[Supras] four cylinder supra

[berniek at technicaldevelop.com]

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You may have an ECU or ECU harness problem.  The injectors are fired in 
pairs as stated in other answers, opposite in the firing order if I'm 
not mistaken (there are several firing modes for all, but that is a 
different matter).  It is not likely that two injectors failed at the 
same time.  Moreover, it sounds as if you have spark if indeed you are 
running on 4 cylinders, not 5 (possible with a sparkplug breakdown which 
I've seen happen in another car).  It sounds as if one of the injector 
drive transistors in the ECU or logic drive to the transistor is 
problematic.  I don't know if the transistors are the same as in the 
turbo ECU, but if so, maximum collector current rating of the parts used 
is only 8A, not leaving much margin on a hot day with low impedance 
turbo injectors.    High impedance injectors in the N/A stress the 
transistors less, but they still can fail, especially if a damping 
capacitor for each in the ECU goes to an open circuit.  If you have 
access to an oscilloscope, you can use a piece of long stiff needle-like 
wire to reach down into each injector connector with the engine running 
and look at the waveforms.  One side of each injector should always be 
near 12-14V.  The other connection will pull down to near ground and 
then overshoot to maybe 50V as a guess before settling back to 12V.  You 
could check harness leadwire continuity for each injector also, by 
disconnecting the ECU connector and measuring the resistance to battery 
voltage (also at the connector) from each injector pin in the connector 
(the injectors are wired to the battery through a fuse all of the time, 
even with the engine off if I'm not mistaken).  I believe the N/A 
injector resistance is about 16-20 ohms, so a pair in parallel would 
measure half that. 


There is an N/A ECU for sale on ebay from a store, but it is for a 
manual transmission and the price is high, $99 from Ryan's resale.  The 
link is:  
http://cgi.ebay.com/ebaymotors/86-87-Toyota-Supra-Engine-Computer-ECU-ECM-Control-Box_W0QQcmdZViewItemQQ_trksidZp1638Q2em118Q2el1247QQcategoryZ33596QQihZ019QQitemZ290192829176QQrdZ1QQsspagenameZWD1V


I don't know if the N/A has an injector ballast resistor the way the 
turbos do, but if it does one section of it may be open circuited, easy 
enough to check with an ohmmeter.  Also, without looking at waveforms, 
it will be difficult to determine if the ECU is the problem if the 
harness is OK. 


Finally, without fuel to 2 cylinders, I'm surprised the engine will run, 
given the high oxygen concentration attempting to richen the mixture 
from O2 sensor readings. 


Good luck.


BernieK
'91T 5 spd non targa, refreshed JDM, 550 ND injectors, Walbro, 57 trim 
CT26 (no clip, wastegate passage bored out) at 17 PSI boost, modified 
stock FPR, Lexus AFM, Treadstone IC, hardpipes, '98 mounts (strong), '98 
wheels and tires, 3" single cat Random Tech downpipe, Lipp, HKS 80 mm 
LET-T16 exhaust, Turbonetics recirculated BOV, strut bar, valve bowls 
deflashed, exh manifold helicoils, lightweight chrome moly flywheel, 
Exedy organic clutch (street use).