LT4 Need help with new cam in my lt4

[pjtblack96]

we put a bigger cam in my 1996 lt4. upon starting the car backfires and tries to run but it wont. we called a tune shop and they said either the cam or distirbutor is in wrong. we took the car apart again to check that the timing marks were lined up correctly and everythings right. what can we do to get it running?

 

[felicity2215]

You probably have two spark plug wires out of order. Start with the #1 spark plug. The sequence around the distributor should match the firing order.

You can also disable the fuel pump and use a timing light to verify that the #1 spark plug is firing at the correct angle before TDC. This will confirm that the distributor is installed correctly.

 

[pjtblack96]

You probably have two spark plug wires out of order. Start with the #1 spark plug. The sequence around the distributor should match the firing order.

You can also disable the fuel pump and use a timing light to verify that the #1 spark plug is firing at the correct angle before TDC. This will confirm that the distributor is installed correctly.

how would you use the timing light to check that with an optispark? please elaborate on how it would show the correct angle

 

[felicity2215]

Rotate the engine to TDC on the compression stroke for cylinder #1. Put a reference mark on the harmonic balancer or crankshaft pulley extending to a non-rotating part of the engine. Put the mark where you can point to it with the timing light. Chalk, white tape, and white paint all work.

Disable the fuel pump so the engine won't try to start. Trigger the timing light off of the #1 spark plug. When you crank the engine with the timing light pointing at the reference marks, the space between the fixed mark and the rotating mark should be small - a few degrees before TDC.

I'd check the spark plug wires first. Much easier and much more likely to be the problem.