cause it? I have no doubt that if I sat in stop and go traffic this would probably come back. But what could it be?

Glad it seems to be running fine now, but like you said, it will likely rear its nasty head again. If it does, check/monitor your fuel pressure.

I saw a couple of posts that suggest you check the fuel filter. The other thing could be you got a bad fill of gasoline. I had that happen and the car ran erratically. I also had a car that ran like yours and it turned out to be a curved vacuum line that fatigued and pinched off the flow.

Water in fuel maybe??

Ok so it is something. No problems have come up since but the other day down shifted to 3rd @ probably 4,000rpm and rolled into it. I felt it stumble and got out. That hasn’t happened before. New tank of gas and tank was about half full.

Do you guys think it’s fuel related or ignition? Car sat for over a year with old gas in the lines (empty tank though) but started up fine with a new pump and gas so I didn’t think there was any issues. Injectors are blue 39s.

You need to log it plain and simple. See if fuel pressure drops etc

Would be helpful if you could find a situation that makes the issue repeatable

DSG2003Mach1 said:

You need to log it plain and simple. See if fuel pressure drops etc

Would be helpful if you could find a situation that makes the issue repeatable

Click to expand...

Never logged these cars. Any way to do that without going on a dyno?

Stopsign32v said:

Never logged these cars. Any way to do that without going on a dyno?

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Absolutely.

You use a handheld tuner and your laptop plugs into it.

Do you have a handheld?


Sent from my iPhone using the svtperformance.com mobile app

No it was chip tuned (sct?) by Pro Dyno probably 15 years ago.