951Porschiste

Well, I’ve been away from Rennlist for close to 9 months now. I’ve suffered through 3 separate computer crashes since. The first crash was caused by a misbehaving hard drive which necessitated the services of a data recovery specialist. I then overhauled my backup procedures (I now back up my notebook data to an external drive at the office and to a NAS at home and I do it daily!).

Now to the heart of the matter:

One of my last posts was concerning the hot engine no-start trouble that I had been chasing since I bought the car back in 2003. The engine would always start when cold, but once the temperature and humidity reached a certain critical point the engine would fail to start. It would turn over fine, but it would not produce the necessary spark to actually fire up. Once the temperature cooled down, it would fire right up again. In the process of tracking down the issue I have changed the following over the last few years (non-exhaustive list):

Fuel pump
Fuel filter
Fuel lines
Vacuum lines
Injector seals
Battery
Battery rewire (IceShark (RIP) kit)
Starter motor
Speed and reference sensors.

I had noticed that whenever the no-start issue showed up, I was able to “cure” the problem by wiggling the speed and reference connectors a certain way.


Last summer I decided to replace said connectors with new AMP female 3-way connectors (EagleDay.com) and to rewire from the connectors on to the DME. For a while it seemed to have cured the problem. However, early in the fall the problem was back. Depending on temperature and humidity I had to again wiggle the connectors to get the engine to start. But I could not resolve the issue because by then, I was too busy at the office and I had those multiple computer problems.

Finally, a few weeks ago I decided to replace both the female and the male AMP connectors with entirely different connectors which I again ordered through EagleDay.com.



I cut off both old female connector attached to the DME side and the old male connector attached to the speed and reference sensors. I then split open the wire looms from both the DME and the connectors.



I crimped and soldered the wires from the DME side to the female prongs of the new connector and those from the sensors to the male prongs.



When you split open the wire loom from the speed and reference connectors, it is important to be careful. The shielding wire lies just under the external rubber covering. This wire must be gently splayed apart and then rolled into a single wire because it has to be connected to one of the three male metal prongs of the connector. I not only crimped the male prong onto the wire but I also soldered it in place. Under the shielding wire is a thin sheet of aluminum paper and plastic paper. Under these are two electrical wires (one black, one yellow) and two all plastic guide wires. You can safely remove these two plastic wires. Then you can remove a short section of plastic covering on the electrical wires to allow you to crimp and solder these to the two other male metal prongs.







Then I just connected the male and female plugs together. Since this mod I have had no ( as in zero, nada, pas du tout, none whatsoever, not even once…) hesitation on startup regardless of temperature or humidity.

lee101315

Excellent Idea, I have the same problem! Nice write up. I always have to jiggle the speed sensor wires to get the car to start when its hot.

You should also notice more consistent performance.

TRP951

very nice work. Although i think lindsey is making a speed and reference sensor harness for those not to comfortable with working on shielded wire

951Porschiste

Yes, I know. However, the Lindsey kit still uses the OEM type of connector. In my opinion, it is these OEM connectors themselves that are the problem. That is why I decided to go to a completely different type of connector. Alternatively, one could have splice the wires together after removing the OEM connectors.

944CS

it is not a problem with the connector, it is a problem with the wires after the connector and the heat in the engine compartment. Over 20 years of heat cycles and exposure, the wires become brittle and crack when you move them (this is why we see so many "replaced vacuum lines, now it won't start" threads, you have to move these wires to take the manifold off, and when you do that the wires underneath the sheathing crack, just like the plastic connectors eventually do

Kool

I only dream about soldering as good as that.

great work and good idea.

schadenfreude

My car has had a hot start problem ever since I bought it, which I haven't been able to figure out. It won't turn over, but can be push/clutch started just fine. Also if I wait for 30-45 mins it seems to be ok. The problem seems to be getting worse, I haven't taken the car to the track for a while but I'm scared of the embarrassment I'll suffer when I have to push start the car for its second 5 lap run

Is this likely to be speed/reference sensor wires also? One guy seemed to think it could be a seized starter motor, any truth to this? Should I just try the 'jiggle the speed/ref sensor wires' trick next time it does it?

Luis de Prat

Yes. Wiggling the speed/reference sensor wires got my car to start every time until I gave in and replaced both sensors.

Sometimes you can get away with replacing just the sensors. Otherwise, you need to splice new wiring into the harness like 951Porschiste did, or get the permanent repair kit from Lindsey Racing that ties back into the DME.

951Porschiste

I agree in part. But in my case, remember that I had initially replaced all the wiring from the DME to the connectors including the connectors. When the problem came back after a few months, replacing just the connectors with a different design has solved the problem completely.

I think that the conclusion should be that if your car has this hot-engine no-start issue, everything from the speed and ref sensors to the connectors to wiring should be looked at/inspected/replaced.

944CS

I agree

david fracolli

I had the the same problem with mine. Used to take a bout an hour to cool down before it would start again. Before I put it away for summer it was taking 3-4 hours before it would start again. Hopefully the new wiring harness i bought will resolve the problem.

951Porschiste

Hey 944CS! I lived in Havertown, Pa for two years (1992-1994). Where are you in the Philly area?

blown 944

I had a problem with a somewhat stripped bolt holding one of them into the housing. It would do the same things mentioned.

schadenfreude

Thanks - I've done a quick visual inspection and the wires look ok, but the connectors have cracked, so definitely a possible culprit. In return, here's a 917/30