Hey guys. Here's the deal. I've got a 91 Firebird Formula with a 5.7 TPI engine. My brother was driving it and the heater core sprung a small leak. So he pulled the car into the yard, removed and replaced the heater core and put everything back together. Put the key in and tried to crank the engine and the engine just spun and spun but would not fire up. Damn!

About this time I realized that my brother did not disconnect the battery before he disconnected the ECM. Is this relevant? I don't know. Hopefully you guys can tell me. So....I ran some quick diagnostics. I checked for fuel at the fuel rail and we had plenty of pressure on the gauge. I checked for fire at the spark plugs, indeed we had plenty of spark. Plugged in my NOID light to check for an injector pulse and got NOTHING. Checked a couple of other injector plugs and none of them lit up the the light. So now I know my problem is no injector pulse.

My first thought was maybe he shorted out the Ignition Control Module and that would prevent the injectors from pulsing. So I went to the parts store and picked up a new ICM and installed it. Still no injector pulse. So now I'm wondering if perhaps the ECM got ruined because he disconnected it without disconnecting the battery. But before I run out and just buy a new ECM I wanted to hear you guys thoughts. Is there any way to test the ECM? Is there another possible problem that I could be overlooking? I would really appreciate some input here.

One more relevant piece of information here...I replaced the injectors in 2015 with a set of Bosch III injectors from Southbay. So....what do you guys think? The car was running great when he pulled it into the yard, a couple hours later it had no injector pulse and wouldn't run. Thoughts??????????

 

Vats light on?

 

VATS has been bypassed for about 4 years.

 

Have you checked all your fuses?

 

Indeed I have. I found no blow fuses.

 

Post 35 on how to check your ecm for a vats signal.
If you have s vats signal sounds like the ecm could be bad.
https://www.thirdgen.org/forums/elec...pass-vats.html

 

If the VATS system is bypassed do I still need to check this?

 

It depends on how it’s bypassed. If it’s reprogramed out of the ecm I would suspect a bad ecm.
If it’s done with a resistor at the column you might want to check the passkey signal to the ecm. Some vom have a hz setting. If not check for a 2.5-5v signal see the other thread for the pinout of your 730 ecm.

 

R&R'ing the ECM with the battery connected doesn't hurt them. My first thought is, was the ECM plugged back in?

RBob.

 

With the key on do you have the check engine light on and did you check the fuse by the battery

 

Here's the things I would check first


Check if your tach is bouncing during cranking. The needle should bounce or have some movement, if it is completely still than your pickup coil is out.


I'd also check the fuse by the battery that it isn't blown.


When you bypassed VATs did you make your own ground for the starter relay and leave the rest alone?


If the TPS is reading too high i.e. WOT it can put the computer in clear flood mode stopping injector pulse.

 

Hey guys,

My apologies for the delayed response. I had a family emergency that has derailed my work up until now. Right before that, however, I did replace the ICM without any improvement. So I can scratch that off my list of possible causes. I hope to get back under the hood this weekend to see what else I can come up with. Thanks for all the input. More updates coming soon...

 

The check engine light is indeed on with the key on. I did, however, forget about the fuse up by the battery. I will check that this weekend when I finally get back to work on it. What exactly is that fuse for?

 

Yes, the ECM was plugged back in.

 

It is for power to the fuel pump relay and oil switch, it also provides power to the ECM. With having the proper fuel pressure, that fuse is OK.

Since the CEL lights up that also points to that fuse being OK. And of course that the ECM has been installed.

RBob.

 

Im not sure if the tach is moving or not during cranking. I'll check it out this weekend. By the pickup coil Im assuming that you are referring to the ICM? If not then what?

The method I used to disable the VATS was this: Alternative: Cut the pigtail to Ignition Lock Cylinder and solder the resistor between the wires. Now you have a "plug and play" resistor that can be plugged back into the vehicle harness, or removed if you want to disable the vehicle. We did this and it worked perfectly. We didn't have to address anything with the starter relay.

I have not looked into the TPS. To find out the TPS reading I assume that I would need to backpin the TPS plug and test the voltage readings? What readings should I be getting?

 

What exactly do you mean by "passkey signal" to the ECM?

 

Since it’s bypassed you don’t need to worry about it. But anyways the passkey module sends a hz signal to the ecm. This handshake tells the ecm that it can fire the injectors. Without the signal upon startup there won’t be any injector pulse.

 

Pickup coil is different from the ICM and is what sends the RPM signal to the ECM. If it's not sending a signal then the injectors will not pulse. Easiest way to see if you're getting a signal or not is too pay attention to the tach during cranking, it should bounce or at least lift off of the peg, if it is completely still during cranking then it's likely the ECM also isn't seeing a signal.

Then if the car is cranking than it is likely that the vats module is working normally.

Yes, that is the procedure. I believe it should read around .5 volts at idle position and around 5.0 volts at wide open throttle. Going off memory, but I'm pretty sure those numbers are right. The tech article on this site about adjusting the TPS would be more accurate about procedure and numbers though.

 

This is the pickup coil. You can also test it with a multimeter

http://easyautodiagnostics.com/gm/4....ed-icm-tests-6

Actually I just re-read your initial post. Did all of the connectors by the ECM get plugged back in? There's the main ones for the ECM and there is a couple other ones (can't remember their connector numbers) that I would check and make sure they're connected and no half seated or something.

Also the wire ground on the rear passenger side head is the ECM ground for the injectors. Shouldn't need to mess with it for a heater core job but maybe it got jossled and broke a wire or something?