TBI stroker SBC tune

[mtrhead]

Hi,
Continued from Intro Post "learning curve".
1992 K1500 Blazer 4x4, Vortec headed SBC 6.3 stroker, TBI 65# bored to 1.930", NV3500 5 speed.
replaced ignition parts chasing misfire, cap, rotor, module. changed fp to 12 psi to bring the tune as close to stock as possible as a starting point. Hooked up the heat to the NB that is hooked to the ECM.

Runs good at idle and cruise, stoc with crossovers, even a part throttle tip under a load and it lugging a little, ain't half bad. But when I lug it and dump it to WOT a get a single lean pop followed by what feels like a dead miss as RPMs come up.

it's got to be a bad spark plug. if it was mixture distribution or lean mixture it should be popping out the intake.

Is the stock tune that far off? 299 AWLD.

I'm starting to dislike TBI and yearn for TPI or MPFI. Is anyone happy with TBI performance?

Certainly I'll check the plugs and maybe compression, it better be good on a fresh build.

Anyone running First Fuel Injection tuned port setup?

[BLG355]

It sounds to me like it is mega lean and you need more fuel. I'm running 22psi with 65# injectors on a 350 and I am maxing out IDC at 5600rpm.

[mtrhead]

Thanks,

this test was stock chip, 12 PSI, 299 AWLD.

The AFR was 12.5 on the WB on WOT and 14.6 at cruise, light tip-in and idle with crossovers, 12.3 AFR open loop fast idle.

I'll try more pressure and even the Harris chip, I was running 20 Psi with it but the idle surge it causes pissed me off, when I had an auto trans it was gone in closed loop but now with stick it's there at every stop light.

If it's a mixture distribution issue or cracked plug though all the tuning in the world won't fix it.
Has GMPP 4BBL Vortec manifold with 1/2 thick Carb/TBI adapter and 1" TBI Closed "individual barrel" spacer!

I want to make sure my tune up is strait before I get into logging.

[BLG355]

Thanks,

I'll try more pressure and even the Harris chip, I was running 20 Psi with it but the idle surge it causes pissed me off, when I had an auto trans it was gone in closed loop but now with stick it's there at every stop light.

I had the worst luck with a Harris chip. I seriously, like hardcore seriousness, swore I had an ignition problem with his chip. I went through half a dozen chips with him and he ended up telling me I had bad cylinder heads...but yet I could install the stock chip, advance the base timing 8-10 degrees, and the truck ran ok. I tired stock injectors are high pressure, larger injectors at lower pressure...same results. His chip was so bad, from 2000rpm and up it had a complete dead miss to it. I tried everything he wanted me to, he swore it was ignition, and it felt like it...but it what his tune. I got a starter chip from EagleMark and never looked back.

My truck was surging at an idle because it was too lean. it would surge enough to enable AE which made it worse. I wanted to really fine tune so I bought everything I needed and started messing around and learning as much as I could from these guys, they are all great. From my limited experience, when the IAC counts are good and it surges, it needs some more fuel.

Has GMPP 4BBL Vortec manifold with 1/2 thick Carb/TBI adapter and 1" TBI Closed "individual barrel" spacer!

That's something I'd like to see a picture of! I have no personal experience with the adapters and spacers on EFI however I see on here often and other forums about the vacuum leaks people often miss with these. That could mess your idle up too I guess but I'd bet on more fuel first.

BLG

[mtrhead]

Ok, I have to look up AE to see what it is.
the adapter is similar to the following, but mine is made better, custom not mass produced and centered not all the way to the back like the one I've referenced. http://www.ebay.com/itm/Trans-Dapt-P...89c0e0&vxp=mtr s

the spacer is just 2 2" holes through a 1" plate aluminum. Idles too nice to have a vacuum leak but I'll spray the gaskets and see if RPM changes.

I have not tried cranking up the timing it is at 0 base and I'll try some more before I bail on the stock chip and drop the Harris one back in. I should not need as much as your config did because I have fast burn heads and .035" quench which I think may help reduce timing requirements.

when I flip the throttle body to change fuel pressure I'll take and post some pics.

the harris chip actually works pretty good at WOT, but idle and very light throttle is no good.

I don't know which table he took the fuel out of to try to get it to tolerate the higher fuel pressure at low RPM.

[Fast355]

Take the Harris chip out and burn it!!! It will never run right with it. Then get to adding timing. Switching to Vortec heads REQUIRES 6-8* more timing nearly across the board compared to TBI heads. The big carb intake takes up to double the AE fuel which can only be tweaked in the chip. Then you need to look at BPWC and VE tables.

You will also never get anywhere with 12 psi and 65# injectors. Try more like 26-30 psi.

[BLG355]

I have not tried cranking up the timing it is at 0 base and I'll try some more before I bail on the stock chip and drop the Harris one back in. I should not need as much as your config did because I have fast burn heads and .035" quench which I think may help reduce timing requirements.

the harris chip actually works pretty good at WOT, but idle and very light throttle is no good.

I don't know which table he took the fuel out of to try to get it to tolerate the higher fuel pressure at low RPM.

I would say since you have a surging idle, you need fuel across the board. If it is not getting enough fuel across the board, it will try to compensate. But there isn't enough at 12psi. I was running logs when I first got Marks chip, I had a rough surging acceleration. I had the "18 PSI" spring in, which was more like 14.5-15psi. I made my regulator adjustable, I used a smaller spring inside the normal spring and ended up with 16-30 adjustability. At 15psi on 65# injectors, I had a surging/missing feeling. It felt like a bad plug or something with the ignition. I kept upping the pressure a couple PSI at a time, it wasn't until I was just around 20psi that it was smoothed out, but Mark said I was too lean top end, so I kept going and 22psi was the point where it was ok, but just ok. Since then, I added headers and bored the intake out to 52mm, I am going to get a larger throttle body eventually and I am planning on settling in around 25PSI or so. I agree with Fast355, I think you need at least 25psi. And your should burn the Harris chip. I spent more money wasting my time with him and his garbage tune then I did in all my tuning stuff and my $430 headers combined.

I actually made a BIN from my Harris chip to try to figure out what the heck he has so screwed up, mine ran good at WOT, but everything else was horrible.

BLG