Vapor lock is more common on carbed setups because the fuel pressure is signficantly lower (5-7psi). The LT1 fuel system is operating at 42psi... it takes a lot of heat to vaporize the fuel at 42psi.

But the "suction" side of the pump is a different story. It involves the engineering principle of "net positive suction head". As the fuel travels upward (particularly when the tank level is low), towards the pump, it loses pressure due to friction. If the negatives (lift distance, fuel vapor pressure, line pressure losses) outweigh the positives (pressure in the tank), the fuel can start to vaporize, causing bubbles to enter the pump. The pump will have a specified "net positive suction head required" to prevent cavitation in the pump. If you don't get this pressure, it cavitates. Once the bubbles enter the pump, they can remain in the fuel flowing to the rails.

The "recycle" part of the design can actually contribute to the problem. If the fuel lines pass near the exhaust system, or are exposed to high heat in the engine compartment, they pick up heat. Having a "recycle" line doubles the exposure of the lines to heat. And, pumping significantly more fuel than you need can cause the pump to add heat to the fuel faster, and then increase the heat pickup with the friction losses through the pressure regulator. Large fuel systems, intended for very high HP engines can suffer from severe overheating problems at low engine power, requiring a fuel cooler to remove the excess heat.

 

I am getting ready to check the codes but I wanted to give this in put first.

When I touched the plastic fuel lines that come into the engine bay on the driver side fender well they were not that hot. When I touched the metal fuel lines near teh fuel psi test port they were too hot to touch.

Not sure if this help but thought it might be another clue.

Thanks again guys!!! I will let you know if there are any codes in a few minutes.

 

***RESULTS OF SESS CODES***

NONE...

Now what?

 

not to jump in your thread but dont want to start a new one on this. when you test the psi and take the car for a wot drive, when your done and take the test gauge off the car gas is going to come out of there or should it not. when i took it off some gas went all over, but is fine now.

 

That's normal. Gas pressurizes the line up to the gauge. Unless you bleed it off before you remove the gauge, it'll spray all over.

 

Could the heat soak get to a point that it vaporizes the fuel in the lines? After the car was not running for a while and the fuel system was re-pressurized (with out starting the car) the gage bled normal then the vapor started again.

 

This sounds like heat soaking on the ICM to me, mine acted very similar and i replaced the icm problem solved.

 

Whats the ICM and where is it located?

 

Ignition Control Module http://shbox.com/1/coil_loc.jpg

 

Thanks! I will replace that and see what happens.

 

So what exactly does the ICM do? I ordered one today and that little sucker was expensive $87. I hope by changing this part it will shed some light on the problem (either fix it or highlight the actual problem).

Thanks guys, I will post the results.

 

The ICM is basically a "switch" that accepts the timing signal from the PCM, and tells the coil to fire.

 

Thanks Injuneer! Makes sence.

I replaced the ICM today and had the old one tested at Advanced Auto. It tested bad so I am hopeful thats the problem. When I take the car for a ride tomorrow I will let you know how it went.

 

I just got back from a test drive after replacing the ICM. The car ran great (better than normal) until 20min past. Then it started the same problem. As I was sitting in the driveway I revved the engine a few times to see how it acted. The check engine light came on so I turned the car off and checked the code.

Looks like a code 36 - Distributor ignition system.

I think I know what this means but could someone confirm it for me?

 

The 36 is a loss of the high resolution pulse from the opti. However if that is the only problem from the opti, nothing will happen.

Each time you describe a problem with the car after about 20 minutes. To me it sounds like you have a closed loop problem.

Have you tried disconnecting one of the O2s to see how it runs then once it warms up?