Bleeding Injectors – or not?
 

Hi – I replaced the fuel injectors on a 1982 930 stock 3.3 with new ones as part of winter maintenance. As recommended by RARLYL8T the steel lines were removed during the process to avoid bending them. When back together the system and control pressures were checked, and all is in spec. No leaks. I ran the fuel pumps to check control pressures by disconnecting the plug at the back of the air mixture thingy, vs jumping the pumps at the relay. I did not activate the plunger / sensor plate and gave no thought to priming the lines and injectors. Continued on with the other regular maintenance items and got 'er ready to go, anticipating that spring will arrive someday.

I don’t want to start the car until it's ready to drive, and last night we were at -20 celcius with lots of snow on the ground, so that’ll likely be another 5 weeks.

Now for today’s dumb question; will the car be unlikely to start unless the injectors are primed? There appear to be two schools of thought on priming. When the sun finally shines I want to be ready to fly, so if stuff has got to come off to access the sensor plate now's the time.

Quick opinion from the experts?

Thanks….Denis

Just push the plunger down till you hear the pumps run and the injectors scream. You'll understand what I mean by scream once you hear it. At that point you'll know fuel is at the injectors. Don't over do it or you'll flood the cylinder. Just a little high pitched squeal once or twice and you should be fine.

You might consider leaving them alone if the car won't be started for a few weeks. That way the engine will have to turn over a few extra times (building oil pressure) while the injectors prime.
Just a thought.

So the injectors will prime by turning the engine over - it'll just take a little longer for fuel to reach the cylinder. Correct? No air lock?

Thanks

I was raised in the south end of Halifax, where you at? Philip

Philip; I'm in St. Margaret's Bay. Wishing I was in Costa Rica this time of the year. :cool:

The injectors do not need to be primed. I've had the system completely apart, put it back together and on, turned the key and it fired within five seconds. This was with no priming/bleeding done whatsoever.

The engine does not need to be cranking to flow fuel to the injectors. As Mr. Turtle suggested, push down the mixture adjusting screw or take off the air box and push down on the metering plate until the pumps start to run. That will flow fuel to the injectors.

Thanks guys for the replies. I will try the cranking method when the weather gods say it's time to go. This has been a brutal winter and the 930 is my reminder that summer cannot arrive quickly enough.

I've had it both ways. After putting my engine back in last month it wouldn't start for anything. After checking a bunch of stuff I started to think about dropping it back out to check my cam timing. As a last-ditch I decided to get the pumps running and push on the plate for a couple of seconds to see if the injectors would squeal. Nothing. Couple more seconds, squeal. Try to start it, bingo.

Gotta push it down far enough to open up the ports in the fuel head. How far that is I don't know for sure, but when that bieatch squeals, you've got her attention!

You mention pushing down till pumps run?
So is the ignition on when you do it?
but how can they run unless motor is cranking?

Robby, the ignition is on, then whether the pumps start right away depends on the plug into the microswitch on the top-back of the fuel head. It detects if the plate is moving, i.e. air is flowing over it. Safety switch to stop the pumps if the engine quits in an accident.

Normally the engine turning over is enough to deflect the plate far enough to turn on the pumps as well as move the plunger enough to flow fuel to the injectors as Mark said. My theory in my case was that some air in the system was causing enough back pressure on the plunger that just turning it over didn't move the plate enough. Manually pushing it further down got the fuel moving and pushed any air out. She has started right up ever since, not that I've been able to drive across the frozen tundra.

By the way, my cold start valve is disabled. If that had fired it probably would have got it running the first try.

I'm talking about the CO adjustment screw/plunger. That way you don't have to take your air filter off to push the plate. Turn key on, walk to back of car, push down on adjustment screw. First thing you'll hear is pumps coming on. Push a little further and you will eventually hear the injectors scream. It could take a few seconds before the injectors scream as you push the air out.

Not what you are asking but...
I'd check the flow and spray pattern of injectors now that you have them out. It is simple and good for peace of mind.

Great feedback with options, thanks all. I'll try mild cranking and if not successful will revert to DSP's suggestion.

Jsveb, I couldn't find evidence of the injectors having been cleaned or replaced in the service history (32 years), so am anxious to learn whether brand new ones will offer a noticeable performance advantage.

I wasn't directly referring to performance gains, but rather check that you have equal flow to all cylinders; identifying an individual cylinder being too lean.

This would also help identifying if the fuel head is not longer in spec.