My LT1 won't start after cam and head swap

Must be a problem with the timing, or maybe the crank sensor and/or cam
sensor.

"Mark357" wrote in message

> I need some ideas on what to look at to get the engine started. The
> car is a 1996 Impala with 40k miles. I installed a LT4 camshaft,
> ported iron heads, roller rocker arms, new timing chain, and optispark
> distributor. Now the engine cranks but won't fire at all. I double
> checked the valve adjustment and the cylinders have 150psi compression
> (good!). The valves open and close in time with the #1 cylinder so I
> have the cam installed properly. I have a good spark on #1 cylinder
> that coincides with the compression stroke on #1. I have fuel pressure
> at the fuel rail. The injector wiring harness is firing the injector
> as indicated by a test light placed at the harness. The plug wires are
> all good and going to the right plug.
>
> The only thing I can think of testing is to try and start the car and
> sniff at the throttle body for gas odor. (to ensure the injectors are
> actually squirting gas.) I will also double check to see if I have gas
> in the gas tank. (never assume anything!!!)
>
> Any ideas are welcome.
>
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 >> Stay informed about: My LT1 won't start after cam and head swap 

"Brian" wrote in message

> Ok...I have NO idea if this will help...
>
> I did a similar job...head swap on 96 Cav. Everything was go...and
> correctly assembled. I spent the next DAY checking it all over because
the
> engine wouldn't START darnit...
>
>
> ...I forgot to plug the fuel pump back in...
>
>
> ...There, my most embarrassing automechanical moment.
>
> B.
>
>

It doesn't qualify as embarrassing Brian, until you do it... twice,

--

-Mike-
mmarlowREMOVE.TakeThisOut@alltel.net
 >> Stay informed about: My LT1 won't start after cam and head swap 

"Mark357" wrote in message

> I need some ideas on what to look at to get the engine started. The
> car is a 1996 Impala with 40k miles. I installed a LT4 camshaft,
> ported iron heads, roller rocker arms, new timing chain, and optispark
> distributor. Now the engine cranks but won't fire at all. I double
> checked the valve adjustment and the cylinders have 150psi compression
> (good!). The valves open and close in time with the #1 cylinder so I
> have the cam installed properly. I have a good spark on #1 cylinder
> that coincides with the compression stroke on #1. I have fuel pressure
> at the fuel rail. The injector wiring harness is firing the injector
> as indicated by a test light placed at the harness. The plug wires are
> all good and going to the right plug.
>
> The only thing I can think of testing is to try and start the car and
> sniff at the throttle body for gas odor. (to ensure the injectors are
> actually squirting gas.) I will also double check to see if I have gas
> in the gas tank. (never assume anything!!!)
>
> Any ideas are welcome.

Do you have good vacuum? I'm not sure how your setup works, but I've
seen the fuel rail get pressurized from turning the key on, then the fuel
pump
turns off. Once you start cranking, the fuel pump won't turn on and pump
fuel until the computer sees the manifold pressure drop, indicating the
motor is actually turning and sucking air. But even if that's the case, you
should still get a 'sputter' from the squirts from the initial pump
pressure.
 >> Stay informed about: My LT1 won't start after cam and head swap 

Thanks for the idea. Last night I checked out the throttle body after cranking the engine and I smell gas. The #1 spark plug also smells like gas and is a little wet so I think I am getting some gas to the injectors.

I disconnected all the injector wires, connected a light to the #1 injector wire and removed the valve cover. When the engine is cranked, I can see the tester on the injecter light up when the exhaust valve is fully open.

This doesn't seem right since the injector is then spraying fuel onto a closed intake valve.

I have a theory. The 1996 LT1 engine has a crank position indicator on the nose of the crank. It is a metal disk with notches that let a sensor in the timing chain cover know where the crank is in rotation. I had to take it off to replace the lower timiing chain gear. Even though I carefully marked the front and back of the disk (the manual said to put it back on in the same orientation) I have probably installed it on the crank in reverse. It slides onto the crank nose and uses the keyway to line up, but I bet the notches are not semetrical around the keyway and it is throwing the injector pulse off.

It looks like I get to yank off the water pump and distributor to test this one out.
 >> Stay informed about: My LT1 won't start after cam and head swap 

In the old days a little squirt of starting fluid would tell you if you got
spark-no fuel. Should isolate no fuel from injectors.
 >> Stay informed about: My LT1 won't start after cam and head swap 

After taking off the water pump, distributor and such, I learned I was wrong about the crank position sensor disk. It is impossible to put it on backwards. So I put it all back together knowing that I had not found the problem.

Then I found it! I had been cranking the engine alot in testing so I thought I would charge the battery befoer I tried again. The water was a little low in 5 battery cells and the sixth was lower than the rest. After charging the battery the engine started right up. I think the battery wasn't puting out 12 volts. It was enough for the starter to work fine, but the computer was not operating properly with the low voltage.

Now I just need to adjust the valves I should be done.

Thanks for the suggestions and support!
 >> Stay informed about: My LT1 won't start after cam and head swap