A fellow club member has a 1996 coupe. It has about 100,000 miles on it and seems to be in good shape. Some times it simply will not start. It runs fine once it does start. Doesn't stall. It cranks over fine but sometimes it will not start. then if you leave it alone for an hour or two, it will usually start. He said that it has been getting progressively worse over the past 5000 miles.

Any idea where to start the diagnosis?

Thanks

 

He might try accessing any trouble codes stored. This link will help: http://www.c4vettes.com/ecm.htm

 

If it is happening more when the car is hot or it is hot outside I think the starter is probably going. It will continue to get worse.

 

I had a fuel pump act the same way once? Just a thought. :crazy: :crazy: :crazy:

 

Does it crank and not start, or does it sometimes just not crank at all?

 

When it cranks but won't start is the time to do some testing. All engines need fuel, air, spark to start and run. Check for spark when cranking. Check for fuel pressure with the ign on. Check for injector pulsing with a low power 12v lamp across an injector socket while cranking.

 

Thanks you guys, Now it looks like we have our work cut out for us.

oh, it always cranks strong, it just some times (when cold or hot) it wont fire. I'm kinda thinking it has to do with a short in the VATS.

Does anyone know of a way to bypass them VATS? Is there a kit somewhere available?

And your right, we need to get down to the elemental issues - Spark, Fuel & Fuel pressure.


[Modified by Ricksc5, 3:32 PM 10/10/2002]

 

VATS measures the resistance of the pellet in your ignition key and if it isn't within several percent , then VATS won't allow the starter motor to crank nor the injectors to pulse. Since your starter always works, VATS isn't involved.

 

Thanks JFB,
So if I understand what you are saying, if the VATS was the problem, the starter would not even engage.

Based on that, it must be spark or fuel.

 

As stated above, the best time to trouble shoot this is when it won't start. Some relatively inexpensive tools are a noid light and fuel pressure gauge. The secondary spark can be checked a number of ways.

There is a secondary circuit within the VATS that could cause a problem but doubtful. Along with providing the ground for the start enable relay, the Powertrain Control Module (PCM)(Electronic Control Module some years) sends a 5 volt signal to the VATS, and upon recognizing the correct key resistance, the VATS will drop the voltage from 5 Volts to around 2.5 volts and the PCM/ECM will see this drop, pulse the injectors. This voltage drop is how the PCM/ECM knows the VATS is happy. Otherwise, a thief could get the starter to turn over and steal the car. The VATS must signal the PCM/ECM the correct resistance has been noted and it's OK to pulse the injectors. Your friend has the Central Control Module (CCM) and should check the factory service manual to make sure this system is correct for the 96. Pretty sure it is.

Get some tools and trouble shoot the system when if fails. Not too hard if properly equipped.

Hope it gets fixed. Darn cars.

dlmeyers 90 coupe zf6 3 speed shocks


[Modified by dlmeyers, 7:45 PM 10/14/2002]

 

Thanks DL :cheers: