originalspaceman

I am having very strange engine issues. When the engine is cold it seems to run and start just fine. When the engine is warmed up it stalls, doesn’t always die, but bucks the car (if in gear) and commonly dies if I don’t hurry up and hit the gas. A few times when it has died I have heard a loud pressure release sound. I can’t tell if that’s coming from my reservoir cap or something else. I have checked all of my injector wires with noid lights. I ran seafoam in the gas to clean out the injectors. I have replaced and properly gapped all of my spark plugs. I am not getting any codes on the scanner other than P0650 (which means I don’t have my MIL light connected, but I know the scanner works). I did once get codes stating that the o2 sensors detected a rich scenario, but I attribute this to my stalling and misfiring. I have a 2004 GTO LS1 with 40K miles in my 1988 Porsche 944. It is running in a standalone setup with o2, IAT, MAP, MAF, TPS, Crank, and Cam sensors. There may be more sensors that I’m not aware of or familiar with, but no VSS, EGR, VATS. I have a returnless fuel rail with a C5 return-to-returnless fuel filter with built in regulator. I have all of my vacuum hookups capped except the TB. The evap line from the fuel tank runs directly to the TB vacuum hookup. After it stalls it will sometimes start right up again, but continue to run rough, or sometimes will take a while to start again. It’s very random. Any input on this is appreciated.
Thanks!

waterbug1999

iTrader: (3)

You sure your temp sensor is working?

If it detects cold temps after it is warmed up, it will flood itself and run like ***.

originalspaceman

Not sure, no. How do I go about testing that?

Thanks

waterbug1999

iTrader: (3)

The temp sensor is on the head. The stock place in on the driver side buy plug #1. Since this is the conversion / hybrid section, I am not sure what your set up is.

originalspaceman

I have the factory temp sensor installed, connected to the harness. I tapped a new location for a 3rd party temp sensor for my gauge. So, the factory setup still applies. Wouldn't a temp sensor problem through a code?

waterbug1999

iTrader: (3)

What does the temp gauge/s say after it warms up?

I know when mine had went out, it did not throw a code. It sounds like some of the symtoms you described and figure it was somethign easy for you to check.
On mine, it would warm like like usual but the computer was still reading a cold detection and flooding out the car.

originalspaceman

Well, the 3rd party temp gauge reads properly, but I don't know what the factory sender reads because it only talks to the computer and doesn't output to a gauge. I'll have to get a fancier scanner to read the temp from the PCM, I guess.

waterbug1999

iTrader: (3)

Well, its just a thought.. Good luck.

garys 68

iTrader: (1)

Who programmed your computer?
I've read that without the VSS, you can have stalling issues. I think it can be programmed to minimize this.

originalspaceman

It was programmed by a guy at autocomputertech.com. He programmed it to work without VSS, and I confirmed the integrity of this with a friend who also has his LS1 in a 944 with the same exact programming.

Old Geezer

iTrader: (3)

"The evap line from the fuel tank runs directly to the TB vacuum hookup."
If you have a sealed tank cap, you are pulling a vacuum on the tank.
Operating that pump w/ a vac on the inlet[tank] will cause problems...
You also said:
"A few times when it has died I have heard a loud pressure release sound".
when the engine is turned off, vac at TB ceases, and the vac you pulled on the tank is pulling air back thru the tb, into the tank...

originalspaceman

Awesome... I was suspecting that for a while now, but a lot of people I know are running it that way. Thanks for logically explaining it. So what do I do with my fuel tank evap now?

Old Geezer

iTrader: (3)

the hose from the TB, plug the TB, and put a plastic, inline fuel filter in the hose. The tank can "breathe", and the filter will keep the dirt out. Make sure that the filter will "flow" both directions.
You could also remove the line to the tank, shorten it up, and tie it at a higher than tank location, with the filter in it.

originalspaceman

That did it... Thanks again for explaining that one. Makes perfect sense.

Old Geezer

iTrader: (3)

You are most welcome!
I don't know how long you've been running this way. I'd keep an eye on the fuel pressure, as a vacuum condition causes cavitation at the pump inlet. The pump may go "Tango Uniform" on you when you are far from help. You know "Murphy's law'!!