924Board.org

[ted von Kampen]

This is a general question for the board concerning problems I have been encountering. I can get my 924 started. It will run for awhile at 2-3 thousand rpm. It will not idle. It will run for maybe 5 minutes, certainly less than warmup time. I have reworked the CIS, cleaned injectors, new cold start valve, reworked AAV valve and reworked WUR and calibrated. Also cleaned throttle body. Checked for vacuum leaks.

I have been suspecting ignition troubles. I ran though the procedures in the Porsche WSM and Haynes. All seems to check out. However, to get a feel for what was going on, I attached my timing light to the battery and the HV wire from the coil. This is to see if the ignition cuts out. I have observed a couple of things.
1. Timing light seems to be in rapid flash mode as suspected. After a couple minutes the flash rate changes and maybe be cutting out as evidenced by a slow down of flashes, a misfire in the engine, a backfire and it seems to bog down and finally dies.
2. it will not idle.
3. It might refire once but stops again. I am getting some flashes of the light while cranking. I have a suspicion that the ignition system is at fault. I have bypassed the EIS module (ie-plug to plug).
4. On occasion while this is going on, when the engine quits I can hear the fuel pump run, then hear a relay click and the pump run again, etc. This will keep on. When this happens, the timing light will flash once with each click of the relay. What causes this clicking relay sometimes and not others?

While I welcome comments from those who have experienced this problem and fixed it, I also have two specific questions about the ignition system.

1. Has anyone had intermittency with the Hall effect transducer in the distributor? Did changing help this out? Also, where can you get one?
2. Has anyone had problems with intermittency on the ignition power module 211905351 as mounted on the fender?
Thanks in advance for comments and help.
Ted

[Paul]

Just to make sure the basics have been checked....

Have you checked valve and ignition timing?

How's your compression?

Vacuum gauge shows steady, no ticking?

Cap, rotor, and spark plug wires in good shape?

Likely an ignition issue as you suspect.

A faulty ignition switch may be causing the last issue.
_________________
White 87 924S "Ghost"
Silver 98 986 3.6l 320 HP "Frank N Stein"
White 01 986 "Christine"
Polar Silver 02 996TT. "Turbo"
Owned and repaired 924s since 1977
Porsche: It's not driving, it's therapy.

[ideola]

[ted von Kampen]

Thanks for the replies and comments. To answer a few of the questions and points:
1. Compression is running about 105psi per cylinder and is about the same on each cylinder. While this is below the spec for compression, over the years I have believed that the balance is probably more important than absolute value. Since this engine sat for 15 yrs it does not surprise me it is a little low. I would need to have a warmed up engine and squirt oil in the cylinders to get a better reading. Since I cannot keep it running long enough to get it warm, these readings are about the best I can get for now. I don't feel that compression is the issue.

2.While I ran the vacuum test that Porsche talks about, I do have a vacuum guage but have not run that yet. Excellent point and I will run tomorrow.

3. Valve timing have been reset several times and remains aligned. I have rough set the ignition timing so I can start it, but since I cannot keep the engine running or at idle I do not have a chance to use the timing light and set correctly.

4. Cap, rotor and plug wires have been checked as well as spark plugs. I judge them to be okay.

5. I have read several posts about the ignition switch problems. However I should connect a 12V test light to the coil to verify it has power when I do have it running. Nevertheless, while I have been running the timing light flashing test I described, I was still getting spark (ie-timing light flash) upon cranking and even when it is bogging down I don't think the ignition switch is cutting out. However intermittencies of the distributor coil Hall pickup or the Power IC on the fender, could still cause a problem when running and the timing light goes on flashing.

6. One additional thought I have had. The cold start valve was replaced because the old one was varnished and stuck and would not flow. As a temporary fix I took one off a VW rabbit. From a part number listing I have found that this VW injector flows at a higher rate (115 vs 85)than the Porsche valve. I need to verify that this valve does warm up and shut off because if it doesnot it could be flooding it. I can disconnect and see if that helps.

7. I have torn the fuel distributor down and cleaned all the varnish out. I have torn the WUR down and recalibrated it so that the control pressure is about 25 psi when cold and 50 psi when warm. I did this by bypassing the fuel pump relay and running the fuel pump. The height of the control slug was adjusted to get the 50 psi and then the small screw post was hammer adjusted to get the 25 psi when cold. I tested the WUR controller after adjustment by running the fuel pump and measuring control pressure when cold and then when hot. The hot numbers were obtained by letting the bi-metallic strip heater come up. The engine temp was simulated by using a heat gun blowing on the back of the WUR. The resulting test pressures both cold and hot were in spec so I am confident that the WUR is setup correctly. The overall system pressure was measured at 75psi and that is in spec I believe. Sorry for English values but I just converted from bar since my pressure gauge is calibrated in PSI.

I also set the CIS up so that with the fuel pump running the fuel height in one of the outlet (as per Porsche WSM) was just at top. I adjusted the mixture control on the fuel distributor to get the correct setting.

I will be working on it again tomorrow and will post the results.
Feel free to add additional comments.

[Eliza]

That ignition module number you state - is that the usual, stock one on US-spec cars? On RoW cars, it looks way different. Google 0227100010 for a picture. Placement is the same, on the left wheel well.

The ignition module I have has six terminals, the one you have seems to have seven, by the looks of it. Interesting... can somebody else with a US-spec car verify?

Eliza
_________________
1985 924 NA RoW
1981 931 S2 RoW

[ted von Kampen]

Eliza, mine does have 7 terminals. Go to this link and you will see a picture of mine.
https://image5.sahibinden.com/photos/77/48/75/265774875yek.jpg
I sent you a separate picture by email. I got a replacement ignition module from China. It has a included heat sink.
I will see what it does tomorrow.
Ted