genikz

Hi Folks,

I've been working with Michael (Black28) and my brother on a '78 928, bringing it back to life after years of neglect.

Here's what we've done so far:

• Cleaned fuel tank
• Replaced in tank fuel strainer
• Replaced fuel pump
• Replaced fuel filter
• Replaced rubber fuel lines up to accumulator
• Rebuilt fuel distributor (new o-rings)
• WUR looks recently replaced; but we cleaned the screen since it got contaminated a bit from junk in the lines.
• Checked control pressure (within acceptable range, 22psi at like 90*F I think. I may be off on the temp, but I remember it being within spec)
• Cleaned injectors
• Adjusted the air/fuel screw to full lean (CCW)
• Verified the "plunger" in the fuel distributor moves freely

When we energize the fuel pump, and it builds pressure, the injectors fire (rusty faucet sound). With the proper control pressure and the air/fuel mixture screw backed all the way out, shouldn't I get zero fuel to the injectors?

It's so bad that the crank case is probably more fuel than oil at this point. Don't panic, I pulled the plugs and haven't tried to fire it. I will wait until the fuel delivery is working properly and then i'll change the oil and try to fire it up.

Any tips would be greatly appreciated. So far I've spent three days on this issue and I'm at my wits end.

Thanks in advance!

SeanR

Is the cold start injector leaking or firing all the time?

genikz

All injectors are firing. Every cylinder is full of fuel, if I leave the fuel pump on.

Before we rebuilt the fuel distributor, we believe only the cold start injector was firing. Now you can hear all fire, and see the large volume of fuel they're spraying.

genikz

Sorry, I didn't answer your question properly. I haven't removed that injector from the plenum to confirm it's actually firing, but I can if that helps in the diagnosis.

SeanR

Don't bother, if you turn the pump on and the injectors are automatically filling the cylinders, something is way wrong in the fuel distributor. I think I read your initial post wrong. I'm going to hazard a guess and say the piston inside is stuck in the full open position. It should move freely and be at the bottom of the distributor, resting on the air flappy thingy.

genikz

That was my best guess as well. I spent all day today breaking down the intake and fuel system, and confirmed it moves freely. With the pump energized and control pressure pushing the plunger down, the large plate (what the airbox feeds) takes firm pressure to push down.

Also, with the system depressurized, I can remove the fuel line at the top of the fuel distributor and feel slight air pressure when I push the plate down. I can repeat that, so I'm assuming the plunger is moving freely and resting on the arm on the plate.

genikz

I wish I could borrow a good working fuel distributor to rule it out

SeanR

Just went out to my shed to see if I could find my good ones, and have no idea where they went. If I come across it in the next day or so I'll send it out for you to try.

karl ruiter

I think micheal said it was doing this since the rebuild of the fuel distributor. I would start by rechecking the control pressure, as my first guess would be that the pin hole in the fuel dist gasket that feeds the WUR is plugged. Zero pressure to the WUR will act exacty this way. If you dont have a pressure gauge and you are flooded anyway you can feel the control pressure on the air flap when you press it with your hand. You should feel a lot more resistance on the air flap with the pump running.

genikz

Sean: very kind of you. Thanks for checking. If you come across them, I'm happy to pay shipping + time and effort fees

Karl: Agreed. I need to borrow my brother's CIS tester again to double check everything now that I tore it apart and put it back together. Maybe I fudged something along the way. Although I do feel firm resistance when pushing the air flap down by hand when the pump is on. Strange, and maybe important, the pitch of the "howl" of the injectors does not change when I manipulate the air flap by hand. I guess that means the plunger is not moving.

I just want to figure out the actual problem before spending $100s on replacement/rebuilt parts.

EDIT: just to clarify, we checked the control pressure after the fuel dizzy rebuild. It was within spec. It's possible the WUR got clogged at this point, given the crap we found in the tank before we cleaned it.

karl ruiter

Clogged WUR would cause to opposite problem. If you are sure you have control pressure and feel resistance on the flap, then I would pull the fuel dist and take it back apart. Does not cost much of anything to do this...just a bottle of indian head shellac. If you have resistance on the flap but it moves then your control plunger is not stuck. My impression was that the car had this problem ever since the fd was opened up and rebuilt. Something probably went wrong with the installtion of the Orings or something. Lots of folks have had a hard time rebuilding these things and had to do it multiple times. I think I just got lucky last time I did one in that it worked the first time.

genikz

You're right, Karl.

I just double checked my pressures, and the control pressure is spot on (34 psi at 80*F). The issue must be with the fuel distributor. The system pressure was low, at 56 psi, but all injectors were firing of course as I tested, so it's possible that's the pressure drop.

I think I'm going to give that eBay CIS rebuilder a try. I did my best to match the sizes of the o-rings, but I must have got them wrong.

Thanks for your help guys.

genikz

And yes, Karl, this "WOT" injector issue only appeared after we rebuilt the dizzy. Prior to that, we got next to nothing from the injectors.

The air/fuel mixture screw was run in (CW) so far, you couldn't engage it anymore. I just assumed that is what was causing the issue (plunger being pushed up too high with the air flap closed). Once I took it apart and put that air/fuel mixture screw at full lean (CCW) I expected the issue to get resolved. Oh well...at least we've narrowed down the actual issue

SeanR

Those dizzy's are a pain in the *** to rebuild. I think I've managed to get 5 right the first time out of 10 I've done. Key part, and the reason I don't do them for anyone but cars I am working on at the time is due to having a test rig. Replacing the seals and cleaning is easy, getting the damn things to seal and perform right is the tough part.

If I can find out who I loaned my 'test' one out to, I'll swap ya and rebuild yours. I have no idea who might have it though, it's been a few months.

genikz

Sean: I feel your pain buddy. Very generous offer. I'll hold off on the eBay rebuild for a bit; please let me know if you track down a known good unit.

Cheers!