Problem with 400 *** stroker w/Vortec heads and EFI

Hi,
I put together a +.020" 400 SBC motor with 350 rods/stroker pistons, Votec heads with a special 4bbl manifold for the heads, in the place of the carburetor I mounted an adapter plate and the stock EFI that was on the original 1990 GM truck with a 350 engine. It has never run right since he day it was started-it always seems to run lean, and won't idle. We have run about every diagnostic test, and replaced almost every electronic component at least once. Has anyone put this combination together and made it work? I'm really thinking that I may need larger injectors like a 454 EFI would use. Can anyone shed some light on this before I resort to going back to a carburetor?
Thanks!!!!  

i bet that you have a lean stumble problem...  off idle....   giving it power at cruise it will stumble...

going to the 454 injectors will work... you might want to install the compete 454 throttle body...   if it still stumbles but less...  you might want to pick up a complete throttle body gasket set.. usually 25 to 30 bucks.. sometimes less.. and swap the 454 injectors into the 350 throttle body...    as that will give you more fuel for less air...

what... why....

there are several programs inside the ecm...

open loop...   this is used at start up.. and when its drops out of closed loop...  this is hard programmed fuel control....


closed loop....  this happens when the oxygen sensors are hot and switching  from rich to lean so many times a second...   called cross counts... on a scan tool....  the fuel ratio is controlled by the oxygen sensors feedback into the ecm...


***

when you accelerate...   apply throttle to increase speed a certain percentage...  the ECM will drop you out of closed loop and fall back to preprogrammed fuel control for acceleration ... which is going to be LEAN for your combination ...  since the ecm is programmed for 350 size injectors and is NOT looking at the oxygen sensors for calculations... its going to lean the motor out...   putting the larger injectors will all more fuel flow for the same amount of milliseconds of pulse width... so it will be richer...  i don't think gm ever made a 400 small block with TBI.. but those injectors would probably be close to perfect.. but the 454 injectors might flow just a tiny bit to much.. ... but you have other improvements... so it might work out just fine..


this same problem exists on cadillac 4.1 to 4.5 and 4.9 swaps.. really wakes up the early transverse cads swapping in that almost liter of extra displacement...    so matching 4.9 injectors fix the problem there... but they are too small for your application...

but i bet at cruise speeds... it runs great...   if not... look for exhaust leaks ... i am taking that you have properly installed oxygen sensors...

and that if you have reinstalled the air injection system.. that you can verify that the upstream air injection tubes... check valves... hoses...  diverter valves are not leaking air into the exhaust manifolds UPSTREAM from the oxygen sensor...    WHY... this uncommanded air... will dilute the exhaust stream.. and totally mess with the fuel control.... making the car or truck really almost impossible to drive...

the check valves loose their reed valve and flow both ways... this allows exhaust flow backwards into the Plastic diverter valve melting the insides... this causes it to leak air all the time..  diluting the oxygen sensor exhaust flow with to much oxygen..

now... the diverter valves do open... for the first 20 or 30 seconds on a cold start during fast idle... and when you drive the ECM out of closed loop and into open loop during acceleration and ... forgot the word... under load... where the intake vacuum drops as the throttle opens and RPMs are increasing slowly..

this gets complex... and i know you have been through a LOT.....  so .. i will try to post as much info over the next few evenings as you reply to...


charts to follow...   and .. you will really really need a OBD1 scan tool that displays live data...

not all current OBD2 and obd1 kits display live data on  obd1 systems..  all you get is codes... and they won't help you at all.. might as well work on diagnosing the problem with the hood closed... the truck parked in a locked garage and you are out at dinner...  its just not going to get fixed right...  unless you know me..

craigs list may have some scan tools...


search for OTC....

look for monitor   2000....  monitor 4000....  monitor 4000E...   genesis...  

snap on...    MT-2500...  or just search for snap on... MT....

most  early autoxray units would display GM live data streams.. but not the OBD2 and obd 1 versions.. sorry..

i looked at the actron site.. they say they have 2 current scan tools that will display live data for gm OBD1 cars and trucks...

but... here is the several hundred page  PDF file..

http://www.actron.com/publish/2007/03/27/pdf_english_16317.pdf

you might want to look carefully at page 115... or printed page 5-11 field service mode...  i think you can enter that without a scan tool.... maybe ... its been a long time since i used it...

these 2 show that they might display GM obd 1 data....

Elite AutoScanner Pro CP9190

Elite AutoScanner CP9185

but they are NOT cheep....

i missed an early genesys for 175 the other day... i see them for 600 to 1500 all the time...

snap on scanners can cost a fortune if you don't have the right stuff with it..

most of the current professional scan tools will display all the live data streams on GM...

they cost 1200 to 2500 for a new genesys...

5 to 8 for a new snap on unit.. grand that is..

oh yea.. there are tech 1 and tech 2 scan tools that are available.. used by gm in dealers... the tech 2 with a proper ABS software.. can monitor the abs wheel sensors live... compare them  as you speed up and slow down.. lets you fix the weird problems that plague some gm truck owners... where the truck may not stop once in a while..  as the antilocks ... wait.. thats a whole different thread....  

look carefully at this chart... ONE LINE at a time...   its to much to absorb if you try to take the whole thing in...




print the chart... several copies...  when you get a scan tool... or borrow one.. or have a professional tech come out with his.. write the data down on the proper line with the engine cold.. key on.. engine off...

then with the engine hot and running...    write it down again...     then see what the chart says...

then post what's out of range... i drop by this forum daily looking for updates..