colmangy

I put new 96 vortec heads on my stock 350TBI with a edelbrook performer intake. I have problems with it falling on its face when I demand power from it. Crusing seems fine, problems are when I demand from it has no power. I have been told millions of things and done them all. But it only takes about 500 miles before I find out the corrections did not work. The last suggestion was: they are selling the wrong intake gaskets and go get the new thicker ones. The problem is in the intake manifold. Under load the center ports leak to each other creating a lean (vaccuum leak condition) specifically on the left bank and #5&#7 plugs misfire all the time and have to be replace. (The only two cylinders that over heat and burn plugs is 5&7). I was reading in another site that the angles on the intake manifold and the heads are wrong and the intake will not seal to the head surfaces correctly. Has anyone any suggestions. All sensors have been replaced 10 times over with no luck. I sure would appreciate it.
Dennis
1989 Chevy Suburban, 1500 4x4, 700r4, 3:73

TurboGibbs

iTrader: (6)

Have you tried the old spray carb cleaner or ether around the ports to see if there is a vacume leak? The engine will idle up if it does. Of course this won't help if it's not leaking at idle.
Did you have it tuned for the new power of the intake and heads? You added about 1.5 points in compression and a much better flowing head. You may just be running lean due to needing more power. #5&#7 are notorious on sbc's to run lean first due to intake design. An generic aftermarket chip won't be enough. You may need bigger injectors as well. The TBI is a speed density system and will not adjust to changes in demand of fuel like a MAF system will. Just a stab in the dark due to the limited info you gave.

86MC_SS

iTrader: (3)

Sounds like a timming problem. Have you checked the distributor? It can be a tooth off and still run.

TurboGibbs

iTrader: (6)

Hell, that just brought up another possibility. These TBI engines have a problem with worn out distributers causing spiradic misfire. Pull the cap and wiggle the shaft side to side. If it moves anything really noticable then replace the distributer and you have your problem solved. My brother had this problem with his and it drove him nuts. His was a 93 model. His had ~130k on it. My 95 has 165k on it and the distributer is still tight.

hog

I hope that you are using an Edelbrock Performer Vortec carb intake on that L31 Vortec headed engine. If not the ports are out of alignment and will cause port stall because the Vortec heads use a raised runner setup.

Here is teh correct TBI/Vortec head intake you should be using.
http://www.gmpartsdirect.com/perform...CATID=995.html

if you are indeed using a Performer Vortec style intake, then you should not have a port interference. Any Vortec raised runner carb intake will do, and will really outflow the stock TBI intake manifold.

does your intake use 8 or 12 bolts? If it uses 8 bolts to fasten to the intake, then you have the correct intake, if it uses 12 then you are using the incorrect intake.
The newer GM gaskets that are black with metal tabs around teh bolt holes are a definite improvement overthe previous blue coloured gaskets. whatever gasket you use, each of the intake bolts only gets 11 lb/ft of torque.

What injectors are you using?
what cam are you running?
What chip are you running?

I am pretty sure that you will need to use the 454 dual 2" throttle bores(50mm) and the 454, 60 or 65 lb/hr fuel injectors.

I think that most of the issue is in the chip. get a hold of Brian at http://www.tbichips.com/ this guy will tell you all you need to get this thing running good. He can burn you a chip, he has done lots of TBI/Vortec conversion chips.
As stated earlier that the TBI is a speed desnity system and is VERY picky in regards to engine mods, it is lost right now, it doesnt know whats going on.

Chips are cheap, and Brian will give you the lowdown, he is a very good guy.

The Vortec heads should really wake up the TBI setup when tuned properly.
Post back
peace
Hog

TurboGibbs

iTrader: (6)

That's a big hell yeah for Brian. I've been using him for 2 years now.