96 and up Vortec PCM revlimit

[Hog]

Hey guys, I recently installed a marine intake manifold to rid my truck of teh poppet style 19 lb/hr injectors. I have Tunercat and was wondering if anyone has come ac5ross a fix to break thru the 5800 rpm barrier on these 1996 and newer truck PCM's??

I am running 24 lb/hr injectors which flow 28.4 lb/hr at 60 psi and before I install a cam, I really need some more rpm.

i am totally impressed withthe increased abpve 5000 rpm power without having all the injection equipement axctually in the intake.

The stock PCM revlimit is 5600 rpm, Ed Wright and my Tunercat when set at 6100 rpm revlimit, only get a 5800 rpm result.
This is on a 1997 rcsb Vortec 350 with auto trans.
Can anyome help??

thanks a lot
Hog

[rat]

Hey hog, it is good to see you over here, i have seen you around the net on a couple of other sites.

I think that is the milion dollar question right there. I haven't tried to rev it over 5800 myself, i am a little afraid to do that. My opinion(not baised on fact just my opinion) is that the pcm just runs out of processing power. Might consider maybe an aftermarket ecm. There are some really nice ones, from cheep megasquirt, to the more featureful stuff. You could run a wideband o2 sensor as well with the aftermarket units.

[ZR1-S10]

You might just be getting valve float. Do you have upgraded valve springs?

[rat]

You might just be getting valve float. Do you have upgraded valve springs?
I think it is more than valve float, it isn't an isolated incident. Several people have been to the dyno, and had the a/f ratio right where it was suposed to be, then at 5800 bam really lean. A lot of us 4.3 guys don't have the internals to need to push the rpm's that high, but for you 350 guys it really stinks.

[Hog]

I really wish that the valvetrain is the problem, but it isnt. I am running the stock valvetrain, but the 1st guy to do the Marine intake conversion on a V8 Vortec is running a valvetrain and cam that should have a shiftpoint of around 6800rpm on his 383 engine. he also got Ed Wright to set his revlimit and shiftpoints above 6000r pm. Ed Wright actually set these inputs above 6000rpm, this was verified with Tunercat, but his rev limit is still also 5800 rpm.

I have tried to get above 5800 rpm by trying Ed Wright and Tunercat. there are a few Pro Tuners working on this, I hope it can be worked through, but it isnt looking good.

Doe sthe factory limiter shut off fuel or spark??

i am guessing fuel, if it is fuel that sucks. I was toying with the idea of installing an older internal coil HEI distributer for ignition, but we will have to see.

The LT4 engine has a 6412 shutoff and a 6380 reenable, is there any way an LT4 could be used piggy back style??

The 2001 and newer fullsize vans used the Vortec 350 with the newer style PCM. There were 4500 series commercoa; GM trucks available with teh Vortec 350 all the way into 2005.

the reluctor wheel on thecrankshaft is suppsoed to be slightly different between the 96-99 and the 2001 and newer Vortec 350.

i am wondering if the newer PCM could be used with a Van flash installed???

This sucks

thanks for the replies, let me know if anyone has any answers

Peace
Hog

[rat]

I see what you are saying, i doubt the ls1 style computer would have this limit. I know the 2001 and up s10 4.3's used the ls1 style. From the looks of acdelco.com you are correct that the vans used the ls1 computer on the 305/350 with the goofy csefi in the intake manifold. As far as converting i think that is a pain to do. Someone over on s-seriesforum converted a 1998-2000ecm to the ls1 2001+ computer. I can see if i can find them if you would like. I think they had to swap insturment clusters, a couple of sensors, and of course harness. I think he also had a custom tune done to get the computer to recognize it all properly.

As far as the crank wheel i know there is no difference between the older computers and newer ones on the 4.3.

If i was going to get rid of the stock computer, i would not replace it with another stock unit. Probably piggy back the stocker to keep the speedo and such, but the engine would be controled with the aftermarket computer. There are so many aftermarket ones that are versitile. Some have wideband o2 support for closed loop fuel control at wot. Others can control a 4l60E, or a 4l80E trans. http://hotrod.com/howto/113_0504_efi/

The only reason i don't think the lt1/4 would work is due to the lt1 having optispark. I think the opti was used as a camshaft position trigger. Other than that it might work.

I am pretty sure it is a fuel cutoff also.

[Sparky2263]

I found it was a fuel cut by data-logging. Hit 5500 and BAM! injector pulsewidth dropped to 0.0ms.