86 Vette with 400 SBC starting problems

[400sbcVette]

I bought an 86 Vette with a 400 ci swap with the original TPI still on it. The guy that had it said he drove it around alot and one day he had it running outside his shop and it simply quit. He thought it might have been the fuel pump, so he replaced it. It runs for about three glorious seconds then shuts off. I've gone through and checked/changed a few things and nothing is different. There are No Injector Pulses to the injectors. Here are a few of the things I have done:

Ohm'd the injectors. They are all at 16 ohms.
Checked computer grounds. They have continuity.
Changed distributor/pickup coil.
Checked for fuel pressure--it's got good fuel pressure.
It has spark.
I checked the ignition switch at the plug for the VATS. The multimeter registered the proper ohms for that key in the wires.
I've got the reference voltage coming from the distributor down to the ECM harness (The purple/white wire).

Is this an ECM problem? Just need some advice on a few tests I should do, so if you guys have anything, let me know.

 

[ecss]

If the proper key pellet resistance is read by the Theft Deterrent Decoder Module it sends I believe a 30hz square wave signal to Connector 2 Pin B6 a Dark Blue wire of the ECM. The ECM should now pulse the injectors.
The TD Decoder Module is located behind the passenger side bread box.

Some people purchase a kit that produces both a 30hz and 50hz signal that covers both passkey 1 and passkey 2 systems. They connect the signal from this module to Pin B6 of the ECM so the TD Decoder module is not needed. If you have a scope you could look at the signal on B6. If no square wave when the ignition key is turned to On the Decoder module is defective.

If the 30hz signal is at pin B2 and 12 volts is at the injector connectors and the injectors don't pulse, the ECM is defective.

Click on the e-bay link below for the bypass module.

Passkey II Bypass Module for LS1 and LT1 GM Vats | eBay


Diagram below lower right shows the location of the Decoder Module.

 

[400sbcVette]

If the proper key pellet resistance is read by the Theft Deterrent Decoder Module it sends I believe a 30hz square wave signal to Connector 2 Pin B6 a Dark Blue wire of the ECM. The ECM should now pulse the injectors.
The TD Decoder Module is located behind the passenger side bread box.

Some people purchase a kit that produces both a 30hz and 50hz signal that covers both passkey 1 and passkey 2 systems. They connect the signal from this module to Pin B6 of the ECM so the TD Decoder module is not needed. If you have a scope you could look at the signal on B6. If no square wave when the ignition key is turned to On the Decoder module is defective.

If the 30hz signal is at pin B2 and 12 volts is at the injector connectors and the injectors don't pulse, the ECM is defective.

Click on the e-bay link below for the bypass module.

Passkey II Bypass Module for LS1 and LT1 GM Vats | eBay


Diagram below lower right shows the location of the Decoder Module.

I forgot to mention that I installed one. Nothing changed. I guess an ECM is my next step. I'll let you guys know how it goes! Thanks so much.

 

[400sbcVette]

If the proper key pellet resistance is read by the Theft Deterrent Decoder Module it sends I believe a 30hz square wave signal to Connector 2 Pin B6 a Dark Blue wire of the ECM. The ECM should now pulse the injectors.
The TD Decoder Module is located behind the passenger side bread box.

Some people purchase a kit that produces both a 30hz and 50hz signal that covers both passkey 1 and passkey 2 systems. They connect the signal from this module to Pin B6 of the ECM so the TD Decoder module is not needed. If you have a scope you could look at the signal on B6. If no square wave when the ignition key is turned to On the Decoder module is defective.

If the 30hz signal is at pin B2 and 12 volts is at the injector connectors and the injectors don't pulse, the ECM is defective.

Click on the e-bay link below for the bypass module.

Passkey II Bypass Module for LS1 and LT1 GM Vats | eBay


Diagram below lower right shows the location of the Decoder Module.

One more thing...
Will a bad ECM shut off all of a sudden while it's running?

 

[ecss]

One more thing...
Will a bad ECM shut off all of a sudden while it's running?

Anything is possible. Depends on what part of a circuit is failing.

I think the initial few seconds of run time is the residual fuel sprayed by the fuel injectors
possibly when you first power on the ECM.

If you continually spray starter fluid into the intake with the MAF sensor removed, will the engine continue
to run?

Have you shorted Pin A to Pin B on the diagnostic connector and verified no ECM codes are set?

The ideal situation is to monitor the ECM and the sensors by using scanner software to verify what's going on.
Example looking at the injector pulse width will tell you if the ECM is pulsing the injectors.

You said you verified the distributor reference signal wire to the ECM.

As long as the engine is rotating is there voltage to the fuel pump fuse?

When you installed the VATs signal generator did you cut the Dark Blue wire so the Decoder
module signal wire was disabled and no longer connected to pin B6? If you didn't and just spliced
the new signal to B6 it's possible the two signals are being intermixed and the ECM is confused.

 

[400sbcVette]

Anything is possible. Depends on what part of a circuit is failing.

I think the initial few seconds of run time is the residual fuel sprayed by the fuel injectors
possibly when you first power on the ECM.

If you continually spray starter fluid into the intake with the MAF sensor removed, will the engine continue
to run?

Have you shorted Pin A to Pin B on the diagnostic connector and verified no ECM codes are set?

The ideal situation is to monitor the ECM and the sensors by using scanner software to verify what's going on.
Example looking at the injector pulse width will tell you if the ECM is pulsing the injectors.

You said you verified the distributor reference signal wire to the ECM.

