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914World.com _ 914World Garage _ Is it needed for FI guys to let the fuel pump prime before start
Posted by: carcus Sep 20 2017, 10:47 PM
Just wondering. I have Bosch FI at Colorado altitude. My car will not start up right away unless I turn the key and wait about 10 seconds for the fuel pump to prime. All plugs and wires new, new fuel pump, and fuel filter. Moroso electronic conversion. New battery. I try to drive the car once a week. Just looking for advice. Car is a 1976 2.0 with 1973 2.0 engine. OEM fuel injection.
Posted by: Mikey914 Sep 20 2017, 10:52 PM
Pretty normal if not driven daily.
At least in my experience
Posted by: Mblizzard Sep 21 2017, 07:09 AM
Best way to tell is to add a fuel pressure gauge and see how quickly the pressure builds on the rail side.
With the D-Jet it is always a good idea to be able to establish you have sufficient fuel pressure. Easy job to add to the fuel line in the engine bay.
Posted by: McMark Sep 21 2017, 07:31 AM
If you listen carefully, a lot of new cars will run the fuel pump for a few seconds when the driver's door is opened in anticipation of starting the car.
So it's normal, not just for our cars, but for all FI cars.
Fuel pumps should have a check valve to keep pressure from bleeding off quickly. I test drove a car yesterday before I left the shop, and now 15hours later it's still got full pressure in the lines. Almost none has bled off. This makes the next startup easier (without priming the pump). But if your system is bleeding off pressure over a couple hours or worse, then you'll have more need for priming the system before starting. If it is bleeding off, you may need a better quality pump (some cheap ones don't include the check valve) or you can possibly add an inline check valve. Just make sure the check valve is a bit oversize to avoid possible flow restrictions.
Posted by: AndyB Sep 21 2017, 07:40 AM
On the 1.8 liter the pump doesn't start pumping until you turn the ignition. On the 2.0 the pump will prime once the key is turned to the on position. I added a hand throttle from Tangerine Racing since the L-jet is picky sometimes.
Andy
Posted by: BeatNavy Sep 21 2017, 08:00 AM
But if your system is bleeding off pressure over a couple hours or worse, then you'll have more need for priming the system before starting. If it is bleeding off, you may need a better quality pump (some cheap ones don't include the check valve) or you can possibly add an inline check valve. Just make sure the check valve is a bit oversize to avoid possible flow restrictions.
Mark, I have a rebuilt, standard 3-port FI pump. Are those SUPPOSED to have a check valve, internal or supplemental on the line? My pressure does bleed off pretty quickly. I have the 2-port Bosch replacement ready to install whenever I get around to it. I want to simplify my fuel line routing in addition to possibly getting more reliable pressure on startup. I know this has been discussed a couple of times before, but I'm not clear about whether I have or need a check valve.
To the OP: I have found that cycling the key 2 or 3 times to build pressure, and depressing the accelerator while cranking (which I didn't realize was normal procedure on our cars until recently), results in it immediately firing up. If I don't do that, it has to crank for 3 to 5 seconds. In either case, I also have to feather the throttle, usually once, about 5 seconds after it fires up, otherwise it'll quit. Just once, like clockwork. Then the FP seems steady after that.
Posted by: McMark Sep 21 2017, 08:46 AM
Right in the middle of the picture is the check valve (and overpressure bleed off). BUT there are a couple of o-rings on that little guy and they can get sticky over time, so it's not uncommon for them to not be working correctly. And these may not be appropriately addressed in the rebuilds.
Posted by: 76-914 Sep 21 2017, 10:09 AM
I have 76 2.0 that I start every week or two. Turn the key on then depress the gas pedal two times holding it to the floor while cranking. Mine starts within 1-2 seconds. 
Posted by: Dave_Darling Sep 21 2017, 11:11 AM
I don't think that valve in the photo is a check-valve to maintain pressure in the system. It is in the return line, not in the supply line. Remember that the high-pressure part of the fuel loop goes from the fuel pump to the fuel pressure regulator, then dumps back into the tank with essentially no further restriction. The return port on the pump is Y'd into the return line, but there should not be much pressure in that line regardless, so the valve shown is not relevant.
The rotor and pucks of the pump body serve as a check for fuel trying to flow back through the pressure line to the tank. The fuel pressure regulator serves as the check valve on the other end. Either could allow fuel to bleed past; I am thinking that it is more likely to happen on the pressure regulator side than the pump side, but that really is a guess.
BTW, the "key on and off a few times" does not work on an L-jet car. The L-jet pump, as stated, only runs when the starter is cranking or the engine is running.
