92 TB42 efi Wiring issues

[cerenamarion]

For the last couple of days I have been dismantling variouse parts of my engine bay trying to locate the component that is stopping my patrol from starting :devilred:, so far i have disabled the LPgas system and managed to get it to run on Petrol only, only to return the next day and find it not starting again, yesterday i speant the day trying to locate a reason as to why i can't get a spark at the plugs, after dismantling the dissy and trying to replace the module ( which I can't get) i realised that there isn't a 12v supply to the dissy, strangly a test light on one of the terminals turns the fuel pump off.
Last night i came across the fault codes and tried to diagnose the ECU but failed to be able to do that as now the damn check engine light doesn't work :icon_bonk:, can anyone help me diagnose the ECU/Dissy and coil cross connections
A copy of the wiring diagram for the ecu may help

[Yendor]

There is an aftermarket workshop manual on this forum for the TB42E. It's not as good as a factory one but should still help you.

I think this the correct link

http://www.nissanpatrol.com.au/forums/showthread.php?293-Nissan-Patrol-GQ-Workshop-Manual.

You shouldn't use a standard test light when checking electronic circuits, they draw too much current and can blow up electronic components an LED test light is ok to use.

When the engine is turning a pulse/signal is sent to the ECU, the ECU then turns on the fuel pump. When you were touching this wire with your test light the ECU was tricked into thinking the engine was turning and switch the fuel pump on. This is normal.

Is it just the check engine light in the dash that doesn't work? or are other warning lights and gauges not working?

I would start by checking all fuses both inside the vehicle and under the bonnet, standard test light is fine for this.

Then check operation of the ECU relay under the bonnet.

Normally when they fit LPG they break the power feed going to the injectors. Did you remove this harness and then reconnect the original wires back together?

Does the vehicle have an alarm fitted?

[cerenamarion]

Thanks for the reply,
only the check engine light seems to be affected, as the engine only cranks I don't know if there are any other faults,
Don't know where the ECU relay is,
LPG disabled by joining the wires on the Fuel rail isolation relay added during lpg install to isolate power to injectors,

is there a relay that affects part of the function of the ecu, or is there some way of diagnosing if i have fried the ECU by using test light on dissy,
I read some info on testing the dissy on an RB30 and followed this but im not getting a signal output when rotating the dissy

yes has allarm fitted but turned off since purchase as we don't have remotes or istructions on how to use it

[Yendor]

With the ignition on you should also have other warning lights on in the dash as well as the check engine light, such as battery light, brake light and the fuel gauge should read.

The ECU relay (ECM relay) will be beside the battery near the fuel pump relay.

ECU relay supplies power to the ECU, airflow sensor and crank angle sensor.

I think you will have to be very unlucky to have damaged the ECU.

Aftermarket alarm/keyless entry systems are always a concern, they are prone to failing causing these sort of problems. Most system isolate the ignition circuit, this might explain why/if the warning lights in the dash aren't working.

Start by checking all fuses and the ECU relay, as well as the main earths.

[cerenamarion]

Thanks heaps for the help,
similar suggestions from a couple of angles,
hey presto 1 mention of car alarm and suddenly she purrs again,

Tip for future, if the Check engine light aint on then the ECU isn't getting power, even if the fuses are good,
Guess whats getting ripped out next weekend

[Yendor]

Excellent, you did really well in finding and sorting out the problem.

You should feel proud.

Good job :smiley_thumbs_up:

Cheers Rodney