Brotan3

Hey everyone. I just bought a 99 T/A the other day and so far I've come across a few issues that need attention. I'm doing my own research as well but figured I'd post here in case anyone has some insight.

The first issue is I get some surging on acceleration, usually when I hit about 40 mph if I'm on the pedal just enough to maintain speed or go a bit faster the engine seems to surge and the RPMs will go up and down as well as exhaust note. Again, only when I'm barely on it, if I open the throttle up a bit more it takes off like normal. I'm assuming this has something to do with either air or fuel delivery.

Second is it seems like right around the same time i get the surging my car vibrates and makes a sound almost like what you would get if you went over rumble strips. This is also on acceleration. Idk if it means anything but the car has been upgraded to 4:10 gears and I believe a somewhat upgraded transmission.

The last one (for now) is a knock that I get when I tap the pedal. Kind of like You would when you rev match to downshift. It comes from the back somewhere under the backseat, possibly the diff. This one most likely won't get a solution on here but hey maybe someone else out there has experienced it.

Also, there's some pretty big tires on the back compared to the ones up front so the speedometer is way off. Is there a way to recalibrate without tuning it? I can only do so much with the tuner I have and writing different tire sizes isn't one of them.

Mods that I know of are as followed:
BBK SSI Intake
BBK TB
BBK Longtubes
SLP Lid Intake
Possible mild cam
Possible stall
4:10 gears
Full BMR Suspension (Extremely Stiff)
3 inch exhaust from headers back .

I've always been a WBody guy and I am New to the FBody world so I don't know too much about them, so any help is appreciated.

JD_AMG

Do you have any error codes?
My guess would be the front 2 02 sensors, some can be finicky with LT headers. This will most definitely cause surging/jerking issues.

Likely exhaust related, probably exhaust hitting the underbody of the car or rubbing something.

You should never get a knock when rev matching...Dont know what you are talking about there.
The noise could be the exhaust hitting the floor boards like above, could be lose suspension pieces (torque arm,rear control arms,panhard bar) the drive shaft u joints, or could be play in the rear end.

No, you need a real tune, like hp tuners.

Did the previous owner give you any paper work or anything? Has the car been dyno tuned?

blackbyrd

iTrader: (14)

Bump in the back is probably the 3" exhaust taping the axle or the lanyard support. I ran into that with my Corsa setup ages ago.

Knock up front could be a engine mount being g bad and allowing the engine to rock during the rev and letting the collector bang the floor board.

Surging could be due to a bad tune for the cam. A/c on when this issue arises?

With all the suspension work I'd look I to nailing down the surge before I get into the vibration if it only occurs in that condition. It would just be due to the weight transfer on the car with the surge.

Also the knocking you are hearing... Do you what kind of end joints the suspension parts have some of those can be rather noisey. Special if it's rod joints

ws6junkie

Any engine lights on when you get surging? Have you put a code reader on to see if there have been previous codes? I agree with JD_AMG about the O2 sensors - they can cause all kinds of issues but usually will throw a code of some sort.

Not to be an alarmist, but were the 4.10 gears done by a professional? It's easy to get an alignment out that could cause any number of sounds.

Good luck - hope you get this all straightened out.

Brotan3

Thanks for the responses guys. Glad to see that this forum actually offers help unlike the LS4 one.

I was able to pull a code from the car that has to do with the 02 sensor so that will be my first order of business getting that sorted out.

As far as the noises I'll have to check on the suspension and see if there's any contact points that shouldn't be there.

And with the work done. I didn't get any sort of paperwork on it, the previous owner bought it with most of it done and only added a few others like the gears wheels and exhaust. I have a shop nearby that a lot of LS guys go to so once I get the car registered and road legal I'll be taking it to him to QC it and get it tuned.

Hopefully this won't be too much of a headache.

JD_AMG

Make sure to do research on this one as the 02s can be tricky. The problem could not only be the brand of sensor itself not reading accurately enough for having LT header but also the fact that with LT headers the exhaust runs cooler (which confuses the sensors) and on some LTs the bung the 02 sensor plugs into may not be deep enough to get a good reading. Ive also heard that the 02s may get extra carbon build up with LT vs stock manifolds so they wear out quicker.
You may have to experiment with different brands and have some extra tuning done as well, you could just luck out and replace them and be good to go, but they may throw a code again in a few thousand miles.

Brotan3

Weird, went to pull the code so I could do some research on it and there was no code to pull. The car had only been driven like 70 miles since PO bought it back in November and I didn't clear the code last time i pulled it so I'm wondering if it just needed a good drive (the 200 total mile trip to buy it) to shake off the dust. Still getting some odd readings regarding the EGR so I'll be looking into that as well.

30thanniv

iTrader: (2)

The first issue is I get some surging on acceleration, usually when I hit about 40 mph if I'm on the pedal just enough to maintain speed or go a bit faster the engine seems to surge and the RPMs will go up and down as well as exhaust note. Again, only when I'm barely on it, if I open the throttle up a bit more it takes off like normal. I'm assuming this has something to do with either air or fuel delivery.

Second is it seems like right around the same time i get the surging my car vibrates and makes a sound almost like what you would get if you went over rumble strips.




THIS SOUNDS LIKE LUGGING. check the tune

y2k_ta

iTrader: (80)

Knowing the stall speed of the torque converter would be helpful. If it's rather loose like a 4,000 stall, that could also be causing some of your surging issue.

RevGTO

iTrader: (12)

Yes, and it will especially make that sound if the torque converter is locking at too low of speed.