Juve88GTA

Sup everybody.
1988 Trans Am GTA 350 5.7L
A few days ago out of nowhere started to surge, then stalled and after a few cranks it would start again. My suspicion was that it was a fuel delivery issue; pump works, plenty of fuel pressure replaced the fuel filter, and after that it wouldn't start, well, it does for about 2 seconds...
After checking the spark and the ICA I squirted gas on the throttle and ran for a few seconds, did it again to check the injectors and 'viola' no pulsations. I checked the pick up coil on my MSD distributor and it had over 600ohms. I know is not the VATS, I have a VATS delete chip from PCMs for less.

What else could be causing the injectors to shut?

8Mike9

Did you verify not firing (injector) with a noid light?...I guess a test light would work as well, but never tried it.

Juve88GTA

Yes sir, I used a test light.
Plus, you could hear and feel the ticking when they're where working.

Juve88GTA

Update.
No voltage to the injectors.
What exactly makes the injectors pulsate? Or could a faulty VATS shut down the I njectors even with a VATS delete chip?

8Mike9

There are two fuses INJ1 and INJ2, in the fuse panel, check them...

The injectors should always have voltage on them, then the ECM will ground one side to fire them.

Now, ohm the injectors out as well, could be a shorted coils in a few, which could cause the fuse to blow...iirc, they should all be around 16 or 18 ohms (search to verify)

If VATs was deleted properly and the car was fine, it should still be okay.

3.8TransAM

VATS may be disabled in the chip but an issue with the relay or a bad VATS module itself can still cause issues.

sparks454

iTrader: (1)

I agree with the VATS module. ECM issue? Fuel pump relay?

Juve88GTA

Ok guys...
So I whent to the junk yard today I got a pass key module just to rule out the VATS system. It still doing the same thing. So, ECM maybe?

8Mike9

I don't have my manual close by, but am going to go out on a limb here, and say there is nothing in the VAT's module or Vat's related...nor the ECM, that would turn voltage off to the injectors.

How were the fuses?

Voltage on both sides of them?

Juve88GTA

I thought I'd narrow aver urging down to the ECM. I replaced it this morning but still nothing. There is no voltage to the injectors when the ignition is on.

sparks454

iTrader: (1)

Verify your fuel pressure?

sparks454

iTrader: (1)

I would still test the injectors with a voltmeter along with the fuses to make sure you have voltage when you're supposed to have voltage. Just sounds so much like the FP relay is spent. Trying to find my wiring diagram.. Found these...

http://i56.photobucket.com/albums/g1...transbody1.gif

http://i56.photobucket.com/albums/g1...transbody2.gif

89rs454

Run your own wires to both sides of injectors to a 12v switched source fuse it off and it should fire right up.

Juve88GTA

Excuse my ignorance, I don't understand this procedure.

8Mike9

As I mentioned before, and as the schematic sparks posted the link to:

https://www.thirdgen.org/forums/atta...ine_wiring.pdf

The ECM only grounds on side of the injectors to fire the bank.

The other side is always with voltage, when key is on.

So...my last time I'll ask, is there voltage off INJ1 and INJ2 fuses?

These wires (post fuses) go directly to the injectors.

Juve88GTA

I checked for the 3rd time. There is voltage to Inj1 and Inj2 with the key on.
Also, there's only voltage to the hot side with the ign on on the injector connectors. I thought both sides where supposed to have 12v and then the ECM would ground one...

gw082008

Look at the above post wiring schematic. With all of the injectors unplugged, voltage will be on one side only - if you leave any of them connected "backfeed" can show voltage on both sides - again study the above schematic.
Connect a noid light or a Radio Shack Led across any one of the injectors connectors - key off should see a dim light. Key on should be bright - indicating ECM is grounding the injector circuit.

8Mike9

You never mentioned that you did

Okay, I think you should see voltage on both sides, at least with just one connector unplugged...as I recall, both lights on the Noid light are lit, and one is "blinking" when turning the engine over/trying to start it...I'll verify both conditions (with DMM and noid light) later this afternoon, or tomorrow for you..I'm knee deep in my '42 Ford right now.

8Mike9

With just one injector clip unplugged, I have voltage on both side of the clip, assume since the injectors are in parallel, that's why.

Juve88GTA

I haven't had time to work on my car recently but here's an update... I replaced the ECM, I have voltage on D15 and D16 pin outs, checked the connectors and only the hot side has voltage, the other side is dead (no + or -). I know one side of the connectors go straight to the ECM, my question is, where does the other side go to? The schematics I've seen are not very clear. Also what gives the signal to the ECM to ground the injectors?

Juve88GTA

Ok people, this is my final diagnosis. THE ECM IS NOT GROUNDING THE INJECTORS, Everything else is fine, all I need to know is what's causing this.
Help please!!!

Tuned Performance

iTrader: (92)

Look at the wiring at the distributor. Especialy the purple/white wire at the icm. If the ecm isnt seeing a distributor reference pulse it will not pulse the injectors. You can still have spark but have a bad icm.

Juve88GTA

I took the ICM to autozone to have it checked and it was good. I Was thinking that it could be something with the distributor wiring, I have an MSD distributor with a MSD 6a ignition box, so the wiring is not stock but it had been working fine for about a year.

Tuned Performance

iTrader: (92)

Hopefully they tested it more than once. The MSd used a cheap Chinese i bit a cdelco one is a direct replacement. The pickup side gets soldered on.

alex722607

iTrader: (3)

If the ECM is not grounding the injectors then check grounds for the ECM. When I pulled my engine, some grounds were so loose in the factory connectors it was nausiating. Check the grounds on the block (heads) That is the only thing I can think of. good luck

gw082008

I've posted this before.
Brand new distributor had a bad ICM - took it to Auto Zone - tested good - made my own ICM testor with an extra coil and a spark plug. ICM would not fire the plug - so much for Auto Zone testing. Replaced the ICM - fired right up.
Go to these sites - lots of tips.
http://easyautodiagnostics.com/gm/4....-of-articles-1
http://easyautodiagnostics.com/gm/4....ed-icm-tests-1
Good Luck

Juve88GTA

She runs again!
Especial thanks to Tunned Performance for providing the final hint.
It was the 4 wire connector in the ICM, it was bad.
Thanks everybody!