--DD
Posted by: andreic Sep 21 2017, 02:06 PM
I have an L-Jet on my car and it behaves as you just described, just that after not starting the car for a day or two (or more) I need to first crank the car for a few seconds, let it sit 10 seconds, then crank again when it starts right up. I also suspected pressure bleeding back into the tank, but never tested it with a gauge on the rail or diagnosed where the bleeding happens. It's on my list of things to do. (I posted a very similar question a couple of weeks ago on this forum.)
My pump is a brand new Bosch, so I guess I'll start with the pressure regulator valve at the other end. For a while I also worried that maybe one of my injectors has a slow leak (which would also bleed pressure). Not sure how to check for that (or for the regulator valve for that matter).
Posted by: brant Sep 21 2017, 02:52 PM
yes and no
I have taken a few 3 port pumps apart
the rubber nipple (not shown in the photo) gets sealed shut by the spring pressure
when the rubber fails (40 years old, and has failed on mine) the valve is no longer sealed...... then it becomes an internal leak that allows the pressure to bleed off
so in a way it is a dual purpose valve
1) to be a blow off for return
2) to also function as a check valve to allow the system to hold pressure when not running.
I repaired my rubber nipple with one from a core pump (also a used piece of rubber)
the car then started perfectly as it used to on the first crank....
that lasted about 3 months and then the used rubber failed also. Now I am currently priming my system by turning the key 3 times after the car has sat overnight
I intend to install a 2 port pump at this point and eliminate this failure
brant
I don't think that valve in the photo is a check-valve to maintain pressure in the system. It is in the return line, not in the supply line. Remember that the high-pressure part of the fuel loop goes from the fuel pump to the fuel pressure regulator, then dumps back into the tank with essentially no further restriction. The return port on the pump is Y'd into the return line, but there should not be much pressure in that line regardless, so the valve shown is not relevant.
The rotor and pucks of the pump body serve as a check for fuel trying to flow back through the pressure line to the tank. The fuel pressure regulator serves as the check valve on the other end. Either could allow fuel to bleed past; I am thinking that it is more likely to happen on the pressure regulator side than the pump side, but that really is a guess.
BTW, the "key on and off a few times" does not work on an L-jet car. The L-jet pump, as stated, only runs when the starter is cranking or the engine is running.
--DD
Posted by: Rand Sep 21 2017, 03:24 PM
Ten seconds makes no sense. If a pump took that long to prime, it wouldn't be able to keep up when running. I must be lucky because I've had 4 914s with Djet that all started promptly.
Posted by: JamesM Sep 21 2017, 10:40 PM
Just wondering. I have Bosch FI at Colorado altitude. My car will not start up right away unless I turn the key and wait about 10 seconds for the fuel pump to prime. All plugs and wires new, new fuel pump, and fuel filter. Moroso electronic conversion. New battery. I try to drive the car once a week. Just looking for advice. Car is a 1976 2.0 with 1973 2.0 engine. OEM fuel injection.
10 seconds of cranking or turn the key wait 10 seconds and then crank? Key on without cranking the pump should only run for roughly a second or two.
If you are talking about 10 seconds of cranking try cycling the key on/off a few times before you attempt to crank. If after cycling a few times the car start immediately upon cranking than it is most likely due to you not holding pressure in the fuel rail properly. If it still takes a bit of cranking to start you have other issues to address.
A properly working d-jet car should start on the first crank without touching the pedal. I had my 1.7 in Colorado last week and was doing exactly that, didnt even need to be in the car to start it.
Posted by: falcor75 Sep 21 2017, 10:50 PM
Get a pressure gauge and install it on the rail before the fuel pressure regulator and check the pressure after turning the key on only once.
My car is converted to a 2-port pump but the pump only runs for 2 seconds and achieves my set 3 bar pressure easily. (EFI not Djet)
Posted by: BeatNavy Oct 19 2017, 05:53 PM
that lasted about 3 months and then the used rubber failed also. Now I am currently priming my system by turning the key 3 times after the car has sat overnight
I intend to install a 2 port pump at this point and eliminate this failure
brant
Brant (and all) - just reviving this thread. I finally installed the 2 port Bosch pump and ditched the 3-port. It was good to simplify fuel line routing. More importantly, the car fires up within a second or two of cranking without repeated "priming" the pump. It also doesn't die without the initial feathering I had to do immediately after start up previously. I think that old 3-port was starting to get sketchy during normal operation, too.
Don't be afraid to dump the 3-port.
Posted by: DM_2000 Oct 20 2017, 06:28 PM
I have 76 2.0 that I start every week or two. Turn the key on then depress the gas pedal two times holding it to the floor while cranking. Mine starts within 1-2 seconds.
Having an engine rev at start up is very hard on bearings since there isn't any oil pressure.
Also, unless the engine is brought up to operating temp ( driven ) for 15 or 20 minutes, weekly starting / run for 5 min is doing more harm than good. Oil becomes contaminated with fuel from cold starts / moisture builds in the oil and exhaust system. ( Water is a by product of fuel combustion )
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