Help W/electrical Gremlins

[devin3200]

Hello Folks I have a question. My Poor 87 944 is suffering form some weird electrical issue. Now before I go on let me tell you what I've done so far. I have corrected corroded wires at the battery, reseated all of the ground wires at contacts ie: several times. Removed the fuse panel and completely torn down to clean contacts. note: I haven't replaced any sockets on the panel yet. I have replaced the DME relay 3 times. Once with a URO and twice with Stribel. Replaced the temp sensor but yet to stripe the wiring to it. But my volt meter is giving a good reading. So here's my problem. With all that I've done. the car runs ok. But it will only run in a straight line for about 15 mins or say 30 mins until hot. Than it shuts down. Wait about 10 mins, than it starts right up and drives until you get it home. So I'm trying to figure out what can be shorting the dme relay to the point it shut down. Some have said that they can re run wires to the dme at the fuse panel, but what and how to where?
If any one can help. Thanks.

Note: Yes my fuel pump is new, rewired the injector wire due to age melting.

[dgcantrell]

You could have a bad ignition switch. If you jumper the DME relay to eliminate the ignition switch and the car runs fine, I'd replace the ignition switch. I'm at work right now and cannot connect to my Picture Hosting site to copy and paste a link to the picture of the jumper I made for my car and how it connects. I will post it when I get home.

Meanwhile, here's a link to the Clark's Garage article concerning the DME relay and jumper. http://www.clarks-garage.com/shop-manual/fuel-05.htm

[devin3200]

Good call. Yes I can jumper it. and yes it does run with the jumper, This weekend it ran again with the same relay after I pulled it and reseated. So I will try and some get some specs on the ignition switch. See where I can meter it and see what's going on. Thanks

[dgcantrell]

Ignition switch power to the relay is on terminal 86 on the relay. It energizes when the ignition switch is turned on. So if the switch is going bad (and they do since they have moving parts in them) it can drop power on terminal 86 to the relay which will cause the DME and Fuel Pump to loose power. Note: Terminal 30 is live power all the time direct from the battery.

But.. It still might be a bad DME relay. The URO ones are junk. I made the mistake of getting one a while back. It only lasted a month or so before it started acting up. Cutting in and out. I stole the OEM Porsche one from the 88S I have been working on not had an issue since. I took the URO one apart just to check it and it is sloppily made.. The relay elements on mine were barely in the sockets on the circuit board...

Changing the ignition switch is not hard to do. You must remove the steering wheel and instrument panel to access it much better. However, the little screws that hold it into the ignition lock housing are hard to get out due to clearance (I used a phillips screwdriver bit in a 1/4" drive, 1/4" socket). Those two screws are the hardest part. Fortunately they're fairly short.

However, since you said you reseated the relay and it ran, leads me to believe it's the relay. There is a guy here selling Solid State DME Relays for these cars and I'm seriously entertaining the thought of getting one. But get an OEM Porsche unit for the extra $30-40 over the crap URO ones and try it before doing the ignition switch.

[Jfrahm]

I would doubt three DME relays are bad. Could be ignition switch, ignition coil, ignition module or the DME itself, or maybe a problem with the speed and reference sensors.

When it won't run, what is missing?
Check for tach bounce while cranking.
Check for a strong spark that will jump at least 10mm (use a spark checker if you have one)
Check for fuel at the rail, maybe start with a quick puff of starting fluid and if that causes the engine to catch for a second then check for fuel pressure at the rail and for an injector pulse signal.

It should be easy enough to see what has dropped out of the mix. My bet would be the ignition coil or the ignition module given the heat factor. If it is the module a good used one from a Volvo or Saab or another Porsche is IMO a better option than a Huco aftermarket replacement. (my recollection is that the S has one of these, the 8v and 968 do not.)

-Joel.

[devin3200]

Thanks Folks, said note Both reference sensors and the coil have been changed. My car is the NA, so I don't think I have an ignition module, if so I'll have to trace it down. I'm interested in the issue with the power drop from terminal 86. Can this line be hot wired to another source to prevent the drop? And yes, 3 relays can't in my opinion be bad. Plus I only drive it short distance's. So heating up is the issue. Is there anything I can ohm out on the ignition switch itself.

[Jfrahm]

Changing parts is not testing, I still recommend testing as above. It'd be way faster to test for what's missing than to speculate for days via the internet.

[devin3200]

jfram, I installed all of the parts I stated earlier as different issues came up and general PM. So I'm not just throwing parts at a problem. Now I have a new problem which is this one. So I'm trying to get it figured out and I appreciate the advise that all posters are giving me. So needless to say I'm not testing with parts. I will administer so of your suggested test, after I reinstall the dash cluster. Since it was already disassembled due to dash recovery. I have removed and cleaned the contacts on the ignition switch. So thanks.

[devin3200]

Update: After removing my ignition switch pulling it apart and cleaning the contacts inside and checking and cleaning the wiring contacts. I was able to drive my car about 40 miles, 20 miles round trip with no issues. Hopefully this is the fix. Thanks for all for your assistance.