96 Crank but no start - Help needed

[mortenals]

Hi.
I have two identical 1996 LT1's with about 85 K miles. One of them wont start. It used to start imediately and run perfectly but after the winter I havent been able to start it and tried almost everything.
The fuel pump starts and runs for a few seconds. The engine cranks fine but there are absolutely NO sparks. I believe I can smell gasoline in the exhaust pipes after cranking but I am not sure. I use Dyno-Scan from Auterra for OBDII-testing but it does not give any errors (present or historical).

Here is the short version of a long story:
New (reman.) computer,
8 spark plugs and wires,
New Ignition Control Module,
New harness to the Opti,
8 new injectors.

Today I wanted to change the Opti with a new one that I purchased, but it turned out that they send the old version that is not vented ad .
And the old one looked perfect and was absolutely dry inside, so I just put it back on.

I suspected the computer so I tested it in my other 96 LT1 (after switching the box (KS module) in the bottom of the computer) and it starts up immediately.
According to the Shop Manual the resistance between terminal D on the Opti connector and ground should be less than 5 Ohms but it is 11-14 Ohms. Both wires between the computer and the Opti connector (Opti-A to pin2. connector2 and Opti-D to pin3.connector2) measure about 1.1 Ohms. Do I have a Grounding-problem?

1. Is there any way to verify the signals coming to and from the Opti?
2. Is there a simple way of testing my scan tool by producing a DTC?
3. Is there a way to use blinking lamps to indicate errors as on the older C4's?
4. The manual talks about reprogramming a replacement computer. Could that be the problem if the car has been starting running a short while after the replacement?

I an running out of options so I Hope to hear from you soon :confused

 

[John Robinson]

Try this

Take the TPS switch from the car that runs and put it on the one that doesn't run. I had a no start on my93 with 82K about three weeks ago and it turned out to be the TPS. It did not give any code because it thought that the engine was flooded and so it told the ECM to shut down the injectors so the engine could clear itself. I removed the air tube to the throttle body and sprayed choke cleaner in there while someone else cranked the engine over. We had a test light on the connector to one of the injectors and when the engine backfired and caught for a second the light showed power to the injectors. Turned over the engine and it started immediately. I did have a high idle so I replaced the TPS with an AC Delco unit and the car runs better now than it ever did with the old TPS which was from a parts store. I hope this gives you a new approach to your problem. Please let us know what you finally do to get the car to run. The only way we can get smarter than the cars is to share our fixes. Good luck and I hope it is something simple

When I had a no start condition I did not have any codes. The scan tool showed the ECM was bad because the TPS was sending a false signal and shutting down the ECM. If you have fuel preassure and spark then something else is the problem. If you have fuel and spark try what I did with the carb cleaner to see if it want's to run.

 

[mortenals]

Will test tomorrow

Hi
Thank you for your prompt reply. I will try to find time to test it tomorrow - it is 00:51 here.

However - one of the things that does work with my scanner is the indication of the throttle position. The scanner program (Dyno-Scan) on my portable PC reacts precisely as expected to any movements of the pedal and follows the scale from 0 to 100 % perfectly.
I will reply tomorrow if I have time to test it tomorrow.

 

[John Robinson]

TPS Test procedure

Throttle Position Sensor​

The scan tool displays throttle position in volts. The voltage should display between .23 - .59, with throttle closed and ignition “ON,” or at idle. Voltage should increase at a steady rate as throttle is moved toward Wide Open Throttle (WOT) about 4.6 volts.

The ECM has the ability to Auto-Zero the TP sensor voltage if it is between .23 and .59 volt. This means that any closed throttle voltage between .23 and .59 volt will be determined by the ECM to be 0% throttle angle, and should display 0% when the throttle is closed. A failure in the TP sensor circuit should (MY OPINION MAY NOT )set a DTC 21 or 23.

Copied from the service manual for a 93 model

Hope this information will be helpful with your scan tool.:confused