Where is the ECM relay at on a 1992 isuzu rodio 3.1 L

Electrical short. Or the ECM may have internal short too. If you have done engine electrical repairs recently, re check to find wires that may have wrongly connected.

1992 no spark on all 6 cylinders.
ok, did you first look at the schematic on ECU and SparK>?
lets do that and see. now.
spark systems are vastly changed, from 1990 to 2000
evolutionary, that means I must look up what's there first.
lets tick them off.
1: fuses good, means test them if they L**k good.
there are 6 fuse here , for this to work. 2 for ECU relay.
2: head lamps work (bright, ok battery seems strong) and cranks.
3:key on , cluster glows, and all those warning lamps, but but the CEL it must glow, or the ECU has no power, the ecu fires the coil via an Ignitor so ECU must have power and CEL glows
Check engine light.
if that work the engage the diag jumper wire clip
this enables flash diagnostic codes.
then crank for 5seconds, if you get the code for dead CKP bingo.
how do to that is here.
http://www.troublecodes.net/isuzu/

now your relay question?
key on, all wires on the relay go hot 12vdc.
but the black wire (its ground)
the 2 green wires on relay must be 12vdc, output to ecu. the inputs are fused x2

to test a so called good looking fuse.
we use 2 methods, ill show 1.
ohms. with your DMM set to Rx1 range (lowest)
measure he fuse. 0 ohms good, infinity bad.
we use volts on key on car, 12vdc both sides of fuse.
there are some rare exception on that, (fused grounds)
but not this car.
the fuse related are hot all time, or hot keyon.

engine runs perfect. no misfiring at all?>??????
the computer dont know,
all it knows, is a reading fails.
in electroncs we do more testing
it can be bad wires. bad connections or bad sensors.
we use a voltmeter do check this, or a scope if fast moving signal.
1991 2.8L

"Electronic Spark Timing Circuit
Specific to 1992-93 models only.
Indicates that the ECM believes the Ignition Module has failed.
Check the wires and connectors between the Distributor and the ECM."

google finds top anwser here
https://www.2carpros.com/questions/isuzu-trooper-1992-isuzu-trooper-code-42--2

best answer ive ever seen, and for old cars, had to find,
most folks long forgot ..24 years ago
and books long ago in land fill....

I included a repair guide from auto zone library hope this helps.

If they hold the ignition switch in the spring loaded start position does it stay running?

Emission control mechanism or relay is either a vacuum plunger type or a relay switch electrical plug that controls vacuum for the smog. Go to the parts store and look at one and ask where it goes or just trace it. This stops from buying one if you remove the hose or connector and the same problem is still there!

I have a 1992 Isuzu Rodio 3.1 injectors not working; but if i put gas in the throttle body it will start up and run. but while driving it down the street it will die and not re-start, until i put gas in the throttle body. the nod light does not work when it wont start. please can you help me with this problem, i have put a new fuel pump in it and two new injectors.

if there is no power to the fuel pump check relays and fuses....UNDERHOOD FUSE & RELAY PANEL IDENTIFICATION Fig. 2: Underhood Fuse & Relay Panel Identification Courtesy of ISUZU MOTOR CO. Fusible Link Identification ? A - 80 Amp (1991-92 3.1L) ? A - 60 Amp Main-1 ? B - 30 Amp Main-2 ? C - 30 Amp (1993-94) ECM (3.2L) ? D - 30 Amp Condenser Fan (A/T Models) Relay Identification ? 1 - Headlight Relay ? 2 - A/C - Heater Relay ? 3 - Starter Relay ? 4 - A/C Compressor Relay ? 5 - Charge Relay ? 6 - Fuel Pump Relay ? 7 - ECM Relay ? 8 - Wiper Relay Fuse & Circuit Breaker Identification ? 1 - 15 Amp (1991) ECM, Fuel Injection System ? 1 - 15 Amp (1992-94 2.6L) ECM, Fuel Injection System ? 1 - 10 Amp (1992-94 3.1 & 3.2L) Heated Oxygen Sensor, Fuel Injection System ? 2 - 20 Amp (1991-92) Fuel Pump ? 2 - 20 Amp (1993-94 2.6L) Fuel Pump ? 2 - 15 Amp (1993-94 3.2L) Fuel Pump ? 3 - 10 Amp (1991) ? 3 - 15 Amp (1992-94) Turn Signal Lights, Hazard Warning Flasher Lights ? 4 - 10 Amp Horn, Door Locks ? 5 - Not Used (1991 3.1L) ? 5 - 10 Amp Charging System, Charge Warning Light WARNING: Always disconnect battery ground cable before servicing "high- current fuses. It is recommended that "high-current" fuses be replaced by a qualified technician. Page 1 of 2 FUSES & CIRCUIT BREAKERS -1994 Isuzu Rodeo LS? 6 - Not Used (1991) (1992-93 2.6L) ? 6 - 10 Amp (1992-94 3.1L & 3.2L) A/T Interlock System ? 6 - 10 Amp (1994 2.6L) Heated Oxygen Sensor, Fuel Injection System ? 7 - 20 Amp Heater/Air Conditioning Blower Controls ? 8 - 10 Amp Air Conditioner Compressor Controls ? 9 - 10 Amp Right Headlight ? 10 - 10 Amp Left Headlight © 2008 Mitchell Repair Information Co., LLC.

Underhood fuse block swap out relay #7 thats the ECM relay.
Ground Circuits Using a DVOM, touch negative voltmeter lead to a good ground. Touch positive voltmeter lead to each ground terminal. With vehicle running, voltmeter should indicate less than one volt. If reading is greater than one volt, check for open, corrosion and loose connection on ground lead. See ECM GROUND LOCATION table for ECM ground location.
Page 1 of 1 SYSTEM/COMPONENT TESTS - 2.6L EFI -1994 Isuzu Rodeo

Either you're not getting it fully engaged or the gears in the transfer case are worn.

the left kick panel by the clutch under the plastic. its a silver box.