Need help identifying this weird thud/

[KMOSES]

The other day i was cruising the highway, and decide I'm gonna get on it a bit.. just for a the fun of it.

here's what's happening,

If i step on the gas pretty hard, not fully WOT... just slamming the pedal from point A to point B almost instantly, boost psi raises fast jumping almost instantly up to about 14/15 psi, i get a weird thud (sounds/feels like its coming from the engine) for a split second then boost qucikly drops to 10/11psi holds there and everything is fine, the thud feels similar to hitting a bump in the road or something of the sort, but I know its not a bump in the road becuase i can relpicate the process over and over, and i feel it, its definitely happening under the hood.

this does not happen if I gradually press the pedal from point A to point B, even if i do it fairly quickly.

is this something I should be worried about, or am I just a retard and I should never jam the gas pedal as mentioned in the first scenario.

 

[KMOSES]

Anyways, yes the spark plugs could be a culprit. Make sure they are gaped correct. When i started running high boost, i had to make the gap smaller.

You said when you started running high boost... I dont understand why im getting such high boost, 15/16 psi seems really high above the stock psi. I dont have MBC or anything that would raise the boost psi. Unless my the few mods that i have ( hks bov, catback exhaust, injen intake) allow for more boost.

Ehhh... how do you slam the pedal without going WOT?

basically i mean going from very little throttle to say 3/4 throttle really fast, as quick as i can move my foot in one quick motion, never smashing the pedal to the floor though. I dont have this problem if i ease the throttle in, I can hit 15 psi with no problems, it only does the stutter when everything is happening so fast.

Spark blow-out sounds (feels) like a machine gun; it occurs as very rapid pulses.

"machine gun" sounds exactly like what im experiencing!, very fast rapid, the whole car jerks very rapidly, but i dont really notice a power loss, i can keep on the throttle where it's at and just push right through the stuttering until everything catches up.
the steering wheel feels like I'm holding a 40 cal, I had my buddy jump in and drive, and i could feel it just the same in the passenger seat, the whole car is getting the machine gun like stuttering.

also, unfortunately i don't have any data logging devices/software what would you recommend?

 

[Calan]

I think you need to slow down a bit and do some reading

Start here:

http://www.dsmtuners.com/forums/newbie-forum/230375-list-loggers-info-tech-article.html

which came from here:

Frequently Answered DSM Questions - DSM Forums

Check back with us after digesting most of that info.

 

[dsmtnr]

Sounds to me like fuel-cut.
Are you running a stock turbo?
Whats the wastegate spring pressure?
Has the car always done this or did it just happen out of the blue?

 

[KMOSES]

I think you need to slow down a bit and do some reading

Start here:

http://www.dsmtuners.com/forums/newbie-forum/230375-list-loggers-info-tech-article.html

which came from here:

Frequently Answered DSM Questions - DSM Forums

Check back with us after digesting most of that info.

Hey thanks for the Logger link, I've been through the FAQ quite a bit, but hadn't checked out the loggers.

I'll probably be leaning towards a cheaper one, $600 for dsmlink just isnt in my budget. Pocketlogger sounds nice but on their site it say's they've discontinued their product. so looks like ODB Gauge or Tunerstein are my options right now.

Thanks for all the help, ill get back to you once I'm up an running some sort of logger

Sounds to me like fuel-cut.
Are you running a stock turbo?
Whats the wastegate spring pressure?
Has the car always done this or did it just happen out of the blue?

yes running stock t-25 turbo, everything is stock other than bov, exhaust, and intake.

as for the wastegate spring pressure, i have no clue, but id be willing to bet that the spring is stock also, probably somewhere in the ballpark of 10psi.

I just recently got this car, had it for a few months now, but it's been doing this since i got it. I'm still pretty new and learning

thanks all for the replies and help. Much appreciated.

 

[94 Talon DL]

hi, ive been reading along and i noticed that some people have mentioned spark plug gaps as a possible culprit, i would agree but only add taht you should probly look into doing a tune up, especially making sure to replace your plugs wire and cap and rotor (if your car has it)

it deffinatly sounds like a misfire to me and that feeling is backed by the severly low mpgs on the highway. i think you would very much enjoy the pull your car would have afterward. i say that cause if you are havinga misfire and dont really notice a loss in power all to much i would say you are always at a lost-power state.
also bieng that you just got the cara couple of months ago, who knows how long those poor little plugs have been in there. get some fresh new guys in there and youll be in business.

let me know if this helps you out.

 

[Calan]

especially making sure to replace your plugs wire and cap and rotor (if your car has it)

I haven't seen a cap and rotor in 20 years (except on old-school race cars).

 

[KMOSES]

Hey Everyone,

I just got some new plugs (NGK BPR6ES) and gapped them to .028, fixed everything. I can WOT catching 15psi boost with no stutter/machine gun feel. car feels awesome!

Thanks everyone for their input and helping diagnosing this. Much appreciation.

oh yeah, when i pulled the old plugs out, they were "champion" brand i believe, and gapped anywhere from .035 to .040, id say they never got gapped and were just dropped in right out of the package.

Thanks again!