Help! 1993 Vette turns over stong but will not start

[Big A]

about a month ago i was riding around with my top out and it just cut off. Would not start back up...had to have it towed. Battery has been replaced, plugs replaced. The owner before me must have had the pass key issue because the resistors have already been added under the steering wheel. The cars turns over stong but will not start. Left battery unplugged for 24 hours and it started but cut off after about 30 seconds. Has not started since. HELP! this is my dream car and i have only had it a year and i can't drive it now.

Any help is appreciated.

Big A

 

[ecss]

about a month ago i was riding around with my top out and it just cut off. Would not start back up...had to have it towed. Battery has been replaced, plugs replaced. The owner before me must have had the pass key issue because the resistors have already been added under the steering wheel. The cars turns over stong but will not start. Left battery unplugged for 24 hours and it started but cut off after about 30 seconds. Has not started since. HELP! this is my dream car and i have only had it a year and i can't drive it now.

Any help is appreciated.

Big A

A month ago

When you turn the ignition On do you hear the fuel pump run for 2 seconds?

Do you have a fuel pressure gauge?

Short pin A to pin G on the diagnostic connector located above the drivers right knee.
Turn the ignition On.
Look at the digital speedometer LCD.
Look at the numbers that are displayed.

Module 1 is the CCM
Module 4 is the PCM
Module 9 is the EBTCM

Post the Diagnostic trouble codes if any are set.

Below is a picture of the connector pin outs.

If no codes are set when you crank the engine does the tach show rpm?

If you have rpm do you have spark at the spark plugs?

If no rpm.
Us a voltmeter set to measure AC volts.
Back probe Pin B White wire on the 4 pin connector at the Ignition coil driver Module. Picture below shows
the location on the passenger side front of engine.
Shown as item 1 in the diagram.

While cranking engine you should about 4 volts AC.

If no 4 volts you have a PCM problem or Optispark problem.

The connector has 4 wires.
Pin C Black wire is ground.
Pin A Pink/Black goes to the coil.
Pin D White wire goes to coil.]
Pin B White wire goes to PCM.

 

[Big A]

hi, thanks for responding. i have got the codes. they are C13 and C25. Can't do the other test u suggest because car will not crank. It only turns over. However it does turn over very strong.

 

[ecss]

hi, thanks for responding. i have got the codes. they are C13 and C25. Can't do the other test u suggest because car will not crank. It only turns over. However it does turn over very strong.

You said the engine cranks but does not start?

Does the tachometer on the dash cluster show any needle movement while you crank the engine even
though it doesn't start? That will tell you if the computer is controlling the Ignition Coil module and
trying to fire the coil.


If the codes are for module 4 which is the Engine Control Module (ECM).

DTC 13 is the Driver side oxygen sensor is not producing a usable signal when it should be after two minutes of run time when the exhaust temperature should be over 600F. (This would not cause the engine to not start).

DTC 25 is a problem with the Intake Air Temperature Sensor. It indicates the incoming air is over 302F
which could cause the engine not to start but not likely.

The IAT sensor is mounted in the passenger side of the accordion tube that goes from the air filter housing to the throttle body. It's a two wire connector plug with a Tan wire and a Black wire.

Unplug the IAT connector and try to start the car.

If the car doesn't start use an ohm meter and do the tests below.

With the IAT connector disconnected measure the resistance across the two pins of the sensor.
At 70F resistance of the sensor should be around 3.5K ohms
at 60F resistance of the sensor should be around 4.4K ohms
at 50F resistance of the sensor should be around 5.6K ohms
at 40F resistance of the sensor should be around 7.2K ohms.

If the resistance checks out.

With the IAT plug still disconnected.

Turn the ignition On. With the meter set to volts DC measure the voltage on the Tan and Black wire
of the IAT connector plug. Should be around 5 volts DC.

The fuel pump pressure test and voltage test at the Ignition Coil Module I posted earlier can be done by cranking the engine.
The engine does not have to start.

 

[Big A]

so the IAT sensor is replaced. Replaced fuel filter and based on the amount of gas that I lost when replacing the fuel filter....it IS getting gas. Car still only turns over...will not start. Please help. Weather is finally nice so i want to ride with the top out.

 

[ecss]

so the IAT sensor is replaced. Replaced fuel filter and based on the amount of gas that I lost when replacing the fuel filter....it IS getting gas. Car still only turns over...will not start. Please help. Weather is finally nice so i want to ride with the top out.

Have you verified fuel pressure with a gauge attached to the schrader valve on the fuel rail?
You can rent a gauge from Autozone for free.

