[Diy_efi] Re: 1990 GM 350 TBI question

Pete Paraska pparaska at comcast.net
Mon Apr 26 20:23:54 GMT 2004

> "David Daniel" <ss396 at pinn.net> wrote:
>Hello again...
>I have another question for you all.  First, a bit of history on the
>vehicle... My dad and I re-built a 5.7 TBI engine for his S-10 Blazer over
>the winter.  I converted it to V-8 last year using a complete wiring
>harness, engine and ECM (1228746) from a '90 Caprice police car.  We are
>currently getting consistent code 44 (Lean exhaust).  I have checked for
>vacuum leaks and found none, fuel pressure is at 14 psi with the engine
>idling, and does not drop.  We are at the end of our rope with this
>thing...it cuts off a lot while pulling into or backing out of parking
>spaces.  It runs great once you get it going, but the low speed stuff is
>very annoying.  We have also run about 3 tanks with dry gas and fuel
>cleaners to make sure there is no moisture in the tank.  It runs better
>after the dry-gas, but is still cutting off occasionally.  During the
>re-build dad ordered roller tip rockers and got 1.6 ratio by mistake.  I
>know the additional ratio changes the effective camshaft lift and duration
>at the valves.  Could this be causing the problems with the lean run?

The rockers might cause a problem, but I'd think it'd make the mixture richer:
>>From  http://www.cfm-tech.com/gm_tbi_camshaft_heads.htm:
"The GM Tbi uses a MAP sensor and programmed tables in the computer that correlates the engine's vacuum levels to a specified amount of air that should be entering the engine. If the vacuum levels are lower than stock, the computer believes that the engine is flowing more air and is under more load. It will then reduce timing and add more fuel. This is why an incorrect camshaft can confuse the computer and cause many drivability problems."

But what MIGHT be happening is that you have the wrong injectors.  All 350 TBIs aren't the same.
The Police package (9C1) has different injectors than the rest of the 350 TBIs.  The 9c1 injectors 
(yellow/brown) flow 68 lb/hr at 13psi, where as the regular injectors (Orange/Black) flow 55 lb/hr
at 13psi:

I'd guess that the pulse width that the 9c1 "Police" ECM puts out is less than the regular 350 TBI ECM,
for the same running conditions, making it run lean just about everywhere but near and at WOT.
The solution is to either get a regular 350TBI ECM, or the 9c1 injectors.

(BTW, if anyone has any 9c1 350 TBI throttle bodies, I'm in the market for two of them.  They're going
on top of an Offy crossram manifold (5893/5903) like the 69 Z/28 had, to feed a 500hp-ish 406.)

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Pete Paraska  (pparaska "at" comcast.net)   IZCC#15
73 240Z V8 - http://alteredz.com
See http://HybridZ.org for Datsun Z car drivetrain/susp/brake/chassis/body mods

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