As long as the engine is rotating is there voltage to the fuel pump fuse?

When you installed the VATs signal generator did you cut the Dark Blue wire so the Decoder
module signal wire was disabled and no longer connected to pin B6? If you didn't and just spliced
the new signal to B6 it's possible the two signals are being intermixed and the ECM is confused.

Thanks for the response! Let me go down the list here:
I shorted A and B terminals. The Check Engine light did not flash. In fact, there were no flashing lights. Hmmmm...
The car WILL run on starter fluid if sprayed continuously.
I did verify Dist. Reference pulse, but the odd thing is whenever I turn it over, the 1.3 volts jumps up to ten, then back down to three, then up to four or five so long as I am trying to crank the engine.
There is voltage going to the fuel pump even when the engine is cranking.
I did not cut the wire, but spliced it in with one of the crimp-style 3-way splicers. That could possibly be a problem. I will check that, as well.
Also, I changed out the ECM. There was still NO PULSE to the injectors.

 

[ecss]

Thanks for the response! Let me go down the list here:
I shorted A and B terminals. The Check Engine light did not flash. In fact, there were no flashing lights. Hmmmm...
The car WILL run on starter fluid if sprayed continuously.
I did verify Dist. Reference pulse, but the odd thing is whenever I turn it over, the 1.3 volts jumps up to ten, then back down to three, then up to four or five so long as I am trying to crank the engine.
There is voltage going to the fuel pump even when the engine is cranking.
I did not cut the wire, but spliced it in with one of the crimp-style 3-way splicers. That could possibly be a problem. I will check that, as well.
Also, I changed out the ECM. There was still NO PULSE to the injectors.

1) When you turn the ignition On the Service Engine Soon indicator should be on solid.

2) You should hear the fuel pump come on for 2 seconds. If you continually crank the engine eventually
the oil pressure switch will close and supply the fuel pump with 12 volts even if the ECM is defective this is the backup in case the fuel pump relay ever fails.

3) If you short Pin A to Pin B and turn the ignition On, the radiator fan should run and you should hear the
IAC valve being retracted to the closed position. (Clicking noise).

4) The Service Engine Soon indicator should flash code 12.
Flash pause Flash Flash long pause Flash pause Flash Flash Long pause Flash pause Flash Flash.

Then if any codes are set the code is flashed three times. When all codes are displayed Code 12 will again flash three times and the cycle repeats.

5) If you get no code 12 flashing, the fan doesn't come on I'd verify if the ECM is getting power and ground.
If that's good I'd suspect the mem calibration pak. That's the small removable circuit board with the Eprom on it that you swap when you install a replacement ECM. It contains the limp home mode circuitry and the engine calibration program.

6) The ECM is not needed to produce spark.

7) When the engine is running does the dash cluster show rpm?

8) Power for the ECM
12 volts when ignition is On or Start
Connector C2 Pin A6 Pink/White wire

ECM constant 12 volts BATT
Connector C2 pin B1 Orange wire
Connector C1 pin C16 Orange wire

ECM Ground is G104 above the oil filter.
Ground wires are
Connector C1 pin D10, D3 both Black/White wires
Connector C2 pin A12 Black/White wire

 

[400sbcVette]

1) When you turn the ignition On the Service Engine Soon indicator should be on solid.

2) You should hear the fuel pump come on for 2 seconds. If you continually crank the engine eventually
the oil pressure switch will close and supply the fuel pump with 12 volts even if the ECM is defective this is the backup in case the fuel pump relay ever fails.

3) If you short Pin A to Pin B and turn the ignition On, the radiator fan should run and you should hear the
IAC valve being retracted to the closed position. (Clicking noise).

4) The Service Engine Soon indicator should flash code 12.
Flash pause Flash Flash long pause Flash pause Flash Flash Long pause Flash pause Flash Flash.

Then if any codes are set the code is flashed three times. When all codes are displayed Code 12 will again flash three times and the cycle repeats.

5) If you get no code 12 flashing, the fan doesn't come on I'd verify if the ECM is getting power and ground.
If that's good I'd suspect the mem calibration pak. That's the small removable circuit board with the Eprom on it that you swap when you install a replacement ECM. It contains the limp home mode circuitry and the engine calibration program.

6) The ECM is not needed to produce spark.

7) When the engine is running does the dash cluster show rpm?

8) Power for the ECM
12 volts when ignition is On or Start
Connector C2 Pin A6 Pink/White wire

ECM constant 12 volts BATT
Connector C2 pin B1 Orange wire
Connector C1 pin C16 Orange wire

ECM Ground is G104 above the oil filter.
Ground wires are
Connector C1 pin D10, D3 both Black/White wires
Connector C2 pin A12 Black/White wire

3) The fan does come on. I can hear it running whenever I short A and B and turn the switch on. I also hear the IAC. It clicks.
5) No code 12 and the fan does come on. The Service Engine Soon light doesn't come on at all.
7) It does show RPMs on the dash gauge cluster.
8) I unplugged the computer and checked the hookups for power and they all checked out at 12 volts.

 

[ecss]

The Service Engine Soon bulb gets power from the INJ1 fuse.
INJ1 fuse is hot in Run, Start or Bulb Check.
When the key is turned to On, the ECM grounds one side of the bulb which turns it On.

You say the bulb doesn't light.

Verify you have 12 volts on the INJ1 fuse when ignition is On.
If you do have 12 volts, I'd say the bulb is burnt out.

Get that fixed and see if any codes are set.

INJ1 fuse also provides 12 volts to 4 of the fuel injectors.