Well today I replaced some leaking copper header gaskets on my Astro Van LT1 conversion. When I got finished with that I tried to crank it to check for leaks.It started up and sounded like it was running on 4 cylinders then it just died. I tried cranking it again and it will turn over but will not start. Checked coil,Spark at the plugs and I have 42 PSI on the fuel guage. It was running fine before I did the gasket change and I have already checked to make sure that I didn't leave somthing unhooked. Anybody have any ideas on what this could be.

ASTROJOE LT1

89 Chevy Astro Van
95 LT1 Engine
4L60E transmission

 

Have you checked to make sure your plug wires are going to the correct cylinders?

 

I had only pulled #5 and # 7 and I know I got those two back right. Can the Optispark go out like this and this quick.

 

It could, but you said you had spark at the plugs, correct?

Are you positive that your battery is charged and good?

And, just to be clear, the only thing that you took off was the #5 and #7 plug wires, the headers, and the gaskets??

 

I had wore the battery down trying to crank it but I re-charged the battery and got the same result. And yes only two plug wires were pulled and I do have spark at the plug boots

 

Just as a check, have you tried hooking up a voltmeter to your battery and cranking the motor while watching the meter? Even though you charged the battery, it could be enough to pull it back down.
I'm just throwing out ideas here.

Maybe Shoebox will read this and throw in his opinion.

 

It was pulling 13.5 volts when I checked it. I have never had a problem trying to crank it untill now. I also have a fuel pressure gage plumbed into the back of the fuel rail. It is still reading 42PSi of pressure so I don't think it is fuel related. I have tried to go with the basics of spark-fuel and air to check 1st. I have all of those but it seems like the PCM is not giving directions right.The PCM was programed by Ian Soltan and it has been working well since I 1st cranked up the engine. Can the ignition module cause a problem like this.

 

It can, but i thought if it was the ignition module you wouldn't get any kind of spark at the coil or plugs?

 

I just got through pulling a valve cover to make sure the valve train was working so I could rule out a broken timing chain. I also bit the dirt and tried a new ignition module. That was $ 86.00 wasted on a part I did not need. I have checked about everthing I know to check so I guess now I am leaning towards the Optispark being the cause of the no starting problem.

 

Try checking out this page first. This Shoebox's website.

http://shbox.com/1/4th_gen_tech2.html#opti_test

 

Ok I did the Shoebox Opti and Spark test. I was getting about 12 volts from both A and D terminals of the ICM connector,but when I tried to read the voltage from terminal B which is the pulses that trigger the coil I got no reading at all. Does that mean for sure that it is the Opti gone bad.

 

If everything was done correctly, that's what it sounds like.

If there's no voltage there, the opti isn't sending the signal to fire the coil.

 

Remember that you use the AC scale to look for the pulses.

If no pulses are seen, the opti is not sending info to the pcm or the pcm is seeing them and ignoring them or maybe there is an open circuit between the pcm and ICM or even between the opti and pcm.
It does seem odd that you were working on something else and this happened. Also confusing that you said you were getting spark to the plugs, but now you can't see the pulses at the ICM? Give a once over to the connection at the opti and on the side of the intake where the opti harness plugs in.

 

Thanks Shoebox for jumpng in on this. I also think it is odd that I was doing another task and this problem popped up. I did the passenger side gasket replace on one day and it cranked fine. I then did the driver side gasket the next day and thats when this problem started . I did check and have spark to the plugs, that was through the boot with a screwdriver and I also pulled a plug and tested the spark with it out of the block But when I was reading the terminal B in the ICM connector on the AC scale I dis not get any kind of reading. Again I did get 12 volts on the A and B terminals . I will go back and try to recheck everthing but I don't think I have missed a disconnected wire. I just didn't know that these Optisparks could go bad this quick.

 

I went back and checked that B terminal in the ICM today and I must have had the meter on the wrong AC scale. It is reading about 7.6 volts today. Now what