N20LT4BIRD my chicken is sick!

[thomas]

I have a 383 and its sick. I need some help. When Im in 6th cruisin at 60-70mph and the rpm are 12-1600 it doesnt like it. Its like it wants to start to jerk. Just like if you going 25mph and throw it into 6th. Just like that. Someone said I need a new fuel pump because I have to start it 2-3 time when it sits for a while. They said something like back bleeding(?). It never did this before. I can go 35-40 mph in 6th and she doesnt complain. Any help from anyone would be grateful. thanks

[Injuneer]

What cam are you running?

The stockers aren't too happy if you get the rev's too low in 6th gear..... a 383 with a decent cam isn't going to like it any better. Not sure why you would even attempt to run it at 1,200rpm in 6th gear?

[N20LT4Bird]

First off, 1200 rpm is too low an RPM to be cruising at - youre bogging the motor. Even 1600 is pushing it. But you should be above 1800 rpm in 6th gear at 65.

You must be mistaken on the RPM's. You should be able to cruise at 65 in 6th. If its stumbling, theres a problem. Are you getting a check engine light? If so, get it scanned, post the code.

Anytime you get into a driveability issue like this you really need to get it on a scanner and watch what is happening to your spark advance, fuel trim, O2 voltages etc. This is something you may want to invest in. There arent alot of driveability issue you can diagnose on these things without one. You can get a PC based scanner that works with a laptop pretty cheap.

You also need to get a fuel pressure on it with a guage while cruising. If you have access to this stuff, I can help lead you through some diag procedures, but if not, you may have to take it somewhere to have it done. The problem is going to be getting someone who is willing to work on a heavily modded LT1.

[thomas]

Im not sure what cam it is. I think it was a comp cam. I jsut bought the car a little while ago. I drove it from TX to delaware and at 70mph I was around 1700-1800 rpm. It has the stock gears. Its a 97 t/a 6sp so I think its 3.42. I know it has The LT4 intake and heads. But Ive had for almost 2 weeks and didnt have this problem. My stock 96 and 97 ws6's ran 90mph around 2000 rpm. Really do it because its 2.20 to 2.30 a gallon over here in the big state of DE. Although I love the sound of a full exhaust at 2500-4000!!!!!! Im going to the store a few miles away and see what happens. Let ya know.

[thomas]

Well it did the same thing. The thing is Im not getting a check engine light on. Nothings coming up. I hope you guys dont think Im stupid but thats were it was running. I was under 2grand until 80mph. At 80 it hit 2000 rpm in 6th. That I'm 100% sure of. My mechanic is going to check it out when he gets here and Ill see what he says. But all that stuff you said I should have or do I dont. I wouldnt know were to start. I am no mechanic. I can change my oil or basic stuff but thats it by myself. But thanks for your info. Its greatly appreciated.

[Mike71]

cant u just leave it in 5th?? will it run fine in 5th??

[N20LT4Bird]

Originally posted by thomas
Well it did the same thing. The thing is Im not getting a check engine light on. Nothings coming up. I hope you guys dont think Im stupid but thats were it was running. I was under 2grand until 80mph. At 80 it hit 2000 rpm in 6th. That I'm 100% sure of. My mechanic is going to check it out when he gets here and Ill see what he says. But all that stuff you said I should have or do I dont. I wouldnt know were to start. I am no mechanic. I can change my oil or basic stuff but thats it by myself. But thanks for your info. Its greatly appreciated.

Like Injuneer and I eluded to before, 1200 rpm is too low of an rpm to put a load on the motor. Youre bogging it and it doesnt like it.

Now, maybe I would have a different opinion if I drove it.......if it truly is a problem, I would start with a fuel pressure test and maybe eventually get it on a scanner. If you dont have any experience diagnosing driveability problems, it might be better left to your mechanic, or you need to be willing to spend some serious time learning. This usually means screwing up a few (dozen) times. Everyone of us started learning somewhere.

[thomas]

Well it wouldnt be the first time i screwed up . It also sounds a little different through the exhaust. My cat is gutted and the guy said I may have a header leak. Could back pressure be a problem? I know Im a pain but thanks for all your guys help.

[N20LT4Bird]

VERY doubtful. I have never heard of low back pressure causing issues like this.....besides a gutted CAT is not considered low back pressure; neither is a header leak - unless its major and it would be so bad you wouldnt want to drive it. A header leak could cause erroneous O2 sensor reading - thats a possibility.

If you are truly NOT BOGGING the motor (which I think you are), it could be one of a hundred problems from optispark, to wires, to fuel pump, regulator, mass air flow, cam selection (like Fred pointed out) etc... This list could go on and on.

You have got to find someone who is real good with late model driveability problems - preferably someone who is not afraid of a modded car.

[thomas]

Thanks guys. Guess Ill head to the speed shop. Anyone know of any around DE?

[Mirroredshades]

Evap Sensor or Modulator. Change both. Seriously though, my TA won't take 6th gear unil about 65 and I'm running 3.73's.