I know this is for the Ls1 Firebirds and I have a 3.8 but I was hoping someone can help. So I have the same problem with the 3.8 engine as most people have. When you give it more than 70% throttle it shutters/bucks and doesn't accelerate. If you keep it with 70% throttle or more for a while it will sometimes backfire. If you let off the throttle and let it catch back up to itself it is fine. I have read many other forums on this topic and I have done everything they suggested. I have replaced air filter, spark plugs, wires, fuel injectors, all three coil packs, the ignition control module, checked and cleaned the EGR (its fine), checked the throttle position sensor volts (fine), cleaned throttle body, check fuel pump pressure (also fine), and it is not throwing any codes. I am at a complete loss as to what to do. I don't know if my engine is just shot. Here is a little more about the car. The car is a 1999 Firebird 3.8l engine with a 5 speed manual trans. It has 170,000 miles on it. Any advice will be greatly appreciated. Thanks in advance.

 

I had an L98 that would do that at part throttle. The TPS was gone. Voltage was fine accept for certain areas of the voltage range. You might have something like that happening. The TPS isn't very expensive to replace, but before you go throwing money after stuff, do a couple of things:

1) Check all your grounds on the engine block and the battery/alterantor/starter. Anything there can cause hesitation.

2) Check fuel filter for any clogs - may not show up at idle but at WOT with a drop in flow. Ditto for the pump. Without a data logger, it may be hard to monitor fuel pressure at WOT however. But certainly the car going lean would be a tell-tell sign. See if you can find someone with a wideband to at least monitor what's happening on a WOT run.

3) Did you replace the injectors with the same size/type as was in there before?

 

ur throttle by wire, right?

 

Jake,
With the TPS I hooked a scan tool to it and the checked the voltage. It went up and down nice and smoothly. I thought about replacing the TPS but on my car it is riveted to the throttle body. I have to buy a whole new throttle body just to replace the TPS. Sorry I forgot to mention I had replaced the fuel filter too. I had monitored it while running it and everything was fine. And yes I replaced them with the same fuel injectors.

 

FirstGen
No on my car the throttle is computerized. I believe there is the one sensor on the throttle body and one by the gas pedal. I may be mistaken though but it is definitely computerized.

 

If it is electronic TB then you may have an issue with it. Sounds like an expensive replacement on a hunch tho.

 

Have the exhaust back-pressure checked. Could be a stopped up cat. Most muffler shops can do this.

Vernon

 

MAF sensor check? Just unplug it and see if it runs fine

 

That would be my first test. If not that then tps as mentioned above or fuel pump is also possible

 

There is a pretty common throttle body coolant leak on the 3.8's. My 97 had it. It leaked behind the throttle into the intake.

 

throttle by wire is a comp. controlled T.B.
any luck finding the issue?

 

The 99 was the year they went to dbw on the v6s. I would advise checking your plugs and wires. They melt the wires and cause the boots to crack open and arc.

I had a 3800 car that would do the same thing under a decent load, going up a hill in too high a gear or too much throttle would do it for me.

I threw some headers on it and changed plugs and wires(I coated the boots with copper rtv) it was great after that for the rest of its life.

It got whacked while parked at my house, used the insurance money to buy my ls1 car.

Edit: for help try visiting a v6 exclusive forum, Idk if I'm allowed to name them here.. but

Fullthrottlev6.com and v6f-body.com are 2 good forums for v6 (mostly) stuff.

 

These were known for clogged cats.

 

Check your MAF and 02's @ WOT. The 02's should be reading over 800mv and the MAF should be around 4.5v.

Also you can do a fuel pump volume check w/ a snap throttle test at idle and see if the fuel pressure holds when the injector pulse width opens up.

Depending on what the sensors are actually doing will help point you in the right direction.