Question after replacing fuel filter and accumulator
 

After replacing the fuel filter and accumulator, is there any particular procedure that I need to follow? I presume just allow the fuel pump to run for a minute or two to bleed the system of air from the new units? I'm asking cuz I'm a wrench dummy. TIA

Remove the air filter from the intake. Turn on the ignition and gently press up on the plunger inside the intake. You will then hear the fuel pump run, and within a few seconds, a vibration/squeal of the injectors spewing fuel. As soon as you hear the injectors, release the plunger. Your system is now primed and ready for starting.

Pressure test.........
 

Running the FP for a minute or two after the removal of the fuel filter and accumulator is imperative. Not only getting the system pressurized but for checking for fuel leak/s before attempting to run the motor.

Tony

Thanks vm.

On my '79 911SC, I am of the impression that by turning the ignition one click, the fuel pump will run, regardless of whether I press up on the plunger ... am I wrong?

Yes, you are wrong--if your SC is operating correctly.

From '76 onward, the cars were fitted with a fuel pump relay which functioned as a safety precaution should the engine die. That set up, which you should have, only allows the pump to run when the plunger in the intake is raised from its stop, as when vacuum from the engine moves it upward. CIS engines prior to '76 did not have the relay and the pump would run as soon as the ignition was in the RUN position.

On your car, the pump should not run with the ignition switch in the "Run" position. If it does, either someone has disconnected the Air Flow Sensor switch in the engine compartment, or the relay/relay circuit is faulty.

Thanks L.J., I will check this week

Hi Tony: reviving this old thread. I completed my fuel filter replacement yesterday, so coming back here to this post that I bookmarked for procedures for fuel pressure/priming and leak detection.

If I follow the procedure described in the post above, and run the fuel pump as you describe below for a minute or two, where's all that fuel going -- flooding the cylinders? Is part of the procedure after running the FB for a minute or two, to wait it out for the fuel to evaporate? One ~ two min seems like a long time, with loads of fuel delivered? I must be missing something.

Would appreciate your further guidance here.

Thanks!

Hi; just throwing this out for consideration. I'm no CIS guru, but am inclined to think the CIS fueling architecture would be similar as my 3.3 turbo. There's a blue electrical plug on the back of fuel head that if disconnected will allow the pump (2 on my car one on yours) to run with the key in the run position, with the excess fuel returned to the tank. I unplug this when testing the WUR circuit, or fuel pressures, or when replacing and priming the fuel filter. Plug it back in and when you turn the key no fuel as per the guidance you are getting until the engine fires. I would be hesitant to play with the plunger for anything more than a few seconds for fear of locking up the engine with raw fuel. Tony knows his CIS stuff, and while I should not speak for him, I expect he assumed you were disconnecting this blue plug first.

My 2 cents.

Cheers....

CIS Troubleshooting..........
 

Jonathan,

Running the FP without running the motor will only deliver the fuel back to the tank. So you could run the FP for an extended period of time without worry flooding the cylinder/s provided the fuel distributor is not leaking. As long as the FD plunger is at rest (all the way down), fuel will NOT be delivered to the fuel injectors unless the FD is defective and leaking.

In your case, running the FP for a minute or 2 after working on your fuel line system is a prudent way to test for fuel leaks. You don’t want to run your motor with a fuel leak. The one-minute or 2 pressure test will allow you to inspect and look around for any fuel leak that you might have missed earlier.

I try to avoid or limit injecting raw fuel to the combustion chambers by lifting the FD plunger. But if you do, 1~2 sec. is more than enough time you need to purge the air in the fuel injector lines.

Tony

There is a good posting about a FP relay jumper you can leverage in your fuel charging efforts

Thanks for chiming in Daytona. Looks like your thoughts are correct, consistent w what Tony (the CIS guru) just mentioned in his reply to my post.

Thanks for your detailed response, Tony. Much appreciated. I will proceed slowly w caution make sure there are no fuel leaks.

FD Plunger - where/how?
 

So, I got back into the engine bay this AM, and drained the engine oil. Only 1 QT drained from the side tank, and ~ 7QTS from the engine case --- total 8 QTS.

While waiting for the oil to drain, I removed the air filter to look for the FD plunger, and see how it moves/works --- up/down as Tony described.