Should be in the low 40 psi range. Pressure should hold and bleed off slowly.
If pressure bleeds off fast, pull the vacuum hose off of the fuel pressure regulator and verify
there is no gas in the hose. If there is gas in the hose the fuel pressure regulator is bad.

Have you verified you have spark at the spark plugs? (Remove spark plug from engine.
Reconnect spark plug wire and lay spark plug on metal part of engine like the intake manifold.
Crank the engine and verify if there is spark).

Does the tachometer show any rpm while cranking the engine?

Even if the engine doesn't start you can verify the above tests.

 

[Big A]

ok...update. was not getting fire. found broken ICM. Replaced. car starts now. GREAT! BUT....now it wont stay started. /cuts off after about 10 seconds. It will start right back up but will NOT keep running.

 

[ecss]

The owner before me must have had the pass key issue because the resistors have already been added under the steering wheel.

Left battery unplugged for 24 hours and it started but cut off after about 30 seconds.

In your first post you said the car started for 30 seconds but cut off.
Now you replaced the Ignition Control Module and it runs for 10 seconds and stalls but restarts and stalls again. :ugh

Did you install thermal heat sink compound on the back side of the new ICM?
It's usually a White colored paste.

Connect pin A to pin G on the diagnostic connector. Turn the ignition On and verify if any codes set.

Did you verify the fuel pressure?

 

[Hib Halverson]

First thing I'd do is fix whatever problem it is that required a previous owner to modify PASSKEY with those resistors.

Then, I'd road test.

If there is still a problem with cranks-but-won't-run or starts-but-won't-run, I'd go back to basics: get the factory service manual and diagnose those two characteristics using the information in the books.

 

[Big A]

hi. yes the thermal heat sink compound was added. yes fuel pressure was checked and is at 40 psi and slowly went down. now it will start and if u keep giving it gas it will run.....somewhat. It will not idle at all on its own, but it will start right back up. The only code it still shows as current is C13. I believe u previously said that would not stop it from running. it also backfires if u keep giving it gas to keep it running. i am pretty sure at this point i have to be missing something simple. ad missed another good day to ride with the top out. ad ad please keep the suggestions coming. thank you!


in response to the suggestion of determining why the resistors are under the dash. i know they are there to bypass the vats system and it was done correctly. I dont believe that is related to the current issue. Thank you for your suggestion.

 

[ecss]

hi. yes the thermal heat sink compound was added. yes fuel pressure was checked and is at 40 psi and slowly went down. now it will start and if u keep giving it gas it will run.....somewhat. It will not idle at all on its own, but it will start right back up. The only code it still shows as current is C13. I believe u previously said that would not stop it from running. it also backfires if u keep giving it gas to keep it running. i am pretty sure at this point i have to be missing something simple. ad missed another good day to ride with the top out. ad ad please keep the suggestions coming. thank you!

DTC 13 indicates the driver side oxygen sensor is not producing a usable signal so the computer will never go into closed loop. (Computer will not use the oxygen sensors for fuel calculation).

Disconnect the negative battery cable to clear the code and see if it comes back.

After engine shutdown the fuel pressure should slowly bleed off over a 10-15 minute time frame.
If it bleeds down fast, remove the vacuum hose at the fuel pressure regulator and verify there is no
gasoline in the vacuum line.

If you have an ohm meter, unplug the electrical connector from each fuel injector and measure across the coil windings of each fuel injector. I believe the LT1 factory fuel injectors should measure around 12.5 ohms.

If you can keep the engine running with the throttle held at a higher rpm it could be you're not running on 8 cylinders and that is causing the stalling.

If you have a clamp on the wire type timing light, verify each spark plug wire has consistent spark going to it.
Probably need two people since the engine only runs for a couple of seconds unless you can keep it running at a higher rpm.

Also run the engine when it's dark and see if any of the spark plug wires are arching.

 

[Big A]

hi again. still not running. no wires are arching. injectors are getting the correct ohms. Replaced IAC valve. Car still starts but will not idle. checked for new codes only code showing is the C13 which u previously advised would not stop it from idling. HELP!
mad

 

[ecss]

hi again. still not running. no wires are arching. injectors are getting the correct ohms. Replaced IAC valve. Car still starts but will not idle. checked for new codes only code showing is the C13 which u previously advised would not stop it from idling. HELP!
mad

In a case like this you really need a scanner to monitor all of the engine sensors in real time.

Try the following.
Disconnect the electrical connector to the MAP sensor.
Start the car and see if runs.

Reconnect the MAP sensor.

Disconnect the Throttle position sensor.
Start the car and see if it runs.

Remove the EGR valve and block the intake and exhaust port with a home made metal plate.
Start the car and see if it runs.

If none of the above works call a mechanic.

 

[12handler]

Big A. I am curious as to what you figured out. Let us know please.