924Board.org

[Ralf]

Hello everyone,

I have a 924 2.0 (EU), naturally aspirated, from 1983 which does not start. It ran before (poorly), but I died and did not start ever since.

When cranking, the car smells like unburnt gas and I hear no sign of ignition. I am methodically examining the patient (see list below), but so far no conclusive diagnosis to find the root cause of the problem. I really would appreciate your advice where to look because I’m running out of ideas, honestly.

Any help is welcome. Thank you for your advice!

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What I have tried so far (fuel, ignition, air and compression):

** FUEL **
Tank. Starting my investigation from the tank. It’s filled with 15L or so with fresh gas.

Fuel pump. The car apparently has two fuel pumps, connected one after the other (‘in series’). No idea if this is the original design, but I took them off the car, tested them by pumping fuel from a bucket and then installed them back into the car.

Accumulator. The accumulator was leaking a bit from the screw at the bottom so I replaced it with a new one.

Fuel lines. I used compressed air to ensure both fuel lines (supply and return) are not clogged.

Fuel filter. Replaced it with a new one.

Fuel distributor. Disassembled it, cleaned it and installed it back on the car. Mixture screw (i.e. the CO-adjustment) setting is difficult to set correctly without a running engine, but I get 4.5 bar fuel pressure to the injectors (see below) which I tells me I should be able to get at least a running engine.

Air flow sensor. Operates freely when I move the value manually (with the air filter removed).

Fuel system pressure. I measured the system pressure, it reads 4.5 bar when cranking the engine. After cranking, the pressure drops to 2.2 bar, and the accumulator keeps it at that value for a long time. My conclusion would be that the system pressure is ok. The set up that I used is identical to what is described here on Youtube: https://www.youtube.com/watch?v=H1UP-CyRcs4&t=711s

Warm up regulator: Disassembled it, cleaned it and installed it back on the car. I can’t really tell if it works once the engine is hot because, well, I need a running engine first. Given that the fuel system pressure looks ok for a cold engine, I'm ruling out the warm up regulator for now.

Auxiliary air value. Disassembled it and tested it. It’s open by default. To test it, I applied 12v directly from the battery. Result: It closes after a few minutes. Installed it back on the car. Seems ok.

Cold start valve. Removed it from the car and when 12v is applied, it sprays fuel. To rule out the thermo-time switch, I tried starting the engine with the connector removed and also with 12v applied directly from the battery. Does not make a difference: Car will not start.

Secondary start valve. This is the electrically operated valve mounted on the fuel distributor. I tried cranking while disconnecting it, I tried cranking while applying 12v on it, it makes no difference.

Fuel pressure to the injectors. Reaches approx. 4.5 bar after a few seconds of cranking. The exact value depends on the mixture screw setting, but 4.5 bar but should be enough to let the injectors spray fuel.

Injectors. Removed them from the engine, cleaned them using a hose full of fuel and compressed air. Visually checked that they do not start leak when a bit of air pressure is applied. Secondly, I checked that they start spraying when enough air pressure is applied, to make sure they are not clogged. Installed them back into the car.

** AIR **
Air intake: Air intake path is open, no blockages.

Vacuum: No obvious vacuum leaks or lose vacuum hoses.

** IGNITION **
Hall sensor. When measuring with an oscilloscope, the Hall sensor gives a waveform as expected (looks like a cotangent graph).

Transistor ignition unit. Has been checked by an expert. Hard for me to measure, but I trust his judgement.

Ignition coil. Is new, NGK U1065.

Distributor. New rotor and new cap.

Timing. Is hard to adjust without a running engine, but I’m taking 10 deg before TDC as a basic starting point. I used a stroboscope to confirm that I have an ignition voltage going to the spark plugs.

Ignition cables. Are new.

Spark plugs. Are new, I used NGK BP7ES. When I remove one and crank the engine, I see the spark.

** COMPRESSION **
Compression reads approx. 1200 kpa, same on all 4 cylinders.

[morghen]

Hello, i can offer you an engine management system that replaces the injection and ignition system of the 924. It looks very very close to the original.
Have a look on my website and let me know if you’re interested.
I also offer full support during installation and after and guarantee that your car will run properly within a weekend of work.
_________________
Supercharger and EFI kits
https://www.the924.com

[924RACR]

I'm leaning heavily on the side of getting some ignition working.

You've done a very good job IMO of really hitting all the things.

One concern; your control pressure should be more like 2 bar than 4.5, I should think, even while cranking. This is with the valve in the pressure tester open, right? So it could well be that the warm-up regulator needs adjusting all the same - as you've checked the fuel return line to the tank is not clogged, correct?

