Need Help LT1 Cranks but will not start

Discussion in 'High Tech Retrofits' started by 3_z28camaro, Apr 19, 2009.

  1. 3_z28camaro

    3_z28camaro Veteran Member Lifetime Gold Member

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    Hey guys, I have been working on my LT1 swap into the '71 for quite some time now and finally I tried to fire it up but is cranks and will not start. I am suspicious of the computer and the harness as the guy who modified it, Jeff Roberts, was far from the best. Horrible customer service.

    I have 42 pounds of fuel pressure at the rail but there is no spark and there is no signal at the injector harness plugs. The optispark, coil and ICM are all new. The engine was rebuilt also.

    I am out of ideas, please help.
     
  2. Knuckle Dragger

    Knuckle Dragger Mayor of Simpleton Staff Member Lifetime Gold Member

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    I have no experience with the LT1, but if you have no injector pulse, and no spark it's usually a cam or crank sensor. Do you have a RPM signal on the scanner when you crank? Are you absolutely sure you have the power wires correct? I chased a no spark for about an hour on my TPI before I realized I had the engine running power on a circuit that was not hot while cranking.
     
  3. 3_z28camaro

    3_z28camaro Veteran Member Lifetime Gold Member

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    I am sure I have all the wires going to the right places. I have checked everything and traced wires to see if anything was the problem there. As far as I know the 1994 LT1 does not have cam and crank sensors.

    I am in the process right now of figuring out how to test the optispark to see if it is sending a signal.

    By a RPM signal do you mean getting a reading on one of those scanners that hooks up to the diagnostic connector? Sorry for my ignorance.
     
  4. Knuckle Dragger

    Knuckle Dragger Mayor of Simpleton Staff Member Lifetime Gold Member

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    Your sensor is most likely the optispark itself. On TPI it's the distributor that gives the signal to the ECM.

    Yes check for RPM on a scanner. If it's not there I always go after the distributor, in your case the optispark. Keep in mind I have no hands on for the LT1 so I'm basing on past GM experience.
     
  5. 3_z28camaro

    3_z28camaro Veteran Member Lifetime Gold Member

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    You are right the optispark contains both the crank and cam sensors, my mistake.

    I am starting to think it is the optispark. The ICM connector is getting power and the ICM/PCM signal. I have even double checked my ignition wires to make sure they are correct.

    By the way, thanks Dave for your help so far.:)
     
  6. tom3

    tom3 Veteran Member

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    Has the Pass Key security system been bypassed? Shuts off the injectors if the ECM is not satisfied.
     
  7. 3_z28camaro

    3_z28camaro Veteran Member Lifetime Gold Member

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    When I had the computer reprogrammed, I asked for the VATS and any of those other security things to be erased. So hopefully the guy did it, I did read if that stuff is not removed the engine will not even crank. Then again I could be wrong, I am still learning about this stuff.
     
  8. 91chevywt

    91chevywt Veteran Member

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    I had a very similar problem myself. It ended up being really dumb...apparently the opti spark connector isn't hard to put on backwards. And since its really tough to see down there due to the water pump I thought I had a bad Opti. I did realize my mistake when I traced the problem down to the opti. On your car, that is what sends the position signal to the ECM in turn telling the spark when to fire. There are only really two ways to test the opti. With a Lab Scope or a Scan Tool. Then you can see the camshaft signal. There is that harness that runs between the opti and the regular harness, so it may be to your advantage to test continuity through that smaller harness and make sure the connector pins are all in good shape. Also, if you get wiring diagrams you can check to make sure there is continuity between all the necessary wires that lead to the ECM, and make sure they lead to the correct pins.

    As far as VATS...if your car can crank, it should fire for about 3 seconds. VATS controlls fuel injector pulse and can cut out the starter from turning. Even if you bypassed the start enable relay it will fire for a second or two with VATS malfunctioning.

    I'm not sure if your too familiar with the GM diagrams and finding the pins, if you need help with that feel free to ask. If you don't have one already, a GM manual is really handy since it will have every single diagram for the engine harness.
     
  9. Mike1970RS

    Mike1970RS Veteran Member

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  10. 3_z28camaro

    3_z28camaro Veteran Member Lifetime Gold Member

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    The engine is out of a 1994 Camaro, so it is an early design optispark. That shbox site is pretty good, I have been using it for diagnostic help. I am going to start doing some continuity tests at the connectors to start finding out where the power is and is not.

    http://www.hotrodlane.cc/newhtml/94lt1nstart.html
     

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