Fuel System Validation Test - Milestone Complete

[OwnerCS]

Today's restoration project activities mark the completion of the fuel system connectivity testing and high-pressure validation milestone. The system was pressure cycled 5 times (ignition switch on to deliver 40 lbs of fuel pressure) over the course of an hour to check for any line or the slightest injector nozzle seepage. A blue shop towel was placed under the injector nozzles to capture and show the slightest amount of fuel seepage. The fuel line hose connections have been double clamped to provide additional protection.

The area outside of the system (including area under FI nozzles) was completely dry after an hour of testing.

Some pictures of the process are listed below.

[qship96]

I assume you kept an eye on the fuel pressure gauge to make sure it held the pressure at the end of your 1 hour test to show there was no leakdown internally also?

[OwnerCS]

Thanks Qship for the tip. New Nissan OEM pressure regulators were installed with the new injectors.

Findings are listed below.

1) During initial "switch on" tests pressure jumped to a high point of 43 then slowly drifted down to zero over the course of 10 to 11 minutes -- hence the 5 cycles over an hour. When the fuel pump automatically shut off after 3 to 5 seconds, pressure started to release. Shutting the key off after 2 seconds produced the same results.

2) When the return line was clamped off, pressure jumped up to 60. Pressure slowly dropped to 50 in approximately 15 to 20 minutes then stayed at 50 for over 30 minutes -- which was longer than I cared to monitor it..

3) Clamping input line on the engine side of the pressure gauge produced a 60 reading. After releasing the clamp on input side and next on the return line allowed pressure drop to 34. Pressure was then maintained at 34 for over 20 minutes which was longer than I cared to monitor it..

4) Clamping only the return line allowed pressure to jump to 60 then slowly drop to 50 like scenario #2. After maintaining 50 for 10 minutes, I slowly released the return line. Pressure dropped to 34 like scenario #3. However, in this scenario, in approximately 40 minutes pressure slowly settled down to a low point of 25.

It seems to be a predictable pattern for pressure to decline fastest when the fuel pump automatically shuts off or the ignition switch shuts off current to the fuel pump. When the return line was closed then opened after 30 minutes, pressure was maintained at 34 for over 20 minutes. After 40 minutes, pressure finally settled down to 25. After an hour pressure is still sitting at 25.

If I recall correctly, the pattern found in scenario #1 is like the pattern found in a test that was conducted before the injectors and regulators were replaced.

What do you think about the tiered pressure points that I'm seeing?

[3Q Jay]

pressure of 45 when engine off (no vacc to regulator) is normal. you will see this again when engine running: idle vac, fp reads 38. blip up the throttle and it goes to 45 as vacc reduces on the reg (can alsoverify by pinching off the line while running).
i see you used the parts store style clamps with the 7mm hex heads. that can be particularly useful when you do the re-tightening ritual after afew weeks of thermal cycling.
visualise where the clamp hex's will be after upper spider is installed and position them for access later.

[3Q Jay]

btw, meant to ask about your fuel tee. is it 5/16? i have found 5/16 tees very difficult to find. i have a 5/16 on the '95 as a permanent install. i also have a 3/8, but i don't want to permanently stretch my hoses.

[OwnerCS]

btw, meant to ask about your fuel tee. is it 5/16? i have found 5/16 tees very difficult to find. i have a 5/16 on the '95 as a permanent install. i also have a 3/8, but i don't want to permanently stretch my hoses.

Thanks for the idea about checking the clamps for post installation accessibility. I did need to adjust a couple.

The T came with the Fuel Injection Pump Testing Kit from Harbor Freight. It supports both hose sizes.

http://www.harborfreight.com/fuel-injec ... 92699.html

I like the hose clamps because of the rounded contact edges and the inner shield to keep the hose from being pinched or damaged during on high torque application. The doubled clamps should provide a backup in the event one of the clamps fails.

The short hoses that connect to the regulators and return feed are R9, R10, and CARB approved MPI 180 lb Multi Fuel capable for Ethanol, Methanol. E85, Diesel, Bio-diesel, Gasoline, and Sour Gas. The OEM hoses from fuel filter and return line look different than the originals as the white line is painted.

[Q451990]

This TSB shows Nissan's idea of what is normal bleed-down on the fuel system... I think that part starts on page 6?

https://docs.google.com/viewer?a=v&pid= ... y=CJHR2qkF

[OwnerCS]

Thanks Heath - Good information for sure. No leaky injectors here.. I have a "new in the box" fuel pump and two FPCUs. Though the old pump is quiet compared to the other cars.