L-Jet debugging questions
 

Hello,

I have reinstalled an original L-Jet fuel injection system on a spare 1.8L Porsche engine that I had running in my garage, on a test stand. (It was previously running on dual Dell'Ortos, but I am now using it as a test platform for the L-Jet.) I am trying to get it to run as it should, so I can then install it on a new engine I am rebuilding for my 1975 914.

I have got it to run, and once it starts running it is running very well, with smooth acceleration and deceleration, no hesitations, it is a pleasure to see it. However, starting it is constantly a problem. It does not seem to matter if the engine has been warmed up or if it is cold, it is still very hard to start.

I did some debugging on it. I know that the cold start valve is working properly (I pressurized the system, and then connected 12V power to it, and saw the pressure slowly decreasing). The injectors are all opening up, the fuel pump operates when it should (when cranking, and after that once the engine starts running). The cylinder head temperature sensor is functioning properly, the throttle position switch was checked OK, and the AFS is in good shape. My thoughts now about the difficult starting are centered around problems with the thermo-time switch and with the ignition system.

1) My first question is about the thermo-time switch. It is now about 30F in my garage, and when I check the thermo-time switch it shows continuity between pin W and the ground, as it should. So the cold start valve is powered up when I first crank. However, if I keep the starter on, then the thermo-time switch disconnects after a very short time, less than 2 seconds. This means that the cold start valve only gives a very brief squirt of gas into the intake plenum, and then shuts off. Is it normal for the TTS to shut off after such a short time? I thought I had read that it was supposed to stay on up to 20 seconds. If I leave it alone, it reverts to the initial condition (continuity between W and ground) after about 15-20 seconds.

2) I pulled out a spark plug and looked for spark when cranking. I do have a spark, but it looks rather weak. By comparison, before installing the L-Jet system I had a pretty strong spark when cranking. Could it be that the L-Jet system pulls too much power and the voltage at the coil drops while cranking? The way I have jerry-rigged the system I have a pretty skinny wire that goes from the main power source (at the starter) to the L-Jet main power source (red wires at the double relay, ports 88Z and 88Y), and from there another skinny one going to the coil. I am thinking this may be the cause of difficult starting, but good running afterwards -- when the starter is not operating, the battery voltage gets back to being high enough to get a good spark.

3) I was a bit surprised to find that after having the system on for 5-10 minutes, without the engine running (as if ignition was on, but starter and engine were off), the coil was quite warm. Not too hot to touch, but certainly warm to touch. Is it normal for the coil to warm up during normal operations?

Any ideas what could be causing my starting problems?

Thanks for any suggestions.
Andrei.

Hallo,
you must take care the coil is not powered when the engine is not running. It gets overheated and defective if the high voltage isn't switched continously as the points do when the engine is running. This is a normal problem at battery-powered ignition systems with points.

- maybe you interchanged the wires at the thermo-time-switch. It then shows misfunction as you described.

'G' must be connected to the cold start valve and Pin 50 - = positive when starting.
'W' must be connected only to the second connector of the cold start valve.

No problem to interchange the wires at the cold start valve - great problems doing this at the thermo-time-switch.

Regards
Norbert

I am using a standard fuel injection harness (that came with the L-Jet), and the plug can only go in over the Thermo-Time Switch in one way. So I don't think I have swapped the wires at the TTS. But I worried about this myself, and so I'll check one more time.

But I don't quite understand how switching the wires at the TTS would make it behave the way I described. My thinking would be that then the TTS would completely short circuit the CSV through its switch (and go straight to the ground), while the other side of the TTS (the heating element) would run in series with the CSV. It seems that in that case most of the current would go through the contacts part of the TTS, and very little would go through the CSV and through the heating element of the TTS... So I should see almost no voltage at the CSV, but this should not change over time (as the heating element would be getting very little current).

My gut feeling at this point is that either this is normal behavior of the TTS (operating for only 1-2 seconds), or the TTS has failed and switches off too early.

Thanks,
Andrei.

Hi,
interchanging the wires at the thermo-time-switch means short-cutting it. Therefor it heats up fast and the bi-metal cuts the electrical contact (and the short-cut..., but the CSV, too) immediately.

Link: Construction of the TTS

Could send a link to a German forum, too - but it's in German, will not be helpfull. The user described the same problem.



Norbert