Vortech s/c car with bucking at WOT

[drhill]

Hello Everyone, I just purchased an '03 marauder with a vortech s/c and recently rebuild engine. I'm fixing up the little things on the car...one of which is that at WOT in 2nd and 3rd gear the car bucks/hesitates at higher rpm. It doesn't pull smoothly.

In my past supercharger experience this is usually one of a couple of things:

- plug gap too large
- fuel pressure dropping
- electrical (like maf etc)

Any ideas what this might be in a vortech'd marauder? I did not do the motor but I can ask questions from the shop that did the work...

Thanks for the help!

[martyo]

Datalog and let us know the results.

[Marauderjack]

What RPM.......possibly hitting the "rev limiter".......don't ask me how I know!!:mad2:

[LANDY]

Did you already check the plugs gap, fuel press?

[sailsmen]

Where is your by pass valve located? What boost level?

[RacerX]

Could even be bad coils.

[Blackmobile]

Is this between 80 MPH - 100 MPH?

[drhill]

Did you already check the plugs gap, fuel press?

Not yet, will do that by tomorrow. Unfortunately I am not "set up" with equipment for this car...no boost gauge on car, no datalogging equipment :( No check engine light...which is good, I can still at least pull codes to see if any stored codes indicating coils etc.


I will check Fp, codes and plugs and report back!! BTW...I just noticed this car has a t trim on it? pretty darn stock otherwise:dunno:

[Vortech347]

Don't floor it again until you either have a wideband in the car or its on a Dyno.

[drhill]

Is this between 80 MPH - 100 MPH?


Hmm...I don't remember...I just figured out the car has 4.10 gears (no wonder it pulls so dang hard from a stop, I thought it was just the PI converter doing it's thing)...and the bucking happens between 5000-6000 rpm WOT. This range in 2nd gear would be 68-80 mph...

[drhill]

Don't floor it again until you either have a wideband in the car or its on a Dyno.


Wow...ok, these engines are pretty fragile? I'm used to 5.0 motors with these vortech's on them...not super dependable with tons of power but still ok to figure out a problem like this. I will heed your advice.

On that note - I know this car has been tuned somehow, speedo reads correctly for 4.10's etc...how do I figure out which program and who to go to? I would prefer a local dyno shop who knows these cars and motors...any recomendations in so cal?

Thanks!!

[Blackmobile]

Hmm...I don't remember...I just figured out the car has 4.10 gears (no wonder it pulls so dang hard from a stop, I thought it was just the PI converter doing it's thing)...and the bucking happens between 5000-6000 rpm WOT. This range in 2nd gear would be 68-80 mph...

A good while back Some memebers had an issue with going 80 MPH, and then stomping on the peddle and before you got to 100mph the Marauder would start bucking badly. It turned out to be in the turn from DR. We gave him a call and he sent us new tunes and all was well.

[GAMike]

Hard to speculate without the info requested, but I have a similar issue...... Don't think its a Centri issue, as I have a Trilogy and have had similar experiences.... Good thing Mo's & Jeff are somewhat close by :)

Bypass Valve
Anytime I am rolling and mash the pedal, my bypass valve hiccups.... (Mo's is replacing it, this Thursday). When this was diagnosed, it was really awful.... Part of the reason was I also had a "T" connecter for some of the vaccume hoses (going into the bypass valve I believe) that had split open......

Jeff @ Mo's had an extra, and made a quick fix for that... That said, when I roll progressively deeper in the pedal vs. mashing, the car performs much better (but you still know there is a problem)... Jeff said I could drive it, but its really no fun with this bypass valve the way it is.....

MAF Issue...
My car's MAF pegs around 78-83mph when pedal is mashed, then goes away. I am told that an upgrade to a 90mm MAF & retune will solve this, but......$$$$

Hopefully this is helpful to you..... Good luck figuring your issue out.

[sailsmen]

Hello Everyone, I just purchased an '03 marauder with a vortech s/c and recently rebuild engine. I'm fixing up the little things on the car...one of which is that at WOT in 2nd and 3rd gear the car bucks/hesitates at higher rpm. It doesn't pull smoothly.

In my past supercharger experience this is usually one of a couple of things:

- plug gap too large
- fuel pressure dropping
- electrical (like maf etc)

Any ideas what this might be in a vortech'd marauder? I did not do the motor but I can ask questions from the shop that did the work...