FAILED!!! Don't know what I'm looking at, or what to look for. What does the plunger look like? I took some fotos. Can someone point me to it in these fotos? Much thanks!!!

http://forums.pelicanparts.com/uploa...1679859523.JPG
http://forums.pelicanparts.com/uploa...1679859523.JPG
http://forums.pelicanparts.com/uploa...1679859523.JPG

Also, while removing air filter, I noticed this piece was wobbling/loose. What is it, what does it do, and should I secure it?

http://forums.pelicanparts.com/uploa...1679859523.JPG

Is this the FD Plunger?
 

I returned to the engine bay, and re-inspected inside of the airbox. Found that this lever moves up/down. Default is down. I can push up, and loaded spring automatically pushes back down to normal state.

Is this the FD Plunger that Tony mentioned?
https://www.youtube.com/watch?v=lo7nS-wsxO0

See if this helps you visualize. The plunger is right next to the 5 and is not visible in the airbox, from memory. The arm you moved up and down in video goes up moving the plunger. Plunger up increases fuel. Sensor plate up increases air.

http://forums.pelicanparts.com/uploa...1679865218.jpg

This also helps visualize

https://youtu.be/a4fJAfXYxWk

Hi SkiVT - thanks for posting the video and the diagram/image. It does help me visualize where the FD Plunger sits. If I interpret correctly, the plunger sits pretty much in the center of the FD unit, and not visible inside the air box (view obstructed by the lever arm) --- is that correct?

Now, as I showed in the video I posted, I can only pull the lever down, but cannot push it up. So, then how do I execute procedure that ossible described in Post #2 above? I'm a bit confused about this --- this is really a big level up for me in terms of wrenching. So, appreciate the support and understanding here.


Post # 2 from Ossiblue above:
"Remove the air filter from the intake. Turn on the ignition and gently press up on the plunger inside the intake. You will then hear the fuel pump run, and within a few seconds, a vibration/squeal of the injectors spewing fuel. As soon as you hear the injectors, release the plunger. Your system is now primed and ready for starting."

I assume I am not pushing up on the actual plunger, but rather pushing up or pulling down on the lever?

Thanks!

You push the lever up from the same spot you pulled down. If it doesn’t go up you got problems. The plunger can get stuck but it’s not really common. When you push the lever up, you feel some slight smooth resistance then remove your hand and it should fall back to resting position. I didn’t see if your engine was running fine before and you were replacing parts or had some other problem. If the plunger is actually stuck, no way i can see an engine running.

Hi SkiVT--- really appreciate your follow ups here, particularly on a Sunday. I searched/watched a few more videos on YouTube, then dove back into engine bay.

This time, instead of pulling that lever down, I gently pushed it up using gradual increasing effort. It broke loose and went up. After that first time, the lever freely moves up w minimal, barely any effort, and drops down by gravity with no resistance. I think it did get somewhat gummed up, but was able to break free. I hope that doesn't indicate signs of gumming up elsewhere.

I wonder if there's a way to verify/validate if the FD plunger is also moving freely, without removing the FD?

Yeah, the car sat for 2 ~ 3 years. I've been doing little projects, getting it ready to start the engine, then take it to get smog'd (SoCal here) and then registered, and back on the road.

- installed new battery
- drained fuel tank, and installed new tank screen/filter
- installed new fuel filter
- changed the oil today

Next weekend, I'll add a 12oz bottle of Techron Complete Fuel Cleaner (Concentrate Plus) then a few gallons of fresh fuel. Then, run the fuel pump testing and fuel pressure priming, and leak detection procedures. If all goes well, the, will attempt to fire up the engine!!!

Pictures of the FD plunger/piston.......
 

Below are some pictures of the FD plunger/piston:

http://forums.pelicanparts.com/uploa...1679886345.jpg

http://forums.pelicanparts.com/uploa...1679886345.jpg

http://forums.pelicanparts.com/uploa...1679886345.jpg

http://forums.pelicanparts.com/uploa...1679886345.jpg

It is difficult to get a good look at the FD plunger with the fuel distributor installed on the AFM (air flow meter). You will need a remote camera to view the bottom section of the plunger if you have the PF installed on the AFM.

If you want to test the upward and downward movements of the plunger, use the lever arm and watch the plunger drops down to its rest point. Removing the FD from the AFM is so far the best method for inspecting a FD.

Tony