Checked for fuel pressure? Any diagnostic codes?

Yes the ECU relies on CAS and Crank signal to fire the injectors. Sometimes you'll get spark if one goes out, sometimes not but most of the time it won't have fuel if either signal is lost.

dwb said:

Checked for fuel pressure? Any diagnostic codes?

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Yes checked pressure.. that was the first thing that was handled. Given power from outside source. To jump an injector with the plugs out , while cranking and fuel sprayed out the cylinder.

jdxnc said:

Yes the ECU relies on CAS and Crank signal to fire the injectors. Sometimes you'll get spark if one goes out, sometimes not but most of the time it won't have fuel if either signal is lost.

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Okay, I will test those two sensors.

CAS sends signal to ECU to tell it to fire the injectors so you may have blown the ECU drivers, or bad CAS, or bad wiring. But first test the 4 injector current limiting resistors (box on firewall) for proper 5.5-6.5 ohm resistance each to rule that out (note that even if the resistors are way too high resistance preventing the injectors from firing, you will still see +12v on the injector harness).

It's harder on a 2G to test the cam and crank sensors than on a 1G where you can turn the CAS by hand and watch the signals switch voltage. You need a good multimeter or an oscilloscope to see them on a 2G.

Noid lights don't always work on our cars and because of the short pulses used for the injectors you again need something like an oscilloscope to see them.

Okay, thanks for some direction. It's been a battle for sure figuring this out.. I'll give an update once I'm able to get back out there.

If all 4 cyls have spark, then CAS and CPS are probably good.
But here's what CAS cranking voltages should be: https://www.dsmtuners.com/threads/wont-start-new-head.379677/#post-152302942.

But… The issue is all connectors produce a signal ( captured by led light ) when cranking.

All injector fire when powered by an independent power source ( injector tester ).

However when the connectors are connected to the injectors, they don’t seem to have the current to activate the injectors.

It’s as if the harness produces a signal but not a power source, think voltage divider how it’s useful (Vout) to create a signal to measure - usually by (GPIO) pins.

but it would not be capable of powering a actuator.

This makes me suspect some kind of ground latching interruption, having no knowledge of the circuitry I don’t know if the CAS / Crank sensor are the interruption or if it’s a device in the ECU

Lastly - a spare resistor box was used during testing and the results were the same.

Power for the injector coils comes from the MPI relay to the injector resistor (If used) to the injector.
The ground side come from the ECU injector drivers. Those are the four transistors on the heatsink in the ECU. There is also a snubber circuit and a sense circuit to tell if things are broken/shorted to throw a fault code.

It's these additional circuits that wind up putting battery voltage on the ECU injector pins when it's not firing the injector (why you see battery voltage on both sides of the injector connector when the injector is disconnected). The driver has to pull all the current needed to fire the injector to ground. If it can't then you get issues.

steve said:

Power for the injector coils comes from the MPI relay to the injector resistor (If used) to the injector.
The ground side come from the ECU injector drivers. Those are the four transistors on the heatsink in the ECU. There is also a snubber circuit and a sense circuit to tell if things are broken/shorted to throw a fault code.

It's these additional circuits that wind up putting battery voltage on the ECU injector pins when it's not firing the injector (why you see battery voltage on both sides of the injector connector when the injector is disconnected). The driver has to pull all the current needed to fire the injector to ground. If it can't then you get issues.

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Thanks for clearing this up, I was unaware the MPI was in the loop between the resistor box and the ECU, I always assumed it was solely for controlling the pump.

We will have to check out the relay as well and report back - currently the relay does latch and ignite the pump when cranking as it should and shuts off when not cranking.

You have two 2G's so you'll have examples of both style MPI setups.

In both cases there are two circuits involved, the main being power for the ECU and much of the engine bay and the second for the fuel pump. The power in the first case comes from Fusible Link #4 and is unswitched until the MPI relay does so. The second (fuel) gets power from the Ignition Switch IG1 contact like the coils and PTU do.

Tested the MPI relay according to the manual and got 73 and 74 ohms on the coils and 12v was applied to pins 2-4 and continuity was confirmed at pins 1-3

. I pulled the ECU and visually it looks fine to me (pic attached), but my scan tool fails to establish communication. On top of that, the IAC valve is warm to the touch even with the engine completely cold. Anyone seen this combo before?

I forget which pair of connectors can get swapped and cause problems. Perhaps others will jump in or you'll find them by searching but I seem to remember something like the ISC and the Injector Resistor both have 6 pin connectors in the same general location that people have mistakenly swapped.

Fortunately no connectors were swapped as the resistor box was never unplugged , but yes I do believe they are very similar.

The ECU had a smell - to me. And the back of it looks like it has some corrosion.
But nothing stands out on the top of front of ECU.

A 3rd known working resistor box will also be tested, but the ECU no longer connecting to scan tools is concerning since it did connect previously while trying to diagnose this no injector start.

Anyone know if ECMLink is still operating?
To send In for further inspection if needed.

I don't see anything obvious going on with the 97 ECU.
ECMTuning is still open as far as I know.

Run through my 2G MPI post and make sure that the ECU is getting turned on. Check to make sure the ODB II port is getting power and that you don't have any pins popping out. https://www.dsmtuners.com/threads/2g-basic-ecu-mfi-mpi-relay-circuit-function.497188/

miliman13 said:

Anyone know if ECMLink is still operating?
To send In for further inspection if needed.

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Tom said that he has his wife sorting through emails but his main focus right now is on other projects. He will get back to you if you send an email. However, it may be a little longer than in the past.

Oscilloscope was used on the CPS and CAS. These are the results before and after cranking the car. First pics are from the CPS





This is the CAS





Also a different scan tool was used and was able to connect with the ECU.

Both measurements don't seem correct. The signals should be 0 to 5v not -2 to 4.3v or 0 to 10.9v. It's good that you see pulses but I'm scratching my head on the levels. The ECU should be outputting about 5v on both signals and the CKS and CPS should be pulling those to ground as the engine rotates.



Can you connect that Oscilloscope to your injector connectors and see what's going on there?

steve said:

Both measurements don't seem correct. The signals should be 0 to 5v not -2 to 4.3v or 0 to 10.9v. It's good that you see pulses but I'm scratching my head on the levels. The ECU should be outputting about 5v on both signals and the CKS and CPS should be pulling those to ground as the engine rotates.

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Can you connect that Oscilloscope to your injector connectors and see what's going on there?

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The scale voltages can change based on the settings on the side of the budget device, so I wouldn’t necessarily be to concerned about the exact values, the goal was to see if a step responce was observable during cranking - suggesting the sensors are functioning.

That’s a good idea placing device on the injector, we will have to try that as well.

I added more grounds and the car sounds like it wants to run when cranking, but still doesn’t. To me something isn’t grounding , allowing current to injectors.

The connectors blink when cranking but can’t drive the injector. ECU passed visual check , MPI passed check, TPS, fuel pump, CAM, Crank- still need to test the working injector box from my own car. Since we don’t know if the spare we used is working.


Is it possible for a sensor to output a signal pulse yet the scale be off ? - again I suspect the device, from experience with it.

But yes most things should be 0-5v scale.


A lill back story - the TB was removed for rebuilding and injectors cleaned and new seals. That’s what stopped the car from turning back on.

Additionally :: the injector harness shows 0v with key on - engine off. I read one of the threads found below - were someone stated you should see 3v at rest at connector.