350 vortec help!
Thread Starter
Teching In
Joined: Mar 2015
Posts: 23
Likes: 0
350 vortec help! Hey guys I need some help I just did a rebuilt on a 350 vortec with aftermarket h/c. I got the truck with a locked up enigne so I didn't get to see what was working properly at the time. So here's my problem it idles fine but as soon as you have it in gear and are at a stop light or stop sign it starts bucking and surging from 450-800 rpms I have replace the injectors and fuel pressure regulator, egr, fuel pump and filter air filter idk I'm at a loss right now and I have no check engine light so that makes it worse
Hey guys I need some help I just did a rebuilt on a 350 vortec with aftermarket h/c. I got the truck with a locked up enigne so I didn't get to see what was working properly at the time. So here's my problem it idles fine but as soon as you have it in gear and are at a stop light or stop sign it starts bucking and surging from 450-800 rpms I have replace the injectors and fuel pressure regulator, egr, fuel pump and filter air filter idk I'm at a loss right now and I have no check engine light so that makes it worse
That cam's not terribly aggressive, but does have a little more overlap due to the 1.6 rockers.
First - no, this will not hurt your transmission if you do not change out your converter. However, this isn't good for the engine (which probably cost more than your transmission). Changing out the torque converter will not require the transmission pan to be dropped. It's a bit tedious to get the transmission out, but swapping the torque converter should be easy. If this is a daily street driver, I'd look at like a 2,000 rpm stall converter (I doubt you're racing or you wouldn't have used the stock low stall converter, ha). I don't know what transmission you have, but be aware of torque converter compatibility due to PWM, TCC lock up strategy, etc.
Second - the torque converter might not be the problem. It could still be a bad tune in the computer at the lower engine speeds. This actually brings up a question - did you have the ECM tuned for the new heads/cam combo? If you didn't yet - I'd do that first before the torque converter.
IMO, if you switch out to a 2k stall converter, you'll like the illusion of a better engine.
First - no, this will not hurt your transmission if you do not change out your converter. However, this isn't good for the engine (which probably cost more than your transmission). Changing out the torque converter will not require the transmission pan to be dropped. It's a bit tedious to get the transmission out, but swapping the torque converter should be easy. If this is a daily street driver, I'd look at like a 2,000 rpm stall converter (I doubt you're racing or you wouldn't have used the stock low stall converter, ha). I don't know what transmission you have, but be aware of torque converter compatibility due to PWM, TCC lock up strategy, etc.
Second - the torque converter might not be the problem. It could still be a bad tune in the computer at the lower engine speeds. This actually brings up a question - did you have the ECM tuned for the new heads/cam combo? If you didn't yet - I'd do that first before the torque converter.
IMO, if you switch out to a 2k stall converter, you'll like the illusion of a better engine.
Trending Topics
You didn't get it tuned yet?! 
Haha, yeah - try that first.
Actually, you might want to check out swapping to a 0411 ECM (often called a LS1 ECM) to control your engine. I don't know if you're looking for another mod. But the 0411 can be flashed with the 2000+ Express 5.7 Vortec calibrations to run a '96-'98 L31 vortec 350. (This is a somewhat popular mod for those owners who have a '96-'98 Silverado.) This is something I'd discuss with your tuner about. (Might even be much cheaper to tune to 0411.)
Or if you already have the 0411, then you're set! Get it tuned!
Let us know how it turns out.
Haha, yeah - try that first.
Actually, you might want to check out swapping to a 0411 ECM (often called a LS1 ECM) to control your engine. I don't know if you're looking for another mod. But the 0411 can be flashed with the 2000+ Express 5.7 Vortec calibrations to run a '96-'98 L31 vortec 350. (This is a somewhat popular mod for those owners who have a '96-'98 Silverado.) This is something I'd discuss with your tuner about. (Might even be much cheaper to tune to 0411.)
Or if you already have the 0411, then you're set! Get it tuned!
Let us know how it turns out.
LS1 Tech Stories
The Best V8 Stories One Small Block at Time
Gas Monkey Built a 6-Wheel Ferrari Testarossa With a Corvette LT4 Engine
Verdad Gallardo
7 Most Reliable High-Performance Engines GM Has Ever Built
Verdad Gallardo
Amazing '71 Camaro Restomod Is Modern Muscle Car Under the Skin
Verdad Gallardo
6 Common C5 Corvette Failures and What's Involved In Repairing Them
Pouria Savadkouei
Retro Modern Bandit Pontiac Trans AM Comes With Burt Reynolds' Autograph
Verdad Gallardo
Top 10 Greatest Cadillac V Series Performance Models Ever, Ranked
Pouria Savadkouei
Top 10 Most Powerful Chevy Trucks Ever Made!
Hennessey's New Supercharged Silverado ZR2 Has 700 HP
Verdad Gallardo
Coachbuilt N2A Anteros Is an LS2-Powered C6 Corvette In Italian Clothes
Verdad Gallardo Thread Starter
Teching In
Joined: Mar 2015
Posts: 23
Likes: 0
And I have looked into getting a 0411 but by the time I get one of those and get it tune it would cost more then just tuneing the stock pcm unless there is a advantage of having the 0411 pcm being cheaper to tune ?
As for the 0411 ECM - I'd suggest you talk with your tuner. There is much more support for the 0411 ECM, but maybe your tuner doesn't mind working with the ECM you already have. The 0411 ECM is so plentiful in junkyards and can usually be picked up from some kind of U-Pick-It or whatever for about $40.
Supposedly, the 0411 calculates engine demands much quicker than the blackboxes of '96-'98 and supposedly helps with a little better throttle response and little more smoother idle. But a surging/bucking idle won't be fixed without a tune regardless of the ECM used.
TECH Resident
Joined: Oct 2006
Posts: 993
Likes: 173
From: Euless, TX
I really doubt that mild cam is making a driveability issue to the point of making the engine backfire while at idle. Granted it won't be running ideal with a stock tune, it will still run. I would look over the mechanical first. Ignition components and valve adjustment specifically. It sounds like you have a firing order or valve lash adjustment issue. I have a 1997 G1500 Express van with the L31 that I ran a production GM LT4 camshaft that is 203/210* @ .050 duration on a warmed over stock tune in a black box for several years. I swapped over to the 0411 and ran a 206/210 Comp Cam ground on a 110* LSA on a stock 0411 Express tune for a short period of time. I have also run my 215/220 @ .050 on a 114* LSA Comp Cam on a stock tune for a short period of time. With the 0411 it ran well, not ideal, but well enough for me to discover I had a mechanical issue rather than a tuning issue. As far as ignition tune-up parts go for these engines goes AC Delco, Delphi or nothing!!! Too many issues with aftermarket caps/rotors and wiresets that will cause exactly the problems you are describing with misfiring. Also you need a scanner to make sure you have the CMP set at IIRC +/- 2* CMP being off can make the engine run like crap.
The 0411 swap is not difficult and can be performed cleanly enough to look almost factory. Some say the Black Box can run just as well and make just as much power...That may be true at WOT, but during transients and part-throttle operation the 0411 blows the Black Box away in driveability, throttle response, transmission shifting, and fuel economy.
The 0411 swap is not difficult and can be performed cleanly enough to look almost factory. Some say the Black Box can run just as well and make just as much power...That may be true at WOT, but during transients and part-throttle operation the 0411 blows the Black Box away in driveability, throttle response, transmission shifting, and fuel economy.