Fuel Return Pressure?

[T4Texas]

I've been chasing a chronic Low BLM issue and just want to eliminate this as a possible cause.

Can anyone tell me how much pressure it should take to blow through the fuel return line (the one going from the bottom of the FPR to the tank)?

I connected a piece of hose to it and blew into it. I could move the fuel in the line this way but I felt like my eyes were going to pop out of my skull. I connected a mighty-vac to the line and it would hold about 15 PSI before it drew fuel back up into the vacuum.

I'm about to take a long road trip from NJ to TX. If I need to I'll run a temporary fix of fuel hose from the FPR to the tank.

Any suggestions or recommendations would be appreciated.

Dave

 

[Ormand]

The return line should flow really easy, if it isn't bent or blocked. At idle, with a high performance fuel pump, it has to flow almost the full capacity of the pump, and it shouldn't take more than a few psi to get that flow.

 

[T4Texas]

Ormand,

Thanks for the reply. Sounds like it may be worth my while to try to rig a temporary by-pass until I get where I'm going.

Dave

 

[Ormand]

It might just be some trash in the line somewhere. Before you rig a temporary line, you might try using air to blow through from back to front. There are some hoses behind a cover plate, up over the rear axle, where you can get to all three fuel lines.

 

[T4Texas]

Thanks again for keeping me in mind. Actually I sprayed a bunch of carb cleaner in the return line where it connects to the FPR and blew it out with shop air this morning. I did it several times, letting the carb cleaner soak a while before blowing it out, until the can of cleaner was empty. Afterward I personally blew into it again but didn't notice any difference.

Unfortunately time has about ran out for me to tinker with it until I get moved. I need to finish cleaning the garage (last room in the house of course). The movers will be here tomorrow morning so I'll just drive it like it is for now. The BLMs and INTs are within range (barely) so the ECM should keep it running good enough until I can spend some more quality time with the car. I'll be bringing the laptop with turbolink with me on the road, so I'll plug it in every day or so just to monitor things. If worse comes to worse I'm no stranger to hotel parking lot pit stops.

I know it isn't related to the topic of this thread, but what brand O2 sensor do you recommend? The AC Delco one I started with a few weeks ago was reading around 750 but the cross counts were very low (usually under 10) so I swapped it out for a heated one I bought a year or so ago (either from Kirban or Caspers). With the heated sensor the cross counts went way up (between 20 and 75), but the actual O2 readings were so low (in the 400s) that the car wouldn't go into closed loop and the chip locked the BLM and INT at 128. Then I bought a new AC Delco sensor from the dealer and am now having the same results I had with the other AC Delco one. Any thoughts on this? I could change out the O2 sensor almost anywhere along the road.

 

[Dennis F]

Did you take the gas cap off?

Just a hunch here but yourr blowing into a giant sealed box and just trying to pressurize it by blowing into it.

 

[Paul Clark]

Aren't CCs supposed to cycle from "X" to over 200 in a certain amount of time, and then start over and do it again?

 

[T4Texas]

Yep, took the gas cap off. I got a pretty good buzz off the fumes I blew out of the tank.

It was my understanding that the CCs should change at every frame, ideally showing between 20 and 75 CCs per frame. Maybe I'm working off of bad info?

 

[Paul Clark]

Man, don't go by what I say.
Wait for those that really know to chime in.