Engine missing under load

[hallowen]

Hi Guys,
I have a 1997 Gt 4.6 Auto that ran good until I installed some Flowmaster 40's.
Now, it runs fine at idle and partial throttle, but starts missing and occasionally backfiring when trying to accellerate.It goes back to normal idle when I back off though.

Is there something I'm missing about adjustments anywhere?

 

[DerekStangGT]

Hi Guys,
I have a 1997 Gt 4.6 Auto that ran good until I installed some Flowmaster 40's.
Now, it runs fine at idle and partial throttle, but starts missing and occasionally backfiring when trying to accellerate.It goes back to normal idle when I back off though.

Is there something I'm missing about adjustments anywhere?

are you sure its missing? please describe the sound its making or how it feels. is it backfiring and "missing" at any particular rpm or speed?

 

[hallowen]

DerekStangGT

When I try to accelerate(Mid to WOT), it feels like i've dropped a few cylinders until I let off.
It will Idle fine and slight throttle, but anything over that and it feels like it shuts off cylinders.

Could it be running lean due to less back pressure?

 

[DerekStangGT]

DerekStangGT

When I try to accelerate(Mid to WOT), it feels like i've dropped a few cylinders until I let off.
It will Idle fine and slight throttle, but anything over that and it feels like it shuts off cylinders.

Could it be running lean due to less back pressure?

if you just have the flows with stock tubing, then backpressure wouldnt be affected much at all, if any. what does the car do when you think it misses? a misfire feels like the car hesitates or stumbles. is it only under load or can you get it to miss when you rev in neutral? if it does miss in N, hold up a piece of paper tight against one of the tailpipes, allowing a little exhaust gas to pass by. if it is missing, the paper will vibrate back and forth and you will hear a whop whop whop sound from the paper. if thats the problem, i dont think it is caused by the muffs. check your timing w/ a timing gun to make sure everything is ok. also check your plug wires.

 

[hallowen]

It doesn't miss when in neutral at idle or when I rev it up either, but when I put it in drive and head down the road, anything past partial throttle all the way to WOT it acts like you pulled off a few cylinders, I mean they just sound like those cylinders just quit abruptly, not firing off and on,but don't fire at all until I let off the throttle!

Possibly I have fuel pressure/filter problems cause the plugs are only a few hundred miles old, and it doesn't sound or feel like an ignition problem.

 

[DerekStangGT]

well, i dont know what it could be. i dont have your car hooked up to any diagnostic equitment so im head to your local autozone b/c they can scan for codes for free (mostly) and tell you what the problem is. if its really that bad, i would def get it looked at.

 

[hallowen]

Thanks For the Help DerekStangGT,

Guess I'll head over to Precision Tune and get it checked out.