Big cam causing misfires??? 490/490 w/1.6 RA

[96c1500FullRebuild]

Hey guys, new here. Obviously. I just put a new 350 in my ‘96 with a 490/490 cam and 1.6 rockers. Right now im dealing with a P0300 code. I bought a good scanner to get live data from the computer but im new to this fuel injection.

I need some help narrowing down what the issue could be before I do my computer swap.

I guess my first question would be could my low intake vacuum be causing my misfires by not sending enough vacuum to the intake parts; IAC, EGR, etc.?

At idle im just shy of 10 inches of vacuum which is low for these engines, im sure.

My second question is, being that my cam is so big, especially with the 1.6 rockers, will these factory intakes even run with it? If not, what intake swaps are you guys doing to make these motors perform?

 

[arrg]

You trying to run that without a computer tune?

 

[96c1500FullRebuild]

Just got it put together. I know it will need a tune, which is why I have a 411 to swap it. I’m just curious if it’s worth it to run this intake and if the cam could be causing these running issues

 

[Schurkey]

I just put a new 350 in my ‘96 with a 490/490 cam and 1.6 rockers. Right now im dealing with a P0300 code. I bought a good scanner to get live data from the computer but im new to this fuel injection.

1. 0.490 LIFT? Is that .490 lift with 1.5 rockers, or .490 with 1.6? Either way, I'm surprised you could get that much lift without screwing with the valve guides to gain clearance. The cam duration and overlap make more difference to the computer than the lift, but the lift matters if it's crushing the valve stem seals.

2. Is that REALLY a P0300 code, or is your scan tool lying to you? Cheap scan tools report "generic" codes even when the computer has a specific code. So a P0302 or P0306 might get reported as a P0300 leading to lots of wasted diagnostic time.




The intake manifold doesn't care what cam you have. The computer programming might.

 

[96c1500FullRebuild]

1. 0.490 LIFT? Is that .490 lift with 1.5 rockers, or .490 with 1.6? Either way, I'm surprised you could get that much lift without screwing with the valve guides to gain clearance. The cam duration and overlap make more difference to the computer than the lift, but the lift matters if it's crushing the valve stem seals.

2. Is that REALLY a P0300 code, or is your scan tool lying to you? Cheap scan tools report "generic" codes even when the computer has a specific code. So a P0302 or P0306 might get reported as a P0300 leading to lots of wasted diagnostic time.




The intake manifold doesn't care what cam you have. The computer programming might.

.490 is before 1.6’s. So around .523 lift total.
I should’ve put all my info on the build but it’s a lot. I have summit vortec heads that have been worked for the cam set up.

my scanner is a launch x-431 v.. I think? Can’t remember the exact model off the top of my head but it’s a quality scanner.
I’m getting a bunch of misfires across all cylinders. Popping, backfiring, etc.

 

[96c1500FullRebuild]

This is the cam specs.

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[arrg]

The tune being that far off can cause all kinds of problems. Vacuum is one of the main references the computer uses for fuel and spark. The stock computer tune is going to think you're way into the throttle at 10 in of vacuum, not trying to idle. I can't see the stock intake making power up at 6000+ RPM where that cam will want to be, but I've never tried it.

 

[96c1500FullRebuild]

The tune being that far off can cause all kinds of problems. Vacuum is one of the main reference the computer uses for fuel and spark. The stock computer tune is going to think you're way into the throttle at 10 in of vacuum, not trying to idle. I can't see the stock intake making power up at 6000+ RPM where that cam will want to be, but I've never tried it.

I figured the tune would effect everything. I’ve heard these intakes flatline above 3500rpm. I don’t expect to run it anywhere above 5k but I want an intake that won’t restrict what the motor can do. What are some intakes that are common swaps for higher flow?

 

[96c1500FullRebuild]

So just FYI everything below the intake has around 10k miles on it from a previous build that was carbed. The heads, block, and whole rotating assembly have been worked and ran perfect with a carb. I’m just looking to get a fuel injection set up for this truck to be able to fine tune and tinker with on my own down the road.

I do have a 0411 computer to swap over when I get to tuning, I am just curious on how to go about it from the intake and up.

On paper this motor should be around 400hp. Never put on a dyno with the carb set up so I want to get every bit of power out of it with a tune.
Thanks

 

[PlayingWithTBI]

It needs to be tuned. With that cam you're running way lean, hence the lean popping. Your timing is probably way off too. If you don't want to wait for the 0411 swap, go to Black Bear Performance, they tune "black boxes" all the time. 10" of vacuum is low, perhaps a vacuum leak???

http://blackbearperformance.com/