924Board.org

[scoper]

I have been part of the 928 community for 4 years or so. 6 months ago a car was listed for sale on a Facebook 928 group and behind it was a minerva blue 924. I asked if it was for sale too and it was. And it was a turbo! I bought it based on the color and that it would run on spray. I've been making slow progress in getting it to run by cleaning grounds, replacing the fuel filter and accumulator, cleaning out the WUR (very clean other than the screens) then rebuilding the fuel distributor and finding no spring under the center shaft. I replaced that and after back-flushing the injectors I see one of them is still leaking and 2 of them flow much less than the other 2.
For the 928, there is a popular swap of injectors to use short ones from a Mercedes CIS system - 0 437 502 047. They look similar to those in the 931, does anyone know if they work in a 931?
Should I replace all 4?
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Scott
'81 931 "Mini"
'78 928 "Orlo"
'01 986S "Viola"
'03 540iT/6 DD

[Cedric]

Injectors are a wear item on kjet, just replace them, the correct ones are readily available if you search around a bit. Then you at least know that the injectors are good, the margins to destruction are much smaller ona Turbo car, especially non intercooled, so its always good to do stuff such as fuelling as good as possible:)
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1980 924 Turbo
www.instagram.com/garagecedric/

[scoper]

I installed new injectors and I also checked the timing. I have 80 to 85 PSI with no washers on the pressure control plunger. Can I do something else to reduce the pressure? And is that why it won't rev well?
_________________
Scott
'81 931 "Mini"
'78 928 "Orlo"
'01 986S "Viola"
'03 540iT/6 DD

[scoper]

In addition to the new injectors, I removed the spring that I had put under the center shaft of the FD. This was based on guidance from a person with more K-Jet experience. As part of rebuilding the FD I replaced the o-rings on the needles for each injector port. I measured each to be 4 full rotations from bottomed out. The Hayne's manual says they should be 2.5 turns out. Does anyone know if this is true and what too far out would do to its performance? My guess is that would make it rich. I'm going to run a smoke test again to be sure there is no air leak.
It fires right up but won't rev at all when cold. Once warmed up it will rev if the throttle is modulated carefully.
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Scott
'81 931 "Mini"
'78 928 "Orlo"
'01 986S "Viola"
'03 540iT/6 DD

[Beartooth]

You'll definitely have to do something about the fuel pressure. Maybe the return line has some blockage? Also check that the plunger isn't binding, and try adding some shims (even though it seems counter-intuitive). Mine would sometimes spike the fuel pressure when I first got it going, and I never really figured out exactly why, but I seem to remember fiddling with different shim combinations and the spring eventually fixed it. On the injector adjustment you mention, is that the four allen screws under another cap-head allen screw? When I rebuilt my FD, the instructions said to measure the depth with a micrometer, record it, and reset it to that depth. My understanding (assuming we're talking about the same thing) is that it's an adjustment to match the flow between injectors, and should left as set as long as the springs and metal plates and such don't get mixed around. I suspect one could calibrate a FD by adjusting the calibration screws until the flow rates match, but it'd be pretty fiddly business; I haven't tried it... yet.

Maybe even more important, make sure your frequency valve is working. Jump the fuel pressure relay with the key off, and you should hear it buzzing. When I first got mine to run, it would idle ok and rev just enough to limp it around the block, but nothing more. One day, while I was tinkering on something else with the FPR jumped, I moved some wiring around and heard a buzzing sound from the frequency valve. I think it was a bad or disconnected ground - the lamba controller is grounded to the engine close to the throttle body. I got that sorted, and it was night and day after that: it pretty much went from undrivable to running fairly well with that, and resetting the idle set screw (which was off because the frequency valve wasn't doing anything).
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1980 931 diamond in the rough

[scoper]

Thank you for the tips Beartooth. I added more washers and the pressure went up over 110 PSI. I confirmed that the return line is not blocked. Any other ideas on what could be costing the high pressure? I sonicated the pressure control valve but that hasn't helped.
I applied 12 volts to the frequency valve and only got a spark. Can it be repaired or cleaned?
_________________
Scott
'81 931 "Mini"
'78 928 "Orlo"
'01 986S "Viola"
'03 540iT/6 DD

[Beartooth]

I can't think of anything on the fuel pressure except that maybe somebody put the wrong spring in it or something else is off with the plunger or regulator. I'd hesitate to jump to replacing parts, but there is the option of replacing the pressure regulator guts. https://www.fcpeuro.com/products/vw-audi-fuel-injection-fuel-distributor-valve-kit-3437010021#fitment should be the right thing, but it doesn't look like it comes with the main spring... Unfortunately, I don't see anywhere you can buy that; I can't find it listed or even a parts breakdown to even get a part number. If it was me and nothing would get the fuel pressure down, I'd start by going to a hardware store to see if you can find a spring that's close enough. If you get close but it's still too high, no problem because you can experiment trimming that spring and just start with a new one if you go too far. You could also trim the spring you've got - cutting off at most a half coil at a time - but I'd be hesitant on that unless I knew somehow that I had the wrong spring. One other thought that jumps to mind: maybe there's a chance that it's got too thin a crush washer where it screws into the FD; it should have a thicker washer than most of the others on the FD (like 2-3mm), and if someone put a thin one on, I'd think it'd be the same as shimming the spring. Along those lines, you could also experiment with adding a crush washer. Actually, that seems like a better place to start than messing with the spring...

On the frequency valve, it'll give a little spark if you apply 12V, which should open the valve under power. It should also make a clicking nose when you apply or remove power. You can try spraying some brake cleaner through it while powered to make sure it's not blocked and to clean it out. Once you're sure it's opening with power applied and allowing flow through, then closing when power is removed, there's the question of whether the lambda control is functioning. There's a round test connector on the left side near the firewall, and if it's working you should get a duty cycle reading (60% on a cold engine with throttle closed, if I'm remembering right) from that with power applied to the fuel pump circuit (you might want to disconnect the fuel pump so you can keep the lambda controller powered without running the fuel pump). And, as I mentioned, you should hear a buzzing sound if everything is hooked up and working correctly. It can be a game of whack-a-mole because blockages can occur and re-occur in the fuel circuits, but you definitely won't get far if the frequency valve is blocked or not being actuated.
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1980 931 diamond in the rough