Brothersmechanic

Hey guys, I'm in the process of fixing/rewiring my brothers 1990 vette so it can be driven on his wedding day and have run into a unusual snag.
This car will not activate the injectors until you short one. Personally I have not seen that before but I work on Turbine engines primarily. Just wondering if this would be an issue with the ECM, or what kind of direction you guys would think I need to go looking. Or have any of you run into this issue before. When I get home I'm going to be changing out all the injectors with new ones as these ones haven't ever been changed before. (Cheap insurance)

Thanks for your help. (Kind of hoping my brother isn't on this forum...)

1993C4LT1

If a C4 has VATS activated, it will not fire the injectors. Maybe because you shorted one, they are being activated? Not sure, just guessing on that. With a good battery, put key in ON position. Get a voltage reading from the coolant sensor, map sensor, throttle position sensor. They all should give you 5 volts. If they do, good ECM. Have you tried scanning codes?

Brothersmechanic

The car wasn't giving any codes or lights, and I will have to check the voltage at those sensors when I get home. That is still a couple weeks away. I do appreciate the options though, and if those all read 5volts then no matter what the ecm is good? Also how can I find out if the vats is working? Cause I was under the understanding that if it was active the engine wouldn't rotate. My brother does currently have the radio removed from the car. (That is the only other thing that is suspect at the moment.

Brothersmechanic

Also for advice on the injectors I have been told a Bosch 3 is the way to go, was hoping to get an opinion on that as well as if some one has a pn for a good set. I was thinking the 22lb or the 24 should do plenty

Brothersmechanic

Bump for info on injectors

1993C4LT1

​​​​​​​Sorry I forgot! Bosch 3 are fine. I would go with whatever pound injectors they came with new. Unless the engine is modded. If the engine does crank over, then VATS isn't being activated.

1993C4LT1

And if you do get 5 volts, it's almost guaranteed the ECM is good.

Brothersmechanic

Awesome that's good to know, the engine turns over smoothly, just for some reason needs the extra for the injectors to get going. When I figure it out then I will let you guys know for future reference.

Thanks

wikdwizard

So, to be clear, when you short one injector all eight work and the car runs after you remove your jumper?

Brothersmechanic

That is correct though smoothly may not be exactly correct. Hence the coming injector change

C409

..... Check , test , or replace the Ignition Control Module in the distributor .....

Brothersmechanic

They have been known to cause this kind of issue?

Cliff Harris

The ECM uses the DRPs (Distributor Reference Pulses) from the ignition module to synchronize the firing of the injectors to the rotation of the engine.

C409

..... This ! ..... it could be as simple as a dirty connection between the ICM , the ESC , and the ECM ... we're dealing with low current , low voltage pulses and any interruption can wreak havoc on an otherwise good running system .....

Brothersmechanic

Ok I know the other two but what is the ESC? Will all the corroded connections that. Have found on his car the added resistance could be a major contributor. Thank you very kindly everyone, I appreciate this assistance in getting this matter sorted out.

C409

..... Electronic Spark Control ... on my '87 the module is located on the passenger side near the Heater/AC blower motor .....

ctmccloskey

Hello there,
That is a very kind thing you are doing for your brother! I have always fixed my brothers cars for him as well.

The car you are working on is very dependent on the signals it gets from its sensors. When your ground is no good it throws off a lot of the readings that the primary controller sees. Be sure to go through the ground connections carefully. Simple tests like verifying that the engine has a good ground can be done with a multi-meter. Check battery voltage, then check engine ground by leaving one lead on battery Positive (12 Vdc) and then take ground lead from meter and check the engine block to see if you have the same or at least a very close to the same as the battery reading.
Behind the battery on my 1988 is a block with a post on it. On the post you will find a bunch of RED leads which feed the fusible links that power most of cars electrical systems. I would check to be sure that there is no corrosion there.
Your injectors have positive voltage going to each one while the key is "on", your computer sends out the ground signal to engage the injector and make it work.
I let my car set for a few years and it was all corroded when I opened it back up. I learned this the hard way.

Good Luck on your "project"!