ECM Issues - No Start

[Macroblock]

I thought I should share some ongoing observations related to the No-Start condition of my 1990 ZR1. It's pointing to an ECM issue.

No negative-GND signal is present on the injector outputs from the ECM. Injectors therefore do not activate.

Vehicle turns over normally.

Fuel pressure is good. Both pumps are working.

Spark is good to each cylinder.

No diagnosis codes.

VATS works correctly.

Note: Changed the Crankshaft Sensor (right-hand underside next to dip stick entry point). No change in symptoms. Old sensor was tested and has an impedance of approximately 1 K-ohms. I suspect it was working correctly.

By removing the yellow harness from the ECM, I was able to ground each injector with a jumper wire, using the service manual as a pin guide. Doing this put a small amount of fuel in each cylinder and verified injector operation. Upon returning the yellow harness, I turned the engine over. It would ignite and/or run briefly.

Next - I will now open the ECM and look for signs of burning or corrosion on the circuit boards. After which, I will verify that each of the 8 Power MOSFETs (-) are operational.

[Macroblock]

I removed the ECM and opened it up and soldered a short wire from an internal 5 volt+ source.

While still apart, I returned the ECM to my car. Hooked up the 4 connectors and connected the battery. I turned the key to ON.

I carefully (and I mean VERY carefully) applied the 5 volt+ to the 8 GATES (marked G on the circuit board) for each of the 8 MOSFETs that correspond to the Fuel Injectors.

I heard each Fuel Injector click, one at a time, with the application of 5 volts+ to the GATE of its matching MOSFET.

This suggests the power transistors inside the ECM are in working order.

[Macroblock]

I turned my attention to the Ignition Diagnostic Connector. I identified "Terminal A", which is Circuit 430/Crank Reference High.

Using a signal generator, I inserted a spoof signal at Terminal A. This spoof was a square wave with a 0-5 VDC range and a 50-50 Duty Cycle.

The objective of the spoof is to simulate a refined Crank Reference signal that would normally come from the Ignition Module after odd-pulse-synchronization of the raw signal provided by the Crank Shaft Sensor.

Starting at .4 Hz, I observed the fuel pumps started to operate. For simplicity, I set the output to 1 Hz. I heard a click, resembling an injector becoming activated. At 10 Hz, the same injector was activating with a consistent on-off pattern.

After a number of subsequent tests, I discovered that only Injector 6 was operating. This remained true when I conducted the same tests with or without the DIS Ignition Module installed. None of the other injectors were activated by the ECM during testing.

Page 6E3-C2-2 of the Factory Service Manual indicates that all 8 primary injectors should be pulsed during start up (not just number 6).

It could be that this is a tell-tale sign that something is 'incorrect' inside the ECM and this is possibly the reason the car will not start.

More testing to follow...

[S.hafsmo]

[Ccmano]

Wow, Your way ahead of me on electronics. Keep us posted. Haibeck provides an ECM testing and rebuild service should you need it. ECMs are bit scarce at the moment. But if you ask someone may make one available from their stash.
H

[Macroblock]

LOL - I built an on-bench emulator, so I can test further in the comfort of my LAB Chair!!!

It turns out that the injector for cylinder #6 correlates to Power MOSFET "Q1", the GATE of which is driven by U15 (16079435). This section is in working order.

Injectors for cylinders, 1,2,3,4,5,7 and 8 are correlated to Power MOSFETS "Q2 thru Q8", the GATEs of which are driven by U13 (23232). This section is NOT in working order.

I suspect, I could readily drive all the transistors with the 5v+ feed provided to Q1 from U15 but this would be a crude workaround because all injectors would fire concurrently (non-sequential-injection).

My preferred approach is to install a general purpose micro-controller inside the ECM and customize firmware to overcome the on-board deficiency and to maintain Sequential Injection capability.

Sidebar: If anyone has a defective, defunct or otherwise useless LT5-ECM, please drop me an email. I suspect I will need some test mules to further this project.

Found a photo here:

https://www.facebook.com/photo.php?f...type=3&theater

[XfireZ51]

I just recently spoke w Marc regarding injector operation and he is putting together an article outlining a test procedure for injectors while on the car. It does not involve modding the ECM.

[tf95ZR1]

From ZR1 Specialist website (Marc H)

http://www.zr1specialist.com/HAT%20W...in%20Place.pdf

Mb, I would talk to Jerry Downey of Jerry's Gaskets.
https://www.jerrysgaskets.com/
He is working on replacement ECM's (and he's
a good guy)

[Macroblock]

Originally Posted by XfireZ51

I just recently spoke w Marc regarding injector operation and he is putting together an article outlining a test procedure for injectors while on the car. It does not involve modding the ECM.

Awesome!

Verifying that the injectors are working is actually straightforward. Remove the Yellow or Gray 22-way Connector to the ECM. Turn the key to ON. One at a time, jump a wire from the (-) Battery Post to positions 1, 2, 3, 7, 8 12, 13 and 18 on the Connector. An injector that makes an audible click, is likely OK.

The injectors used in the early years of the ZR1 are susceptible to damage from ethanol in the fuel (not normally found in premium blends). The injectors develop shorts within their respective solenoid windings. Bad injectors will not produce a healthy click (a totally failed injector will not click). A current measurement can be used to verify the health status of an injector but the simple 'click' test provides discernible results.

Verifying the ECM is sending a (-) signal to each injector, without pulling the plenum, involves opening the ECM and ---CAREFULLY---checking each DRAIN PIN on the 8 Power MOSFETS. Use a 12 volt test light connected to (+) post of the battery. Have a friend turn the engine over (not literally). The test light should blink for each transistor. The ECM PC Board is marked "D" to guide you.

It is also possible to skin some of the jackets on the wires that feed the injectors and utilize a 12v test light, but by doing this you damage the wiring. To repair, coat the bare copper with heated solder and while still hot apply vinyl electrical tape.

In the case at hand, the ECM is unfortunately at fault. It looks like I.C. Component number U13 has failed (Sequential Injection Controller). As a result, only Injector 6 gets a (-) signal from the ECM.

[A26B]

Originally Posted by tf95ZR1

...........
Mb, I would talk to Jerry Downey of Jerry's Gaskets.
https://www.jerrysgaskets.com/
He is working on replacement ECM's (and he's
a good guy)

Thanks for the referral Ted, but the ECM is not a project we are working on.