There's another really good recent thread here about adjusting the regulators...

So that could be causing/very badly exacerbating your flooding condition. Cranking the car with the throttle pinned wide-open should help clear that...

But I'm still suspicious of ignition. Given you've checked all the bits and confirmed that it's sparking while cranking, that checks out most of the system, only option might be timing adjustment.

When putting one of these together and trying to get the first start, before it runs enough to set timing, sometimes we have to try moving the distributor around to different timing points, try cranking there, and again, until you get it to fire.

Again, especially with the flooding wide-open throttle (WOT) will help in this state...
_________________
Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

[Ralf]

Thanks for your advice 924RACR. It looks indeed like my engine is flooding, given that everything smells like gas and no signs of any ignition at all.

I can confirm that fuel return line is open. I tried starting the car with the throttle wide-open, but that doesn’t help, unfortunately. I’ll follow your advice and look at the WUR again. Back soon!

N.B. I see that I wrote ‘system pressure’ above while I meant ’control pressure’. Sorry, my bad.

[morghen]

Remove all sparkplugs, disable the fuel pump and crank the engine for a few seconds to clear all fuel in the cyls.
Dry the sparkplugs properly in the sun for a couple of hours, degrease them if needed.

Check that the engine timing is on point, cam and crank.

Then put the crank at tdc for cyl1 (engine at the signs)

Loosen the ignition distributor and remove the cap.
Rotate the distributor housing so that the plastic rotor will point directly at where the ignition lead that goes to cyl1 will sit when the cap is back on.
Tighten the distributor and put the cap back.
Check that the next slots on the cap take the leads to cyls 3,4,2.

If you do this, the ignition will be set at 0deg. It should start like this as well if you have decent fueling.
You may need to hold it running with the throttle open, but it will run.
Once it started, you can rotate the ignition distributor counterclockwise about 8-10deg and it should be at its proper place.
_________________
Supercharger and EFI kits
https://www.the924.com

[Ralf]

Finally some good news. Last night I got the engine running for the first time.

The suspect was a wrongly calibrated WUR causing the engine to flood, so first thing to do is to connect a gauge to read the control pressure. Unfortunately, the nipple on one of the fuel lines to the distributor snapped off in the process. Ugh…

There are many instructions online to make the WUR adjustable while installed in the vehicle, but my intention is to keep things original, tune the WUR, get the car running and then take it from there.

With the fuel line repaired and the gauge in place, the next thing to do is to remove the WUR from the car and recalibrate it. Even though calibration of the factory-original WUR is not described in the Porsche K-Jetronic workshop manual (or in Haynes), this is actually possible.

MRC Technics in Belgium only not sells K-Jetronic revision kits, but they also provide excellent documentation for the revision and calibration process. Highly recommended reading! Download here: https://mrc-technics.com/downloads/. The 3 PDFs are in Dutch, so use Google Translate if needed.

Once the WUR housing is open on the workbench, the pin that holds the bimetal strip and heating element are visible. As a starting point for the calibration, the pin needs ‘pushed out’ (with a hammer) such that the end is flush with the WUR housing. This feels like brain surgery with a hammer.

Somehow, after reinstalling the WUR in the car, I still read a control pressure of 4.5 bar while cranking (??). However, after some fiddling with the timing and the fuel mixture, the engine finally starts. Huge progress !

Any thoughts on the readout of the control pressure? I did not expect the same value….

[morghen]

I also fiddled with the WURs at one point, they have to be individually calibrated, the operation is not really repeatable from wur to wur, you need to adjust it until yours provides the specified pressure, and then hope it stays there, otherwise you have to do it again.
Even so, chances are that it will be perfect cold and not perfect when warm, or the other way around, as not only the range moves, it also seems to scale a bit so its an analogic hunt for the best compromise.
_________________
Supercharger and EFI kits
https://www.the924.com

[Legitimate Salvage]

I was having major issues with my WUR (system pressure and control pressure were practically equal). I opted to try the UTCIS-V from https://unwiredtools.com/utcis-v.asp. The difference was immediate and noticeable. Cold and hot starts aren't a real problem any longer. The car would idle (and idle more smoothly). Acceleration was much improved. The car didn't feel like it was fighting itself to accelerate. It's much more pleasant to drive now.

The WUR was not my only issue, but it made the single largest positive difference in how the car runs.

I know there are several threads here regarding poor communication, service and products from unwiredtools. That was not my experience, however.
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1979 924 NA - AKA the Mid-life Crisis
2012 Audi A3 - The Daily
1991 MB 300D
1984 MB 300D
1966 Mustang I6