Thanks for the help!

Can you post all your mods or tell us if you bought from a member?

[drhill]

Can you post all your mods or tell us if you bought from a member?

I actually fixed one problem - bucking/hesitation is gone...took out fresh platinum densos :shake: with a .040 gap and installed TR6's with a .030 gap. IT was blowing out the spark previously. But, still detonates a bit at high rpm in each gear. (I know, I know...but I had to try WOT). Turns out previous owner's wife put a tank of 87 octane in it:mad2:so this last test was with less than 1/4 tank of 87 and the rest full of 91 (which is our best gas in CA). I also suspect that the car may have a stock 195 t stat instead of a 180.

As far as mods, I'm still learning what this car has. Someone spent a lot of time and money on it, but I didnt get much info. I know for sure the vortech kit (looks like the early style DR kit) with T trim and vortech aftercooler. Definately has 4.10's and a PI converter but I can't quite determine stall due to tire spin. The shop that rebuilt the motor said it had mild blower cams in it but stock motor otherwise. complete stock exhaust(even 2 inch intermediate piping) with flowmasters welded in.

Taking it in tomorrow for the shop to do the diagnosis and repair of HVAC stuff...mostly their cost.

I will say, I've had a lot of high power and specifically votech cars in the past...this is one of the most fun! The gears and converter are a perfect match for this engine and the vortech...I'm never in want fo more low end...I would venture to say this marauder is on par or very close to my brother's new CTS-V...the maurader has a bit less midrange torque around town but...not bad overall!!

[boatmangc]

MAF Issue...
My car's MAF pegs around 78-83mph when pedal is mashed, then goes away. I am told that an upgrade to a 90mm MAF & retune will solve this, but......$$$$



Diablo Maf Extender Mike

[Vortech347]

Wow...ok, these engines are pretty fragile? I'm used to 5.0 motors with these vortech's on them...not super dependable with tons of power but still ok to figure out a problem like this. I will heed your advice.

On that note - I know this car has been tuned somehow, speedo reads correctly for 4.10's etc...how do I figure out which program and who to go to? I would prefer a local dyno shop who knows these cars and motors...any recomendations in so cal?

Thanks!!

Most 5.0's have forged pistons which can tolerate detonation a little bit. Theses cars have hypercraptastic pistons that shatter with detonation. So it has a tune but you aren't in possession of the hand held? That could make things a little complicated. I would definitely make a dyno appointment with a local tuner. Good luck.

Adam at ST performance is a decent tuner. Just be specific with him what you are looking for transmission feel wise.

[LANDY]

Hard to speculate without the info requested, but I have a similar issue...... Don't think its a Centri issue, as I have a Trilogy and have had similar experiences.... Good thing Mo's & Jeff are somewhat close by :)

Bypass Valve
Anytime I am rolling and mash the pedal, my bypass valve hiccups.... (Mo's is replacing it, this Thursday). When this was diagnosed, it was really awful.... Part of the reason was I also had a "T" connecter for some of the vaccume hoses (going into the bypass valve I believe) that had split open......

Jeff @ Mo's had an extra, and made a quick fix for that... That said, when I roll progressively deeper in the pedal vs. mashing, the car performs much better (but you still know there is a problem)... Jeff said I could drive it, but its really no fun with this bypass valve the way it is.....

MAF Issue...
My car's MAF pegs around 78-83mph when pedal is mashed, then goes away. I am told that an upgrade to a 90mm MAF & retune will solve this, but......$$$$

Hopefully this is helpful to you..... Good luck figuring your issue out. I'll take it you are still rocking the stock maf. If so a 90 will take you up to low 400s and fan be bought for around $100 then the tune is the big expense.

[drhill]

All is good...got the 91 octane in her and no pinging. I'm sure I'll still get it re-tuned so I have the baseline and will be starting fresh with no unknowns. Is Adam at ST in Southern California? I couldn't find him with a google search...thanks!

I think I may still have the stock speed limiter? Felt like the car was no longer accelerating at about 5300rpm in 3rd...it was not a harsh limiter like the aftermarket ignitions...hard to believe someone would leave this in...but who knows!

[Paul]

MM's do NOT have forged internals_They cannot take knock. Do not test this unless you want to buy anew engine/rebuild.

[Vortech347]

ST Motorsports.

http://www.spankintime.com/