LT1 Optispark/timing issues

[barno68]

It started! Well, sort of... At this point I do not have a throttle cable installed, so I used a folded piece of paper between the idle screw and the throttle body. It turned over as usual without starting, so I pulled on injector connector and hooked up a noid light which flashed without a problem as I cranked. Then the engine roared to life, I nearly messed myself! It ran for about 2 seconds at about 1500-2000 RPM and shut down. I removed the noid light and hooked the injector back up and tried it again with the remote starter- fired up again then died. I then moved into the car and used the key, started again and the tach registered about 2000 RPM before dying. I then removed the paper on the throttle body and it would not start.

For the short duration that it runs it sounds smooth, then there is as hesitation, RPM drops and it dies. Currently there is no anti-freeze in the car and I am leary to fill it again (about the 8th time) in case I need to pull the opti again.

Ideas?

[barno68]

It is starting consistantly now without having to open the throttle, but is still only running about 5 seconds. It will start right back up with out cycling the key. May not be relevent, but it is really difficult to get to start via the key but fires right up using the remote starter.

I will be replacing the starter down the road as the solinoid froze up once already today.

There is a fuel pressure gauge hooked up currently and it reads 41psi with engine off and about 39-40 running. Odd thing, earlier today it would only go up to 38 psi and dropped to 30 when running. This did not make a difference in how long it ran.

Still runs smoothly, no hesitation now, just stops running after 5 seconds.

[barno68]

Maybe this will help, here is a screen shot of what I could get while it was running

[barno68]

The problem is that the signal to the injectors is cut and the engine dies. What would cause this?

I keep hearing VATS, but I do not think it effects the injector ciruit just the starting and fuel pump??? Supposidly it is programed out of the PCM, however I have no idea how to check.

[paul67]

It might be the fuel pump not running constant,when it first starts the pump pressure's the injectors, but then switches off it could be the relay not having a constant live feed.

[barno68]

It might be the fuel pump not running constant,when it first starts the pump pressure's the injectors, but then switches off it could be the relay not having a constant live feed.

Pump is running fine, I have a pressure gauge hooked up to the rail when running. Plus the pump is running after the engine shuts down.

Someone on another forum has said that the Corvette PCMs have an extra switch that is sometimes missed that is a fuel enable causing my symtoms. I need to get a tuning program and see if that is the problem.

[paul67]

Was there not anti theft device fitted to some cars that if they started they could be driven few yards then the engine would shut down.

[paul67]

Have you removed the fuel pipe's off the rear of the tank ,I did this and fitted them the wrong way round, this caused what you seem to have .

[HectorM52]

Vacuum leak. I remember that from when I first started mine. Major culprit = connection to brake booster from the side of the intake.

I would suggest cracking the throttle to about 50% and letting it rip. My money contends that it will continue running.

[WS6]

I can't remember if the LT1 cars had this switch but the L98 Corvettes did have an oil pressure switch hooked into the fuel pump relay. So if after a couple seconds there was no signal from the oil pressure the fuel pump relay would shut off.

Regardless, this makes me think of other tests. You'll need a test light and another person. You'll also need the pin outs for each connector. The Factory Service Manual has all this info. You really need to have an FSM and not a Haynes type manual to be doing this type stuff. In short, go through all the power leads on the PCM and make sure they are all on in the respective states. Meaning the ones that have battery power should be powered when the key isn't even in the ignition. The ignition ones come on when the key is turned on and stay on after the car is started. You may find one or two that turn off when you start the key but they should come back on while the car is in run and running. You'll also want to look and make sure none of them turn off after a few seconds once the car does start. Yes, it's tedious but I believe at this point it's an electrical problem. I'm also going on the basis that the car is shutting off like the key has been turned off and not dying like it's out of fuel.

You should also get an FSM because it will have a flow chart for diagnosing problems like this.

[barno68]

I got the answer from a member on LS1LT1.com:

"Is the PCM from a Corvette too? If so, they have an extra VATS switch that not everyone toggles, it's called Data Stream Fuel Enable. It will cause your exact symptoms, it lets the engine run for a few seconds and if it doesn't detect the VATS signal, it will kill the fuel injectors."

I reprogrammed the computer this morning by toggling off the Data Stream Fuel Enable switch and the engine runs just fine. I am very excited as the last time the car ran was 2004 (different engine of course)!

Now I just have to figure out why it will start with the remote starter and not the key... but that is for another posting.

Thanks to all that helped with this!

[paul67]

Glad you finally got it sorted ,just keep starting it every week to stop the opti corroding which was my failing.What plugs are you using by the way and gap.

[barno68]

Glad you finally got it sorted ,just keep starting it every week to stop the opti corroding which was my failing.What plugs are you using by the way and gap.

I am using Autolites at .045 gap.

[WS6]

good job!