Fuel pressure issue

[rickpaw]

So I just completed a LM7/4L60e swap in my 67 Firebird. I had about 300 miles on the car after the swap, mostly around town with 30-40 minute trips. Last week I took it to Cruisin the Coast (CTC) from Houston and ran into fuel pressure (FP) issues 4 times.

Here's my fuel set up:
-LM7/4l60e combo. Tank is Tanks Inc FI tank with Aeromotive 340 pump. Corvette fuel filter/regulator mounted just in front of the tank. Brian Fich duel vent tank vent, along with stock vented fuel cap.
-Fuel line is -6AN from tank to stock 3/8 hard line on the frame rail. 6AN from pass side rail in front of firewall looping along the top of firewall to the driver side fuel rail inlet.
-Stock LS1 intake/fuel rail/injector. Stock LS1 ECM with mail order tune from PSI Conversion.
-Voltage at the pump: 13.5V. Alternator puts out 14V. Pump is triggered by ECU and powered thru 30A relay directly from the battery in the trunk. 10awg pos/neg wires.

The issue:
-The first 250 miles the car ran great. The last leg of the trip (Houston to CTC), the weather got warm so we had the AC on. After about 2 hrs driving with AC on, the car started stumbling and lost power. Pulled over and the car barely idled. I hooked up FP gauge and it only showed 20 psi. Took the pump out and found some debris blocking about 50% of the screen at the pump inlet. Cleaned it out and put everything back together. Got 40 psi of FP. Not enough but enough to get the car running to CTC (we were 30 mins away). During CTC it died 2 more times with FP of 20 psi. All while AC was on and in stop and go traffic. Both instances we took the pump out and the inlet was clean. The fuel filter/regulator was removed and checked for debris. It was clean also.
-We ordered/overnighted a 2nd Aeromotive 340 pump and changed it out on Sat, figured the 1st one was bad. Drove the car around Sat with no issues (AC was not on). Drove back to Houston from CTC Sunday. About 250 miles into the trip (after the AC had been on for 1.5 hrs), the car stumbled and died again. FP was at 20 psi. Let the car sat for around 15 mins, and FP jumped up to 40 psi. We drove the car back to Houston without the AC the rest of the way without any issues.
-Let the car sit over night and start the car. FP shows steady 58 psi.

Question:
-I don't think it's fuel pump related since the pumps are practically brand new. The 1st one has 500 miles. The 2nd one has 200 miles on it.
-Did I get vapor lock in the fuel system from the heat in the engine compartment? I have heat wrap on the tail pipe where the fuel line crosses over from the tank, and the fuel line has thermotec heat sleeve at that location. There's no excess heat on the pipe. In fact I can grab hold on the exhaust wrap and it was just warm. I have heat reflection tape on the fuel line where it crosses over the top of the header pipe on the pass side. One common thing was the car had been running for awhile with AC on full blast.

Sorry for the long post. I tried to describe it as much detail as possible. I really enjoyed the car after the swap, and I'd like to get this sorted out as I have many long trips planned.

Here's a picture of the engine compartment. You can see the fuel line (with a section of heat tape) running from pass side to the fuel rail) by the firewall.

https://static1.pt-content.com/images/pt/2013/08/P1030111_zps4c512046-1.jpg (http://s616.photobucket.com/user/rickpaw/media/67%20Firebird%20LS%20swap/P1030111_zps4c512046.jpg.html)

[rickpaw]

Also, several people had suggested I change the pump to AC Delco. I'm willing to do that as well, just want to make sure that I nail down the issue, not randomly replacing parts.

[Bygblok]

did you change the filter/regulator or just check it for being clean? I think I'd look there first. I sat in traffic at CTC for hours and never had any issues with my FAST system with an in-tank pump(all spectra parts) on my 70 Camaro. Exhaust runs pretty close to the fuel system on the passenger side and my tank is vented also. Sorry you had problems at the cruise. Nice ride.

[sccacuda]

Sounds as if it might be a voltage issue. You can do a quick voltage drop test on the power and ground at the pump when this happens. Where are your power and ground feed coming from to the pump?

[rickpaw]

Sounds as if it might be a voltage issue. You can do a quick voltage drop test on the power and ground at the pump when this happens. Where are your power and ground feed coming from to the pump?

The power for the pump comes from a 30A relay fed by battery. The ground connects to frame rail.

[rickpaw]

did you change the filter/regulator or just check it for being clean? I think I'd look there first. I sat in traffic at CTC for hours and never had any issues with my FAST system with an in-tank pump(all spectra parts) on my 70 Camaro. Exhaust runs pretty close to the fuel system on the passenger side and my tank is vented also. Sorry you had problems at the cruise. Nice ride.

I just checked the filter/regulator for debris. I/we had fun at the cruise. Our group all had issues one way or another on the trip to/from the cruise.

[sccacuda]

The power for the pump comes from a 30A relay fed by battery. The ground connects to frame rail.

I would still test for a voltage drop at the pump when this occurs. You said the A/C was on high when this is happening which makes me believe it's voltage related. Your fan is probably wired to come on with the compressor, combined with the blower motor, etc, your pulling a pretty good amp load when this occurs.

[Ollie8974]

Is the fuel system dead head or return. If dead head the system is vapor locking. Need to have a return style fuel system with AC. .

[rickpaw]

I would still test for a voltage drop at the pump when this occurs. You said the A/C was on high when this is happening which makes me believe it's voltage related. Your fan is probably wired to come on with the compressor, combined with the blower motor, etc, your pulling a pretty good amp load when this occurs.

It's possible, but will the voltage drop immediately if the AC was on along with the fans? I was able to drive 160 miles before it happened, both trips from/to Houston. The other exceptions are stop and go traffic during the cruise.


Is the fuel system dead head or return. If dead head the system is vapor locking. Need to have a return style fuel system with AC. .

I have a corvette filter/regulator installed next to the fuel tank. Basically it's a copy of C5 fuel system. The filter/regulator has a return line back to the tank.

This afternoon I ran the car in the driveway with the AC on full blast, weighted the gas pedal down so the engine revved to 2500 rpm (cruise rpm when it happened). Obviously there's no load on the engine since the car was just sitting. Ran the car for 30 mins with the hood closed. Got it pretty warm to the point of the coolant overflow was puking, temp got to 242. Everything in the engine compartment was hot, but the fuel pressure showed a steady 58 psi. I think that's just ruled out vapor lock.